cdma_tr_zte

CBB_001_E2CDMA Basic Theory (1XRtt&EV-DO)

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Revision History

Date Revision No. Serial No. Reason for Revision

08/30/2006 R1.0 sjzl20061409 First edition

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Document Name ZXC10 BSSB CDMA2000 Base Station System Common Operation Manual

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Contents

Chapter 1..........................................................................1

CDMA Development .........................................................1

Introduction .........................................................................1 Mobile Communication History and CDMA Standard ...................1 ZTE and cdma2000 ...............................................................7

Chapter 2..........................................................................9

Basic CDMA Principles .....................................................9

Introduction .........................................................................9 Spread Spectrum Technology .................................................9 Multiple Access Technology .................................................. 12 CDMA System Implementation.............................................. 13 Speech Coding Technology................................................... 17 Channel Encoding Technology............................................... 19

Chapter 3........................................................................27

IS-95 System Principles ................................................27

Introduction ....................................................................... 27 IS-95 System Overview ....................................................... 27 IS-95 Air Interface Parameters ............................................. 27 Forward Channels ............................................................... 28 Reverse Channels ............................................................... 34 Comparison of Reverse Channels and Forward Channels ........... 38 Service Flow....................................................................... 39

Chapter 4........................................................................45

cdma2000 1x System Principles ...................................45

Introduction ....................................................................... 45 System Overview................................................................ 45 Air Interface Parameters ...................................................... 46 Forward Channels ............................................................... 46

Reverse Channels................................................................54 cdma2000 1x Technical Features ...........................................59 Service Flow.......................................................................61

Chapter 5........................................................................73

cdma2000 1x EV-DO System Principles........................73

Introduction .......................................................................73 System Overview ................................................................73 Forward Channels................................................................77 Reverse Channels................................................................81 Key Technologies in 1x EV-DO...............................................87 Service Flow.......................................................................95 Comparisons with 1x ......................................................... 101

Chapter 6......................................................................103

CDMA Key Technologies and Advantages...................103

Introduction ..................................................................... 103 Key Technologies .............................................................. 103 CDMA System Advantages.................................................. 129

Confidential and Proprietary Information of ZTE CORPORATION 1

C h a p t e r 1

CDMA Development

Key points:History of mobile communications

CDMA standards and their evolution

History of ZTE CDMA products research & development

Introduction

After studying this chapter, you will have an overall picture about mobile communications, ZTE CDMA products R&D process and get prepared for the later chapters.

Mobile Communication History and CDMA Standard

The history of mobile communication can be traced back to the early 20th century, but its fast growth did not come until recent 20 years. The development of mobile communications technologies is basically focused on opening new frequency ranges for mobile communications, effective frequency utilization, and mobile station miniaturization and portability. Here, the technology for effective frequency utilization is the core of mobile communications.

The first mobile telephone system was commissioned in the United States in 1940’s of the 20th century.

CBB_001_E2 CDMA Basic Theory (1XRtt&EV-DO)

2 Confidential and Proprietary Information of ZTE CORPORATION

Bell Labs in the United States introduced the concepts and theory of cellular systems in the early 1970’s. The evolution of cellular mobile communication systems is shown in Table 1.

T AB L E 1 E V O L U T I O N O F CE L L U L AR M O B I L E C O M M U N I C AT I O N S Y S T E M S

1st Generation 2nd Generation 3rd Generation

Analog Digital Digital

Voice Voice/Data Voice/High Rate Data

AMPS CDMA cdma2000

TACS GSM/TDMA GPRS W-CDMA

1980’s 1991 1999 2001 2002

AMPS： Advanced Mobile Phone System

TACS： Total Access Communication System

GPRS： General Packet Radio Services

In the late 1970’s, the first generation cellular mobile communication system was born in Bell Labs, United States, that is, the famous Advanced Mobile Phone System (AMPS). Afterwards, NMTS（Nordic Mobile Telephone Systems） and TACS（Total Access Communication System） mobile communication systems were developed in North Europe (Denmark, Norway, Sweden and Finland) and Britain. China started to use analog cellular telephone communications in 1987. The first mobile telephone office was opened in Guangzhou in November 1987.

After only a few years, the first generation mobile communication system using analog system revealed serious problems, such as insufficient capacity, singular service, and poor voice quality. These urged the development of the 2nd generation cellular mobile communication systems.

The 2nd generation cellular mobile communication systems (2G) adopt digital system, providing higher spectral utilization, better data service and communication quality, and more advanced roaming function than 1st generation systems.

The typical 2nd generation cellular mobile communication systems include the leading Global System for Mobile Communication (GSM), IS-54/IS-136 and IS-95 (United States), and PDC (Japan). The IS-95 is a cellular mobile communication standard defined by the Telecommunications Industry Association (TIA), United States in 1993. It employs the CDMA technical specifications proposed by Qualcomm Company.

The first CDMA cellular mobile communication system was commissioned in Hong Kong in 1995, signifying CDMA has been put into commercial application. However, the Federal Communication Commission (FCC) in the United States restricted the development of IS-95. It required IS-95 be compatible with AMPS, that is, its bandwidth must fall within the frame of AMPS’s frequency band. Therefore, IS-95 is a narrowband CDMA system,

1st Generation Cellular Mobile Communicatio

n Systems

2nd Generation Cellular Mobile Communicatio

n Systems

Chapter 1 错误！未找到引用源。


which can only provide limited services, and still has many weaknesses.

In recent years, the voice-oriented mobile communication services provided by 2G have attracted more and more users. There are over 100 million mobile service subscribers in China up to now. And this number is increasing at the rate of 0.2 million/year. 2G’s huge success has strongly pushed the development of the 3rd generation mobile communication systems (3G).

In 1985, the International Telecommunication Union (ITU) introduced the Future Public Land Mobile Telecommunication System (FPLMTS), that is, the 3rd generation mobile communication system. FPLMTS was later renamed IMT-2000. European Telecommunication Standard Institute (ETSI) also introduced the Universal Mobile Telecommunication System (UMTS).

IMT-2000 and UMTS delivered very similar concepts and purposes. Both aimed at unifying frequency bands and standards globe wide, realizing worldwide roaming and providing diverse services with functions and quality equivalent to fixed circuit telecommunication systems.

The 3rd generation cellular mobile communication and personal communication systems provide greater system capacity, more flexible high- and multi-rate data transmission capabilities. Current 3G systems can transmit data at a rate up to 144 kbit/s on vehicles, 384 kbit/s when walking outdoors, and 2 M bit/s in buildings. And it is potential that these rates be further increased in the future. 3G services include video/audio streams, mobile interconnection, mobile e-commerce, and e-mail. And the final development will come up to video e-mail and file transfer, truly realizing the target of “Anyone can easily communicate with anyone, anywhere, anytime”.

Radio Transmission Technology (RTT) is most critical for IMT-2000. According to ITU-R proposal M.1225, by the end of June 1998, ITU had collected 10 terrestrial interface standards from Europe, Japan, United States, China, and Korea respectively.

Although ITU was going all out for harmonizing the standards, the two trans-regional standard organizations, 3GPP and 3GPP2 represented by Europe and United States, have become the two major ones based on W-CDMA and cdma2000 respectively. 3GPP is a 3rd generation partnership project initiated by ETSI in Europe; and 3FPP2 is another such project initiated by ANSI in the United States. China also founded a Wireless Telecommunication Study Group (CWTS) in April 1999, and formally participated 3GPP and 3GPP2 in May 1999.

In order to define the critical IMT-2000 RTT’s, ITU-R worked very hard in converging various wireless access schemes (excluding satellite access), with the intention to come up with a possibly unified RTT standard. However, after one year’s study, ITU found it totally impractical to completely converge different RTT technologies. Therefore, ITU TG8/1 adopted the proposal

3rd Generation Cellular Mobile Communication System and

CDMA Standard

RTT Technology



“IMT-2000 Radio Interface Specifications” at a meeting held in Finland in November 1999, and finalized the 5 RTT’s for IMT-2000. These technologies include W-CDMA (Europe and Japan), cdma2000 (United States), and TD-SCDMA (China).

W-CDMA is a wideband standard proposed and agreed upon with minor differences by Europe and Japan. Its technical features include frequency division duplex, adaptation to multiple rates and services, rapid forward link power control, reverse link coherence demodulation, support of carrier switch, no requirement of base station synchronization, and suitability for high rate environment. It is a highly promising scheme.

cdma2000 is an evolution of IS-95 system in North America. Its technical features include reverse link coherence reception, forward link transmit diversity, base station synchronization by GPS, good compatibility with IS-95, technical maturity, low risk, and good comprehensive economic and technical performance.

TD-SCDMA is based on TDMA and synchronous CDMA technical standards. It adopts time division duplex (TDD) mode and combines intelligent antenna and software radio technologies, suitable for low rate access environment. This is the first time China has ever proposed to ITU with its own intelligence property right.

Among the 10 candidate technologies for IMT-2000 RTT, 8 are CDMA technology, that is, CDMA technology is leading the 3rd generation communication systems. Japan took the lead in W-CDMA commercial commissioning in March 2001, and starting 3G services in the world at the end of the same year. 3G’s success in the process from conceptual model to commercial application again pushed us to think about the next generation mobile communication system. Although no standard for the next generation mobile communication network (4G) has been created yet, we are sure that 4G will provide even higher data transmission rate than 3G. Now, it has been predicted that 4G data transmission rate will reach 10 M bit/s ~ 100 M bit/s.

The complete evolution process of cdma2000 technology is as shown in FIGURE 1.

cdma2000 Standard Evolution



FIGURE 1 E V O L U T I O N O F C D M A2000 T E C H N O L O G Y

IS-95A14.4Kbps

IS-95A14.4Kbps

IS-95B64Kbps

IS-95B64Kbps

Cdma2000Phase One144Kbps

cdma2000Phase One144Kbps

Cdma2000Phase Two

2Mbps

cdma2000Phase Two

2Mbps

2GcdmaOne

3Gcdma2000

1999 2000 In correspondence with the evolution process of cdma2000 technology, CDMA radio standard evolution has seen the phases in TABLE 2.

T ABLE 2 CDM A S Y S T E M E V O L U T I O N

System Rate Service Generation

cdmaOne IS-95, IS-95B voice 2nd

cdma2000 1x 153 kbit/s voice/data 3rd

cdma2000 1x

EV-DO

Max forward rate: 2.4 M bit/s data Enhanced version

of 1x phase 2

cdma2000 1x

EV-DV

Max data rate: 4 M bit/s or

higher

voice/data Enhanced version

of 1x phase 2

IS-95A is the first CDMA standard that is widely applied globally. IS-95A supports 8 k encoded voice service and STD-008 standard for 1.9 GHz CDMA PCS system. The 13 k encoded voice service quality has been very close to that of a circuit telephone.

As mobile communication demand for data service increases, Qualcomm Company announced in February 1998 that they would apply IS-95B standard to CDMA foundation platform. IS-95B can promote CDMA system performance, increase the data flow of subscriber’s mobile equipment, and support 64 kbit/s data service.

After that, cdma2000 has become a standard for narrowband CDMA systems to migrate to the 3rd generation systems.

As the era advances, people are creating more challenges for mobile communications. 2G can provide better voice mobile communication, but it is helpless facing user’s increasing

3G Concept



expectation for mobile data sharing and multimedia. In addition, 2G systems’ capacities are experiencing a technical bottleneck in densely populated, developed areas where the capacity demand cannot be satisfied.

We are all looking forward to the day when we can use 3G multimedia services. 3G’s feature is using bandwidth consolidating data and multimedia in IP and ATM networks. Now, globe wide 3G standards have been made and put into commercial operations in many countries. They are cdma2000, W-CDMA, and China proposed TD-SCDMA technologies. Among the 3G schemes that are presently attracting most global attention, W-CDMA standard has been consistently and frequently upgraded to new versions, which makes it appear unstable. In this case, it is difficult for manufacturers to choose a version and make equipment and terminals for it.

In contrast, cdma2000 was developed directly from existing last generation CDMA and evolved rather smoothly from 1x to 1xEV-ED. During the process when cdma2000 1x is extended, only partial change needs to be done to the radio subsystem hardware and software, which is relatively stable.

Therefore, we will focus on the discussion of cdma2000 technology.

In terms of mobile subscribers

2G (2.5G) and 3G networks will coexist for a long time. As with other new technologies, the popularity of 3G takes time. Many mobile subscribers are satisfied with the available 2nd generation products, but business and high-end subscribers are expecting to use wideband wireless data products brought about by 3G. Mobile service providers will help their subscribers migrate smoothly to 3G by gradually introducing new services, so as to consolidate their present subscriber base. In this way, they must provide both 2nd generation and 3rd generation services at the same time.

In terms of technology

The important difference between IS-95B and IS-95A is that IS-95B can bind multiple channels. When the supplementary traffic channels are not used, IS-95B and IS-95A are basically the same and can share the same carrier.

cdma200 1x, evolved from cdmaOne, is the first phase of cdma2000 3rd generation wireless communication system. Its main features include backward compatibility with current TIA/EIA-95-B standard, and capability of frequency band sharing or overlapping with IS-95A/B systems. cdma2000 1x is different from IS-95 in radio configuration (RC). It can support both 1x and IS-95A/B terminals through proper RC. So, cdma2000 1x and IS-95A/B can coexist on the same carrier.

cdma2000 can effectively support existing IS-634A standard. With the core network based on ANSI-41, it can be run on GSM-MAP core network after network expansion.



ZTE and cdma2000

As information is highly demanded, data service has been developing towards diversity, large capacity, and asymmetricity. In order to satisfy data service market and keep pace with the world telecommunication, ZTE commissioned the first cdma2000 1x mobile communication system and successfully developed the first cdma2000 1x EV-DO mobile communication system in China.

The evolution path of ZTE products is IS-95A→cdma2000 1x→cdma2000 1x EV-DO.

1. In 1995, launched CDMA mobile communication project.

2. In March 1998, this project was approved by the State Planning Committee.

3. At the end of 1998, launched large-scale research and development in CDMA base station system.

4. In November 1999, ZTE took the lead in signing “CDMA Research and Development Agreement” with Qualcomm Company.

5. In March 2000, used the BSS to dial through a call to IS-95.

6. In April 2001, put BSS into large-scale commercial operation at China Unioncom, making an epoch of national mobile communications.

7. In April 2000, launched large-scale research and development in cdma2000 1x system.

8. In October 2001, put cdma2000 1x into commercial operation.

9. In November 2001, launched large-scale research and development in cdma2000 1xEV-DO products.

10. In February 2002, launched research and development in cdma2000 base station system based on all-IP technology.

11. In June 2002, ZTE, for the first time, exhibited complete cdma2000 1x EV-Do equipment on Hong Kong 3G annual fair.

12. In October 2003, commissioned a field trial cdma2000 1x EV-DO.

13. In June 2004, had the capability to supply cdma2000 1x EV-DO products in batch.

14. In July 2004, commissioned a field trial cdma2000 1x Release A.

15. In November 2004, put cdma2000 1x Release A and cdma2000 1x EV-DO products into commercial operation.

16. In 2004, launched research and development in cdma2000 1x EV-DV products.

17. In April 2005, introduced cdma2000 1x EV-DO enhanced version and LMSD network elements for ALL-IP core networks.

History of ZTE cdma2000

Research & Development



Currently, ZTE is capable to provide the completed cdma2000 1x and cdma2000 1x EV-DO solutions. The ZTE cdma2000 product series is shown in Table 3

T AB L E 4 ZTE C D M A2000 P R O D U C T S E R I E S

Specification Product Introduction Band

ZXC10-

BSS 1x

This system is based on the IS-95A/B and

cdma2000 1x. Inside the system, there’s a high

speed packet based network platform to perform

the baseband modulation/demodulation, radio

resources assignment, call processing, power

control, soft handoff as well as the system

operation and maintenance.

450M,

800M and

1.9 G

1x

ZXC10-

BSS 1x（GoTa）

GoTa (Global Open Trunking Architecture) is

the global first cdma2000 1x based trunked

communication system. It integrates the

interconnected clustering system and the

trunked radio system. With GoTa, operators

can provide the customers with both

interconnected clustering communication

services and trunked radio services.

450M

and 800M

1x EV-DO ZXC10-

BSSB

This system is Real IP based. It provides high

speed packet switch and be compatible with

HIRS system. It can be upgraded seamlessly.

The system has significant capacity, integration

ability and extensibility.

450M,

800M and

1.9 G

1. Briefly state the history of wireless communications.

2. Briefly state the CDMA standard evolution.

3. Name the cdma2000 equipment supplied by ZTE.

ZTE cdma2000 Products Overview

Review


C h a p t e r 2

Basic CDMA Principles

Key points CDMA spread spectrum principles Voice and channel encoding technologies in CDMA systems

Introduction

Code Division Multiple Access (CDMA) includes two basic technologies: code division based on spread spectrum and multiple access technology. These two basic technologies in combination with the other key technologies form the technical support of today’s CDMA mobile communication systems.

After studying this chapter, you will master the basic CDMA principles, understand CDMA voice and channel encoding technologies, and get prepared for the understanding of IS-95, cdma2000 1x (hereinafter called 1x) and cdma2000 1x EV-DO (hereinafter called 1xEV-DO) systems principles.

Spread Spectrum Technology

Spread spectrum technology (Spread Spectrum Communication), together with fiber optical communication, and satellite communication are regarded as the three major high-tech communication transmission modes.

The basic idea and theoretical basis of spread spectrum communication is Shannon formula.

Shannon worked out a formula for channel capacity in his research of information theory:

)1(log2 NSBC +×=

Where C is channel capacity in bit/s; B is signal bandwidth in Hz; S is average power for signal in W; N is average power for noise in W.

Theoretical Foundation of

Spread Spectrum

Communication



This formula shows that if the information transmission rate C is fixed, the bandwidth and the signal-to-noise ratio S/N can be exchanged. By increasing the bandwidth, information can be reliably transmitted at the same rate with a smaller signal-to-noise ratio. In addition, reliable communication can be retained by increasing the signal bandwidth accordingly even when the signals are submerged in noise. This means the advantage of high signal-to-noise ratio can be obtained by spreading spectrum and transmitting information in wideband signals.

Spread spectrum technology is an information transmission mode involving modulation with spread code at the transmitter to make the signal bandwidth much greater than the bandwidth required for the data, and demodulation at the receiver using the same spread code to recover the original data.

The following figure shows the whole process of spread and despread.

FIGURE 2 SP R E AD AN D D E S P R E AD P R O C E S S

S(f)

ff0

B1

S(f)

ff0

B1

S(f)

ff0

B2

S(f)

ff0

B2

Transmission end

Receiving end

Signal

Signal

Spectrum before spread Spectrum after spread

Spectrum before despread Spectrum after despread

Signal

Singal

Interference nosie Interference noise

1. The information data is converted into a narrowband signal

(assume bandwidth=B1) through regular modulation.

2. The narrowband signal is spread with the pseudo noise (PN) code generated by the spread spectrum code generator to form a wideband spread spectrum signal (assume bandwidth=B2>>B1) of low power spectrum density.

3. There are some interferences or noises (narrowband noise or broadband noise) in the transfer.

4. The receiver demodulates the signal received using the same PN code used by the transmitter and restores the wideband

Spread and Despread Processes



signal back into a regular base band signal. That is, to extract from the wideband signal in PN code regularity, the data corresponding to that transmitted and integrate them to form an ordinary base band signal.

Processing gain and anti-interference allowance are two important concepts in spread spectrum communications:

Processing gain shows the S/N (signal/noise) improvement of a spread spectrum system. It is an index of the system’s anti-interference performance. Generally, the ratio of spread spectrum signal bandwidth W to data bandwidth F∆ is called processing gain pG , that is:

.FWGp ∆

=

Theoretical analysis shows that the anti-interference performance of various spread spectrum systems is related to the ratio of signal bandwidths before and after spreading. The processing gain alone cannot sufficiently show the system performance in an interference environment. Since the normal functioning of the system requires certain S/N output after reducing other system losses, we introduce anti-interference allowance JM , as defined

below:

])[( sopJ LNSGM +−=

Where, ( oNS ) = S/N output

sL = system losses

The spread spectrum technology has the following features:

1. Strong anti-interference capability

In spreading communications, signals are spread to wideband for transmission at the transmitting end. The spread signals are compressed to recover the narrowband signals at the receiving end. Interference signals are irrelevant to the spread spectrum PN code, so they are spread to wideband to reduce the in-band interference power and hereby increase the output signal/interference ratio. Therefore, the anti-interference capability is strong. The anti-interference capability is in direct proportion to the times that the band is spread. Greater spectrum will produce stronger anti-interference capability.

2. Multiple access communication

Although the CDMA spread spectrum communication system occupies a quite wide band, its spectrum utilization ratio is even higher than that of a single-carrier system because various networks can use the same band at the same time. So multiple access communication is supported.

Processing Gain and

Anti-interference Allowance

Spread Spectrum

Technology Features



3. Good security

As the spread spectrum system spreads the information to be transmitted to wideband signals, the power density is reduced and even fades in the noise, so it has good security. It is very difficult to intercept or detect such signals. It is even impossible to do so unless the same spread spectrum code as used by the transmitting end is used and the signals are synchronized, and also correlation detection is made.

4. Anti-multipath interference

In some communication environments, such as moving and indoor communications, multipath interference is very significant. In order to guarantee smooth communication in such environments, the system must have very strong anti-interference capability. The spread spectrum technology provides strong anti-multipath interference capability by making use of the correlation property of spread codes. It can even improve system performance by taking advantage of multipath energy.

Certainly, spread spectrum communications have many other advantages, such as precise timing and distance measuring, anti-noise, low power spectrum density and random addressing etc.

Multiple Access Technology

Multi-access is a communication mode where many users use the same resource (frequency) to communicate with each other. In a CDMA system, many users use the same frequency at the same time. Normally, these users are at different places and possibly are moving. For example, multiple earth stations for satellite communications use the same repeater to communicate with each other, or many mobile stations communicate through base stations etc. Due to using the same transmission frequency, there may be interference between the users, which is called multiple access interference or self-interference. To eliminate or reduce multiple access interference, the signals sent by different users must have some characteristics so that the receivers can distinguish them. This process is called signal division.

The mathematic foundation of multi-access mode is the signal orthogonal division principle. Signal transmission can be expressed by the function of time, frequency, and code type.

The multi-access modes used to discriminate channels based on the characteristic of signal transmissions can be classified into the following:

FDMA (Frequency Division Multiple Access)—different users use different frequencies.

TDMA (Time Division Multiple Access)—different users use different time slots.



CDMA (Code Division Multiple Access)—all users use the same frequency at the same time. The signals are divided using the orthogonality or quasi-orthogonality of the access code waveforms for different users.

FDMA, TDMA, and CDMA are represented by graphics as follows:

FIGURE 3 M U L T I P L E AC C E S S M O D E S

CDMA System Implementation

Code Division Multiple Access (CDMA) is an advanced multiple access mode of promising future. Now, it has become a hot topic for research and development in many countries.

CDMA uses a group of orthogonal (or quasi-orthogonal) random PN sequences and related processes to implement the functions that allow multiple users to share frequency resource in air transmissions, and to access and connect simultaneously.

The spread spectrum technology is implemented in three ways: Direct Sequence Spread Spectrum (DSSS), Frequency Hopping Spread Spectrum (FHSS), and Time Hopping Spread Spectrum (THSS).

CDMA adopts the DSSS as shown in FIGURE 4.

CDMA Spread Spectrum Principles



FIGURE 4 CDM A S P R E A D S P E C T R U M P R I N C I P L E

The transmitter broadens the frequency spectrum of useful signals through spread processes. The receiver recovers the narrowband spectrum of these signals through despread processes using the correlation of PN codes.

The useless wideband signals are irrelevant to local PN codes so they cannot be despread and still remain in wideband. The useless narrowband signals are expanded into wideband with local PN codes. Since useless interference signals are wideband and useful signals are narrowband, we can use a narrowband filter to remove the out-of-band interference levels, thereby greatly increasing the narrowband S/N.

In normal situations, CDMA systems can spread signals by applying multiple spread sequences in succession and then reapply them in opposite order to compress the spectrum and recover the original data, as shown in FIGURE 5.

FIGURE 5 M U L T I P L E S P R E AD S E Q U E N C E S I N S U C C E S S I O N

Spread codes need to be able to differentiate, that is, so-called orthogonality. The appropriate spread codes should have the following characteristics:

Correlation

The signal can only be despread by its own spread code but not any other spread codes.

Self-correlation

Its own latency does not influence signal despreading.

CDMA Spread Code Selection



Easy to generate

Randomness

Have possibly the longest period so as to resist interference

At present, CDMA spread codes include Walsh and PN codes (m and M sequences).

Walsh code is a quadrature spread code, generated by the Walsh function set. Walsh function is a two-variable orthogonal function system that values 1 and –1. It has multiple equivalent definition methods. Handmard numbering method, used in IS-95, is the most frequently used.

Walsh function set is a complete nonsinusoidal orthogonal set, often used as user access codes.

The IS-95 standard gives out a Walsh function construction table for r=6, n=26=64.

The characteristics of Walsh function set are orthogonality and normalization. Orthogonality is the multiplication of two different Walsh functions with the same rank, and the integral within a specified range is 0. Normalization means to multiply a Walsh function by itself, and the average of the integrals within a specified range will be +1.

Multiple methods can be used to generate Walsh sequences, but the one used most is Handmard matrix. Iteration is used in the process of forming a Walsh sequence with Handmard matrix.

The self-correlation and correlation of Walsh function are not ideal for asynchronous case, and will be worse when synchronization error becomes large.

Walsh codes are available in a small number and lacking in the characteristics of random signals, so we need to use PN code sequences when a large number of spread codes are needed. PN code possesses the property similar to noise sequence. It is seemingly like a random sequence but it is a regular and periodic binary sequence. The mostly used PN code is m sequence. m sequence is the abbreviation of the longest linear shift register sequence. As its name indicates, m sequence is the longest code sequence generated by a multistage shift register or other delay elements with linear feedback.

The structure of an m-sequence generator is an n-stage shift register, which can be constructed by two equivalent methods:

Simple sequence random generator (SSRG)

Its input is the modulo-2 sum of the stage outputs of a shift register. It is equal to a feedback input, which contains at least the output from the last stage.

The polynomial used to express the feedback input is called the generator polynomial of m sequences.

f(x) = C0+C1x1+C2x2+……+ Cn-1xn-1+Cnxn

Walsh Code

m Sequence



Where f(x) represents feedback input; xn represents the output of the nth stage; and C0~Cn represents feedback. Note that the addition in the formula is modulo-2 addition. The m sequence generator requires that C0 and Cn be 1.

Modular sequence random generator (MSRG)

The output of each stage can be modulo-2 added to that of the last stage and the sum be used as input for the next stage. The m sequence generator with this structure is called a modular sequence generator.

SSRG is slightly different from MSRG in the following:

SSRG’s multistage outputs module-2 adders are in series, so it has a large latency and low speed.

MSRG’s module-2 operations are in parallel, so it has a small latency and high speed.

CDMA (IS-95) uses MSRG to generate m sequences.

The m sequence is not as good as Walsh code in orthogonality. This is shown by the correlation characteristic of m sequences at the same stage. m sequence correlation is greater than 0. This is also an important reason why Walsh code is directly used and m sequence is not.

m sequence has strong self-correlation. When the stage number is large, m sequences at different phases can be treated as orthogonal.

m sequence period is 2r-1, where r stands for the number of stages a shift register has. The number of m sequences that can be obtained is related to the stage number.

When r=15, it is called PN short code.

When r=42, it is called PN long code.

The CDMA systems use the following two m sequences:

PN short code: The code length is 215.

PN long code: The code length is 242-1.

The following is a comparison of the three codes used in CDMA systems.

PN short code is used for orthogonal modulation of forward and reverse channels. Different base stations use different short codes in forward channels to identify themselves. The length of short code is 215.

PN long code is the modulo-2 sum of a pseudo random code generated by a 42-bit shift register and a 42-bit long code mask. The long code mask, which is different for each channel, is also generated by a 42-bit shift register. It has a length of 242-1. In CDMA systems, long code is used to scramble forward link signals and spread reverse link signals.

Walsh code, due to its orthogonality, is used to spread forward signals in CDMA systems.

Comparison of the Three

Codes



T AB L E 5 C O M P AR I S O N O F T H E TH R E E CO D E S U S E D I N CDMA S Y S T E M S

Code

Sequence Length Usage Purpose Code Rate Characteristics

Reverse access

channel

Reverse traffic

channel

Direct

sequence

spreading

Identify mobile

stations

1.2288 M

PN long

code 2

42 – 1

Forward paging

channel

Forward traffic

channel

Data

scrambling 19.2 K

Have sharp

2-value

self-correlation

All reverse

channels

Quadrature

spreading good

for modulation

PN short

code 215

All forward

channels

Quadrature

spreading good

for modulation;

identify base

stations

1.2288 M

Equalization

All reverse

channels

Orthogonal

modulation 307.2 K

Walsh

code 64

All forward

channels

Quadrature

spreading;

identify

forward

channels

1.2288 M

Orthogonality

We can combine the advantages of Walsh and PN codes in a supplementary way in real applications, that is, using composite code to overcome their respective weaknesses.

Speech Coding Technology

Data transmission efficiency has been a critical issue in the development of telecommunication networks for a long time so it is extremely important. To date, researchers have been studying this issue in two ways.

Study new modulation methods and techniques to improve channel transmission bit rate. The index is the number of bits transmitted per Hz bandwidth.

Compress source encoding bit rate. For example, using standard PCM encoding, a 3.4 k Hz frequency band signal needs to be transmitted at a encoding bit rate of 64 kbit/s.



Obviously, compressing this bit rate can increase the number of voice paths carried in a channel.

Voice encoding, a kind of source encoding, is completed by three encoding techniques: waveform, parameter, and hybrid.

Then, what kind of voice encoding technique is appropriate for mobile communication? This is mainly decided by the mobile channel conditions. Because frequency resource is limited, the signal-encoding rates must be low. Because mobile channel transmission conditions are bad, the encoding algorithms must have good capability to prevent code errors. In addition, from users perspective, it must also offer good voice quality and small latency.

To sum up, mobile communication has the following requirements for voice digital encoding.

Low rate means pure encoding rate should be lower than 16 kbit/s.

Voice quality must be possibly the best for a given coding rate.

Encoding latency should be small, controlled within tens of seconds.

In a very noisy environment, the algorithm should have good error resilience so as to maintain good voice quality.

The algorithm complexity should be moderate and easy for large-scale integration.

Due to the rapid development of cellular systems all around the world, the CDMA cellular systems capacity now is 4~5 times other cellular mobile systems in the past, and their service quality and coverage are much better.

In order to adapt the development trends, current CDMA systems employ an effective voice encoding technique, Qualcomm Code Excited Linear Prediction (QCELP).

It is a voice-encoding standard (IS-95) for the 2nd generation digital mobile systems (CDMA) in North America. This voice-encoding algorithm is Qualcomm’s patent. It can work for both fixed rates of 4/4.8/8/9.6 kbit/s etc, and variable rates within the range of 800 bit/s~9600 bit/s. This technique can reduce the average data rate, which in turn doubles the capacity of CDMA systems.

QCELP algorithm is considered the most effective to date. One of its characteristics is using an appropriate threshold to decide the rate needed. The threshold varies with the background noise level, and thereby cancels the noise so that good voice quality can be achieved even in a clamor environment. CDMA 8 kbit/s voice quality is approximate to GSM 13 kbit/s.



Channel Encoding Technology

Due to the peculiarity of mobile communication systems, high requirement is imposed on channel encoding—mainly the error control encoding, also known as error correction encoding, in order to obtain a specified bit error rate (BER) index. Error control encoding techniques include cyclic redundancy check (CRC), convolutional code, block interleaving code, Turbo code, and scramble code. They are used in different combinations in different systems.

PHS uses CRC and scramble codes.

GSM uses convolutional and block interleaving codes.

CDMA uses CRC, convolutional, block interleaving, and scramble codes.

cdma2000 uses CRC, convolutional, block interleaving, Turbo, and scramble codes.

Since radio signals may encounter various interferences during propagation, mobile channels are the most complicated communication channels. Besides the interferences encountered in cabled channels, radio signals may come across various obstacles, such as terrain and buildings, during its propagation, which might induce multipath and shadow effects on signals and make them disperse, diffract, and fade.

In addition, the weather change might also influence radio signals and make them fade slowly. It is even worse when the mobile station is moving at a high speed, where signals may have Doppler frequency shift effect.

All these factors may vary with the mobile station’s movement; so mobile communication channels have the following features:

Multipath propagation

Multipath interference refers to inter-symbol interference at the receiving end, induced by radio waves arriving at different times from different paths. It may attenuate the amplitude of transmitted data signals, broaden the waveforms, and thereby limit data transmission rate.

The multipath in mobile channels is mainly caused by signal reflection on large buildings. From the perspective of mobile station, it receives the same signal at different times from different directions, as shown in FIGURE 6.

Mobile Communicatio

n Channel Features



FIGURE 6 R AD I O S I G N AL M U L T I P AT H P R O P AG AT I O N

Multipath significantly disperses the signal power and makes the mobile station receive only a part of the transmitted signal power. Also, multipath signals reach the mobile station at different times through different paths, resulting in different phases. Thus, multipath signals will weaken each other, leading to serious fading, big S/N drop, and bad receiving effect.

Furthermore, for wideband communication where signal frequency spectrum is wide, frequency selective fading might also happen. This is mainly because in different multipath situations, different frequencies may have a variable degree of fading such that some frequency components are totally cancelled by multipath effect. The details are shown in FIGURE 7.

FIGURE 7 R E AL S E L E C T I V E F R E Q U E N C Y R AY L E I G H F AD I N G C H AN N E L

In the figure, the vertical axis indicates the gain in dB, and the horizontal axes are frequency and time respectively.

We can see there are many “valleys”, where serious fading happens. The Rayleigh fading means the probability density function of signal electromagnetic strength complies with Rayleigh probability distribution of multipath fading. Another major contributor to Rayleigh fading is Doppler frequency shift effect.

Multipath is unavoidable in mobile communications. Although it seriously interferes communications, people can also take advantage of it. For instance, when a mobile station moves to the back of a large building and enters the signal shadow area, radio signals can only reach the mobile station by reflection. People can make use of the reflected waves and/or wound waves to guarantee voice continuity. The technical measures taken against multipath in GSM and CDMA are time-domain equalization and receive diversity.



Doppler frequency shift

We all have experienced such a situation in our daily life. That is, as a police car screams towards us, we feel the siren becomes louder and sharper; and as it disappears, the siren dulls down. This is the frequency change resulted from Doppler frequency shift.

Doppler frequency shift means multipath effect can change both the amplitude and frequency structure of transmitted signals, making the phases going up and down. This can cause data signal receive errors.

The amount of Doppler frequency shift can be calculated using the following formula:

Doppler frequency shift = (moving speed/wave length) * COS (angle formed by incident wave and moving direction)

When people talk on mobile phones while walking slowly, Doppler frequency shift can be neglected. But when people talk on mobile phones in a speedy car, the influence of Doppler frequency shift has to be considered.

Signal shadow and transmission loss

Fading refers to the phenomenon that the amplitude of received signals keeps going up and down at random. The duration of fading is used to distinguish fast and slow fading.

Fast fading is mostly caused by multipath propagation. It seriously distorts signals.

Slow fading is induced by various types of atmospheric reflection or obstacles (such as terrain) in the environment of a moving mobile station.

With frequency increase, the curvature of signal levels varying with time gradually approaches Rayleigh distribution. Therefore, Raleigh distribution can be used to estimate the worst situation of fast fading.

CRC uses cyclic code to check and correct independent random errors and accidental errors. Cyclic code is easy to implement in hardware by using a feedback shift register. It is the advantages of cyclic code -- clear algebraic structure, good performance, easy encoding and implementation, that make it the most frequently used anti-interference method. CRC tends to be used only for error check in real applications.

Convolutional coding technique can effectively overcome individual random data errors. Elias is the first to introduce convolutional code in 1995 and named it so because the coding process can be expressed with a convolutional arithmetic operation.

Convolutional coding uses a memory system, that is, for any given time period, the n encoder outputs are not only related to the k inputs within this period, but also related to the m inputs stored in the encoder.

Cyclic Redundancy

Check

Convolutional Coding



Convolutional codes have a constraint length of l=m+1, where m is the number of bytes (memory length) that the register in the encoder has.

Convolutional codes require the selection of constraint length and rate. The constraint length should be as large as possible so as to produce good performance. However, the decoding complexity grows with the constraint length. Today’s super large-scale integrated circuits can process the convolutional codes with a constraint length of 9. The code rate is decided by the channel coherence time and the interleaver depth to be discussed below.

The purpose of block interleaving technique is to correct impulsive data errors in series, so that the number of errors in each received word after de-interleaving is not greater than the error correction code can handle.

On these variable-parameter channels in terrain mobile communications, bit errors often come in series. This is because the long fading valley can influence the next series of bits. But the channel encoding is only effective in checking and correcting limited number and short series of errors.

To solve this problem, hopefully a way can be found to scatter the sequential bits of a message, that is, sending the sequential bits of a message in a non-sequential order (in disperse). In this case, even if a series of errors happened during transmission, the message recovered after de-interleaving would contain only one or a few errors. This technique is called interleaving.

Using error correction code can correct the random errors contained in a de-interleaved word and recover the original message.

Radio channels can produce impulsive errors. And interleaving can randomize these errors so convolutional coding is very effective in preventing random errors. Interleaving scheme falls in block interleaving and convolutional interleaving. The cellular systems usually use block interleaving.

The performance improvement brought in by interleaving is decided by channel diversity level and average fading interval. The interleaving length is determined by service delay requirement. Voice service requires shorter delay than data service. Therefore, the interleaving depth should be matched to the specific service.

Turbo code is a new channel-coding scheme introduced in 1993, and is an important breakthrough in the area of error correction coding in recent years.

Turbo code is encoded using relatively simple RSC (Recursive Systematic Convolutional) code and interleavers, and decoded using iteration and de-interleaving. Turbo code can produce an error correction performance close to the theoretic limit so it has strong anti-fading and anti-interference capabilities. Therefore, Turbo code is defined as one of the core systems in the 3rd generation mobile communication systems.

Block Interleaving

Technique

Turbo Code



However, due to the decoding complexity and delay, Turbo code is suitable for data services that have slack delay requirement. As for voice and data services that have stringent delay requirement, convolutional code is used.

Turbo code encoder comprises two member encoders (RSC1 and RSC2), a Turbo interleaver, and a deletor, as shown in FIGURE 8.

FIGURE 8 TU R B O C O D E E N C O D E R

RSC1

Turbo interleaver

RSC2

Symbol deletion and repetition

Nturboinformation

bit input

( Nturbo+6) /Rsymbol output

1. Member encoders

Each RSC outputs two check bits. The generator polynomial for RSC is G=[1, 15/13, 17/13]. The designed coding rate R can be 1/2, 1/3 or 1/4. Turbo encoder takes Nturbo bit inputs, including information data, frame check (CRC), and two reserved bits, and outputs (Nturbo+6)/R symbols, the last 6/R bits of which are tail bits containing the system bit and check bit. The tail bits are used to zero out the encoder.

The encoding process starts from RSC1 at the top of Fig 2.6-3 every time. Before that, the RSC1 registers are initialized to zero. Then, the switch is turned upward within the clock cycles from 1 to Nturbo. The input data is fed to RSC1 bit by bit, and at the same time it is written to the Turbo interleaver. Within the three clock cycles after Nturbo, the switch is turned downward, and the tail bits are generated to zero out the RSC1.

RSC2 works the same way as RSC1 does, except that the input for RSC2 comes from the Turbo interleaver, and it has to wait until the Turbo interleaver becomes full before it can start to work. The Turbo interleaver is a storage area, which has its input data read-in in a normal sequence and its output read-out in a pre-defined sequence.

Finally, the outputs from these two RSCs, including those corresponding to the tail bits, are deleted and multiplexed to form an encoded Turbo code. Both of the RSCs in the cdma2000 Turbo coding are zeroed out at the end of encoding,

Turbo Code Encoder



but the tail bits do not participate interleaving. This is different from the “classic” Turbo code published by C．Berrou.

2. Interleaver

Turbo interleaver interleaves the input data, frame quality indicator bit (CRC), and reserved bit. Its function is to sequentially read-in a frame of input bits and read-out the whole frame of data in a pre-defined address sequence.

The interleaver size is Nturbo, and the input address is numbered from 0 to Nturbo-1. To define an interleaver is to determine the address numbers of Nturbo outputs for read-out. For example, if Nturbo=5, the input address is [01234]. We need to define a group of 5 output addresses, for example, [10423]. The process in which the read-out addresses are generated by a Turbo interleaver in cdma2000 is described as follows:

1) Define interleaver parameter n. n is the minimum integer that satisfies Nturbo≤2n+5.

2) Construct an n+5 bit counter and initialize it to 0.

3) Take out the high-end n bits from this counter, plus 1, and then take the low-end n bits of the sum.

4) Use the low-end 5 bits of the counter as an index to search for the corresponding Turbo interleaver parameter.

5) Multiply the values obtained from step 3 and 4, and take the low-end n bits.

6) Take the low-end 5 bits of the counter, and get its opposite bit by bit.

7) Use the outcome of step 6 as high-end 5 bits and that of step 5 as low-end n bits to form an n+5 bit address.

8) If this address is valid (<Nturb), it is an output address; otherwise discard it.

9) Add 1 to the counter, and repeat the operations from step 3 to step 8 until all the Nturbo interleaver output addresses are obtained.

3. Delete

The output symbols from the two member encoders must go through deletion operation to form the final Turbo code block.

The basic decoder structure is as shown in FIGURE 9. Its main components are two decoders for soft input/output and two encoder-related interleavers/de-interleavers.

Turbo Code Decoder



FIGURE 9 TU R B O C O D E D E C O D E R

De-interleave

Interleave

Interleave

DEC2

De-interleave

DEC1

Soft information

Softinformation

Soft information

DecisionoutputCheck bit of 2nd encoder

Check bit of2nd encoder

Receivedinformation bit

The critical part of a Turbo decoder is the member decoders corresponding to the encoders at the transmitter, that is, DEC1 and DEC2 in FIGURE 9. Seen alone, RSC1 and RSC2 are the encoders directly corresponding to DEC1 and DEC2 in FIGURE 8. But these member encoders must be able to output soft information and take input of prior information. It can be seen from FIGURE 9 that the member decoders have three inputs. Besides the system bit and check bit inputs that all common decoders have, there is one more prior information input.

The decoding process is as follows:

1. Send the soft decision information corresponding to the system bit and check bit of the first member encoder (RSC1) to the first decoder unit (DEC1) for decoding.

The soft information output from DEC1 can be decomposed into two parts: internal and external information. The external information is prior to DEC2, but sequentially, it must go through de-interleaving process so as to match the system bit of DEC2.

2. The second member decoder starts to decode.

Since the RSC2 system bit duplicates that of RSC1, it is deleted at the transmitting end. The interleaved system bit of RSC1 can be sent to DEC2 as its system bit input. The external information output from DEC1 is used as DEC2’s prior information input.

The second decoder unit (DEC2) also outputs soft information at the end of decoding. The external information parsed from it can be sent back to the first decoder unit for the next round of decoding. The connection between the rounds of decoding is attained through external information.

3. The decoding process can be repeated many times. After iterating for a specified times, make over-zero decision on the soft information to get the final output.

1. Briefly sate spread spectrum principles. Review



2. Briefly describe CDMA features.

3. Briefly state the differences between the three spread spectrum codes used in CDMA systems.

4. Briefly describe the voice and channel encoding techniques used in CDMA systems.


C h a p t e r 3

IS-95 System Principles Key points:IS-95 air interface parameters

Types and functions of forward/reverse channels in IS-95 systems

Forward/reverse channels encoding, modulating processes in IS-95 systems

IS-95 System Service Flow

Introduction

After studying this chapter, you will know the basic types and functions of IS-95 forward/reverse channels, as well as their respective encoding, modulation, and decoding processes.

IS-95 System Overview

TIA published a series of standards coded with IS-95 for narrowband CDMA cellular communication systems in 1993. The full name for IS-95 standard is “Mobile Station – Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System”.

IS-95 Air Interface Parameters

Is-95 system is the first being required to be compatible with analog communication systems (AMPS), its frequency numbering inherits that of AMPS, whose frequency description is complicated. The relationship between frequency number N and carrier f (in MHz) is as follows:

fuplikn=825+0.03×N

fdownlink=870+0.03×N



CDMA systems use much less frequency numbers than GSM systems. Of course, in CDMA systems, each frequency occupies 1.23 MHz bandwidth, far greater than GSM.

The IS-95 air interface parameters are shown in Table 6.

T AB L E 6 IS -95 AI R I N T E R F AC E P AR AM E T E R S

Item Index

Downlink frequency 870 MHz ∼880 MHz

Uplink frequency 825 MHz ∼835 MHz

Frequency difference

between uplink and

downlink

45 MHz

Wavelength About 36 cm

Frequency bandwidth 1230 kHz

Multi-access mode CDMA

Work mode FDD

Modulation mode QPSK

Voice encoding CELP

Voice encoding rate 8 kbit/s

Transmission rate 1.2288 Mbit/s

Bit duration 0.8μs

Max transmitting power of

mobile station

200 mW~1W

Forward Channels

Forward links (from base station to mobile station) provide the communication from base station to mobile station.

A forward link comprises the following logic channels:

Pilot channel

Used to transmit pilot signals to identify different base stations and guide the mobile stations to access the network.

Sync channel

Used by the base station to transmit time and frame synchronization signals to the mobile stations.

Paging channel

Used by the base station to transmit system messages and paging messages to the mobile stations.

Forward traffic channel

Channel Types and Functions



Used by the base station to transmit user and signaling information to the mobile stations. Each forward traffic channel contains the service data and power control information sent to the mobile station.

The characteristics of these logic channels are shown in Table 7.

T AB L E 7 IS -95 S Y S T E M FO R W AR D C H A N N E L S

Channel Quantity Rate (bit/s) Function

Pilot channel 1 1200 Broadcast base station frequency and phase

information to help with coherence

demodulation on mobile stations

Sync channel 1 1200 Broadcast base station synchronization

information and system parameters

Paging

channel

1~7 9600/4800 Broadcast base station paging information

and system parameters, and transmit base

station commands

Forward

traffic channel

1~55 9600/4800

2400/1200

Transmit voice and data services

The forward pilot channel only provides frequency reference for coherence demodulation on mobile stations. It contains all 0’s and has no frame structure. The structures of the other channels are described below.

1. Sync channel

Has a bit rate of 1200 bit/s and frame duration of 26.67 ms.

Information is transmitted in hyper frames on sync channel, which comprises three common frames.

The start time of a hyper frame aligns with that of a pilot PN sequence from the base station.

2. Paging channel

Transmits information at a fixed data rate of 9600 bit/s or 4800 bit/s. It does not support the data rates of 2400 bit/s and 1200 bit/s. In a given system, all the paging channels use the same transmitting data rate.

The paging channel has frame duration of 20 ms. It uses the same pilot PN sequence offset as the pilot channel on the same CDMA forward channel. The starts of a interleave block and a sync channel frame aligns with that of a pilot PN sequence used to spread the forward CDMA channels.

3. Forward Traffic channel

Transmits information at variable data rates of 9600 bit/s, 4800 bit/s, 2400 bit/s and 1200 bit/s. Greater data rate requires higher transmitting power. This makes it easy to understand the purpose of using variable rates, that is, to reduce the data rate when there is no voice activity and thus reduces the interference of the traffic channel to other users.

Channels Frame

Structures



The forward traffic channel has frame duration of 20 ms. Each frame (20 ms) may have a different data rate, but the modulated symbol rate is constant, that is 19200 s/s, which is implemented by symbol repetition.

Each of the forward channels in IS-95 systems is encoded in a different process, as described below.

1. Pilot channel

The encoding process for pilot channel is the simplest among all the forward channels, as shown in FIGURE 10.

FIGURE 10 IS -95 P I L O T C H AN N E L E N C O D I N G P R O C E S S

+

Pilot channel

Walsh

an

Since the pilot channel contains all 0’s, convolution and interleaving are not required. The pilot channel is first spread with W0, and then modulated. The Walsh code rate is 1.2288 M chip/s.

2. Sync channel

The encoding process for sync channel is as shown in FIGURE 11.

Channel Encoding and

Modulation



FIGURE 11 IS -95 S Y N C H R O N I Z AT I O N C H AN N E L E N C O D I N G P R O C E S S

+

Sync channel

Walsh

an

Convolution

Coderepetition

Interleave

1） Convolution. The information transmitted on sync channel is convolutional coded (rate=1/2, constraint length=9), and becomes 2400 bit/s.

2） Symbol repetition (that is, each symbol is transmitted twice in succession.) After symbol repetition, it becomes 4800 bit/s signal.

3） Interleave. The interleaving process accesses the columns of a 16×8 matrix, containing 128 bit data and equivalent to 26.67 ms data quantity.

4） Spread. The synchronization channel is spread with W32, and then modulated.

3. Paging channel

The encoding process for paging channel is as shown in FIGURE 12.



FIGURE 12 IS -95 P AG I N G C H AN N E L E N C O D I N G P R O C E S S

+

Paging channel

Walsh

an

Convolution

Coderepetition

Interleave

+Scrambling

1） Convolution. The signals are convolutional coded (rate=1/2, constraint length=9) and becomes 9600 bit/s or 19200 bit/s.

2） Symbol repetition. If the original signals are 4800 bit/s, they need to go through symbol repetition and become 19200 bit/s. But the original 9600 bit/s signals need not go through symbol repetition.

3） Interleave. The interleaving process uses a 24×16 matrix, containing 384 bit data, and equivalent to 20 ms data quantity.

4） Scramble. The paging channel is scrambled with a 42-bit PN code.

5） Spread. The paging channel is spread with W1~W7, and then modulated.

4. Forward traffic channel

The encoding process for forward traffic channel is as shown in FIGURE 13.



FIGURE 13 IS -95 F O R W AR D T R AF F I C C H AN N E L E N C O D I N G P R O C E S S

+

Traffic channel

Walsh

an

Convolution

Coderepetition

Interleave

+Scrambling

Multiplex

Powercontrol

1） Convolution. The data on forward traffic channel is convolutional coded (rate=1/2, constraint length=9).

2） Symbol Repetition. Similar to the paging channel, the original 9600 bit/s signals need not be repeated. But 4800 bit/s signals are repeated once, 2400 bit/s three times, and 1200 bit/s seven times, finally turned into 19200 bit/s signals.

3） Interleave. The interleaving process uses a 24×16 matrix, containing 384 bit data and equivalent to 20ms data quantity.

4） Scramble. The scrambling is done in the same way as the paging channel but with a long code in different mask format. The forward traffic channel also contains a power control bit with a rate of 800 bit/s. “0” instructs the terminal to increase its output power, and “1” to decrease.

5） Spread. The forward traffic channel is spread with W8~W31 and W33~W63. There can be 55 forward traffic channels at maximum, but this number cannot be actually attained due to system self-interference.

All the forward channels are modulated in the same mode, as shown in FIGURE 14.



FIGURE 14 IS -95 F O R W AR D C H AN N E L M O D U L AT I O N P R O C E S S

90?+

X

~

X

Lowpassfilter

+

+

Pilot PNI

PilotPNQ

coswct

-sinwct

I

Q

S(t)

Lowpassfilter

an

wc

First, the input signals for I and Q are the same. Second, these input signals are modulo-1 added to a PN code before going to the baseband filters, that is, being scrambled. The input signals for I and Q use different generator polynomials, as shown in the following equations:

fI(x)=1+x5+x7+x8+x9+x13+x15

fQ(x)=1+x3+x4+x5+x6+x10+x11+x12+x15

The modulation process for forward traffic channel is as shown in Table 8.

T AB L E 8 IS -95 S Y S T E M FO R W AR D TR AF F I C C H AN N E L P AR AM E T E R S

Rate

(kbit/s)

PN

Subcode

Rate

(Mc/s)

Convoluti

onal

Coding

Rate

Code

Occurrences

after

Repetition

Modulated

Symbol Rate

(s/s)

Subcodes

per

Modulated

Symbol

Subcodes

per Bit

9600 1.2288 1:2 1 19200 64 128

4800 1.2288 1:2 2 19200 64 256

2400 1.2288 1:2 4 19200 64 512

1200 1.2288 1:2 8 19200 64 1024

The decoding process for each channel is to reverse the encoding process. Here, we will not delve into it. But, we should know that the decoding process contains these steps: demodulate, despread short code, and despread long code.

Reverse Channels

Reverse links (from mobile station to base station) provide the communication from mobile station to base station.

A reverse link comprises the following logic channels:

Access channel

Used by the mobile station to initiate communication with a base station or respond to a paging message.




It is a random access channel. Each paging channel can support up to 32 access channels simultaneously.

Reverse traffic channel

Used by the mobile station to send user and signaling information to a base station.

1. Access channel

Contains 96 bits. Each access channel frame is composed of 88 information bits and 8 encoding tail bits.

The access channel preamble contains 96 frames of all 0’s, and is transmitted at the rate of 4800 bit/s. It is used to assist the base station to capture the access channels.

2. Reverse traffic channel

Used by the mobile station to transmit information at the variable rates of 9600 bit/s, 4800 bit/s, 2400 bit/s and 1200 bit/s.

The reverse traffic channel has frame duration of 20 ms. Each frame may have a different data rate. The mobile station supports offset frames on traffic channel. The time offset is defined by the FRAME-OFFSET parameter in channel assignment message on the paging channel. When the system time is an integer multiple of 20 ms, a zero offset frame is transmitted on the traffic channel. The latency frame is transmitted 1.25×FRAME－OFFSET ms later than the zero offset frame. On the reverse traffic channel, the interleave block aligns with the frame.

1. Access channel

The encoding process for access channel is as shown in FIGURE 15.

Channels Frame

Structures


Modulation



FIGURE 15 IS -95 AC C E S S C H AN N E L E N C O D I N G P R O C E S S

+

Access channel

Longcode

an

Convolution

Coderepetition

Interleave

OrthogonalModulation

1） Convolution. The information transmitted in access channel is first convolutional coded (rate=1/3, constraint length=9), and becomes 14400 bit/s.

2） Symbol repetition. After symbol repetition, it becomes a 28800 bit/s signal.

3） Interleave. The interleaving process accesses the columns of a 32×18 matrix, containing 576 bit data and equivalent to 20ms data quantity.

4） Orthogonal modulation. After this process, the signal rate is raised from 28800 bit/s to 307.2 kbit/s. The access channel uses PN long code for spreading.




The encoding process for reverse traffic channel is as shown in FIGURE 16.

FIGURE 16 IS -95 R E V E R S E T R AF F I C C H AN N E L E N C O D I N G P R O C E S S

+

Traffic channel

Longcode

an

Convolution

Coderepetition

Interleave

Randomization

OrthogonalModulation

1） Convolution. The data in reverse traffic channel first goes through convolution (rate=1/3, constraint length=9).

2） Symbol repetition. Similar to the forward traffic channel, the original 9600 bit/s signals need not be repeated. But the 4800 bit/s signals are repeated once, 2400 bit/s three times, and 1200 bit/s seven times.

3） Interleave. The interleaving process accesses the columns of a 32×18 matrix, containing 576-bit data and equivalent to 20ms data quantity.

4） Orthogonal modulation. Same with access channel. The reverse traffic channel uses PN long code for spreading, which is generated in the same process as the paging channel long code.

5） Randomization. Data randomization guarantees each symbol, after symbol repetition, is still transmitted only once.

All the reverse channels use the same modulation mode, the process of which is as shown in FIGURE 17.



FIGURE 17 IS -95 R E V E R S E C H AN N E L M O D U L AT I O N P R O C E S S

90?+

X

~

XLowpassfilter

+

+

Pilot PNI

PilotPNQ

coswct

-sinwct

I

Q

S(t)

Lowpassfilter

an

wc

Delay

Modulation differences from the forward channel:

Half chip latency (410 ms) is introduced to Q signals, and hereby it becomes OQPSK modulation mode. In this case, sharp change can be avoided, that is, the signal crosses zero point.

The I and Q signals are binary added to a PN code before going to the baseband filters. The PN code used is the zero offset of pilot PN sequence.

The modulation process for reverse traffic channel is as shown in Table 9.

T AB L E 9 IS -95 R E V E R S E TR AF F I C C H A N N E L P AR AM E T E R S

Rate

(kbit/s)

PN

Subcode

Rate

(Mc/s)

Convolut

ional

Coding

Rate

Transmis

sion duty

ratio (%)

Code Rate

(s/s)

Subcodes

per

Modulated

Code

Modulated

Code Rate

(s/s)

Walsh

Subcode Rate

(kc/s)

9600 1.2288 1:3 100 28800 6 4800 370.20

4800 1.2288 1:3 50 28800 64 4800 370.20

2400 1.2288 1:3 25 28800 6 4800 370.20

1200 1.2288 1:3 12.5 28800 64 4800 370.20

Comparison of Reverse Channels and Forward Channels

Similar with the forward channels, reverse channels also use PN code of the same length for spreading and modulation, but with a fixed phase difference. The digital signals sent by the mobile station also go through convolutional coding, block interleaving, Walsh code 64-system orthogonal modulation, long code spreading, and 4-phase PN spreading modulation. However, they are different from forward channels in the following aspects:



The transmitted digital data are convolutional coded with rate 1/3 and constraint length 9. Thus the encoded symbols have a rate of 28.8 kbit/s.

The data is interleaved at 20 ms interval. The interleaved signals have every 6 binary symbols put into a group, which is used to select one of the 64 different Walsh orthogonal functions as the transmitting signal.

Obviously, here the Walsh function is applied differently from forward links. The Walsh function is used to distinguish the channels allocated to the mobile stations in forward links, while in reverse links, the Walsh function is used to modulate the information for transmission, that is, 64-ary orthogonal modulation. After modulation, the symbol rate is 307.2 k chip/s, and the chip rate is 1.2288 M chip/s.

The PN long codes in reverse links are not used for scrambling, but for direct spreading and identifying different mobile stations. Since there is a valid address for each possible phase shift of the PN long code, it can provide a quite big address space and high confidentiality.

When PN short codes are used for 4-phase modulation, the zero shift PN code is selected for all the mobile stations. This is because the base station need not be identified in the reverse links.

Service Flow

IS-95 supports voice service only. A typical voice service includes: calling, called, hang-up, registration and handoff. They are introduced in detail in the following sections (please refer to “0 Handoff”for details of handoff).

The Calling flow is shown in FIGURE 18 Calling flow



FIGURE 18 C AL L I N G F L O W

MS

A

B

C

D

BS

E

Origination

Base Station Acknowledgement Order

Channel Assignment

Null

Access

Paging

Paging

Traffic

TrafficPreamble

Base Station Acknowledgement Order Traffic

Mobile Station Acknowledgement Order Traffic

Service Connect Message Traffic

Service Connect Complete Message Traffic

Base Station Acknowledgement Order Traffic

Calling Flow

F

H

G

I

J

K

A． Terminals send origination message to the base station via access channel and wait for the acknowledgement from base station;

B． Once the origination message is received, the base station sends a Base Station Acknowledgement Order to the terminals via paging channel. It means the authentication succeeds.；

C． The base station assigns an idle traffic channel to the terminal. It sends a Channel Assignment message to the terminal via paging channel to inform the dedicated traffic channel assigned by the terminal;

D． Meanwhile, the base station sends a Null message to the terminal via the dedicated traffic channel;

E． Once the channel assignment is received by the terminal, turn to the dedicated traffic channel assigned by the base station to listen to the forward traffic channel quality. If two consecutive good frames are detected, means this traffic channel is available. The terminal sends Preamble to the base station via this traffic channel;

F． After receiving the leading frame from the terminal, the base station sends a Base Station Acknowledgement Order to the terminal via traffic channel;

G． Once the message is received, the terminal sends a Mobile Station Acknowledgement Order message to the base station. The traffic channel established;



H． The base station sends a Service Connect Message to the terminal via traffic channel to initiate a traffic negotiation;

I． Once the message is accepted, the terminal sends a Service Connect Complete Message to the base station. The traffic negotiation is over;

J． The base station sends a Base Station Acknowledgement Order to the terminal via traffic channel;

K． Now the terminal and the base station can communicate with each other.

The called flow is more complex than the calling flow. It is shown in FIGURE 19

FIGURE 19 C AL L E D F L O W

MS

A

B

C

D

BS

E

General Page Message

Page Response Message


Channel Assignment

Paging

Access

Paging

TrafficNull

Preamble Traffic

Traffic

Traffic

Service Connect Complete Message

Traffic


Traffic

Called Flow

F

H

G

I

J

Paging


Mobile Station Acknowledgement Order

Service Connect Message

Alert With Information Message Traffic

Mobile Station Acknowledgement Order Traffic

Ringing

Connect Order Traffic

Traffic

K

L

M

N

P

O

A． If the terminal is power on and is ready to receive calls, when being called, it will receive a paging channel broadcasting General Page Message from the base station;

B． Once the common paging message is received, the terminal sends a Page Response Message to the base station via access channel;

Called Flow



C~J． The Same as B~I in Calling Flow introduced above;

K． The base station sends an Alert with Information Message to the terminal via forward traffic channel to request the terminal ringing;

L~M． Once the ringing message is received, the terminal sends a Mobile Station Acknowledgement Order to the base station via reverse traffic channel. This means the terminal is ringing;

N． After ringing for a while, user hook-off. The terminal sends a Connect Order to the base station via reverse traffic channel to inform that user hook-off;

O． Once the Connect Order is received, the base station sends a Base Station Acknowledgement Order to the terminal via traffic channel;

P． Now the terminal and the base station can communicate with each other.

Hang-up is the call release. There are two types of hang-up: terminal earlier hang-up and terminal later hang-up. The hang-up flow is show in FIGURE 20 and FIGURE 21.

FIGURE 20 TE R M I N AL E A R L I E R H AN G -U P

MS

A

B

BS

Release Order (

normal release ) Traffic

TrafficRelease Order (no reason given)

Hang-up Flow

C

A． The terminal and the base station are in a call;

B． The terminal tends to hang-up, therefore sends a Release Order to the base station via reverse traffic channel;

C． Once the order is received, the base station sends a Release Order to the terminal via forward traffic channel. Then the hang-up is over. The Release Order sent by the terminal and the base station has different parameters.

FIGURE 21 TE R M I N AL L AT E R H AN G -U P

MS

A

B

BS

Release Order(normal release) Traffic

TrafficRelease Order(no reason given)

Hang-up Flow

C

Hang-up Flow



A． The terminal and the base station are in a call;

B． The base station tends to hang-up, therefore sends a Release Order to the terminal via forward traffic channel;

C． Once the order is received, the terminal sends a Release Order to the base station via reverse traffic channel. The hang-up is over.

The registration flow is shown in FIGURE 22.

FIGURE 22 R E G I S T R AT I O N F L O W

MS

A

B

BS

Registration Message


Access

Paging

A． The base station sends a Registration Message to the terminal via access channel;

B． Once the message is received, the base station feedbacks a base station acknowledgement on paging channel. That means the authentication and the registration succeed.

1. Briefly state the types and functions of forward/reverse channels in IS-95 systems.

2. Briefly state forward/reverse channels encoding, modulation, and decoding processes in IS-95 systems.

3. Compare IS-95 forward and reverse channels.

4. What call flows are there in the IS-95? Please briefly state the called flow.

Registration Flow

Review


C h a p t e r 4

cdma2000 1x System Principles

Key points:cdma2000 1x air interface parameters

Types and functions of cdma2000 1x forward/reverse channels

Encoding, modulation processes of cdma2000 1x forward/reverse channels

cdma2000 1x technical features

cdma2000 1x System Service Flow

Introduction

After studying this chapter, you will get the basic knowledge of cdma2000 1x, such as air interface parameters, structures and functions of forward/reverse channels, as well as the encoding, modulation, and decoding processes.

System Overview

cdma2000 is one of the radio transmission technologies for the 3rd generation communication specified by ITU. cdma2000 systems fall into 1x and 3x according to the bandwidth they use. The 1x systems use 1.25 MHz bandwidth, so the data service rate it provides can reach 307 kbit/s at maximum. From this angle, cdma2000 1x systems can be regarded as 2.5 generation systems.

The major difference between 1x and 3x lies in that 3x employs multi-carrier technique and improves its bandwidth by using three carriers.

A complete cdma2000 1x system is composed of network subsystem (NSS), base station subsystem (BSS), and mobile station (MS).

cdma2000 1x systems can support a data rate of 308 kbit/s. The network incorporates packet switch technique, and supports



mobile IP service (a new carrier service developed on existing IS-95 systems, the purpose of which is to provide packet switch IP data service for CDMA subscribers).

Air Interface Parameters

cdma2000 1x air interface parameters are shown in Table 10.

T AB L E 10 C D M A2000 1 X AI R I N T E R F AC E P AR AM E T E R S

Item Index

Downlink frequency 870~880 MHz

Uplink frequency 825~835 MHz

Frequency difference between uplink and

downlink

45 MHz

Wave length About 36cm

Frequency bandwidth 1230 kHz

Work mode FDD

Modulation mode QPSK、HPSK

Voice encoding CELP

Voice encoding rate 8 kbit/s

Transmission rate 1.2288 Mbit/s

Bit duration 0.8μs

Forward Channels

Forward links (from base station to mobile station) provide the communication from base station to mobile station.

The forward links comprise the following logic channels:

Forward pilot channel (F_PICH)

It functions the same as the IS-95A forward pilot channel. The base station uses this channel to transmit the pilot signals that identify it and guide the mobile stations to access the network.

Forward sync channel (F-SYNCH)

It functions the same as IS-95A forward sync channel. The base station sends the system time and frame synchronization information to the mobile stations via this channel to keep timing and synchronize with the system.

Forward paging channel (F-PCH)

It functions the same as IS-95 forward paging channel. The base station transmits paging, command, and traffic channel allocation information to the mobile stations via this channel.




Forward quick paging channel (F-QPCH)

It is used by the base station to quickly instruct the mobile station from which time slot to receive the control message on F-PCH or F-CCCH. The mobile station does not need to monitor F-PCH or F-CCCH time slot all the time, so it saves much battery.

Forward broadcast control channel (F-BCCH)

It is used by the base station to deliver system messages to the mobile station.

Common assignment channel (F-CACH)

The F-CACH is always used together with the F-CPCCH, R-EACH and R-CCCH. When the base station demodulates an R-EACH header, it instructs the mobile station, via F-CACH, which R-CCCH to use to send the access message, and from which F-CPCH sub channel to receive the power control bit.

Forward common power control channel (F-CPCCH)

When the mobile station sends data in R-CCCH, the base station transmits reverse power control bit to the mobile station via this channel.

Forward common control channel (F-CCCH)

It is used by the base station and the mobile station to exchange control messages and short impulsive data when the mobile station has not set up a traffic channel yet.

Forward dedicated control channel (F-DCCH)

When the mobile station is in traffic channel state, it is used by the base station to transmit messages or low-rate packet and circuit data services to the mobile station..

Forward fundamental traffic channel (F-FCH)

This channel is used to carry signaling, voice, low-rate packet service, circuit data services or auxiliary service when the mobile station enters traffic channel state.

Forward supplemental channel (F-SCH)

This channel is used to carry high-rate packet data service on the forward link when the mobile station enters traffic channel state.

Forward supplemental code channel (F-SCCH)

This channel is used for data transfer.

Forward power control sub-channel (F-PCSCH)

This channel transmits persistently on the forward traffic channel. It is used for reverse power control.

F_PICH, F-SYNCH, F-SCCH，F-PCSCH and F-PCH have the same structures as the pilot channel, sync channel, and paging channel of IS-95. The structures of other channels are described below.

1. F-QPCH

Channels Frame

Structures



The base station uses F-QPCH to transmit quick paging information. The information on this channel is transmitted in time slots, called F-QPCH time slots. The F-QPCH time slot has a rate of 4800 bit/s or 9600 bit/s and duration of 80 ms. A base station can provide three F-QPCHs at most.

The start of F-QPCH time slot aligns with that of the zero shift pilot PN sequence.

2. F-CACH

The base station uses F-CACH to transmit access procedure related signaling. The information on F-CACH is transmitted in frames, called F-CACH frames.

The F-CACH frame has a rate of 9600 bit/s and duration of 5 ms.

The CACH frame structure comprises 32 bit frame information, 8 bit frame quality indicator (CRC), and 8 tail bits.

32 bit 8 bit 8 bit

frame information CRC tail bits

The frame quality indicator (CRC) is calculated from the frame information as:

g（x）=x8+x7+x4+x3+x+1

The start of F-CACH frame aligns with that of the zero shift pilot PN sequence.

3. F-BCCH

The base station uses F-BCCH to transmit system information. The information on F-BCCH is transmitted in frames, called F-BCCH frames. A F-BCCH frame contains 768 bits with the duration of 40 ms. The F-BCCH frames are combined into time slots. The three kinds of time slots, 40 ms, 80 ms, and 160 ms, contain one frame, two frames, and four frames respectively. The F-BCCH time slot starts from the time that is an integer multiple of the system time at 4 s interval.

All the frames in a time slot have the same content. This means the content of the four frames in a 160 ms time slot are the same. From this point, the baud rates of the three time slots can be calculated as 19200 bit/s, 9600 bit/s, and 4800 bit/s.

The F-BCCH frame structure comprises 744 bit frame information, 16 bit frame quality indicator (CRC), and 8 tail bits.

744 bit 16 bit 8 bit

Frame information CRC tail bits

The frame quality indicator (CRC) is calculated from the 744 bit frame information as:

g（x）=x16+x15+x14+x11+x6+x5+x2+x+1



4. F-CCCH

The base station uses F-CCCH to transmit access procedure related signaling. The information on F-CCCH is transmitted in frames, called F-CCCH frames. The F-CCCH frame structure comprises frame information, frame quality indicator (CRC), and 8 tail bits.

The F-CCCH frame has multiple rates: 9600 bit/s, 9200 bit/s or 38400 bit/s. Thus the frame length varies; so do the frame information and frame quality indicator.

For example, a 9600 bit/s F-CCCH frame with the duration of 20 ms contains 192 bits, of which 172 bits are for frame information and 12 bits for frame quality indicator.




g（x）=x12+x11+x10+x9+x8+x4+x+1

The start of F-CCCH frame aligns with that of the zero shift pilot PN sequence.

5. F-DCCH

The base station uses G-DCCH to transmit service procedure related signaling. The information on F-DCCH is transmitted in frames, called F-DCCH frames.

The F-DCCH frame structure comprises frame information, frame quality indicator (CRC), and 8 tail bits.

The F-DCCH frame has a rate of 9600 bit/s and duration of 5 ms or 20 ms. Thus the frame length varies; so do the frame information and frame quality indicator.

For example, a 9600 bit/s F-DCCH frame with the duration of 5 ms contains 48 bits, of which 24 bits are for frame information and 16 bits for frame quality indicator.

24 bit 16 bit 8 bit



g（x）=x16+x15+x14+x11+x6+x5+x2+x+1

Similar to the frames of IS-95 traffic channels, the F-DCCH frame starts from the time specified by FRAME_OFFSET. F-DCCH cannot be transmitted continuously.

6. F-FCH

The base station uses FCH to transmit voice, low speed data or signaling. The information on F-FCH is transmitted in frames, called F-FCH frames.



The F-FCH frame structure comprises frame information, frame quality indicator (CRC), and 8 tail bits.

With RC3, the FCH frame has multiple rates: 9600 bit/s, 4800 bit/s, 2700 bit/s and 1500 bit/s. It is slightly different with RC1. Normally, the frame length is 20 ms, but. it can be 5 ms at 9600 bit/s.

For example, a 9600 bit/s F-FCH frame contains 48 bits, of which 24 bits are for frame information and 16 bits for frame quality indicator, and 8 tail bits.

24 bit 16 bit 8 bit



g（x）=x16+x15+x14+x11+x6+x5+x2+x+1

Similar to the frames of IS-95 traffic channels, the F-FCH frame starts from the time specified by FRAME_OFFSET.

7. F-SCH

The terminal uses F-SCH to transmit data only with RC3. The information on F-SCH is transmitted in frames, called F-SCH frames. The F-SCH frame structure comprises frame information, frame quality indicator (CRC), and 8 tail bits.

The F-SCH frame has multiple rates: 153600 bit/s, 76800 bit/s, 38400 bit/s, 19200 bit/s、9600 bit/s, 4800 bit/s, 2700 bit/s, 2400 bit/s, 1500 bit/s, 1350 bit/s, and 1200 bit/s. Normally, the frame duration is 20 ms, 40 ms or 80 ms, so the frame information and quality indicator also vary.

For example, a 38400 bit/s F-SCH frame has a duration of 40 ms and contains 1536 bits, of which 1512 bits are for frame information and 16 bits for frame quality indicator.




g（x）=x16+x15+x14+x11+x6+x5+x2+x+1

The F-SCH frame starts from the time specified by FRAME_OFFSET and REV_SCH_FRAME_OFFSET[i], where i=1 or 2, representing the first or second supplementary traffic channel.

The encoding processes for cdma2000 1x air interface logic channels are different from each other. The IS-95 channel encoding technique is still used for the following forward channels: pilot, synchronization, and paging, and the traffic channels with RC1. The encoding process for other logic channels is as shown inFIGURE 23.


Modulation



FIGURE 23 C D M A2000 1 X F O R W AR D C H AN N E L E N C O D I N G P R O C E S S

F-QPCH

X +

F-BCCH

Convolution

Interleave

Coderepetition

F-CACH/F-CCCH

Convolution

Interleave

+Scrambling

F-DCCH

Convolution

Interleave

+Scrambling

Multiplex

Powercontrol

F-FCH/F-SCH

Convolution

Coderepetition

Interleave

+Scrambling

Multiplex

Powercontrol

Coderepetition

Scrambling

X X X X

1. F-QPCH

The F-QPCH encoding process is rather simple. It does not involve convolutional coding and interleaving. Symbol repetition turns the signals into 28800 bit/s, and then spread. The first F-QPCH is spread with W80

128. If there is a second F-QPCH, it will be spread with W48

128. If there is still a third F-QPCH, it will be spread with 112

128. The Walsh code bit rate is 1.2288 M bit/s. It is the same for all the following channels and will not be explained any more.

2. F-BCCH

The encoding process for F-BCCH is as shown in FIGURE 23..

1） Convolution. The information on F-BCCH is convolutional coded (rate=1/2, restraint length=9) and becomes 4800 bit/s, 9600 bit/s or 1920 bit/s signals.

2） Interleave. The interleaving method is changed from IS-95 column access into sequential array read-in, and the output is read-out in a sequence calculated from a specified formula. The data is interleaved in groups of 1536 bits.

3） Symbol repetition. After symbol repetition, the signals become 38400 bit/s.

4） Scramble. The scrambling method is the same as paging channel.

The F-BCCH uses the following long code mask format:

41------29 28------24 23------21 20------9 8------ 0

1100011001101 01100 BCN 000000000000 PILOT-PN



Where, BCN stands for the channel number of F-BCCH. The system can support a maximum of 8 F-BCCHs.

F-BCCH can only use the Walsh codes in rank 128.

3. F-CACH

The encoding process for F-CACH is as shown in FIGURE 23.

1） Convolution. The information transmitted on F-CACH is convolutional coded (rate=1/2, constraint length=9), and becomes 19200 bit/s signals.

2） Interleave. The data is interleaved in groups of 96 bits with the method changed from IS-95 column access into sequential array read-in. The output is read out in a sequence calculated from a specified formula.

3） Scramble. The scrambling method is the same as IS-95 paging channel. The F-CACH uses the following long code mask format:

41 ------29 28------24 23 ------ 21 20 ------ 9 8 ------ 0

1100011001101 01100 CACN 000000000000 PILOT-PN

Where, CACN stands for the channel number of F-CACH. The system can support a maximum of 7 F-CACHs.

F-CACH can only use the Walsh codes in rank 128.

4. F-CCCH

The F-CCCH encoding process is as shown in Fig 4.4-1.

1） Convolution. The information transmitted on F-CCCH is convolutional coded (rate=1/4, constraint length=9).

2） Interleave. Since the information on F-CCCH is transmitted at multiple rates: 9600 bit/s, 19200 bit/s or 38400 bit/s, the frame length varies, and so does the length of data block for interleaving process. For example, for a F-CCCH frame with a frame length of 20 ms and a rate of 9600 bit/s, the length of data block for interleaving is 384 bits. The discussion on other cases will be omitted.

3） Scramble. The scrambling method is the same as paging channel.

The F-CCCH uses the following long code mask format:

41 ------ 29 28 ------ 24 23 ------ 21 20 ------ 9 8 ------ 0

1100011001101 01100 000 000000000000 000000000

The F-CCCH can only use the Walsh codes in rank 128.

5. F-DCCH

The encoding process for F-DCCH is as shown in Fig 4.4-1.

1） Convolution. The F-DCCH is convolutional coded (rate=1/4, constraint length=9), and becomes 38400 bit/s signals.



2） Interleave. The length of data block for interleaving is 192 or 768 bits.

3） Scramble. The scrambling method is the same as IS-95 forward traffic channels.

Same as IS-95 reverse traffic channels; the F-DCCH uses the following long code mask format for spreading:

41 ------ 32 31 ------ 0

1100011001101 Reorganized ESN

Similar to IS-95 forward traffic channels, the DCCH contains a power control bit. The DCCH can only use the Walsh codes in rank 128.

6. F-FCH

The encoding process for F-FCH is as shown Fig 4.4-1.

1） Convolution. The F-FCH is convolutional coded (rate=1/4, restraint length=9).

2） Symbol repetition.

3） Interleave. The length of data block for interleaving varies with the fame length.

4） Scramble. The scrambling method is the same as IS-95 forward traffic channels. The long code mask format is the same as F-DCCH.

Similar to IS-95 forward traffic channels, F-FCH contains a power control bit.

7. F-SCH

The encoding process for F-SCH is as shown in Fig 4.4-1

1） Convolution. The F-SCH frame is convolutional coded (rate=1/4, restraint length=9) or Turbo coded (frame content at least 360 bits) and becomes 38400 bit/s signals.

2） Interleave. The length of data block for interleaving varies with the fame length.

3） Scramble. The scrambling method is the same as IS-95 forward traffic channels. The long code mask format is the same as F-DCCH.

Similar to IS-95 forward traffic channels, F-SCH contains a power control bit.

All the forward channels use the same modulation method, the process of which is as shown in FIGURE 24

FIGURE 24 C D M A2000 1 X F O R W AR D C H AN N E L M O D U L AT I O N P R O C E S S

Parallelconversion

X YI

YQ



Reverse Channels

Reverse links (from mobile station to base station) provide the communication from mobile station to base station.

The reverse channels include:

Reverse pilot channel (R_PICH)

It is used to assist the base station to detect the data transmitted by mobile stations.

Reverse access channel (R-ACH)

Its functions are the same as the IS-95A reverse access channel.

Reverse common control channel (R-CCCH)

It is used by the base station and the mobile station to exchange control messages and short impulsive data when the mobile station has not set up a traffic channel yet.

Reverse enhanced access channel (R-EACH)

The mobile station sends control messages on this channel to the base station when it has not yet set up a traffic channel, thus improving mobile station accessibility.

Reverse dedicated control channel (R-DCCH)

When the mobile station is in traffic channel state, it uses this channel to transmit messages or low-rate packet and circuit data services to the base stations.

Reverse fundamental channel (R-FCH)

It is used to carry signaling, voice, low-rate packet and circuit data services, or auxiliary services on the reverse link when the mobile station enters traffic channel state.

Reverse supplemental channel (R-SCH)

It is used to carry high-rate packet data service on the reverse link when the mobile station enters traffic channel state.

Reverse supplemental code channel (R-SCCH)

It is used to send user information to the base station during a call.

Reverse power control sub-channel (R-PCSCH)

This channel is the sub-channel of reverse pilot channel. It includes reverse main power control sub-channel and reverse auxiliary power control sub-channel. The channel is used for forward power control.

1. R-CCCH

The mobile station uses R-CCCH to transmit access procedure related signaling. The information on R-CCCH is transmitted in frames, called R-CCCH frames. The R-CCCH frame structure


Channels Frame

Structures



comprises frame information, frame quality indicator (CRC), and 8-bit padding bits.

The R-CCCH frame has multiple rates: 9600 bit/s, 19200 bit/s or 38400 bit/s. The frame length varies, so do the frame information and quality indicator lengths.

For example, a 9600 bit/s R-CCCH frame has duration of 20ms and contains 192 bits, of which 172 bits are for frame information and 12 bits for frame quality indicator.

8 bit


The frame quality indicator (CRC) is calculated from the frame information. A 12-bit quality indicator is calculated as:

g(x)=x12+x11+x10+x9+x8+x4+x+1

The R-CCCH frame starts from the time that is an integer multiple of the system time at 1.25 ms interval.

2. R-EACH

The mobile station uses R-EACH to transmit access procedure related signaling. The information on R-EACH is transmitted in frames, called EACH frames. The R-EACH frame structure comprises frame information, frame quality indicator (CRC), and 8-bit padding bits.

The R-EACH frame has multiple rates: 9600 bit/s, 19200 bit/s or 38400 bit/s. The frame length varies, so do the frame information and quality indicator lengths.

For example, a 9600 bit/s R-EACH frame is 20ms in length and contains 48 bits, including 32-bit information and an 8-bit quality indicator.

8 bit


The frame quality indicator (CRC) is calculated from the frame information. An 8-bit quality indicator is calculated as:

g(x)=x8+x7+x4+x3+x+1

The R-EACH frame starts from the time that is an integer multiple of the system time at 1.25 ms interval.

3. R-DCCH

The mobile station uses R-DCCH to transmit traffic procedure related signaling. The information on R-DCCH is transmitted in frames, called R-DCCH frames. The R-DCCH frame structure comprises frame information, frame quality indicator (CRC), and 8 tail bits.

The R-DCCH frame has a rate of 9600 bit/s and duration of 5 ms or 20 ms, so the lengths of frame information and quality indicator are variable.



For example, a 9600 bit/s R-DCCH frame has duration of 5 ms and contains 48 bits, of which 24 bits are for information and 16 bits for quality indicator.

8 bit



g(x)=x16+x15+x14+x11+x6+x5+x2+x+1

Similar to the IS-95 traffic channel frames, the R-DCCH frame starts from the time specified by FRAME_OFFSET. The R-DCCH can be sent discontinuously.

4. R-FCH

The mobile station uses R-FCH to transmit voice, low rate data or signaling. The information on R-FCH is transmitted in frames, called R-FCH frames. The R-FCH frame structure comprises frame information, frame quality indicator (CRC), and 8-bit padding bits.

The R-FCH frames have multiple rates: 9600 bit/s, 4800 bit/s, 2700 bit/s, and 1500 bit/s. Generally, the frame duration is 20 ms. It can also be 5 ms for 9600 bit/s rate. Thus the lengths of frame information and frame quality indicator are variable.

For example, a 9600 bit/s R-DCCH frame has duration of 5 ms and contains 48 bits, of which 24 bits are for frame information and 16 bits for quality indicator, and 8 bits for tail bits.

8 bit



g(x)=x16+x15+x14+x11+x6+x5+x2+x+1

Similar to the IS-95 traffic channel frames, the R-FCH frame starts from the time specified by FRAME_OFFSET.

5. R-SCH

The mobile station uses R-SCH to transmit high-rate data with only RC3. The information on R-SCH is transmitted in frames, called R-SCH frames. The R-SCH frame structure comprises frame information, frame quality indicator (CRC), and 8 tail bits.

The R-SCH frames have many rates: 307200 bit/s, 153600 bit/s, 76800 bit/s, 19200 bit/s, 9600 bit/s, 4800 bit/s, 2700 bit/s, 2400 bit/s, 1500 bit/s, 1350 bit/s and 4800 bit/s. Generally, a frame is 20 ms, 40 ms or 80 ms in duration. Thus the lengths of frame information and quality indicator are also variable.



For example, a 38400 bit/s R-SCH frame is 40 ms and contains 1536 bits, of which 1512 bits are for frame information, 16 bits for frame quality indicator, and 8 bits for tail bits.

8 bit


In reverse channels, the access channel and the traffic channel for RC1 still use the same encoding method as IS-95 channel. The encoding processes for other channels are as shown in FIGURE 25. All of them contain convolution coding, symbol repetition, interleaving, and spreading. The significant difference from IS-95 lies in that, like the base station, the mobile station also uses Walsh code to distinguish the channels and therefore removes the orthogonal modulation process.

FIGURE 25 C D M A2000 1 X R E V E R S E C H AN N E L E N C O D I N G P R O C E S S

R-EACH/R-CCCH/R-DCCH/R-FCH/R-SCH

Frequencyspread

Convolution

Coderepetition

Interleave

1. R-CCCH

FIGURE 25 describes the encoding process for R-CCCH channel.

1） Convolution. The R-CCCH frame is convolutional coded (rate=1/4, restraint length=9).

2） Symbol repetition. Due to the variable frame length on R-CCCH, all the data rates after symbol repetition are turned into 38400 bit/s.

3） Interleave. The block length for interleaving varies with the frame length. For example, for a 20 ms, 9600 bit/s R-CCCH frame, the interleave block length is 3072 bits.

R-CCCH uses the following long code mask format for spreading:

41 ------ 33 32 ------ 28 27 ------ 25 24 ------ 9 8 ------ 0

110001110 RCCCN FCCCN BASE-ID PILOT-PN


Modulation



where RCCCN represents the reverse common control channel number; FCCCN represents the forward common control channel number; BASE-ID represents the base station number; and PILOT-PN represents pilot PN sequence offset factor. The RCCCN corresponds to the FCCCN. One FCCCN can support up to 32 RCCCNs.

2. R-EACH

FIGURE 25 describes the encoding process for R-EACH channel.

1） Convolution. The R-EACH frame is convolutional coded (rate=1/4, restraint length=9).

2） Symbol repetition. Due to variable R-EACH frame length, all the data rates after symbol repetition are turned into 38400 bit/s.

3） Interleave. The block length for interleaving varies with the frame length. For example, for 20 ms, 9600 bit/s R-EACH frame, the interleave block length is 3072 bits.

R-EACH uses the following long code mask format for spreading:

41 ------ 33 32 ------ 28 27 ------ 25 24 ------ 9 8 ------ 0

110001101 EACN FCCCN BASE-ID PILOT-PN

Here, EACN represents the R-EACH number; FCCCN represents the forward common control channel number; BASE-ID represents the base station number; PILOT-PN represents pilot PN sequence offset factor.

3. R-DCCH

FIGURE 25 describes the encoding process for R-DCCH channel.

1） Convolution. The R-DCCH frame is convolutional coded (rate=1/4, restraint length=9).

2） Symbol repetition. The data rate after symbol repetition is 768000 bit/s.

3） Interleave. The block length for interleaving varies with the frame length. For a 5 ms R-DCCH frame, the block length is 384 bits. For a 20 ms R-DCCH frame, the block length is 1536 bits.

The R-DCCH uses the following long code mask format for spreading, which is the same as IS-95 reverse traffic channels:

41 ------ 32 31 ------ 0


4. R-FCH

FIGURE 25 describes the encoding process for R-FCH channel.



1） Convolution. The information on R-FCH is convolutional coded (rate=1/4, restraint length=9) or Turbo coded.


3） Interleave. The block length for interleaving varies with the frame length.

The R-FCH uses the following long code mask format for spreading, which is the same as IS-95 reverse traffic channels:

41 ------ 32 31 ------ 0


5. R-SCH

FIGURE 25 describes the encoding process for R-SCH channel .

1） Convolution. The information on R-SCH is convolutional coded (rate=1/4, restraint length=9) or Turbo coded.


3） Interleave. The block length for interleaving varies with the frame length.

cdma2000 1x uses a hybrid modulation method that combines BIT/SK and QPSK.

The advantages of HPSK (Hybrid Phase Shift Keying) are as following:

Lower the peak-to-average ratio of waveforms (that is, peak factor) in the reverse link transmitted by mobile stations.

Lower the performance requirement for power amplifiers in mobile stations, and make it simple and low-cost, and capable of effectively utilizing the battery power.

Reduce the out-of-band radiation at CDMA signal margins: 4 dB.

cdma2000 1x Technical Features

The cdma2000 1x systems are backward compatible with IS-95 systems, but, compared with IS-95 systems, they have some new substantial technical features.

Multiple channel bandwidths

On the forward links, the Multiple Carrier (MC) and Direct Spread (DS) are both supported. However, on the reverse links, only DS is supported. In the MC mode, multiple RF bandwidths are supported. In other words, the RF bandwidth can be N×1.25MHz (N=1、3、5、9 or 12).

Forward transmit diversity

Radio Component



The cdma2000 1x transmission diversity divides the data into two parts which use different Walsh codes to perform band spread and be transmitted by the respective antenna.

Fast forward power control

cdma2000 1x adopts fast forward power control. AT sends transmission power adjustment instructions to the base stations according to the measured intensity forward traffic channel.

Turbo code

cdma2000 1x uses Turbo code to encode the channels to improve the error correction capability.

Reverse auxiliary pilot channel, reverse link demodulation

cdma2000 1x provides reverse auxiliary pilot channel to enable reverse link demodulation. It improves the reverse capacity.

Flexible frame length

cdma2000 1x channel supports 5 ms、10 ms、20 ms、40 ms、80 ms and 160 ms frame lengths.

When these new features are added, cdma2000 1x systems still retain backward compatibility with IS-95 systems by using Radio Configuration (RC) for its baseband system. Different radio configurations represent different baseband processing modes for encoding, interleaving, and error correction etc：

RC1 and RC2 are completely the same as IS-95. The other RCs (that is, RC 2 and above) are newly added to cdma2000 1x systems；

The RC mode is set by the respective negotiation program during call setup；

For voice service, IS-95 mobile station can work with cdma2000 1x carrier, and cdma2000 1x mobile station can also work with IS-95 carrier.

Enhanced A1 interface – supports concurrent services and emergency call.；

Subscriber zone – provides subscribers with different services in different geographical regions；

A10/A11 interface – supports packet data；

Security alliance between PCF and PDSN – supports secure, reliable transmission；

Mobile IP support – supports packet data macro mobility (between PDSN/FA)；

Provides triangular positioning function.

Network component



Service Flow

cdma2000 1x service flow includes: voice service flow, registration flow, data service flow, handoff flow and circuitry data service flow.

Each service flow is performed by the interactions and collaborations between different components in the CDMA network.

This section focuses on the voice service flow and data service flow.

The voice service flow includes：

Mobile station originates calls

Mobile station answers calls

Mobile station initiates call release

BSS initiates call release

MSC initiates call release

The flow of mobile station originates calls. See FIGURE 26.

FIGURE 26 M O B I L E S T AT I O N O R I G I N AT E S C AL L S

A

B

C

D

E

F

G

H

I

J

K

L

A． On the air access channel, MS sends an Origination Message to the BSS to request response;

Voice Service Flow

Mobile Station Originates

Calls



B． After receiving the Origination Message, the BSS sends a BS Ack Order to the mobile station;

C． BSS creates a CM Service Request message and sends it to the MSC after encapsulation. For those calls need circuit switch, the BSS will provide some terrestrial circuit recommendation information in the message to request circuit assignment from the MSC;

D． MSC sends an Assignment Request message to the BSS and request radio resource assignment. If MSC is able to support the terrestrial circuit recommended in the CM Service Request message, MSC will assign this terrestrial circuit in the Assignment Request message; otherwise other terrestrial circuits will be assigned;

E． After assigning the traffic channel for the mobile station, BSS sends out a Channel Assignment Message / Extended Channel Assignment Message on the paging channel to establish radio traffic channel;

F． The mobile station transfers Traffic Channel preamble (TCH Preamble) on the assigned reverse traffic channel;

G． BSS captures the reverse traffic channel and then sends out a BS Ack Order on the forward traffic channel, what’s more, requests response from the mobile station;

H． The mobile station sends out an MS Ack Order on the reverse traffic channel to answer the BS Ack Order from the BSS;

I． BSS sends a Service Connect Message / Service Option Response Order to the mobile station to specify the service configuration which will be used in calls;

J． After receiving the Service Connect Message, the mobile station begins to carry out the service according to the specified service configuration and responds as a Service Connect Completion Message;

K． After the successful connection establishment of the radio traffic channel and the terrestrial circuit, BSS sends an Assignment Complete message to the MSC and considers the call in an activated status;

L． In the case of the call process tone is provided in the band, the ring-back tone will be sent to the mobile station via voice circuit.

The flow of mobile station answers calls is shown in FIGURE 27 Mobile Station Answers Calls



FIGURE 27 M O B I L E S T AT I O N AN S W E R S C AL L S

A

B

C

D

E

FG

H

I

J

K

L

M

O

P

N

Q

R

A． When paging an MS is in the MSC service area, MSC sends a

Paging Request message to the BSS to start the call establishment of paging the MS;

B． On the paging channel, the BSS sends a General Page Message which contains MS identification code;

C． After the MS identifies the paging request which contains its identification code on the paging channel, it sends back a Page Response Message to the BSS;

D． BSS composes a Paging Response message by using the received message from MS. It is sent to the MSC after encapsulation. BSS can recommend terrestrial circuit in this message and request circuit assignment from MSC;

E． After receiving the Paging Response, the BSS sends Ack Order to the mobile station;

F～M．Please refer to the step D～K in the flow of mobile station originates calls;

N． The BSS sends an Alert with Info message to the MS to force MS rings;



O． After receiving the Alert with Info, the MS sends an MS Ack Order to the BSS;

P． When MS answers the call (hook off), it sends band layer 2 to the BSS to confirm the Connect Order;

Q． After receiving the Connect Order, on the forward traffic channel, BSS sends a BS Ack Order to the MS as the response;

R． BSS sends a Connect message to the MSC to tell it that the mobile station has answered the call. The call is considered in the activated status.

After initiating the network access, in case of service requirement, for example, user hooks off, MS can initiate the call release. SeeFIGURE 28.

FIGURE 28 MS I N I T I AT E S C AL L R E L E AS E

A

B

C

D

E

A． The mobile station transfers Release Order on the reverse channel to initiate call release;

B． BSS sends a Clear Request to the MSC;

C． MSC sends a Clear Command to the BSS to force it release the resources (e.g. terrestrial circuit);

D． BSS sends a Release Order to the MS and then release the radio resource;

E． After receiving the Clear Command from the MSC, BSS releases the terrestrial circuit recourses and responds a Clear Complete. Once MSC receives the Clear Complete, the SCCP connection is released.

If the radio link connection between the MS and the BSS fails due to the inactivation of the MS, or calls failure due to some BSS errors, BSS can send a release request to the MSC to trigger the call release flow. SeeFIGURE 29.

Mobile Station Initiates Call

Release

BSS Initiates Call Release



FIGURE 29 BSS I N I T I AT E S C AL L R E L E A S E

A

B

C

A． In case of radio link fails or inactivation of MS, BSS sends a Clear Request to the MSC;

B． MSC sends a Clear Command to the BSS to force it release the resources (e.g. terrestrial circuit);

C． Once the Clear Command is received, BSS responds a Clear Complete. MSC receives it and then release the SCCP connection.

The flow of MSC initiates call release is shown inFIGURE 30.

FIGURE 30 MSC I N I T I AT E S C AL L R E L E A S E

A

B

C

D

A． MSC sends a Clear Command to the BSS to force it release the resources. Meanwhile, the MSC initiates a UM interface call release.

B． The BSS transfers a Release Order on the forward channel to initiate the call release;

C． Once the Release Order is received, the MS responds a Release Order on the reverse channel;

D． The BSS sends a Clear Complete to the MSC. Once it is received, MSC releases the SCCP connection.

In cdma2000 1x data service flow，the wireless data subscribers have three status:

ACTIVE： There’s an air traffic channel between the handset and the base station. Data can be transferred from both sides. A1, A8, A10 connection retains;

MSC Initiates Call Release

Data Service Flow



Dormant： There’s no air traffic channel between the handset and the base station. But there’s a PPP link between them. A1 and A8 connection is released, A10 connection retains;

There’s neither air traffic channel nor PPP link between the handset and the base station. A1, A8 and A10 connections are released.

The flow of mobile station originates calls is shown inFIGURE 31.

FIGURE 31 C AL L O R I G I N AT E S I N D AT A S E R V I C E

A

B

C

D

E

F

G

H

I

JK

L

M

O

P

N

Q

A． MS sends a call originating message to the BSS on the access

channel of air interface;

B． Once the message is received, BSS sends a base station confirmation to the MS;

C． The BSS creates a CM request and sends it to the MSC;

D． The MSC sends an assignment request message to the BSS to request radio resource assignment;

E． The BSS will transfers the channel assignment message on the paging channel of the air interface;

F． The MS begins to transfers the preamble on the assigned reverse traffic channel;

Mobile Station Originates

Calls



G． Once the reverse traffic channel is received, the BSS will send a confirmation to the MS on the forward traffic channel;

H． Once the base station confirmation is received, the MS transfers mobile station confirmation, on the reverse traffic channel, it also transfers vacant service frames;

I． The BSS sends a Service Connect Message / Service Option Response Order to the MS to specify the service configuration for calls. The MS begins to carry out the service follow the specifications;

J． Once the Service Connect Message is received, the MS responds a Service Connect Completes Message;

K． The BSS sends an A9-Setup-A8 message to the PCF to request the A8 connection establishment;

L． The PCF sends an A11-Registration-Request to the PDSN to request the A10 connection establishment;

M． The PDSN accepts the A10 connection establishment request and sends back an A11-Registration-Reply to the PCF;

N． The PCF sends back the A9-Connect-A8 message to the BSS. Thus, the A8 connection and A10 connection established;

O． When the radio channel and the terrestrial circuit are established and interoperated, the BS will send an assignment complete message to the MSC;

P．The MS negotiates with the PDSN to establish a PPP connection. If using the Mobile IP access, the Mobile IP connection is also needed. The PPP messages and Mobile IP messages are transferred on the traffic channel. They are transparent to the BSS/PCF;

Q． Once the PPP connection is established, the data service goes into a connected status.

The flow of the call release initiated by mobile station is shown in the FIGURE 32.

Mobile Station Initiates Call

Release



FIGURE 32 C AL L R E L E AS E I N I T I AT E D B Y MS

A

B

C

D

E

F

G

H

I

A．MS sends a Release Order to the BSS on the dedicated channel of the air interface;

B． Once the message is received, the BSS sends a Clear Request to the MSC;

C． The MSC releases the resources at the network side as soon as sends a Clear Command to the BSS;

D． Once the message is received by the BSS, it sends a Release Order to the MS;

E． The BSS sends an A9-Release-A8 message to the PCF to request the A8 connection release;

F． The PCF sends an activation stop accounting record to the PDSN via the A11-Registration-Request;

G． PDSN returns an A11-Registration-Reply；

H． PCF uses the A9-Release-A8 Complete message to confirm the connection release;

I． BSS sends a Clear Complete message to the MSC. The release completes.

The flow of the Cross-PCF dormant handoff in PDSN is shown in FIGURE 33.

The Cross-PCF Dormant

Handoff in PDSN



FIGURE 33 C R O S S -PCF D O R M AN T H AN D O F F I N PDSN

A

B

C

DE

F

G

H

I

JK

L

M

O

P

N

Q

A． The connection of packet data service is in dormant;

B． MS sends the call originating message to the target BSS on the access channel of the air interface;

C． Once the message is received, the target BSS sends the base station confirmation to the MS;

D． The target BSS creates a CM service request and send it to the MSC;

E． MSC sends the assignment request to the target BSS to request the radio resources assignment;

F． The target BSS sends an A9-Setup-A8（DRS=0）message to the target PCF;

G． The target PCF sends an A11-Registration-Request to the PDSN to establish the A10 connection;

H． PDSN replies an A11-Registration-Reply;

I． The target PCF sends an A9-Release-A8 Complete message to the target BSS;

J． The target BSS sends an Assignment Failure to the MSC (Cause value = Packet Call Going Dormant);



K． The MSC sends a Clear Command to the target BSS (Cause value = Do Not Notify Mobile);

L． The target BSS sends back a Clear Complete message to the MSC;

M． The PDSN sends an A11-Registration-Update to the source PCF to request the old A10 connection;

N． The source PCF uses the A11-Registration-Ack to confirm the A10 connection release request;

O． The source PCF sends an A11-Registration-Reply（Lifetime = 0）to release the A10 connection;

P． For the valid A11-Registration-Request, PDSN replies a A11-Registration-Reply which contains acceptance and lifecycle value. PDSN will save the billing information before sending the A11-Registration-Reply.

The flow of the cross-PCF active handoff in PDSN is shown in FIGURE 34.

FIGURE 34 CRO S S-PCF A C T I V E S W I T C H I N PDSN

A

B

CD

E

F

G

H

IJK

L

M

O

P

N

Q

R

STU

V

WX

The Cross-PCF Active Handoff

in PDSN



A． According to the MS’s report, the signal intensity in the target cell is stronger than the threshold specified by the network, the source BSS requires the hard handoff to the target cell. Thus the source BSS sends the handoff request with the cell list;

B． Because in the handoff request, the specified handoff type is hard handoff, the MSC sends the handoff request to the target BSS;

C． The target BSS send an A9-Setup-A8 message to the target PCF to establish A8 connection;

D． The target PCF sends back an A9-Connect-A8 message to the target BSS;

E． The target BSS sends the handoff request confirmation to the MSC;

F． MSC is ready to perform the handoff from the source BSS to the target BSS and sends a handoff command to the source BSS;

G． The source BSS sends an A9-AL-Disconnected message to the source PCF, the source PCF stops sending data to the source BSS;

H． The source PCF sends back an A9-AL-Disconnected Ack to the BSS;

I． The source BSS sends the extensive or common handoff commands to the MS on at the air interface. If MS allows return to the source BSS, the source BSS will start the timer Twaitho;

J． The MS sends a mobile station confirmation to the BSS which acts as the response to the extensive or common handoff commands;

K． The source BSS sends a handoff commence message to the MSC to tell the MS that it is changed to the target BSS channel by the command.

L． The MS sends a handoff completes message to the target BSS;

M． The target BSS sends a base station confirmation to the MS;

N． The target BSS sends an A9-AL-Connected message to the target PCF;

O． The target PCF sends an A11-Registration-Request to the PDSN to request the A10 connection;

P． PDSN accepts the A10 connection establishment request and sends an A11-Registration-Reply to the target PCF;

Q． The target PCF sends back an A9-AL-Connected Ack message to the target BSS;

R． The target BSS sends a handoff completes message to the MSC to tell MS that the hard handoff completes;

S． The MSC sends a Clear Command to the source BSS to clear the whole resources;



T． The source BSS sends an A9-Release-A8 message to the source PCF to release the A8 connection between them;

U． The source PCF sends an A11-Registration-Request（Lifetime = 0）message to the PDSN to release the old A10 connection;

V． PDSN accepts the A10 connection release request and sends back an A11-Registration-Reply to the source PCF;

W． The source PCF sends back an A9-Release-A8 Complete message to the source BSS;

X． The source BSS sends a Clear Completes message to the MSC to tell MSC that the clear is finished.

1. Briefly state the types and functions of forward/reverse channels in cdma2000 1x systems.

2. Briefly state encoding, modulation, and decoding processes for forward/reverse channels in cdma2000 1x systems.

3. Briefly state the technical features of cdma2000 1x system.

Review

73

C h a p t e r 5

cdma2000 1x EV-DO System Principles

Key points:The forward/reverse channels (types, structures and functions) in 1x EV-DO

The key technologies of 1x EV-DO

The service flow of 1x EV-DO

The difference between 1x EV-DO and 1x

Introduction

This chapter gives an introduction to the Forward/Backward Channels as well as the key technologies and the service flow of cdma 1x EV-DO system. Upon finishing this chapter you will have a deep understanding of the principles of cdma2000 1x EV-DO technology and be able to differentiate it from cdma2000 1x.

System Overview

EV-DO is the abbreviation for “Evolution, Data Only”. As a dedicated technology for high speed data transfer, 1x EV-DO is considered as the upgraded version of 1x. 1x EV-DO is based on IS-856 specification which was developed by Qualcomm and Lucent.

The system structure of 1x EV-DO can be regarded as a combination of the 1x system with an extra wireless component. 1x provides voice and other low speed services while 1x EV-DO is focus on the high speed packed data services. In addition, 1x EV-DO and 1x use different carrier frequency to transfer data. This feature helps optimize both the voice services and the high speed packed data services and ensure them the best performances.

1x EV-DO uses the same frequency bandwidth as narrowband CDMA. The highest data transfer rate is 2.4 Mbit/s.



Take the inheritance from 1x system into account, the 1x EV-DO is compatible with the 1x in wireless features. It can be seen as a new frequency point of 1x. This makes the RF equipments of 1x EV-DO and 1x system are replaceable to each other.

The 1x EV-DO system structure is shown Figure FIGURE 35

FIGURE 35 TH E 1 X EV-DO S Y S T E M S T U R C T U R E

AT BTS BSC PCF PDSN

HAMSC

HLR

Internet

AN

AN

A12

A13

AAA

AAA

The Differences from the 1x system:

1xEV-DO is data only, so there is no interface to MSC/HLR.

Packet Data Domain equipment(PDSN、AAA、HA), same as 1X.

Independent Access Network AAA server is added.

2 A interfaces are added. A12 for access system authentication, and A13 for interaction between AT roaming home AN and Foreign AN.

The 1x EV-DO protocol family is shown as FIGURE 36.

System Structure

Protocol Family



FIGURE 36 TH E 1 X EV-DO P R O T O C O L F AM I L Y

1. Application Layer: The Application Layer provides multiple

applications. It provides the Default Signaling Application for transporting air interface protocol messages and the Default Packet Application for transporting user data.

2. Stream Layer: The Stream Layer provides multiplexing of distinct application streams. Stream 0 is dedicated to signaling and defaults to the Default Signaling Application. Stream 1, Stream 2, and Stream 3 are not used by default.

3. Session Layer: The Session Layer provides address management, protocol negotiation, protocol configuration, and state maintenance services.

4. Connection Layer: The Connection Layer provides air link connection establishment and maintenance services.

5. Security Layer: The Security Layer provides authentication and encryption services.

6. MAC Layer: The Medium Access Control (MAC) Layer defines the procedures used to receive and transmit over the Physical Layer.



7. Physical Layer: The Physical Layer provides the channel structure, frequency, power output, modulation, and encoding specifications for the Forward and Reverse Channels.

Each layer may contain one or more protocols. Protocols use signaling messages or headers to convey information to their peer entity at the other side of the air-link. When protocols send messages, they use the Signaling Network Protocol (SNP).

1. Different requirements on Voice Services and Data Services, as shown in Table 11.

T AB L E 11 TH E 1 X EV-DO’S R E Q U I R E M E N T S O N V O I C E S E R V I C E S AN D D AT A S E R V I C E

Items Voice Services Data Services

Delay (Processing

Time in total)

Beyond 100ms is

unacceptable

A few seconds delay is almost not detected

as it changes constantly

(Bit Error Rate) BER Not strict Strict (Using ECC to reduce the BER)

Forward/Backward

Data Rate

Adhering to the

symmetry is

required while

performing two

way voice

services

the need to Forward Link on speed is

likely to be several times greater than the

Backward Link (Forward Link: 38.4

kbit/s~2.4 Mbit/s, Backward Link: 4.8

kbit/s~153.6 kbit/s)

Throughput Low throughput

The actual throughput available to any one

user depends on the total number of users

being served and the level of interference

(C/I) present.

2．The Compatibility with IS-95/1X Networks

As shown in FIGURE 37，the 1x EV-DO system band is 1.25 MHz，it has the same spectrum as IS-95/1x.

FIGURE 37 TH E S P E C T R U M O F 1 X AN D 1 X EV-DO

No changes are required to the existing network deployment. The 1x EV-DO system and IS-95/1x can be deployed together on the basis of the existing Base Stations, towers and antennas.

Functions & Features



Forward Channels

The Forward Channel (AN to AT) provides the connections between AN and each AT. The Forward Channel has following features:

1. The data rate is in a range of 38.4 kbit/s~2457.6 kbit/s; 2. Always at full power transmission, no power control; 3. Selecting the best service area according to the measurement

of C/I in Forward Channel and working at the highest data rate;

4. The subscribers in a certain service area will share an unique data service channel in a way of TDM.

1x EV-DO is an independent system with a new channel structure The forward channels structure is shown as Figure FIGURE 38.

FIGURE 38 TH E 1 X EV-DO F O R W AR D C H AN N E L S S T R U C T U R E

1. Pilot channel

The pilot channel is used for the pilot signal transmission from Access Net (AN) to Access Terminals (AT). This signal handles system acquisition, clock synchronization, demodulation, decoding and C/I assessment.

2. Forward MAC channel

The forward MAC channel is composed of Reverse Power Control (PRC) channel, Reverse Activation (RA) channel and Data Rate Control (DRC) locking channel.

PRC channel is used for power control of AT which are transferring data on the Reverse Channel.

RA is used to dynamically control the workload of Reverse Channel. When overload is detected, the bit stream in RA channel forces the AT which are transmitting data on RA




randomly lower their reverse data rate in order to reduce the emission power and the collisions when terminals accessing.

In case the AN can not receive the DRC signals from an AT, the DRC channel will stop the particular AT from sending data to AN.


Forward traffic channel is used by AN to send data. It works at full power when sending data. Forward traffic channel power control but rate control.

4. Forward control channels

Forward control channel is used to send broadcasting common configuration parameters from AN to AT. Additionally, it also sends signalling messages to a particular AT in case the traffic channels are not activated. These messages are used in the way of TDM on forward channel by individual user. Moreover, forward control channel can be used by AN to send data.

In forward channel series, most of the channels work at TDM mode and transmit to AT at full power mode. However, the RPC and RA in MAC channel work at CDM mode.

The TDM mode of forward channels is presented by channel time slot structure. Time slot is the basic unit to depict a channel. 1 time slot equals to 1.67ms. There are two types of time slot – activated time slot and idle time slot. The former bears the information of traffic channel and control channel.

The time-slot structure of forward channels is shown in FIGURE 39The data section involves the information about the control channel and traffic channel.

FIGURE 39 TH E T I M E -S L O T S T R U C T U R E O F 1 X EV-DO F O R W AR D C H A N N E L S

Frame is the data unit for forward channels. 16 time slots consist of a frame which is 26.67ms long.

1. Pilot Channel

Time-slot Structure of

Channel



The sector uses all the activated forward channels all along to transmit pilot signals.

2. Forward Control Channel

There are two different data transfer rates of forward control channel (76.8kbit/s and 38.4kbit/s). Its time slot structure is different from that of the forward traffic channel.

3. Forward MAC Channel

There are four identical MAC contents in one time slot.

4. Forward Traffic Channel

AN modulates data transfer rate in forward traffic channel according to DRC request from AT. The rate ranges from 38.4kbit/s to 2.4576Mbit/s. Packet was introduced into forward traffic channel as the data unit. It contains messages of 1024bits, 2048bits, 3072bits and 4096bits with the duration from 1.67ms to 26.67ms (1~16 time slots).

In comparison with 1x, the modulation mode was improved significantly in 1x EV-DO in order to reach a high data throughput. Two efficient modulation modes (8-PSK and 16QAM) were introduced into AN side.

8-PSK is an extension of QPSK. In 8-PSK, eight different carrier frequency phases are corresponding to eight different binary codes (000, 001, 010, 011, 100, 101, 110 and 111). The usage of band is improved as each modulation signal is corresponding to a 3bit-data.

16-QAM is another extension of QPSK. It uses two different amplitudes. Each signal is corresponding to a 4bit-data. In other words, 16-QAM is a combination of ASK and PSK.

1x EV-DO adopts QPSK、8-PSK and 16-QAM as its modulation modes. Its encoding technologies include interleaving, insertion, repetition and symbol-multiplexing. In addition, quadrature spread and Base Band filtering technologies were also introduced into 1x EV-DO.

1. Pilot Channel

Pilot signal is a unmodulated BIT/SK signal (Walsh code is 0).

2. Forward control channel

The forward control channel and the forward traffic channel with same data rate are using a same modulation mode.

The transmission of forward control channel is different from that of the forward traffic channel. It has a leading code which contains an MAC Index 2 (76.8kbits/s) or an MAC index 3 (38.4kbit/s) biorthogonal sequence.

It transmits every 400ms with duration of 13.33ms (76.8kbit/s) or 26.66ms (38.4kbit/s). A circle period of the forward control channel is defined as 240 time slots which is synchronized with 1x EV-DO.

Channel Modulation



3. Forward MAC Channel

The forward MAC channel is comprised of quandrature Walsh channels. It is modulated (Inphase or Quandrature Phase) by BIT/SK at particular carrier frequency.

Each Walsh is identified by a MAC Index value (0~63). This value determines a unique 64bit Walsh cover and a unique modulation phase. If the value is an even number, MAC channel is assigned to the in-phases, otherwise, assigned to quadrature phases.

The relationship between MAC channel and MACIndex is shown in FIGURE 38

T AB L E 12 TH E MAC C H AN N E L AN D M AC I N D E X

MACIndex The usage of MAC channel\ The usage of leading code

0 and 1 Not use Not use

2 Not use 76.8 kbit/s control channel

3 Not use 38.4 kbit/s control channel

4 RA channel Not use

5~63 Available to the RPC

channel and DRCLock

channel for transfer

Available to the forward traffic

channel for transfer

RA channel adopts Walsh464 band spread technology and

performs modulation in BIT/SK mode at I channel. PRC channel and DRC locking channel take up MAC channel in a time-sharing manner. Messages come from different terminals are identified by 64-level Walsh codes. These codes are used in modulation by means of BIT/SK in I channels or Q channels. One AN is able to provide 60 Walsh codes. In other words, one AN can serve up to 60 users simultaneously.


The forward traffic channel (and control channels) needs some encoding procedures such as Turbo encoding and interleaving. According to different data transfer rate, the forward traffic channels firstly carry out QPSK, 8-PSK or 16-QAM modulations. The modulated code elements are divided into 16 concurrent data flows and each flow is identified by different 16-level Walsh code. These 16 concurrent data flows are modulated again after integration.

A symbol which is corresponding to a data packet will take up 1~16 time slots when the modulated symbols are being mapped to channels. It depends on the data rate and the number of bits a data packet contains. The leading codes (all zeros) section must be added before mapping. The length of this section depends on the data rate and the number of time slots of a data packet. The leading sections of different user data and control data with different rates are identified by 64-level Walsh codes.



The modulation parameters of forward traffic channels at different data rate are indicated in Table 13.In this table, the number of bits, modulation symbols, as well as leading codes are sharing a c data unit – data packet.

T AB L E 13 TH E M O D U L AT I O N P AR AM E T E R S O F 1 X EV-DO F O R W AR D T R AF F I C C H AN N E L

Rate（kbit/s）

Number

of

time-slot

Number

of bit

Turbo

code

Modulation

mode

Modulation

symbol

Leading

code

38.4 16 1024 1：5 QPSK 2560 1024

76.8 8 1024 1：5 QPSK 2560 512

153.6 4 1024 1：5 QPSK 2560 256

307.2 2 1024 1：5 QPSK 2560 128

614.4 1 1024 1：3 QPSK 1536 64

307.2 4 2048 1：3 QPSK 3072 128

614.4 2 2048 1：3 QPSK 3072 64

1228.8 1 2048 1：3 QPSK 3072 64

921.6 2 3072 1：3 8-QPSK 3072 64

1843.2 1 3072 1：3 8-QPSK 3072 64

1228.8 2 4096 1：3 16-QAM 3072 64

2457.6 1 4096 1：3 16-QAM 3072 64

Reverse Channels

The reverse channels provide connections between AT and AN. They have the following features:

Data rates is up to 153.6kbit/s;

Soft switch;

Dynamic power control;

Workload of reverse channels is adjusted by rate control.

The structure of 1x EV-DO reverse links is shown in FIGURE 40. Channel Functions and

Features



FIGURE 40 S T R U C T U R E O F 1 X EV-DO R E V E R S E L I N K S

1. Reverse Access Channels (Reverse Pilot Channels and Data Channels)

Reverse Access Channels are used by AT to initiate calls or respond to AN paging messages

2. Reverse Traffic Channels (Pilot Channels, MAC Channels, Data Channels and ACK, MAC Channels is comprised of DRC and PRI)

Pilot channel

Coherent demodulation

DRC sub-channel

DRC channels are used by AT to give instructions to AN. These instructions include the requested data rate of forward traffic channels and the service areas selected by forward channels. DRC Value and DRC are two types of information in DRC channels.

RRI channel PRI channels are used to indicate the data rate of in operation reverse data channels.

Data channel

Data channels are used to transfer reverse data packets.

ACK sub-channel

ACK channels are used by AT to AN to confirm the delivery of data packets in forward traffic channels. NAK bits will be sent if demodulation failed.

The forward channels and reverse channels have the same time slot structure

The data packing duration of reverse links is 26.67ms;

Each packet takes up a 26.67ms frame;

Time-slot structure of

Channels



Each frame contains 16 1.67ms time slots;

Each time slot contains 2,048 PN code snippets;

Transfer starts from any time-slot in the 16 time-slots to randomize the transfer in reverse links.

1. Reverse access channel

The reverse access channel encoding is shown in FIGURE 41.

FIGURE 41 1 X EV-DO R E V E R S E AC C E S S C H AN N E L E N C O D I N G P R O C E S S E S

1） Pilot channel

The data in pilot channels are all zero. Encoding is not required as the spread spectrum is performed straightforward by W0

16.


Modulation



2）Data channel

The data rate in data channels is 9.6kbit/s. Each frame contains 256 bits. It is called an access channel packet. This packet is converted into a 38400bit/s signal by performing 1/4 Turbo encoding and then interleaved. The data unit is 1024bit when interleaving. After completing 8 times code element repetitions on the interleaved data, the W2

4 band spread is carried out.


The reverse traffic channel encoding processes is shown in Figure FIGURE 42 and FIGURE 43.

FIGURE 42 R E V E R S E T R AF F I C C H AN N E L E N C O D I N G P R O C E S S E S (F I R S T H AL F )



FIGURE 43 R E V E R S E T R AF F I C C H AN N E L E N C O D I N G P R O C E S S E S (S E C O N D H AL F )

Pilot channels, DRC channels and ACK channels all use Walsh functions (4, 8 or 16 in length) to implement quantrature band spread.

Aiming at different reverse channels, further explanations to the encoding processes is given as follows:

1） Pilot channel

FIGURE 44 TH E TDM AS S I G N M E N T O F P I L O T C H AN N E L AN D RRI C H AN N E L

AT transmits unmodulated symbols. The values in the pilot channels are 0 (binary).

The transmissions of pilot channel and RRI channels is multiplexed (TDM) on the Walsh W0

16 channel.



The emission power of pilot channel and PRI channel is the same.

2） DRC channel

The forward traffic channel data transfer rate in DRC channel is in line with a 4-bit value which is defined by forward traffic channel MAC protocol.

DRC channel uses 8-level Walsh function to perform band spread.

The data rate of transferring DRC value is 600/DRCLength per second. The DRCLength is the public data in forward traffic channel MAC protocol.

3） RRI channel

The signal transmitted by AT is presented by a 3-bit RRI symbol (Physical Layer pack a 3-bit symbol every 16 time-slots)

Each RRI symbol is converted into a 7-bit code word by a single encoder. After this conversion, each code word repeAT 37 times and the last 3 symbols will be omitted. The acquired 256 binary symbols of each Physical Layer packet and the pilot channels symbols are multiplexed (TDM). This is the same as the period of the corresponding Physical Layer packet.

T AB L E 14 RRI S Y M B O L AN D S I N G L E E N C O D E R AS S I G N M E N T

Data rate(kbit/s) RRI symbol RRI code word

0 000 0000000

9.6 001 1010101

19.2 010 0110011

38.4 011 1100110

76.8 100 0001111

153.6 101 1011010

Reserved 110 0111100

Reserved 111 1101001

The TDM pilot and RRI channel sequence use W016 to fulfill band

spread. It generates 256 RRI code snippets every time-slot.

AT will transfer RRI code words on RRI channels at 0 data rate when Physical Layer packets are not transferred on reverse channels.

The pilot channels and RRI channels perform transfer on I channels.

4） ACK channel

Each forward traffic channels time-slot is relative to the detected leading codes that sent to AT. AT will generate an ACK channel bit as the acknowledgement to each forward



traffic channels time-slot. Otherwise, the ACK channels are closed.

ACK channels will generate a “0” bit if a forward traffic channels physical layer packet is received successfully. Otherwise a “1” bit (NAK) will be generated.

The time-slots in the head half of W48 channel are used when

transferring ACK channels bits.

BIT/SK is used to the ACK channels modulation.

5） Data channel

AT is able to transfer data at 9.6kbit/s, 19.2k/bits, 38.4kbit/s. 76.8kbit/s and 153.6kbit/s on the data channels of reverse traffic channels. The data transfer rates comply with the MAC protocol in reverse traffic channels.

The packed length is fixed 26.67ms in order to achieve better time diversity.

Turbo decoding uses concurrent connections codes (code rate = 1/2 or 1/4). The performance is closed to the capacity.

Reverse channels interleaving and repetition are implemented to take the advantages of time diversity.

Data transfer only starts from a particular time-slot to randomize user signals.

Frame Offset is the common data in reverse traffic channels. All the data transferred on reverse traffic channels are encoded, code-block interleaved, sequences repeated and as well as to use W2

4 function to realize quandrature band spread.

Key Technologies in 1x EV-DO

In this section, some key technologies in 1x EV-DO are introduced.

Power control is essential to the system maximization. The forward power control is not required in 1x EV-DO because of its constant power. Therefore, power control is mainly adopted by reverse channels.

The purpose of power control in reverse channels is to minimize the interference as well as control the AT’s output power in order to ensure the best performance of reverse data links. When the average reverse links SNR of each user reaches the minimum value that is acceptable for maintaining the operation, the maximum capacity is obtained.

1. Opened-loop power control

The assessments of 1x EV-DO opened-loop power include the assessment of access channels (pilot channels and data channels) and reverse traffic channels.

Reverse link power control



AT sends a random heuristic accessing sequence to AN before the establishment of reverse traffic channels. The original emission power of pilot channels is defined by the following formulas:

mean pilot channel output power (dBm)=

-Mean Received Power (dBm)

+OpenLoopAdjust

+ProbeInitialAdjust

OpenLoopAdjust and ProbeInitialAdjust are public variables of access channels. They are defined in Access Parameter Message. For Band Classes 0, 2, 3, 5 and 7, OpenLoopAdjust+ProbeInitialAdjust is in a range of -81~-66dB; For Band Classes 1, 4, and 6, its range is from -100dB to -69dB.

Each heuristic accessing emission power is increasing in the first accessing heuristic sequence. During the number i heuristic accessing, the emission power of pilot channels in the access channels can be formulated as follows:

mean pilot channel output power (dBm)=

-Mean Received Power (dBm)

+OpenLoopAdjust

+ProbeInitialAdjust

+（i-1）×PowerStep

In access channels, the power of data channels is relative to the power of pilot channels. It can be formulated as follows:

mean data channel output power（dBm）=

- Mean Received Power (dBm)

+ OpenLoopAdjust

+ ProbeInitialAdjust

+（i-1）×PowerStep

+ DataOffsetNom

+ DataOffset9k6

+3.76

PowerStep, DataOffsetNom and DataOffset9k6 are common variables in access channel MAC protocol. They are defined in the power parameters of access channel MAC protocol configuration messages.

A heuristic accessing includes a prefix and one or more Physical Layer packets. only contains a pilot channel while the data segment contains a pilot channel and a data channel. In order to reach an equalization, the pilot channel power of the prefix segment must be higher than the pilot channel power of the data segment. Their difference equals to the output power of data channel.



According to this, in access channels, the opened-loop output power in pilot channel is mean pilot channel output power; the opened-loop output power in data channel is mean pilot channel output power + mean data channel output power,

See FIGURE 45.

FIGURE 45 TH E H E U R I S T I C AC C E S S

Once the indication of reverse traffic channel MAC protocol is received, AT will initialize the transmission of reverse traffic channels. In reverse traffic channels, the reverse rate indication channel and the pilot channel are multiplexed (TDM). They are still called pilot channel. Transmit at the same power.

AT transfers pilot channel, DRC channel, ACK channel and data channel when the reverse traffic channels are transferred. These channels must be transferred at a particular power level. The level depends on the opened-loop power control and closed-loop control.

In the reverse traffic channels, the pilot channel original output power can be formulated as follows:

Mean pilot channel output power (reverse traffic channel) =

Mean pilot channel output power (access channel)

- Mean Received Power 1

+ Mean Received Power 2

The “Mean pilot channel output power” on the left is the original emission power of pilot channel while the one on the right is the last heuristic accessing pilot channel emission power in access channels. Mean Received Power 1 is the forward link receiving power at the last heuristic access; Mean Received Power 2 is the forward link receiving power when the transfer of reverse traffic channel begins.

Refer to the cdma2000 protocol, the pilot channel original output power can be formulated as follows:

mean pilot channel output power(dBm)=

-Mean Received Power(dBm)



+OpenLoopAdjust

+ProbeInitialAdjust

+（N-1）×PowerStep

Here the Mean Received Power is the current forward links receiving power. N is the number of heuristic accessing times that before successful access.

The emission power of DRC channels, ACK channels and data channels are determined by relative pilot channel power gain.

Mean DRC channel output power（dBm）=

+mean pilot channel output power(dBm)

+DRCChannelGain

Mean ACK channel output power（dBm）=


+ACKChannelGain

The DRCChannelGain and ACKChannelGain are defined in the Traffic Channel Assignment Message.

mean Data channel output power（dBm）=


+Data channel gain

Data channel gain

The data channel gain varies according to the variation of data rates.

T AB L E 15 TH E D AT A C H A N N E L G AI N V A R I E S AC C O R D I N G T O T H E V AR I AT I O N O F D AT A R AT E S

Data rate（kbps）

Data rates

Corresponding to the Pilot channel，data channel gain（dB） Data channel gain (corresponding to the pilot channel)

0 -∞ (data channel not transferred)

9.6 DataOffsetNom + DataOffset9k6 + 3.75





The parameters listed in the table are configured in the reverse traffic channel MAC protocol.

2. Closed-loop power control

Once the connection established, according to the measured signal quality of reverse links, AN continuously sends “0” (ascending power) or “1” (descending power) PRC bits to AT. If the



signal quality is greater than the SetPoint, a “1” bit will be sent. On the contrary, a “0” bit will be sent.

Based on the successful receiving of the reverse power controlling bits, AT will adjust its output power according to the direction indicated by power controlling bits and the step length indicated by RCStep. If AT doesn’t transfer the reverse traffic channel at time-slot n, the power controlling bits will be neglected at time-slot n+1.

The data rate in reverse power control channel is 600bit/s. That means the PRC symbols are transferred four times every time-slot and every PRC symbol is corresponding to 64 code snippets. Based upon the receiving of the 64 code snippets of MAC channel after the second pilot of the first time-slot, the power controlling bits are received.

AT provides different PRC channels with diversity combination when it is at a soft-switch status. What’s more, AT must acquire at most 1 power controlling bit from each PRC channel. The output power will be raised by AT if all the PRC bits are ‘0’. However, AT will reduce the output power according to the PRCStep step length.

AT modifies pilot channel emission power in terms of power controlling bits. This enables AT figure out the emission power of DRC, ACK and data channels in accordance with the relative pilot channel power gain.

Similar to the IS95/1x, reverse closed-loop power control is comprised of inner-loop control and outer-loop control. Inner-loop control keeps the received pilot signal-noise ratio at the Power Control Threshold (PCT) level. Outer-loop control dynamically adjusts the PCT in order to keep PER at a particular level (1% in most cases) under any channel condition.

PCT is used to the outer-loop power control. It is figured out by the outer-loop power control algorism. Each PCT frame and reverse links’ frames change at the same rate. The change of PCT is the function of the reverse links frame qualities and the status of the reverse opened-loop power control algorism. If a reverse traffic frame passes the CRC, it is considered a good frame, or it is a bad one.



FIGURE 46 P O W E R C O N T R O L T H R E S H O L D C H AN G E S W I T H T I M E

The letters on the Time axis stand for the status of the reverse traffic channels at a particular time. (G

stands for ‘Good Frame’, B stands for ‘Bad Frame’, N stands for ‘No frame received”

FIGURE 46 demonstrates a typical PCT change. The PCL status depends on the existence or nonexistence of reverse traffic channel data.

In 1x EV-DO specifications, AT’s reverse rate can be freely adjusted by AT from 9.6kbit/s to 153.6kbits. In order to avoid all the AT become unavailable, the workload of reverse links must be constrained to prevent too many users in the same sector from transferring data to AN at a high rate.

AN uses two mechanisms to constrain the AT emission power:

1. Reverse Rate Limit. AN can constrain AT’s rate at a particular level which has the highest reverse rate at 153.6kbit/s.

2. RAB and Transition probability. RAB is set ‘0’ when the sector detects that the reverse links are underloaded. The AT in this sector can raise their reverse rate according to a set of predefined probability values (Transition009k6_019k2 ，

Transition019k2_038k4 ， Transition038k4_076k8 ，

Transition076k8_153k6). RAB is set ‘1’ when the sector detects that the reverse links are overloaded. In this situation, all the AT must reduce their transfer rates according to a set of predefined probability values. If the AT is at soft switch status and the RAB in any sector is ‘1’, the AT’s rate will be going down.

The key issue in reverse links rate control is how to measure the busy-idle status of reverse links. Measuring the Rise Over Thermal (ROT) at each sector antenna is a relative precise method.

Reverse link rate control

Forward link TDM



The forward links of 1x EV-DO is different form 1x. It uses TDM to server all AT. In a sector, only one user is served at a particular time-slot.

Like IS-95/1x, the forward pilot channel helps AT fulfill system acquisition and channel assessment of modulation and demodulation.

In 1x EV-DO, AT chooses the service sector and determines the highest rate it can support. All of these are done by the measurement of forward pilot quality and the wireless channels quality assessment of the environment where AT is in. all the BTS transfers pilot simultaneously at full power. Therefore, AT can figure out precise pilot intensity to promptly respond to each BTS signal and interference.

In order to provide users with the highest transfer rate, AT requests the most suitable data rate according to the C/I value of AN.AN uses the scheduling algorism to assign different users with corresponding services according to the requests from AT.

The purpose of the scheduling strategy is to maximize the system throughput as well as ensure the fairness among the users. Due to the complexity of radio environment, AT informs AN of the highest data rate that it can accept through the DRC channel. The system informs the maximum DRC value in order to reach the maximum throughput. In this case, other users are not served by the system. Therefore, the purpose of the scheduling algorism is to balance the throughput and the fairness.

1x EV-DO uses ratio-fair algorism. It not only ensures the fairness to the users buy also as many as possible expand the system capacity.

The following section gives some details of this algorism.

For each user k, scheduler has a corresponding variable Tk. This variable updates every time-slot. The variable index is the time-slot n. therefore Tk[n] represents the scheduler value of user k at time-slot n. there are two steps with this algorism:

1. Scheduling——at each time-slot n, DRC1[n], DRC2[n], …are known，among the DRC users who need to transfer data, choose those who has the maximum DRCk[n]/Tk[n].

2. Renewal——at each time-slot, the scheduler variable Tk of each user is renewed by the following formula. Tk is related to the actual data acquisition at a particular period.

Here, tc stands for time. If at time-slot n, the part of the first time-slot of a packet (length = Ik[n] time-slots, rate = Nk[n], early termination of multi-slot packet is not considered here) is sent to

Scheduling strategy in

forward link



user k, then the Sk[n]=Ik[n]*Nk[n]; for any other user or time-slot, the Sk[n]=0.

Based on the two steps above, the system is able to maintain the Tk and ensure the fairness among the users.

For example, the system will raise Tk to show more fairness. It can be observed that the system transfers data by choosing the maximum DRCk[n]/Tk[n] at the first step. Even the user k now has the maximum DRCk[n], it doesn’t mean it can subscribe to the data service without Tk[n].

If was served before, Tk[n] will be greater. The DRCk[n]/Tk[n] won’t be the maximum in the system when Tk[n] is great enough. Under this circumstance, the user k won’t be served at the next time-slot.

Due to the bad radio environment, some users are not served all along. They report the less DRCValue. Tx[n] is much less. Therefore, the DRCx[n]/Tx[n] is greater than the user k. The user k will be served at the next time-slot. This mechanism ensures the fairness.

Same as 1x, the 1x EV-DO handoff control supports various soft/hard handoff. In addition, a new mode called forward Virtual Handoff is introduced into 1x EV-DO.

In The forward Virtual Handoff, there’s only one sector sends data to the terminals at a particular time in the AT active set. According to the quality of each received pilot, AT can use the DRC Cover to specify the sectors which are expected to transfer data. In AN, all the sectors within the active set are listening to the reverse channels of the AT. AN decides which sector is the Serving Sector of the AT according to the DRC channel received.

There’s no signaling messages exchange between AN and AT in the forward Virtual Handoff as it is very quick. It only takes up one sector’s forward air resource at anytime. The usability of forward channels are improved significantly.

AT can request 9 different data rates according to the transfer quality of forward RF links. The lowest rate is 38.4 kbit/s and the highest rate is 2457.6 kbit/s. The combination of higher order modulation/demodulation and error correction enables such high data transfer rate on the 1.25MHz carrier wave.

In 1x EV-DO, the IMSI/MIN is not required to be allocated in advance when routing. For R-P session, the switch between BSC and PDSN needs other solutions. AT and IMSI should be identical to ensure the successful sessions between BSCs within a PDSN.

An IMSI is allocated to AT when a session is initiated by BSC between AT and PDSN. A new interface called A12 was introduced into the 1x EV-DO specification. It is the interface between BSC and AN-AAA server.

AN-AAA has two functions:

1. AT authentication

Virtual soft handoff in

forward link

Adaptive Modulation and

Encoding

R-P Session Establishment



2. An IMSI is returned to BSC from its authentication message center. The IMSI is used to the establishment of BSC and PDSN.

If the AN-AAA server is not deployed in 1x EV-DO, BSC has to allocate IMSI to AT by using other dedicated methods. The IMSI must be unique in the network. The R-P session between 1x EV-DO BSC and 1x BSC can not be completed without AN-AAA server. Depends on mobile IP, AT can remain its IP address unchanged when crossing the network borders. The deployment of AN-AAA facilitates the prompt switch and improve the AT performance when crossing the network borders.

Service Flow

The 1x EV-DO service involves session management service and connection management service. This section describes their service flows.

A session between AT and AN must be established before the AT be served in 1x EV-DO system. The session management includes UATI allocation and maintenance, session negotiation and session release.

1. UATI Assignment and Maintenance

The Unicast Access Terminal Identifier (UATI) is the unique identifier allocated by AN. Its length is 128bit. The UATI allocation is the first step of a session establishment. It means a session which uses the default configuration is initiated. The UATI assignment flow can be demonstrated FIGURE 47.

FIGURE 47 U ATI AS S I G M E N T

AT

A

B

C

D

AN

E

UATIRequest

ACAck

UATIAssignment

UATIComplete

ACAck

The UATI allocation flow is descript in detail as follows:

A. AT sends a UATIRequest message to AN via access channels;

B. AN responds an ACAck message;

C. AN assigns and sends the UATI to AT by UATIAssignment message;

Session Management

Flow



D. AT responds AN by UATICompetele message. UATI assignment completes;

E. AN responds a ACAck message. AT and AN can initiate UATI update during the session.

2. Session Negotiation

During the session establishment between AT and AN, there will be some negotiations about the system configurations (protocols and the parameters in the protocols) between both side. A session can be established successfully once the negotiation reaches an agreement. The negotiated configurations will take effect at the reconnection. The negotiation procedures are show in the FIGURE 48:

FIGURE 48 S E S S I O N N E G O T I AT I O N F L O W

AT

A

B

C

D

AN

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

Connection Establishment

Key exchange

ConfigurationRequest

ConfigurationResponse





Type X ConfigurationRequeste

Type X ConfigurationResponse

Type Y ConfigurationRequeste

Type Y ConfigurationResponse

ConfigurationComplete



Type X ConfigurationRequest

Type X ConfigurationResponse

ConfigurationComplete

The UATI session negotiation flow is descript are as follows:

A. AT and AN open a connection in default configuration to prepare for the session negotiation.

B-G. AT initiates the protocol negotiation.

H-K.AT initiates protocol configuration (Type X and Type Y represents the protocols that the negotiation parameters belong to).



L. The negotiation initiated by AT completes.

M. Key exchange is used by the system to authenticate the AT during the session.

N-Q.AN side initiates negotiation.

R. The negotiation completes.

3. Session Release.

AT is not likely o establish or release sessions frequently in the 1x EV-DO system. After the session establishment, AT can open and close the connections many times during the session. Some reasons such as KeepAlive timeout or subscriber’s request will cause the session release.

The session release is a simple process. Both sides exchange a SessionClose message and release the corresponding resources will end the process. It must be noticed that the PPP Session established by AT and PDSN needs to be released as well when releasing the 1x EV-DO session.

In the 1x EV-DO, a connection is opened between AT and AN means AT is assigned reverse power control channel and reverse traffic channel; the Forward Traffic Channel (FTC is TDM shared by all the users who has opened the connection) is available to AT. AT can use the high speed packet service provided by 1x EV-DO as long as the connection established.

1. AT originates Calls and Establishes Connection

During a session, AT and AN can open and close the connection many times. The connection establishment can be initiated by either AT or AN.

The connection initiated by AN supports common mode and fast mode. In common mode, AN sends a paging message out, once it is received, AT responds as a ConnectRequest message to enter the connect establishment procedures; In fast mode, AN sends a channel assignment message out (the Page/ConnectRequest interaction is neglected) to speedup the connection establishment.

AN AAA will fulfill an access authentication on every AT before the first trying to connect to the PDSN. Only those AT who passes the authentication can continue initializing the connections to the PDSN. Based on the successful authentication, AN AAA returns an IMSI number to AT. AT uses this number as the identifier on the A10/A11 links to communicate with PDSN.

If a session between AT and AN has been established before the connection establishment, the connection establishment procedures initiated by AT is demonstrated in FIGURE 49.

Connection Management

Flow



FIGURE 49 C O N N E C T I O N E S T AB L I S H M E N T F L O W I N I T I AT E D B Y AT

AT PDSN

AB

CD

AN PCFAN_AAA

EF

G

H

I

JKL

MNO

P

Q

R

S

ConnectionRequest +RouteUpdate

ACAckTrafficChannelAssignment

Pilot + DRCRTCAck

TrafficChannelComplete

AT or AN indicatesready to exchange data

on access stream

PPP and LCPnegotiation

CHAP challenge andresponse

CHAP Authenticationsuccess

AT ready to exchangedata on service stream

A12AccessRequestA12AccessAccept

A9SetupA8

A9ConnectA8

A11RegistrationRequestA11RegistrationReply

Establishing PPP connections

Transmitting packet Data

The connection establishment flow initiated by AT is introduced in detail as follows:

A. In access channel, AT sends out a ConnectRequest and a RouteUpdate message to request the connection establishment;

B. In control channel, AN receives the messages sends back an ACAck message;

C. AN sends out the TrafficChannelAssignment message which includes the MAC_ID assigned to AT and other related information;

D. AT sends out the Pilot and DRC message based upon the receiving of TrafficChannelAssignment message from AN;

E. AN acquires the Pilot and DRC from AT and then send a RTCAck message to AT in FTC channel;

F. in RTC channel, AT sends back a TrafficChannelComplete message to indicate that the air-connection is established;



G. AT informs AN that the data exchange in access flow is available;

H. AT and AN initiate the PPP connection and the LCP negotiation which will be used in access authentication;

I. AN sends a CHAP message to AT to initiate a random query. AT sends back a CHAP response message as the response;

J. AN collects the authentication messages (Username, CHAP-ID, CHAP-Challenge, CHAP-Response) about the AT and send them to the AN AAA through A12 interface;

K. AN AAA sends back a AccessAccept message once authenticate successfully;

L. AN sends back the information about successful authentication to AT;

M. AT initiates the connection to the PDSN;

N-Q.The connection towards PDSN initiated by AN via PCF is established;

R. AT tries to connect to the PDSN with PPP connection;

S. The data packet exchange between AT and PDSN becomes available after the establishment of PPP connection.

2. AT Originates Calls and Closes Connections

There are many reasons will cause the connection release such as the timeout of idle timer or AN overload control. The connection release processes initiated by AN is shown in FIGURE 50.

FIGURE 50 TH E C O N N E C T I O N R E L E AS E P R O C E S S E S I N I T I AT E D B Y AN

AT PDSN

A

B

C

AN PCFAN_AAA

D

E

ConnectionClose

A9-Release-A8

A9-Release-A8 Complete

A11-Registration-Request

A11-Registration-Reply

The connection release processes initiated by AN is introduced in detail as below:



A． AT sends out a ConnectClose message in the access channel to request the connection close;

B． AN sends an A9-Release-A8 (value cause is ‘the packet service begins to hibernate’) to PCF and request the A8 connection release;

C． PCF sends an activated stop accounting record to PDSN through an A11-Registration-Request message;

D． PDSN returns an A11-Registration-Reply;

E． PCF uses an A9-Release-A8 Complete message to confirm the release of A8 connection. The release completes.

In the above figure, only the air-link and A8 link is released; The connection between AT and PDSN as well as the 1x EV-DO session between AT and AN are still activate.

3. Switchover Control

In the commercial environment, generally, 1x EV-DO and cdma2000 1x coexist in one network to provides users with voice and high speed data service. The dual mode (1x and 1x EV-DO) handsets can easily switchover between two AN. In this switchover, the PPP connection between AT and PDSN won’t be interrupted. Furthermore, in order to ensure the priority of voice service, when an AT is transferring data on the 1x EV-DO network, it must be timely .switched to 1x network listening paging channel. When the voice paging from AN is received, the dual mode AT immediately stops the data transfer on the 1x EV-DO network and begin to establish a voice connection on the 1x network.

The following situations may occur when the dual mode AT switches cross network.

Switch from 1x to 1x EV-DO when dormant;

Switch from 1x EV-DO to 1x when dormant;

Switch from 1x to 1x EV-DO when active;

Switch from 1x EV-DO to 1x when active;

Receive the 1x voice calls when the 1x EV-DO data are active.

If AT has already established the 1x EV-DO session on the 1x EV-DO network and the 1x EV-DO and 1x are sharing one PDSN, 1x can provide concurrent service.

When at a dormant status, the switching procedures of AT from 1x to 1x EV-DO are briefly introduced:

A． When AT accesses 1x EV-DO from 1x, it launches a position renew procedure to enable 1x EV-DO acquire the PANID of AT;

B． The destination AN initiates a request of establishing a connection towards PDSN;

C． PDSN stops the connection with source AN when the request is received and then connect to the destination AN.



In this processes, the PPP connection between the dual mode AT and PDSN doest not interrupt.

The 1x voice paging receiving processes during the 1x EV-DO data activation period is briefly introduced as follows:

A． At the source AN, AT turns to dormant from active;

B． At dormant status, AT performs the cross network switch;

C． At the destination AN, AT turns to active from dormant.

When the dual mode AT transfers data on the 1x EV-DO, in order not to neglect any voice call from 1x, it must switch to the 1x timely to listen to the time-slots that assigned to the handset. Once the voice paging message is received, the dual mode will switch to the 1x according to the voice priorities to answer the voice calls. The data sessions on 1x EV-DO can be switched to 1x if the concurrent service is supported on the target 1x. This makes the concurrency of voice calls and data packet transfer available.

Comparisons with 1x

The core differences between 1x EV-DO and 1x are shown in Table 16.

T AB L E 16 CO R E D I F F E R E N C E S B E T W E E N 1 X EV-DO AN D 1 X

Feature 1x 1x EV-DO

Service Voice/Data Data

Highest rate Forward: 153.6 kbit/s (RC3)

Reverse: 9.6 kbit/s (RC3)

Forward: 2.4 Mbit/s

Reverse: 153.6 kbit/s

Core network ANSI-41 based Real IP

Channel

multiplexing

CDM (Forward/Reverse) Forward: CDM+TDM

Reverse: CDM

Switch Hard handoff and soft handoff

(Forward/Reverse)

Forward: VHO Reverse：Soft handoff

Power

control and

rate control

Fast power control

(Forward/Reverse);

Rate control is not available

Reverse: Rate control +

Power control

Forward: rate control

Access

procedures

Access channel procedures

Enhanced access channel

procedures

Same as access channel

procedures

RF and

encoding

Convolution code and Turbo

code

48-level FIR filterer

Turbo code only

48-level FIR filterer

Compared with 1x, 1x EV-DO has the following advantages in high speed data packet services:



1. Air interface: 1x EV-DO eliminates the transfer bottleneck of data service at air interfaces.

2. RF parameters: 1x EV-DO fully takes the downward compatibilities into account.

3. Technologies: 1x EV-DO and 1x have the same power control, soft handoff, access procedures and Turbo encoding technologies. The developers can easily develop the 1x EV-DO products by taking the advantages of existing 1x technologies.

4. Networking：1x EV-DO is very flexible. For those users only need data packet services, an independent 1x EV-DO network with minimum configuration cam provide high speed data packet services. In this case, the sophisticated ANSI-41 structure is not required for the core network configuration because it is IP network based. For those users who need both voice and data services, the combination of 1x and 1x EV-DO is also available. What’s more, for the dual mode (1x/1x EV-DO) AT, 1x EV-DO provides a mechanism to make the switchover between the two systems available.

1. Briefly state the functions of 1x EV-DO forward channels.

2. Briefly state the principles of rate control in 1x EV-DO reverse links.

3. Briefly state the principles of power control in 1x EV-DO reverse links.

4. Briefly state the principles of scheduling strategy in 1x EV-DO forward links.

5. Briefly state the principles of the call originating procedures in 1x EV-DO AT.

6. Compare 1x EV-DO and 1x.

Review

103

C h a p t e r 6

CDMA Key Technologies and Advantages

Key points CDMA key technologies CDMA advantages

Introduction

After this chapter, you will learn the CDMA key technologies and have a deeper understanding of CDMA basic principles.

Key Technologies

This section describes CDMA key technologies: power control, diversity, and soft switching, and some other key technologies used in 3G..

In CDMA systems, power control is regarded as the core of all key technologies. Power control is to allocate the power resources of CDMA systems (including mobile station and base station). If this technology is not well implemented, the advantages of CDMA systems will not be realized. Let alone the implementation of large capacity and high quality CDMA systems.

FIGURE 51is a simple diagram of power control process.

FIGURE 51 P O W E R C O N T R O L S K E T C H

A B

If all the subscribers in a cell transmit signals at the same power, signals sent by the MSs closer to the base station will be strong,

Power control



and those sent by the MSs farther away will be weak. In this case, the strong signals will cover the weak ones. This is the “far-near-effect” problem in the mobile communications.

CDMA is a self-interference system, where all subscribers share the same frequency, so the “far-near-effect” problem becomes serious. In CDMA systems, subscribers’ strong signals will be properly received, but they may cause interference to other subscribers’ signals within the same frequency band, and even submerge useful signals. As a result, other subscribers’ communication quality will be degraded, and the system capacity lowered. To overcome the “far-near-effect”, the power used by the transmitter should be adjusted in real time according to communication distances. This is called “power control”.

The CDMA power control includes forward power control, reverse power control, and cell breath power control.

The CDMA system capacity is mainly limited by inter-MS interference. If the signals from each mobile station reach the base station at the minimum required Signal-to-Noise Ratio (SNR), the system capacity would be the maximum.

In real systems, subscribers’ transmitting environment changes as they move, so the signal paths to the base station, signal strength, time delay, and phase shift also keep changing, and the received signal power fluctuates around the desired value. Hence, power control is introduced to the reverse links of CDMA systems.

The power control for reverse links of CDMA systems adjusts subscribers’ transmit power, so that all signals reaching the BS receiver will have the same power. Meantime, the power should be within the threshold SNR value, and meet the communication quality requirements. All subscribers’ signals can be adjusted to ensure that they have the same power when reaching the base station receiver, regardless of subscribers’ locations and transmitting environments.

Reverse power control contains three parts: open-loop, closed-loop, and outer-loop.

1. Reverse open-loop power control

In CDMA systems, each MS calculates the signal loss in the path from the BS to the MS. If the signals received by the MS from the BS are strong, it indicates that the MS is very close to the BS, or the transmission path is extremely excellent. In this case, the MS may lower its transmit power, and the BS can still properly receive the signals. On the contrary, if the signals received by the MS from the BS are weak, the MS strengthens its transmit power to compensate the signal loss. This is called open-loop power control.

The open-loop power control is simple and direct. It is unnecessary to exchange control information between the MS and the BS. Moreover, the control speed is fast, and the overhead can be saved.

Reverse power control



However, the frequencies used for forward and reverse transmission are different in CDMA systems (the frequency difference specified in IS-95 is 45MHz). And the difference well exceeds the coherence bandwidth of the channel. Therefore, it cannot be assumed that the fading characteristic of forward channels is equivalent to that of reverse channels. This is a restriction of open-loop power control.

The algorithm used for open-loop power control mainly uses a constant, that is,, the sum of the forward received power and the MS reverse transmit power, to implement the control function. The detailed implementation involves response time control and power estimate correction factor, etc.

The following describes the principle of open loop power control for reverse channels in cdma2000 1x systems.

The offset value of output power in open loop power control is calculated differently for different reverse channels. The value of offset_power for reverse channels in cdma2000 1x system are as shown in Table 18.

T AB L E 17 O F F S E T _ P O W E R V AL U E S F O R O P E N L O O P P O W E R C O N T R O L

Band Class Forward

Spreading

Rate

Reverse

Spreading

Rate

Reverse Channels Offset

Power3

Access Channel Reverse Traffic Channel（RC＝1，2）

-73 1 1

Enhanced Access Channel

Reverse Common Control Channel Reverse Traffic Channel（RC＝3，4）

-81.5

1 Reverse Traffic Channel（RC＝3，4） -76.5

0，2，3，5，

7，9

3

3 Enhanced Access Channel


-76.5

Access Channel Reverse Traffic Channel（RC＝1，2）

-76 1 1

Enhanced Access Channel


-84.5

1 Reverse Traffic Channel（RC＝3，4） -79.5

1，4，6，8

3

3 Enhanced Access Channel


-79.5

1) Open loop power control for access channel

Before the reverse traffic channel is set up, AT transmits a random probe access sequence to connect the AN. The initial transmit power of access channel is as follows:



mean output power(dBm)=

-mean input power(dBm)

+offset power (see Table 18)

+interference correction

+NOM_PWRs-16×NOM_PWR_EXTs

+INIT_PWRs

+PWR_LVL×PWR_STEPs

where interference correction = min(max(-7-Ec/Io,0),7), as shown in FIGURE 52.

This parameter is the interference correction factor based on the received pilot strength at current location. The IS-95 has already introduced this correction factor. Obviously, when SN ratio is low, the correction factor is big. In such a situation, the access success rate is high.

FIGURE 52 I N T E R F E R E N C E C O R R E C T I O N F AC T O R V S R E C E I V E D P I L O T S T R E N G T H I N O P E N L O O P P O W E R C O N T R O L F O R AC C E S S C H AN N E L

-7-14

Interference Correction

EcIo

7

NOM_PWRs and INIT_PWRs have the same meanings as IS-95A. NOM_PWRs is used to compensate the difference between forward/reverse links. And INIT_PWRs is used to improve access success rate. NOM_PWR_EXTs=0 for frequency band 0, 2, 3, 5, 7, and 9; NOM_PWR_EXTs=1 for frequency band 1, 4, 6, and 8. PWR_LVL and PWR_STEPs represent the number of probe accesses and the power increment for each probe access respectively.

All these parameters can be obtained from the access parameter message on paging channel. The structure of this message is completely the same as IS-95 and will not be repeated here.

2) Open loop power control for reverse traffic channel (RC1, RC2)

For reverse channels with RC1 and RC2, the initial transmit power is:







+ACC_CORRECTIONS

+RLGAIN_ADJs

where Interference Correction = MIN(MAX(–7 – ECIO,0),7); ACC_CORRECTIONS is the accumulated value of power offsets before entering the traffic channel.

The average output power after receiving the first power control bit is:



+offset power(see Table 18)


+ACC_CORRECTIONS

+RLGAIN_ADJs

+the sum of all closed loop power control corrections(dB)

+10×log10(1+NUM_RSCCH)(dB)

where NUM_RSCCH, ranging from 0~7, is the times Reverse Supplemental Code Channel is transmitted. Upon receiving the first power control bit, the mobile station does not update the interference correction factor.

RLGAIN_ADJ is used to set the transmit power offset relative to access channel or enhanced access channel. This parameter is sent to MS by extending the channel assignment message on PCH.

3) Open loop power control for reverse traffic channel (RC3, RC4)

For reverse channels with RC3 and RC4, the initial transmit power of reverse pilot channel is:



+offset power(see Table 18)


+ACC_CORRECTIONS

+RLGAIN_ADJs

where Interference Correction = MIN(MAX(IC_THRESHs – ECIO,0),7). The waveform is as shown in FIGURE 53.



FIGURE 53 I N T E R F E R E N C E C O R R E C T I O N F AC T O R V S R E C E I V E D P I L O T S T R E N G T H I N O P E N L O O P P O W E R C O N T R O L F O R RC3 AN D RC4 T R AF F I C C H AN N E L S

Interference Correction

EcIo

7

IC_THRESIC_THRES

Similarly, ACC_CORRECTIONS is the accumulated value of power offsets before entering the traffic channel. The enhanced access channel and reverse common control channel are not implemented in 1x systems, and ACC_CORRECTIONS is set to the evaluation of NOM_PWRs – 16×NOM_PWR_EXTs + INIT_PWRs + PWR_LVL* PWR_STEPs.

The average output power after receiving a valid power control bit is:





+ACC_CORRECTIONS

+RLGAIN_ADJs

+the sum of all closed loop power control corrections.

The MS will not update the interference correction factor.

IC_THRES in the above is a negative value and the threshold to start the application of interference correction. This parameter is sent to MS through the enhanced access parameter message on BCCH. The cdma2000 1x systems do not support BCCH, so it cannot change the value of IC_THRES. But the protocol specifies that every time an access parameter message is received, it will be set to –7.

2. Reverse closed loop power control

Reverse closed loop power control is also called inner loop power control, that is, the BS checks the SNR from MS, compares it with a threshold, and sends an instruction over the downlink channel to the MS according to the comparison result, informing it to increase or lower its transmit power.

So, when the mobile station works in non-gating mode, the power control subchannel transmits a power control bit every 1.25 ms (800 Hz).



When the mobile station works in gating mode, the 1/2 and 1/4 power control subchannels transmit power control bits at 400 bit/s or 200 bit/s.

The time slots in both gating and non-gating modes of forward power control subchannel is as shown in FIGURE 54.

FIGURE 54 T I M E S L O T S I N G AT I N G AN D N O N -G AT I N G M O D E S O F F O R W AR D P O W E R C O N T R O L S U B C H AN N E L S

The PCG within a 20 ms frame is numbered from 0 to 15. When the mobile station works in gating mode of 1/2 reverse pilot channel, the forward power control subchannel transmits a power control bit only in even PCG. When the mobile station works in gating mode of 1/4 reverse pilot channel, the forward power control channel transmits power control bits only in PCG 1, 5, 9, and 13.

When the radio configuration is RC3~RC6 and the mobile station is in gating mode, the base station starts to transmit power control bits in PCG T ms after the mobile station completes transmission, where T=(REV_PWR_CNTL_DELAY+ 1)×1.25.

The ‘0’ bit instructs the mobile station to increase its average power output, while the ‘1’ bit is for decreasing average power output.

3. Reverse closed loop power control response in lock losing status

Due to the existence of data burst randomization (DBR), the power control bits in those PCGs that do not contain a transmit



power will be ignored. When all the fingers of base station receiver are in lock losing status, the DBR effect must be corrected so as to control the power of mobile station, that is, maintain the ratio of power control bits to all the frame rates. The reverse closed loop power control response in lock losing status of CSM5000 comes in to complete this function.

There are four choices for reverse closed loop power control response in lock losing status, as shown in Table 18. They are determined by the 2-bit PC_GAIN field in CHAN_ELEM_INFO2 register.

T AB L E 18 RE V E R S E C L O S E D L O O P P O W E R C O N T R O L R E S P O N S E I N L O C K L O S I N G S T AT U S

PC_GAIN value Power control response in lock losing status

00 +0dB/sec gain

01 +25dB/sec gain

10 +50dB/sec gain

11 +100dB/sec gain

PC_GAIN=00 is for +0 dB/sec gain. Set the number of power up/down control bits for all frames to the same value will make the MS maintain the same transmit power.

PC_GAIN=01 is to replace the 8th power down control bit in every 4th frame with a power up bit. This will lead to +2 dB gain for every 4 frames, that is, +25 dB/sec gain.

PC_GAIN=10 is to replace the 8th power down control bit in every 2nd frame with a power up bit. This will lead to +2 dB gain for every 2 frames, that is, +50 dB/sec gain.

PC_GAIN=11 is to replace the 8th power down control bit in every frame with a power up bit. This will lead to +2 dB gain for every frame, that is, +100 dB/sec gain.

4. Reverse outer loop power control

The SNR threshold is not constant but is dynamically adjusted in reverse closed-loop power control. This dynamic process is called reverse outer-loop power control.

In reverse outer loop power control, the BS counts the received Frame Error Rate (FER) in the reverse channel.

If the FER is greater than the FER threshold, it indicates that the fading in the reverse channel is serious. Then the MS should increase its transmit power so as to increase the SNR.

On the contrary, if the FER is less than the FER threshold, the MS should lower its transmit power so as to decrease the SNR.

The adjustment based on the FER statistics is achieved by the reverse outer-loop power control algorithm. This algorithm is based on three operation states: variable rate, full rate, and delete. These three states fully show the actual working of the MS, and the power threshold is adjusted in each state.



To ensure the best quality of voice frame at rate 9600bit/s, many criteria, such as 1% FER threshold, are added in the full rate operation state.

This algorithm involves such techniques as step-adjustment, state transition, accidental error judgment, and soft handoff FER statistical control.

In real systems, all the three power control modes are used to realize the reverse power control. That is, first, make open-loop estimate of MS transmit power; then this estimate is further corrected by the closed-loop and outer-loop power control, trying to achieve the accurate power.

In forward links:

A mobile station receives more interference from the adjacent BS as it moves towards the cell edge.

A mobile station receives more interference from multipath in the local cell when it moves towards the BS.

These two kinds of interference will affect the receiving effect of signals, hence degrading the communication quality, and even unable to set up the links. Therefore, power control is introduced in the forward links of CDMA systems.

The forward power control ensures each subscriber’s communication quality by appropriately allocating the power in forward traffic channels. This minimizes the transmit power in the forward traffic channels, provided that it meets the minimum SNR required by MS demodulation. As a result, the interference to the traffic channels of adjacent cells can be reduced, and the forward link subscriber capacity can be maximized.

In the ideal single cell model, the forward power control is not mandatory. If the inter-cell interference and heat noise are considered, the forward power control becomes an indispensable key technique because it can deal with the following forward link problems in the communication process.

If an MS is closer to one or more adjacent BSs than to its own BS, this MS will be more seriously interfered by the adjacent BSs, and the interference change will be independent of its BS signal strength. In this case, the BS that the MS belongs to is required to increase its signal power by several decibels to maintain the communication.

If an MS is right at the converging point of several strong multipath interferences, the signal interference will exceed the allowable limit. In this case, the BS that this MS belongs to is also required to increase its signal power.

If an MS locates at a place where the signal transmission performance is excellent, the signal transmission loss will be decreased. The BS can reduce the signal transmit power to the MS, provided that certain communication quality is maintained. Due to the total BS transmit power limit, the forward link

Forward power control



capacity can be increased, and the interference to other inside- and outside-cell subscribers can be reduced.

Similar to reverse power control, forward power control also has forward closed loop power control and reverse outer loop power control modes. In addition, forward fast power control (FFPC) mechanism is introduced in cdma2000 1x systems.

1. Forward closed loop power control

The closed loop power control decides the the value of power control bit to send to the BS on reverse power control subchannel, by comparing the Eb/Nt (the Eb is the mean bit energy; the Nt is the noise which includes the interference from other cells and the flat noise) of signals received on forward traffic channels with the setpoint of corresponding outer loop power control.

Every 1.25 ms (PCG) of the reverse pilot channel contains 1536*N chips, where N is the spreading rate. N=1 when spreading rate=1; N=3 when spreading rate=3. Here the first 1152*N PN chips are used to transmit pilot signals; the following 384*N PN chips are used to transmit other signals generated by the mobile station. The contents in the signals are related to the FPC_MODEs. Please refer to the Table 19.

T AB L E 19 S I G N AL C O N T E N T S T R AN S M I T T E D B Y T H E R E V E R S E P O W E R C O N T R O L S U B C H AN N E L U N D E R D I F F E R E N T C I R C U M S T AN C E

FPC_MODEs The signal contents transmitted by the reverse power control

subchannel

000，001，010 The forward power control bit generated by the mobile station is

retransmitted in every 384*N PN chips after PCG

011，100，101 The Erase Indication Bit (EIB) generated by the mobile station or

QIB in 3GPP2 C.S0002-A is retransmitted in every 384*N PN chips

of reverse power control subchannel

110 The forward power control bit generated by the mobile station is

retransmitted in every 384*N PN chips of reverse power control

subchannel. Whereas the Erase Indication Bit (EIB) generated by the

mobile station is retransmitted in every 384*N PN chips of reverse

supplement control subchannel.

The mobile station must transmit pilot signals in the first 1152*N PN chips of each PCG of reverse pilot channel and reverse power control subchannel in the following 384*N PN chips.

All the PN chips sent in each PCG of reverse pilot channel must be transmitted at the same power. The structure of reverse power control subchannel is shown in FIGURE 55.



FIGURE 55 S T R U C T U R E O F R E V E R S E P O W E R C O N T R O L S U B C H AN N E L

The forward power control algorithm for RC1 and RC2 in cdma2000 1x systems is described below.

1) Forward power control algorithm for RC1

The working of this algorithm can be described with the following two rules:

Rule 1: If a power measurement report is received, increase the transmit power.

Rule 2: If no power measurement report is received, decrease the transmit power.

In voice communications, it is actually error frame rate that influences the voice quality. When the error frame rate is high, the user will perceive poor voice quality. When the error frame rate is low, the user will perceive good voice quality. To guarantee certain voice quality in IS-95 based CDMA systems, it is specified that the uplink/downlink error frame rate cannot exceed a threshold value, that is, 1% normally. This ratio can be achieved by defining the ratio of power increase to power decrease. In this case, the ideal parameter setting is such that if a power measurement report is received the transmit power of this channel is increased by 1 dB; if no power measurement report is received the forward transmit power is decreased by 0.01 dB.

Since the communication environment may suddenly change for the worse, so the above algorithm will continuously increase the power at big steps to resist the fast deep fading.



After the environment becomes better, the algorithm will slowly lower the transmit power.

2) Forward power control algorithm for RC2

The IS-95A standard specifies that the mobile station uses EIB to express the frame quality of forward link at rate set 2, and sends the EIB value to the base station over reverse link. For the centralized forward power control algorithm, the controller obtains the EIB value from reverse layer 3 data on the BSC side, and carry out forward power control correspondingly.

The basic idea of this algorithm is the same as that of forward power control algorithm for 8 K vocoder configuration. It can be described with the following two rules:

Rule 1: If the received EIB=1, increase the transmit power.

Rule 2: If the received EIB=0, decrease the transmit power.

With 13 K vocoder, the controller does not need the power measurement report any longer, and the mobile station can provide an EIB for each frame so that the forward power control can be performed faster. This will expand the dynamic range of forward power control, making it around 20 dB.

The big dynamic range requires the using of variable steps in the algorithm and the power increase step in inverse proportion with the transmit power at that moment. To speed up the calculation, the relation between the increase step and the transmit power at that moment is defined as the following non-linear function:

+≤+<<+

+≥=

2/)(_2/)(2/)(_

2/)(__

min

maxmin

max

PPpowerdeltaBigupPPpowerPPdeltaNormalup

PPpowerdeltaSmallupdeltaup

normal

normalnormal

normal

where deltaSmallup _ =0.5 dB, deltaBigup _ =3 dB , and

deltanormalup _ =1 dB.

The forward outer-loop power control is implemented at the MS. The BS sends, with the paging message, the threshold value for outer-loop power control to the MS.

2．Forward outer loop power control

The implementation point of forward outer loop power control is on the mobile station. The responsibility of the base station is to send the threshold of outer loop control to the mobile station in the paging message. It includes the outer loop upper/lower threshold and the original threshold of FCH and SCH.

The outer loop power control sets the threshold according to the Eb/Nt required by the forward traffic channel’s goal FER. This threshold either informs the base station to control the power via the close-loop or, in case of the forward traffic channel has no close-loop, sends messages to inform the base



station to control the emission power according to the threshold difference.

3．Forward fast power control

When the forward outer power control is enabled, the forward outer power control and the forward close-loop power control take effect together to reach the forward fast power control. Its principle is shown in FIGURE 56.

FIGURE 56 P R I N C I P L E O F F O R W AR D F AS T P O W E R C O N T R O L

Although the forward fast power control is implemented on the base station side, the power control bits and the outer loop parameters for power control are the checked result of forward channel signal quality outputted by the mobile station. The final result are sent to base station via power control sub-channel on the reverse pilot channel.

In the RC3~RC6 reverse channels, the reverse pilot channel is added into. This is the footstone of forward fast power control; Because the power control bits used for forward fast power control is sent to base station by the reverse power control sub-channel on the reverse pilot channel.

Cell breath is an important function of the CDMA systems, which is mainly implemented to adjust the cell burden. The forward link border indicates a physical place between two BSs. If an MS is located at this place, its receiver will perform the same regardless of which BS the signals are received from. The reverse link handoff border indicates that the receiver of the two base stations will have the same performance as the mobile station located at this

Cell breath power control



place. Base station cell breath control is to retain the overlap of the handoff borders between the forward link and the reverse link, in order to maximize system capacity and avoid handoff failure. The cell breath algorithm is based on the fact that the sum of the reverse received power and the forward pilot transmit power is a constant. The specific approach is to adjust the proportion of the pilot signal power in the total BS transmit power so as to control the cell coverage. The algorithm involves initial state adjustment, reverse link monitoring, and forward pilot frequency gain adjustment.

If the first-generation mobile system based on analog FM modulation uses a narrowband modulation system, the multpath effect will cause serious fading. However, in the CDMA modulation system, the multipath signals can be received separately so as to significantly mitigate the signal fading caused by multipath. But the multipath fading is not completely eliminated because sometimes the demodulator alone cannot handle the multipath effect, still inducing some fading.

Diversity receive is a satisfactory approach to weaken the fading. It takes full advantage of the multipath signals energy in transmission to improve the transmission reliability. It also collects the scattered energy in time, space and frequency domains.

Different paths, which are almost independent of each other at the receiving end, can be obtained based on different angles, methods and measures in space, time and frequency domains. There is three typical types of diversity receive: time diversity, space diversity, and frequency diversity. All of them are used in the CDMA systems.

The MS movement will induce Doppler frequency shift in the received signals. In a multipath environment, such frequency shift forms Doppler spread. The reciprocal value of Doppler spread is defined as coherence time, which indicates the time variation channel corresponding to the signal-fading beat. This fading usually happens at the specified time of the transmission waveform. This is called time selective fading. It will seriously influence the bit error of the digital signals.

If the amplitude is sampled in sequential order, two sample points will not be correlated when the time interval is long enough (longer than the coherence time). Therefore, the time diversity can be adopted to weaken the influence, that is, the given signals are repeatedly transmitted for N times at a certain time interval. As long as the time interval is longer than the coherence time, N independent diversity branches can be obtained.

From the analysis of the communication principle, we know that the time interval ∆t in time domain should be greater than the coherence time ∆T in time domain, that is,

BTt 1=∆≥∆

Receive diversity

Time diversity



Where B is the diffusion interval of the Doppler spread shift, which is directly proportional to the MS moving speed. Therefore, time diversity is useless for the MS in a relatively static state.

Compared with space diversity, time diversity has the advantage of less receive antennas but it has the disadvantage of occupying more timeslot resources, thus decreasing the transmission efficiency.

It is a process to modulate the information to be transmitted into different carriers for transmission in the channels. Due to the frequency-selective fading feature, when the interval between two frequencies is greater than the correlation bandwidth, their fading is not correlated. That is, as long as the interval between the carriers is large enough, that is,, the carrier interval ∆f is greater than the frequency correlated bandwidth, we will have:

LFf 1=∆≥∆

Where L is the delay diffusion of the received signals’ delay power spectrum. The correlative bandwidth for urban and suburb areas is 50 kHz and 250 kHz respectively, whereas the signal bandwidth for the CDMA systems is 1.23 MHz. Therefore, frequency diversity is possible. Specifically, the frequency band is 800~900 MHz for urban area, and the typical delay diffusion is 5µs, so we have:

kHzsLFf 200511 ===∆≥∆ µ That is, the carrier interval for frequency diversity should be greater than 200 kHz.

Compared with space diversity, frequency diversity has the advantage of less receiving antennas and devices, and the disadvantages of more frequency spectrum occupation and transmitters.

At a base station, several antennas are installed with some distance from one another so that they can receive or transmit signals independently. This guarantees the independence of signals fading. One of the signals is selected by using the selective combination technique to reduce the influence of fading. This method makes use of the independence of the signals received at different positions (space) to resist fading.

The basic structure of space diversity contains one antenna for transmission at the transmitting side and N antennas for receiving at the receiving side.

The distance between the receiving antennas is d. According to the communication principles, d is the correlative interval ∆R. It should satisfy the following expression:

ϕλ≥∆= Rd where λ is the wavelength and ϕ is the diffusion angle of the antenna. In urban areas, usually the diffusion angle ϕ=20o. Then we have:

λπλλπ 86.29)2(120360 ≈=××≥ ood

Frequency diversity

Space diversity



More diversity antennas will produce better diversity effect. The diversity gain is proportional to the tuple of diversity N. But when N>2, the improvement of diversity gains decreases as N increases gradually. There is a tradeoff between performance and complexity in practice. Usually N=2~4. There are two variants for space diversity:

Polarization diversity

The two antennas that are orthogonal in polarization direction are used to transmit the same signal and the signals received by two antennas with different polarization show different fading characteristics. That is, horizontal and vertical polarization antennas are installed at the transmitting and receiving ends respectively. At the receiving end, the two signals of different fading characteristics can be obtained due to polarization diversity. It has the advantages of compact structure and saving space, and the disadvantages that the transmit power is allocated to two antennas, incurring 3 dB loss.

Angle diversity

The receiving environment varies in terms of terrain and building. This may in effect make the signals from different paths look like from different directions. Thus directional antennas can be used at the receiving side to point to different directions. The multipath signals received by two directional antennas are uncorrelated.

In space diversity, there are N antennas at the receiving side. If the size and gain of these N antennas are the same, apart from the anti-fading diversity gain that the space diversity obtains, there is additional 3 dB equipment gain for each antenna.

For soft handoff, to obtain better communication quality, the mobile station can keep contact with the previous base station and select a better signal from the two before it begins communication with the new base station.

The spectrum signals transmitted by the transmitter will be reflected and refracted by buildings, hills, and other obstructs before they reach the receiver with different delays from different paths. If the delays of these multipath signals exceed that of the pseudo-code’s chip, then the receiver will differentiate these different beams. These different beams pass through different delay lines, being aligned and combined. What was disadvantageous becomes advantageous: the original interfered signals become useful combined signals. This is the principle of RAKE receiver. That is, it makes use of the space diversity technique.

A RAKE receiver is composed of a searcher, finger, and combiner. The searcher searches the paths by making use of the code’s auto-correlation and cross-correlation features. The finger despreads and demodulates the signals. The number of fingers

RAKE receiver



determines the number of demodulated paths. Usually a RAKE receiver in the CDMA base station system is composed of 4 fingers and a RAKE receiver in the mobile station is composed of 3 fingers. The combiner combines the signals from the demodulator. The commonly used combination algorithm includes selective combination, equal-gain combination, and maximal ratio combination. The combined signals are output to the decoder unit for channel decoding.

Specifically, the correlator of the RAKE receiver despreads the received signals from each path. In terms of coherent demodulation, the despread signals are multiplied with a complex amplitude to correct the phase error, and the path is weighted according to the selected combination (maximal ratio or equal-gain combination). The impulse-response metering module measures the multipath profile continuously. When the pulse response delay changes, the metering module will assign a new code phase to the code-tracing module to trace the minute changes. The signals from different RAKE paths are combined, and the channel codes are interleaved and decoded. Furthermore, the searcher continuously searches the pilot signals from the adjacent cells to provide pilot signal measurement for the handoff. The number of RAKE paths is determined by the channel profile and chip rate. Higher chip rate offers more separable paths. However, when there are too many RAKE paths, more energy is needed from the channel to maintain good performance. Too many RAKE paths may lead to combination loss.

The following discusses the measurement of impulse response, code acquisition, code tracing, complex amplitude estimation, and the searcher. The impulse response measurement correlates the pilot codes at different phases and the received signals to find out the multipath component. The required metering rate for the impulse response measurement is determined by the mobile station’s moving speed and radio environment. The mobile station moving at a faster speed requires faster measurement of the RAKE paths to obtain better multipath components. However, a broader scanning window is required for an environment of longer delay. Apart from metering, this module assigns the multipath components to the RAKE paths. Different policies can be applied to the codes assignment. The assignment can be carried out when the impulse response measurement is finished or a strong enough multipath component has been found. The code searching is carried out before the system synchronous searching.

The mobile station scans the pilot signal. The pilot signal priority sequence can be determined by the nearest or adjacent pilot signals. If the connection is lost for some reason, the scan will begin from the pilot signal of the highest priority. In an environment of strong interference, code search may be a bottleneck. The matching filter may be used for fast codes search. The typical code tracing loop leads and lags the locked loop. It includes two correlators (leading and lagging). The chips assigned to them are half-chip short from the standard timing. The code phase is adjusted according to the correlation result. The performance of the tracing loop is determined by the loop



bandwidth. If the update is faster than the movement of the multipath component delay, then the synchronization error can be ignored. Otherwise the loop noise will increase. This, however, also depends on the detection policy (that is, applying regular or multi-user detection).

The estimate of complex amplitude includes that of amplitude and phase. In the maximal ratio combination, the signal weight is the complex conjugate of the complex amplitude. In case of equal-gain combination, only phase error is corrected, and each RAKE path can be regarded as having equal weight. The estimate of the complex amplitude should be averaged in a reasonable period duration. In this case, the coherent time is regarded as the upper limit of the average time. The searcher scans the pilot signals from other cells. During a session, the mobile station searches the pilot signals, measures the downlink interference, and possibly receives uplink interference results. As there are a large number of pilot signals, it may take a long time to search the pilot signals in the adjacent diversity set.

Therefore, the search time may limit the system performance, particularly, in cellular environment, where a new base station can be activated due to the corner effect. One possibility to reduce the needed hardware is to flexibly assign RAKE and path searchers. It will increase the effectiveness of scanning in a low multipath environment. The number of paths scanned is determined by the expected rate of the preamble signal scanning.

Soft handoff is unique to the CDMA mobile communication systems. Its principles are as follows: when a mobile station moves to the adjacent BTS controlled by the same BSC, the mobile station keeps radio connection with the source BTS while connecting the target BTS, and then releases the radio connection with the source BTS. The soft handoff that happens between different sectors of the same BTS controlled by the same BSC is called softer handoff.

There are the following soft handoff modes:

Handoff between different sectors of the same carrier in a BTS is called softer handoff.

Handoff between different BTSs of the same carrier in a BTC.

Handoff between different BSCs of the same carrier in a MSC.

Soft handoff means that when a mobile station wants to communicate with a new base station, it maintains connection with the previous base station while being handed off to the new base station. Soft handoff can only happen between CDMA channels of the same frequency. It acts as traffic channel diversity on the border between two areas covered by two base stations. This significantly reduces the call-drop caused by handoff. According to the testing statistics on analog TDMA, 90% of the call-drops in radio channels happened during handoff. The soft handoff greatly reduces the probability of call-drop, ensuring the reliability of communication.

Handoff

Soft handoff



FIGURE 57 S O F T H AN D O F F

Before we discuss the soft handoff processes, a few concepts need be introduced: pilot set, search window and handoff parameters.

1. Pilot set

Like standby handoff, the pilot set was introduced into the handoff as well. Terminals categorize the pilot into four types according to the bias of pilot PN sequence:

Active set: the pilot set which corresponds to the current forward traffic channel.

Candidate set: the pilot set which is not within the active set but is intensive enough to support the normal service.

Neighbor set: the pilot set designated by the base station neighbor cells list message.

Residual set: the pilot set except the three pilot sets mentioned above.

When search the pilots, the terminals measure the pilot intensity in a sequence of active set, candidate set, neighbor set and residual set. If in the active set and candidate set, there are PN1, PN2 and PN3, in the neighbor set, there are PN11, PN12, PN13 and PN14 and in the residual set, there are PN’……, then the terminals measure the pilot in the following sequence:

PN1、PN2、PN3、PN11、



PN1、PN2、PN3、PN14、PN’、


PN1、PN2、PN3、PN12、……

It’s obvious that compared with the active set and the candidate set, the residual pilot has less opportunity to be searched.

2. Search window

Except the number of pilot searching times, the range of searching area is also taken into consideration. There is a delay between terminals and base station. As shown in FIGURE



58, the delay between the terminal and the base station 1 is t1, the dealy between the termianl and the base station 2 is t2.

FIGURE 58 D E L AY D I F F E R E N C E B E T W E E N B AS E S T AT I O N S

BTS1 BTS2

BTS3

t1t2

Assume the terminal is synchronized with the base station 1, if the distance between them is less than the distance between the terminal and the base station 2, then t1<t2. For the terminal, the pilot from base station 2 comes later than the terminal reference time; the time difference is t2-t1. If the distance between the terminal and the base station 1 is greater than the distance between the terminal and the base station 2, then t1>t2. For the terminal, the pilot from the base station 2 comes earlier than the terminal reference time; the time difference is t1-t2.

When measure the pilot, terminals have to search in a particular area to avoid pilot skip in each pilot set. The search window is used by terminals to capture pilot. That means for a certain pilot sequence bias, terminals will search the pilot by bring forward or delay some code chip time.

As shown in FIGURE 59 the terminal will set the short code of itself as the center and search the pilot ahead of and behind the short code range of the half size of the search window.

FIGURE 59 S E AR C H W I N D O W AN D P I L O T S

PN offsetPN

Search window

Slower search speed comes with the larger search window. But if the search window is too small, the pilots with more delay



difference can not be searched out. For each pilot set, the search window size is defined by the base station for terminals.

SRCH_WIN_A：The search window size of active set and candidate set;

SRCH_WIN_N：The search window size of neighbor set;

SRCH_WIN_R：The search window size of residual set;

SRCH_WIN_A depends on the predicted propagation environment. It must be big enough to capture all the pilots’ multipath from the target base station. However, it must be small enough to optimize the search window.

SRCH_WIN_N is generally larger than SRCH_WIN_A. It depends on the distance between the current base station and the neighbor base station. In general, it is twice larger than the maximum signal delay.

In most cases, SRCH_WIN_R and SRCH_WIN_N have the same size. But SRCH_WIN_R can be very small if the residual set is not used.

3. Handoff parameters

T_ADD：The base station sets this parameter as the threshold when the mobile station monitors the pilot. Once the mobile station finds that the pilot intensity of a certain base station in the neighbor set or residual set is stronger than the T_ADD, it sends out a Pilot Set Measurement Message (PSMM).

T_DROP：The base station sets this parameter as the threshold when the mobile station monitors the descent pilot. Once the mobile station finds that the pilot intensity of a certain base station in the active set or candidate set is weaker than the T_DROP, it starts the handoff-elimination timer at this base station.

T_TDROP：The base station sets this parameter as the preset value of the descent pilot monitoring timer on the mobile station. If the pilot intensity in active set is weaker than the T_DROP, the mobile station starts the T_TDROP timer. In case of timeout, the pilot moves back from the active set to the neighbor set. If the pilot intensity becomes stronger than the T_DROP again, the timer will be deleted automatically.

T_COMP：The base station sets this parameter as the pilot intensity comparing threshold of active set and candidate set. When the mobile station finds that the pilot intensity in a certain base station is over the pilot intensity of the current active set by T_COMP×0.5 dB, it sends a PSMM message to the base station and starts the handoff.

The flow diagram of soft handoff on mobile station is shown in FIGURE 60.



FIGURE 60 IS -95 S O F T H AN D O F F F L O W D I AG R AM

The detailed soft handoff flow：

1） To carry out soft handoff, the mobile station first searches all the pilot components and measures their intensity. When the pilot intensity Ec/Io is stronger than a specific value of T_ADD, the mobile station will assume that the intensity of that pilot is strong enough to perform correct demodulation. But when the mobile station does not establish connection with the base station corresponding to that pilot, it sends a PSMM message to the original base station to report such situation and bring the pilot set into candidate set.

2） The original base station forwards the report to the MSC. The MSC requests the new base station to assign a forward traffic channel for the mobile station, and the original base station sends a HDM message to the mobile station, instructing it to carry out the handoff.

3） After it receives the handoff instruction from the base station, the mobile station integrates the new base station pilot into its active pilot set and begins to demodulate the forward traffic channels of both the new and previous base stations. After that, the mobile station sends a Handoff Comple Message (HCM) Message to the base station, informing the base station that it begins to demodulate the signals from both base stations.

4） Then, as the mobile station moves, one of the two base stations’ pilot intensity becomes less than a specific value T_DROP, at which time the mobile station will start a handoff-drop timer. The mobile station maintains one timer for each pilot in its active pilot set and candidate pilot set. When a pilot intensity is weaker than a specific value D, the corresponding timer will start.



5） When the handoff-drop timer T expires (during this time, the pilot intensity must be always weaker than D), the mobile station sends a PSMM.

6） The base station will forward the PSMM to the MSC once it is received. MSC will send back a HDM to the base station. The base station then forwards it to the mobile station.

7） Mobile station will eliminate the timer-expired pilots and move them from active set to the neighbor set. At this stage, mobile station only communicates with the base station represented by the pilot in the current active pilot set. Meanwhile, the mobile station sends out an HCM to tell the base station that the handoff is finished.

8） Mobile station receives a NLUM exclude pilot.

The softer handoff is carried out by the base station, and MSC is not notified. The signals received from a mobile station through antennas of different sectors look like different multipath components from the perspective of the base station. These signals are combined into one voice frame, which is sent to the selector as the voice frame of the base station. As the soft handoff is carried out by the MSC, all the signals from different base stations are sent to the selector, which will choose the best signal for voice encoding/decoding.

FIGURE 61 S O F T E R H AN D O F F

Since the procedure for softer handoff is already included in the above soft handoff, the steps will not be described here. Its working is essentially the same as that of the soft handoff.

The previous section describes handoff types, procedure, and concept. When the system is in operation, these handoffs may occur in combination, that is, soft handoff, softer handoff, and hard handoff may happen at the same time.

For example, when a mobile station is at the border area of two sectors of one base station and the other base station, both soft handoff and softer handoff will happen. If it is at the edge of three base stations, three-party soft handoff will happen.

The above two soft handoffs assume that the base stations have the same carrier frequency and free capacity. If the adjacent base station having the same carrier frequency is in full load, the MSC will request the base station to instruct the mobile station to hand off to the other carrier of that adjacent base station, known as hard handoff.

Softer handoff



When three parties are involved, if any of the other two parties has free capacity, soft handoff will be preferred. That is, only when soft handoff is impossible will hard handoff be considered. If, however, the adjacent base stations happen to be in different MSCs, even if they have the same carrier frequency, only hard handoff is available at present because the vocoder needs to be changed. If, later on, the IPI interface and ATM are used between BSCs, then the soft handoff between MSCs is available.

Another concept should be mentioned is idle handoff. In IS-95 and 1x, the idle handoff has different handoff timing and operation mechanism.

1. The idle handoff in IS-95A

When mobile station is at the idle state, if move from one cell to another, it must be switched to a new paging channel. When the new pilot is 3dB stronger than the current service pilot, the mobile station performs idle handoff automatically.

Pilot channel is identified by the relative bias of PN sequence against the pilot with no 0 bias. The pilot bias can be categorized into a few groups according to their states. These states are related to the pilot search. At the idle state, there are three pilot sets: active set, neighbor set and residual set. Each pilot bias only belongs to one of the sets and one of the groups.

At the idle state, when mobile station monitors the paging channel, it searches the strongest pilot in the current CDMA frequency assignment.

If mobile station detects that the pilot intensity in neighbor set or residual set is much stronger than the pilot intensity in active set, it performs idle handoff.

At the moment of idle handoff completes, the mobile station operates in a non-timeslot mode. It does not change its operation mode until at least one valid message is received. After receiving the message, the mobile station can again operate in a timeslot mode.

When the idle handoff completes, the mobile station will abandon the unprocessed messages all on the original paging channel.

2. The idle handoff in cdma2000 1x

cdma2000 1x applies Ec Threshold and Ec/Io Threshold to handle the MS idle handoff. When MS detects a pilot which is stronger than the current pilot, MS may not perform an idle handoff unless the Ec of current pilot < Ec Threshold. Similarly, when MS detects a pilot which is stronger than the current pilot, MS may not perform an idle handoff unless the Ec/Io of current pilot < Ec/Io Threshold, i.e. an idle handoff occurs when Ec<Ec Threshold and Ec/Io <Ec/Io Threshold.

In IS-95A, idle handoff is prohibited during accessing. On the contrary, it is allowed in IS-95B and cdma2000.

Idle handoff



Besides the key CDMA technologies, some other key technologies of 3G include: multi-user detection, intelligent antenna, multi-carrier, fast forward power control, transmit diversity, and Turbo code. For the detailed description of Turbo code, please refer to “2.6.5 Turbo Code ”.

1. Multi-user detection

In communications with CDMA systems, the multi-access interference (inter-user interference) is the primary interference. Since CDMA systems are interference limited, multi-access interference not only seriously affects systems anti-interference, but also seriously restricts the improvement of systems capacities. CDMA systems adopt the multi-user detection technology to resist and limit multi-access interference. This technology improves receive performance and increases system capacity by eliminating the intra-cell or inter-cell interference in CDMA systems. Its basic idea is:

1) Based on the optimal signal detection theorem of information theory, seek the optimized joint detection for multi-user cellular code division multiple access.

2) Fully utilize the known structural information and statistical information of the spread sequence to further remove interference induced negative influence, so as to achieve the purpose of improving system performance.

3) Eliminate and weaken multi-access and multipath interference at the same time, which also means eliminating and weakening the near-far effects.

4) Under the theoretical guidance of the optimal signal detection theorem of information theory, fully utilize the known structural and statistical information of the spread sequence to carry out multi-user joint detection, and try to eliminate all other users’ useful interference. This scheme is wholly feasible in theory.

Multi-user detection generally requires knowing the main characteristic parameters of user’s spread sequence. This is not easy for real multipath time variable channels. It is to be realized with continuous channel estimation, and the precision of such estimates will directly influence the performance of multi-user detectors. Therefore, multi-user detection also has some disadvantages.

5) Increased the complexity of system equipment

6) Increased system delay, especially when self-adaptive algorithm is adopted, and the system uses longer spread sequence.

2. Intelligent antenna

The intelligent antenna can, according to the signal wave direction, adjust its direction map adaptively, trace strong signals, reduce or cancel interference signals, improve signal-to-interference ratio, expand the coverage of mobile communications, and hereby improve the comprehensive

Other key technologies



performance of mobile communication systems. So the intelligent antenna technology plays an important role in cdma2000 1x systems.

Theoretically, the intelligent antenna firstly considers the antenna narrow beam that combines M waves to provide M-fold antenna gain, and secondly considers self-adaptiveness. The received signals of antenna narrow beam that combines multiple wave beams are those of maximum signal-to-interference ratio. This kind of antenna theoretically eliminates N interferences, where N<M, and the maximum value of N is M-1.

The intelligent antenna has two outstanding advantages:

1) Use M antenna units and combine their weighted outputs into a single direction narrow beam. The signal-to-interference ratio obtained in a given direction is M times that of a forward antenna. This can enlarge the coverage of mobile cells by M times. Then, the number of base stations required for this coverage will reduce in reverse proportion. R is the power factor of wave propagation loss, which is generally 3~4.

2) Use M antenna units and M-1 antenna beam zero points can be formed to completely suppress interference in M-1 directions. This reduces the external interference encountered in the intelligent antenna beam direction by M times, but increases the mobile communication capacity by M times.

3. Multi-carrier mode

3G utilizes wideband radio channels to transmit high rate data. Its nominal bandwidth is 5 MHz. Wideband signals can be generated by single- or multi-carrier direct sequence spreading.

The idea for multi-carrier technology is different from that for a RAKE receiver. Using serial/parallel switches can lower the rate of the information symbols to be transmitted, extend the symbol period, reduce the multipath delay disperse, and thus weaken the multipath interference affect on transmission system performance. The advantage of this method is that every narrowband signal is compatible with the modulated signals in IS-95 systems. This is good for existing 2G networks to smoothly transit to 3G.

It can be seen that multi-carrier has some unique advantages that single-carrier does not have.

1) Multi-carrier systems have strong resistant ability against multipath propagation and frequency selective fading.

The modulation of multi-carrier signals is to integrate within the period with many symbols such that the affect of impulsive interference can be dispersed; so multi-carrier systems have much stronger resistant ability against impulsive interference than single-carrier systems. Multi-carrier systems scatter the information over many carriers, greatly reducing the carrier signal rates and multipath propagation influence. If protective



separation is added to this, inter-symbol interference can be totally eliminated.

2) Multi-carrier systems have high spectral efficiency.

Multi-carrier systems use dynamic bit allocation technique to achieve the maximum bit rate. By selecting sub channels, the number of bits per symbol, and the power allocated to the sub channels, the total bit rate is maximized. Meanwhile, the spectral efficiency of multi-carrier system is improved.

However, the multi-carrier systems also have some disadvantages:

3) Multi-carrier systems are more sensitive to symbol timing and carrier frequency deviation than single-carrier systems.

4) Multi-carrier signals are formed by iteratively adding multiple single-carrier signals. The peak-to-average power ratio is lager than single-carrier systems. Thus it imposes higher linear requirement for front-end amplifier.

4. Power control

The forward channel power control technology in cdma2000 1x systems is quite different from IS-95 systems. In IS-95 systems, forward channels use synchronous code division, and the reverse channels use asynchronous code division. The transmission bottleneck is on the reverse channels so it imposes slack requirements for forward channels. But in cdma2000 1x systems, the reverse channels also use coherent detection (need to transmit pilot). Forward channel close- and outer-loop power control is added to equalize forward/reverse performance. The reverse channel power control technology in cdma2000 1x systems is the same as IS-95 systems.

5. Transmit diversity

cdma2000 1x systems use open-loop orthogonal and time switch transmit diversity, and closed-loop selective transmit diversity and antenna array.

CDMA System Advantages

Compared with FDMA and TDMA, the CDMA system has many unique advantages. Some of them are inherent in the spread spectrum communication system, and the others are results of such techniques as soft handoff and power control. The CDMA mobile communication network integrates several kinds of techniques, including spread spectrum, multi-address access, cellular networking and frequency reuse, with the coordination of 3-D (frequency domain, time domain and code domain) signal processing. Therefore, it provides excellent resistance against interference and multipath fading, high privacy, frequency reuse in many cells, requiring small Carrier-to-Interference ratio (C/I), and convenient tradeoff between capacity and quality. These



features enable CDMA to have much more advantages than other systems. They are specifically shown in the aspects described below.

FIGURE 62 FR E Q U E N C Y R E U S E C O M P AR I S O N B E T W E E N CDMA AN D GSM

GSM: CDMA:N

In the CDMA systems, as the frequencies for all cells are the same, the reuse factor is 1. But in the GSM systems, due to the frequency interference in the cells, the frequencies for the adjacent cells are different, and the frequency reuse factor is 1/3. The following table gives a comparison of the frequency use between GSM and CDMA.

T AB L E 20 MH Z F R E Q U E N C Y S P E C T R U M (5MH Z F O R T R AN S M I T T I N G AN D 5MH Z F O R R E C E I V I N G )

Parameter CDMA GSM

Carrier bandwidth 1.25MHz 0.20MHz

Carrier number 3 25*

Frequency reuse 1/1 3/9

Effective carrier 3/1=3 25/3=8.3

Voice call/carrier 25 to 40+ 7.25**

Voice call/cell 75 to 120+ 7.25×8.3=60.2

Sector/cell 3 3

Voice call/sector 75 to 120+ 60.2/3=20.0

Erlang/sector*** 64 to 107E 13.2

* In the best case, the GSM and AMPS have no protected band.

** The remaining 0.75 of 8 voice call/carrier is used for overhead (e.g. control/frequency pilot).

*** Based on 2% blocking

It can be seen from the table that the capacity of CDMA is 5.5 times that of GSM for the same frequency spectrum.

The coverage radius of the CDMA systems is twice as much as that of a standard GSM system. As the code division technique is adopted in the CDMA systems, the fading resistance capability is stronger than that of the GSM systems, hence increasing the coverage radius. For example, if the coverage area is 1,000 km2,

Unique Frequency

Reuse

Large Coverage



200 base stations are needed by a GSM system, but only 50 by a CDMA system. For the same coverage area, the number of base stations in a CDMA system is greatly decreased, and the investment cost is obviously cut down.

The CDMA network is a self-interfering system. The users using the same frequency are identified in the channel code. So the signal of one user is interference to other users. Likewise, the signals of other users are interference sources to this user. Increasing the number of users will not cause call failures, and it just slightly degrades the voice quality. The network capacity depends upon the allowable interference margin.

As the power control technique is adopted in the system, the system power is very weak. The CDMA power control technique enables the signal transmit power to be kept at the minimum level, provided that it guarantees the excellent call quality. The weak power indicates less power consumption, which results in less interference and larger call capacity. If each base station can provides larger call capacity, it indicates that only less base stations are required to achieve a certain quantity of traffic.

With the spread spectrum technology adopted, the CDMA systems can provide larger system capacity with less frequency spectrum resource and electric power resource. The capacity of the CDMA networks is 4~6 times larger than GSM, which leads to cost reduction.

The variable rate voice encoder can decrease the number of channels occupied by the call process when the calling and called parties do not speak. Therefore, the channel can be effectively utilized, hence indirectly increasing the call capacity of the whole system.

The call quality in the CDMA systems is better than that in the AMPS or TDMA systems.

The voice quality of the CDMA systems is excellent. The vocoder can dynamically adjust the data transmission rate, and select different transmission levels according to appropriate threshold value. Meanwhile, the threshold value varies with the background noise. Therefore, better call quality can be obtained even though the background noise is strong.

High-quality voice encoder: The channel structure of the TDMA systems can only support the voice encoder of 4 kbit/s at maximum, and it cannot support the voice encoder of 8 kbit/s or more. The QCELP voice code is adopted in the CDMA systems, hence tremendously suppressing the background noise. The excellent communication quality of these systems brings about the advantages of clear voice and weak background noise. The performance is obviously better than that of other wireless mobile communication systems, and the voice quality can compete with that of the wireline phone.

When a subscriber moves between mobile cells, he can obviously feel the call interruption due to the hard handoff of the TDMA systems. This phenomenon is particularly obvious in cities with

Large Capacity

Good Voice Quality



centralized subscribers and dense base stations because the hard handoff will be conducted for 2~4 times per minute in such areas. With the unique soft handoff technique of the CDMA systems, the subscriber’s communication with the previous base station will not be interrupted when he moves from one to another base station until the communication is handed off to the new base station. That is, the user communicates with two base stations at the same time during handoff. This increases the signal strength at the cell border, prevents the voice from being weakened or the call quality from being degraded, greatly decreases the possibilities of call drop, and ensure the quality of long mobile conversation. The soft handoff technique enables the calling and called parties to receive the signals from the adjacent 3~5 mobile sites. After the received signals are combined, the conversation interruption can be eliminated in the handoff process, and the signal quality can also be fully improved (by choosing the best signals from the received 3~5 signals all the time).

With the wideband carrier transmission and the advanced power control techniques, the phenomenon of discontinuous signals can be avoided. Moreover, due to the powerful error correction code, the subscriber can also make a stable conversation on a car driving at the speed of 200 kilometers/hour.

Spread spectrum communication technique is the latest wireless communication technique in the world. One of its features is the excellent confidential performance. Being integrated with the perfect authentication and privacy technique of the CDMA systems, it can prevent the user from being intruded, that is, users’ conversation will not be easily intercepted.

The widband spectrum signal is very hard to intercept just like it is difficult to hear a person’s low sigh in a noisy room. But for other techniques, the signal energies are all centralized in a narrow waveband, which enables other people to easily intercept the transmitted signals.

Even on occasion, it is also difficult for an eavesdropper to intercept the conversation over the CDMA systems. This is because it is impossible for a simple radio receiver to separate a channel of digital signal from all the radio frequency (RF) signals on a frequency band, which is otherwise possible in the analog system.

Using the Pseudo-Number (PN) as address code and the unique code scrambling mode, the CDMA systems have incomparable advantages over other networks in the aspects of preventing cross talk and illegal use, which further protect the privacy of the conversation in the CDMA network.

Due to the special techniques, the CDMA systems have many advantages, which can provide users with more satisfactory services. This can be shown in the following aspects:

Low call drop and high voice quality

Higher data transmission rate

More multimedia services

Good Confidentiality

User Satisfaction



Low transmit power, longer standby duration, less mobile phone radiation, honored as “Green Mobile Phone”. The average transmit power of a GSM mobile phone is 125 mW, with the maximum transmit power of 2W, but the average transmit power of CDMA mobile phone is 2 mW, with the maximum transmit power of 200 mW.

Compared with other systems such as AMPS and GSM, some of the CDMA systems’ advantages, such as cell coverage and capacity, must be carefully considered in the cost budget.

One of them is power saving. CDMA can save 2~4 dB more power than GSM. This value considered such factors as transmit power, transmitter duty cycle, modulating and encoding.

As the maximum path attenuation ratio of the CDMA systems can be 6 dB~10 dB more than that of the GSM systems, less base stations are required for a CDMA system to provide the same conversation quality as that in a GSM system. As a result, in the same coverage condition and area, less base stations are required in the CDMA systems, hence tremendously saving the investment cost.

Generally, when a system starts to provide services, the number of corresponding base stations is less due to fewer users. But the CDMA system can bear stronger path attenuation than the GSM system, hence providing wider coverage areas to satisfy the requirements of the users. When the number of users increases, due to the large capacity, the CDMA system still works on fewer base stations. In view of cost saving, this is very important for an operator that just starts its service.

Additionally, another significant advantage is the compatibility of the CDMA systems. First, the IS-95 systems can be smoothly upgraded to the 1x system. The upgrade can be realized by upgrading the software without changing any hardware. Secondly, the IS-95 systems can coexist with the 1x systems, with the feature of backward compatibility.

1. Briefly describe the types and roles of power control in the CDMA systems.

2. How many kinds of soft handoff are there? What are the situations where they happen? What are the advantages brought about by this technique?

3. How many kinds of diversity receive are there? What is the technology adopted by the RAKE receiver?

4. Briefly describe the advantages of the CDMA systems.

5. What are the situations where the soft and hard handoff will happen?

6. What is the difference between the soft handoff and the hard handoff?

7. What are the roles of power control?

8. How many kinds of power controls are there?

Economy

Review



9. How many kinds of diversity techniques are there?

10. What is the diversity technique adopted by the RAKE receiver? What is the feature of this diversity technology?

11. Briefly describe the working of the RAKE receiver?

12. Briefly describe the advantages of the CDMA systems.

13. Please compare the coverage area of a CDMA base station with that of a GSM base station.

14. Briefly describe similarities and differences between the GSM and CDMA systems in frequency reuse.

15. Briefly state the key 3G technologies.

1xEV-DO Data Only or Data Optimized

AAA Authentication, Authorization Accounting

AMPS Advanced Mobile Phone System

AN Access Network

ANSI American National Standards Institute

ARQ Automatic Request for Repetition

AT Access Terminal

ATM Asynchronous Transfer Mode

BER Bit Error Rate

BSC Base Station Controller

BSS Base Station Subsystem

BTS Base Transceiver Subsystem

CDMA Code Division Multiple Access

CRC Cyclic Redundancy Check

CWTS China Wireless Telecommunication Study Group

DRC Data Rate Control

ETSI European Telecommunication Standard Institute

1xEV-DO Data Only or Data Optimized

AAA Authentication, Authorization Accounting

AMPS Advanced Mobile Phone System

AN Access Network

ANSI American National Standards Institute

ARQ Automatic Request for Repetition

AT Access Terminal

ATM Asynchronous Transfer Mode

BER Bit Error Rate

BSC Base Station Controller

BSS Base Station Subsystem

BTS Base Transceiver Subsystem

CDMA Code Division Multiple Access

Acronym List



CRC Cyclic Redundancy Check

CWTS China Wireless Telecommunication Study Group

DRC Data Rate Control

ETSI European Telecommunication Standard Institute

FCC Federal Communication Commission

FDMA Frequency Division Multiple Access

FER Frame Error Rate

FFPC Forward Fast Power Control

FIR Finite Impulse Response

FL Forward Link

FPLMTS Future Public Land Mobile Telecommunication System

GPRS General Packet Radio Services

GPS Global Positioning System

GSM Global System for Mobile Communications

HA Home Agent (mobile IP)

HDR High Data Rate

HRPD High Rate Packet Data

IP Internet Protocol

ISM Industrial, Scientific, Medical

ITU International Telecommunication Union

ITU-R ITU-Radiocommunication Standardization Sector

LMSD Legacy MS Domain

MAC Media Access Control

MMD Multi-Media Domain

MS Mobile Station

MSC Mobile Switch Center

MSRG Modular sequence random generator

NMTS Nordic Mobile Telephone. Systems

PCF Packet Control Function

PCM Pulse Code Modulation

PDSN Packet Data Serving Node

PCS Personal Communication System

PCT Power Control Threshold

PDC Personal Digital Cellular

PER Packet Error Rate

QCELP Qualcomm Code Excited Linear Prediction

QPSK Quadrature Phase Shift Keying

RC Radio Configuration

RF Radio Frequency



RL Reverse Link

RRI Reverse Rate Indictor

RTT Radio Transmission Technology

RSC Recursive Systematic Convolutional Code/Encoder

RX Receive

SNP Signaling Network Protocol

SNR Signal-to-Noise Ratio

SSRG Simple sequence random generator

TACS Total Access Communication System

TDMA Time Division Multiple Access

TD-SCDMA Time-division synchronous CDMA

TIA Telecommunications Industry Association

TDD Time Division Duplex

TX Transmit

UMTS Universal Mobile Telecommunication System

W-CDMA Wideband CDMA

WLL Wireless Local Loop

FCC Federal Communication Commission

FDMA Frequency Division Multiple Access

FER Frame Error Rate

FFPC Forward Fast Power Control

FIR Finite Impulse Response

FL Forward Link

FPLMTS Future Public Land Mobile Telecommunication System

GPRS General Packet Radio Services

GPS Global Positioning System

GSM Global System for Mobile Communications

HA Home Agent (mobile IP)

HDR High Data Rate

HRPD High Rate Packet Data

IP Internet Protocol

ISM Industrial, Scientific, Medical

ITU International Telecommunication Union

ITU-R ITU-Radiocommunication Standardization Sector

LMSD Legacy MS Domain

MAC Media Access Control

MMD Multi-Media Domain

MS Mobile Station

MSC Mobile Switch Center



MSRG Modular sequence random generator

NMTS Nordic Mobile Telephone. Systems

PCF Packet Control Function

PCM Pulse Code Modulation

PDSN Packet Data Serving Node

PCS Personal Communication System

PCT Power Control Threshold

PDC Personal Digital Cellular

PER Packet Error Rate

QCELP Qualcomm Code Excited Linear Prediction

QPSK Quadrature Phase Shift Keying

RC Radio Configuration

RF Radio Frequency

RL Reverse Link

RRI Reverse Rate Indictor

RTT Radio Transmission Technology

RSC Recursive Systematic Convolutional Code/Encoder

RX Receive

SNP Signaling Network Protocol

SNR Signal-to-Noise Ratio

SSRG Simple sequence random generator

TACS Total Access Communication System

TDMA Time Division Multiple Access

TD-SCDMA Time-division synchronous CDMA

TIA Telecommunications Industry Association

TDD Time Division Duplex

TX Transmit

UMTS Universal Mobile Telecommunication System

W-CDMA Wideband CDMA

WLL Wireless Local Loop

cdma_tr_zte

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