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WCDMA RAN Fundamental
Confidential Information of Huawei. No Spreading Without Permission
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www.huawei.com
Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
WCDMA RAN
Fundamental
WCDMA RAN Fundamental
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Page1Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Objectives
� Upon completion of this course, you will be able to:
� Describe the development of 3G
� Outline the advantage of CDMA principle
� Characterize code sequence
� Outline the fundamentals of RAN
� Describe feature of wireless propagation
WCDMA RAN Fundamental
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Page2Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Contents
1. 3G Overview
2. CDMA Principle
3. WCDMA Network Architecture and protocol structure
4. WCDMA Wireless Fundamental
WCDMA RAN Fundamental
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Page3Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Contents
1. 3G Overview
2. CDMA Principle
3. WCDMA Network Architecture and protocol structure
4. WCDMA Wireless Fundamental
WCDMA RAN Fundamental
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Different Service, Different Technology
AMPS
TACS
NMT
Others
1G 1980sAnalog
GSM
CDMA IS-95
TDMAIS-136
PDC
2G 1990sDigital
Technologies
drive
3G IMT-2000
UMTSWCDMA
cdma2000
Demands
drive
TD-SCDMA
3G provides compositive services for both operators and subscribers
� The first generation is the analog cellular mobile communication network in the time
period from the middle of 1970s to the middle of 1980s. The most important
breakthrough in this period is the concept of cellular networks put forward by the Bell
Labs in the 1970s, as compared to the former mobile communication systems. The
cellular network system is based on cells to implement frequency reuse and thus
greatly enhances the system capacity.
� The typical examples of the first generation mobile communication systems are the
AMPS system and the later enhanced TACS of USA, the NMT and the others. The
AMPS (Advanced Mobile Phone System) uses the 800 MHz band of the analog cellular
transmission system and it is widely applied in North America, South America and
some Circum-Pacific countries. The TACS (Total Access Communication System) uses
the 900 MHz band. It is widely applied in Britain, Japan and some Asian countries.
� The main feature of the first generation mobile communication systems is that they
use the frequency reuse technology, adopt analog modulation for voice signals and
provide an analog subscriber channel every other 30 kHz/25 kHz.
� However, their defects are also obvious:
� Low utilization of the frequency spectrum
� Limited types of services
� No high-speed data services
� Poor confidentiality and high vulnerability to interception and number
embezzlement
� High equipment cost
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� To solve these fundamental technical defects of the analog systems, the digital mobile
communication technologies emerged and the second generation mobile
communication systems represented by GSM and IS-95 came into being in the middle
of 1980s. The typical examples of the second generation cellular mobile
communication systems are the DAMPS of USA, the IS-95 and the European GSM
system.
� The GSM (Global System for Mobile Communications) is originated from Europe.
Designed as the TDMA standard for mobile digital cellular communications, it supports
the 64 kbps data rate and can interconnect with the ISDN. It uses the 900 MHz band
while the DCS1800 system uses the 1800 MHz band. The GSM system uses the FDD
and TDMA modes and each carrier supports eight channels with the signal bandwidth
of 200 kHz.
� The DAMPS (Digital Advanced Mobile Phone System) is also called the IS-54 (North
America Digital Cellular System). Using the 800 MHz bandwidth, it is the earlier of the
two North America digital cellular standards and specifies the use of the TDMA mode.
� The IS-95 standard is another digital cellular standard of North America. Using the 800
MHz or 1900 MHz band, it specifies the use of the CDMA mode and has already
become the first choice among the technologies of American PCS (Personal
Communication System) networks.
� Since the 2G mobile communication systems focus on the transmission of voice and
low-speed data services, the 2.5G mobile communication systems emerged in 1996 to
address the medium-rate data transmission needs. These systems include GPRS and IS-
95B.
� The CDMA system has a very large capacity that is equivalent to ten or even twenty
times that of the analog systems. But the narrowband CDMA technologies come into
maturity at a time later than the GSM technologies, their application far lags behind
the GSM ones and currently they have only found large-scale commercial applications
in North America, Korea and China. The major services of mobile communications are
currently still voice services and low-speed data services.
� With the development of networks, data and multimedia communications have also
witnessed rapid development; therefore, the target of the 3G mobile communication
is to implement broadband multimedia communication.
� The 3G mobile communication systems are a kind of communication system that can
provide multiple kinds of high quality multimedia services and implement global
seamless coverage and global roaming. They are compatible with the fixed networks
and can implement any kind of communication at any time and any place with
portable terminals.
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3G Evolution
� Proposal of 3G
� IMT-2000: the general name of third generation mobile
communication system
� The third generation mobile communication was first proposed in
1985,and was renamed as IMT-2000 in the year of 1996
� Commercialization: around the year of 2000
� Work band : around 2000MHz
� The highest service rate :up to 2000Kbps
� Put forward in 1985 by the ITU (International Telecommunication Union), the 3G
mobile communication system was called the FPLMTS (Future Public Land Mobile
Telecommunication System) and was later renamed as IMT-2000 (International Mobile
Telecommunication-2000). The major systems include WCDMA, cdma2000 and UWC-
136. On November 5, 1999, the 18th conference of ITU-R TG8/1 passed the
Recommended Specification of Radio Interfaces of IMT-2000 and the TD-SCDMA
technologies put forward by China were incorporated into the IMT-2000 CDMA TDD
part of the technical specification. This showed that the work of the TG8/1 in
formulating the technical specifications of radio interfaces in 3G mobile
communication systems had basically come into an end and the development and
application of the 3G mobile communication systems would enter a new and essential
phase.
� The 3GPP is an organization that develops specifications for a 3G system based on the
UTRA radio interface and on the enhanced GSM core network.
� The 3GPP2 initiative is the other major 3G standardization organization. It promotes
the CDMA2000 system, which is also based on a form of WCDMA technology. In the
world of IMT-2000, this proposal is known as IMT-MC. The major difference between
the 3GPP and the 3GPP2 approaches into the air interface specification development
is that 3GPP has specified a completely new air interface without any constraints from
the past, whereas 3GPP2 has specified a system that is backward compatible with IS-
95 systems.
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3G Spectrum Allocation
� ITU has allocated 230 MHz frequency for the 3G mobile communication system IMT-
2000: 1885 ~ 2025MHz in the uplink and 2110~ 2200 MHz in the downlink. Of them,
the frequency range of 1980 MHz ~ 2010 MHz (uplink) and that of 2170 MHz ~ 2200
MHz (downlink) are used for mobile satellite services. As the uplink and the downlink
bands are asymmetrical, the use of dual-frequency FDD mode or the single-frequency
TDD mode may be considered. This plan was passed in WRC92 and new additional
bands were approved on the basis of the WRC-92 in the WRC2000 conference in the
year 2000: 806 MHz ~ 960 MHz, 1710 MHz ~ 1885 MHz and 2500 MHz ~ 2690 MHz.
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Bands WCDMA Used
� Main bands
� 1920 ~ 1980MHz / 2110 ~ 2170MHz
� Supplementary bands: different country maybe different
� 1850 ~ 1910 MHz / 1930 MHz ~ 1990 MHz (USA)
� 1710 ~ 1785MHz / 1805 ~ 1880MHz (Japan)
� 890 ~ 915MHz / 935 ~ 960MHz (Australia)
� . . .
� Frequency channel number=central frequency×5, for main band:
� UL frequency channel number :9612~9888� DL frequency channel number : 10562~10838
� The WCDMA system uses the following frequency spectrum (bands other than those
specified by 3GPP may also be used): Uplink 1920 MHz ~ 1980 MHz and downlink
2110 MHz ~ 2170 MHz. Each carrier frequency has the 5M band and the duplex
spacing is 190 MHz. In America, the used frequency spectrum is 1850 MHz ~ 1910
MHz in the uplink and 1930 MHz ~ 1990 MHz in the downlink and the duplex spacing
is 80 MHz.
WCDMA RAN Fundamental
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3G Application Service
Time Delay
Error Ratio
background
conversational
streaming
interactive
� Compatible with abundant services and applications of 2G, 3G system has an open
integrated service platform to provide a wide prospect for various 3G services.
� Features of 3G Services
� 3G services are inherited from 2G services. In a new architecture, new service
capabilities are generated, and more service types are available. Service characteristics
vary greatly, so each service features differently. Generally, there are several features
as follows:
� Compatible backward with all the services provided by GSM.
� The real-time services (conversational) such as voice service
generally have the QoS requirement.
� The concept of multimedia service (streaming, interactive,
background) is introduced.
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The Core technology of 3G: CDMA
CDMA
WCDMA
CN: based on MAP and GPRS
RTT: WCDMA
TD-SCDMACN: based on MAP and GPRS
RTT: TD-SCDMA
cdma2000CN: based on ANSI 41 and MIP
RTT: cdma2000
� Formulated by the European standardization organization 3GPP, the core network
evolves on the basis of GSM/GPRS and can thus be compatible with the existing
GSM/GPRS networks. It can be based on the TDM, ATM and IP technologies to evolve
towards the all-IP network architecture. Based on the ATM technology, the UTRAN
uniformly processes voice and packet services and evolves towards the IP network
architecture.
� The cdma2000 system is a 3G standard put forward on the basis of the IS-95 standard.
Its standardization work is currently undertaken by 3GPP2. Circuit Switched (CS)
domain is adapted from the 2G IS95 CDMA network, Packet Switched (PS) domain is
A packet network based on the Mobile IP technology. Radio Access Network (RAN) is
based on the ATM switch platform, it provides abundant adaptation layer interfaces.
� The TD-SCDMA standard is put forward by the Chinese Wireless Telecommunication
Standard (CWTS) Group and now it has been merged into the specifications related to
the WCDMA-TDD of 3GPP. The core network evolves on the basis of GSM/GPRS. The
air interface adopts the TD-SCDMA mode.
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Contents
1. 3G Overview
2. CDMA Principle
3. WCDMA Network Architecture and protocol structure
4. WCDMA Wireless Fundamental
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Multiple Access and Duplex Technology
� Multiple Access Technology
� Frequency division multiple access (FDMA)
� Time division multiple access (TDMA)
� Code division multiple access (CDMA)
� In mobile communication systems, GSM adopts TDMA; WCDMA, cdma2000 and TD-
SCDMA adopt CDMA.
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Multiple Access Technology
Frequency
Time
Power
FDMA
FrequencyTime
Power
TDMA
Power
Time
CDMA
Frequency
� Frequency Division Multiple Access means dividing the whole available spectrum into
many single radio channels (transmit/receive carrier pair). Each channel can transmit
one-way voice or control information. Analog cellular system is a typical example of
FDMA structure.
� Time Division Multiple Access means that the wireless carrier of one bandwidth is
divided into multiple time division channels in terms of time (or called timeslot). Each
user occupies a timeslot and receives/transmits signals within this specified timeslot.
Therefore, it is called time division multiple access. This multiple access mode is
adopted in both digital cellular system and GSM.
� CDMA is a multiple access mode implemented by Spreading Modulation. Unlike FDMA
and TDMA, both of which separate the user information in terms of time and
frequency, CDMA can transmit the information of multiple users on a channel at the
same time. The key is that every information before transmission should be modulated
by different Spreading Code to broadband signal, then all the signals should be mixed
and send. The mixed signal would be demodulated by different Spreading Code at the
different receiver. Because all the Spreading Code is orthogonal, only the information
that was be demodulated by same Spreading Code can be reverted in mixed signal.
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Multiple Access and Duplex Technology
� Duplex Technology
� Frequency division duplex (FDD)
� Time division duplex (TDD)
� In third generation mobile communication systems, WCDMA and cdma2000 adopt
frequency division duplex (FDD), TD-SCDMA adopts time division duplex (TDD).
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Duplex Technology
Time
Frequency
Power
TDD
USER 2
USER 1
DLUL
DLDL
UL
FDD
Time
Frequency
Power
UL DL
USER 2
USER 1
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Contents
1. 3G Overview
2. CDMA Principle
3. WCDMA Network Architecture and protocol structure
4. WCDMA Wireless Fundamental
WCDMA RAN Fundamental
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WCDMA Network Architecture
RNS
RNC
RNS
RNC
Core Network
Node B Node B Node B Node B
Iu-CS Iu-PS
Iur
Iub IubIub Iub
CN
UTRAN
UEUu
CS PS
Iu-CSIu-PS
CSPS
� WCDMA including the RAN (Radio Access Network) and the CN (Core Network). The
RAN is used to process all the radio-related functions, while the CN is used to process
all voice calls and data connections within the UMTS system, and implements the
function of external network switching and routing.
� Logically, the CN is divided into the CS (Circuit Switched) Domain and the PS (Packet
Switched) Domain. UTRAN, CN and UE (User Equipment) together constitute the
whole UMTS system
� A RNS is composed of one RNC and one or several Node Bs. The Iu interface is used
between RNC and CN while the Iub interface is adopted between RNC and Node B.
Within UTRAN, RNCs connect with one another through the Iur interface. The Iur
interface can connect RNCs via the direct physical connections among them or
connect them through the transport network. RNC is used to allocate and control the
radio resources of the connected or related Node B. However, Node B serves to
convert the data flows between the Iub interface and the Uu interface, and at the
same time, it also participates in part of radio resource management.
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WCDMA Network Version Evolution
3GPP Rel993GPP Rel4
3GPP Rel5
2000 2001 2002
GSM/GPRS CN
WCDMA RTT
IMS
HSDPA 3GPP Rel6
MBMS
HSUPA
2005
CS domain change to NGN
WCDMA RTT
� The overall structure of the WCDMA network is defined in 3GPP TS 23.002. Now,
there are the following three versions: R99, R4, R5.
� 3GPP began to formulate 3G specifications at the end of 1998 and beginning of 1999.
As scheduled, the R99 version would be completed at the end of 1999, but in fact it
was not completed until March, 2000. To guarantee the investment benefits of
operators, the CS domain of R99 version do not fundamentally change., so as to
support the smooth transition of GSM/GPRS/3G.
� After R99, the version was no longer named by the year. At the same time, the
functions of R2000 are implemented by the following two phases: R4 and R5. In the
R4 network, MSC as the CS domain of the CN is divided into the MSC Server and the
MGW, at the same time, a SGW is added, and HLR can be replaced by HSS (not
explicitly specified in the specification).
� In the R5 network, the end-to-end VOIP is supported and the core network adopts
plentiful new function entities, which have thus changed the original call procedures.
With IMS (IP Multimedia Subsystem), the network can use HSS instead of HLR. In the
R5 network, HSDPA (High Speed Downlink Packet Access) is also supported, it can
support high speed data service.
� In the R6 network, the HSUPA is supported which can provide UL service rate up to
5.76Mbps. And MBMS (MultiMedia Broadcast Multicast Service) is also supported.
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WCDMA Network Version Evolution
� Features of R6
� MBMS is introduced
� HSUPA is introduced to achieve the service rate up to 5.76Mbps
� Features of R7
� HSPA+ is introduced, which adopts higher order modulation and MIMO
� Max DL rate: 28Mbps, Max UL rate:11Mbps
� Features of R8
� WCDMA LTE (Long term evolution) is introduced
� OFDMA is adopted instead of CDMA
� Max DL rate: 50Mbps, Max UL rate: 100Mbps (with 20MHz bandwidth)
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Uu Interface protocol structure
L3
control
control
control
control
C-plane signaling U-plane information
PHY
L2/MAC
L1
RLC
DCNtGC
L2/RLC
MAC
RLCRLC
RLC
Duplication avoidance
UuS boundary
L2/BMC
control
PDCPPDCP L2/PDCP
DCNtGC
RRC
RLCRLC
RLCRLC
BMC
� The layer 1 supports all functions required for the transmission of bit streams
on the physical medium. It is also in charge of measurements function
consisting in indicating to higher layers, for example, Frame Error Rate (FER),
Signal to Interference Ratio (SIR), interference power and transmit power.
� The layer 2 protocol is responsible for providing functions such as mapping,
ciphering, retransmission and segmentation. It is made of four sublayers: MAC
(Medium Access Control), RLC (Radio Link Control), PDCP (Packet Data
Convergence Protocol) and BMC (Broadcast/Multicast Control).
� The layer 3 is split into 2 parts: the access stratum and the non access stratum.
The access stratum part is made of “RRC (Radio Resource Control)” entity and
“duplication avoidance” entity. The non access stratum part is made of CC, MM
parts.
� Not shown on the figure are connections between RRC and all the other
protocol layers (RLC, MAC, PDCP, BMC and L1), which provide local inter-layer
control services.
� The protocol layers are located in the UE and the peer entities are in the NodeB
or the RNC.
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General Protocol Mode for UTRAN Terrestrial
Interface
� The structure is based on the principle that the layers and planes are
logically independent of each other.
Application Protocol
Data Stream(s)
ALCAP(s)
Transport Network
Layer
Physical Layer
Signaling Bearer(s)
Control Plane User Plane
Transport NetworkUser Plane
Transport Network Control Plane
Radio Network
Layer
Signaling Bearer(s)
Data Bearer(s)
Transport NetworkUser Plane
� Protocol structures in UTRAN terrestrial interfaces are designed according to
the same general protocol model. This model is shown in above slide. The structure is based on the principle that the layers and planes are logically
independent of each other and, if needed, parts of the protocol structure may be changed in the future while other parts remain intact.
� Horizontal Layers
� The protocol structure consists of two main layers, the Radio Network Layer (RNL) and the Transport Network Layer (TNL). All UTRAN-
related issues are visible only in the Radio Network Layer, and the Transport Network Layer represents standard transport technology that is selected to be used for UTRAN but without any UTRAN-specific
changes.
� Vertical Planes
� Control Plane
� The Control Plane is used for all UMTS-specific control signaling. It
includes the Application Protocol (i.e. RANAP in Iu, RNSAP in Iur and NBAP in Iub), and the Signaling Bearer for transporting the Application Protocol messages. The Application Protocol is used, among other
things, for setting up bearers to the UE (i.e. the Radio Access Bearer in Iu and subsequently the Radio Link in Iur and Iub). In the three plane
structure the bearer parameters in the Application Protocol are not directly tied to the User Plane technology, but rather are general bearer parameters. The Signaling Bearer for the Application Protocol may or
may not be of the same type as the Signaling Bearer for the ALCAP. It is always set up by O&M actions.
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� User Plane
� All information sent and received by the user, such as the coded voice
in a voice call or the packets in an Internet connection, are transported
via the User Plane. The User Plane includes the Data Stream(s), and the
Data Bearer (s) for the Data Stream(s). Each Data Stream is
characterized by one or more frame protocols specified for that
interface.
� Transport Network Control Plane
� The Transport Network Control Plane is used for all control signaling
within the Transport Layer. It does not include any Radio Network Layer
information. It includes the ALCAP protocol that is needed to set up the
transport bearers (Data Bearer) for the User Plane. It also includes the
Signaling Bearer needed for the ALCAP. The Transport Network Control
Plane is a plane that acts between the Control Plane and the User Plane.
The introduction of the Transport Network Control Plane makes it
possible for the Application Protocol in the Radio Network Control
Plane to be completely independent of the technology selected for the
Data Bearer in the User Plane.
� About AAl2 and AAL5
� Above the ATM layer we usually find an ATM adaptation layer (AAL). Its
function is to process the data from higher layers for ATM transmission.
� This means segmenting the data into 48-byte chunks and reassembling
the original data frames on the receiving side. There are five different
AALs (0, 1, 2, 3/4, and 5). AAL0 means that no adaptation is needed.
The other adaptation layers have different properties based on three
parameters:
� Real-time requirements;
� Constant or variable bit rate;
� Connection-oriented or connectionless data transfer.
� The usage of ATM is promoted by the ATM Forum. The Iu interface
uses two AALs: AAL2 and AAL5.
� AAL2 is designed for the transmission of connection oriented,
real-time data streams with variable bit rates.
� AAL5 is designed for the transmission of connectionless data
streams with variable bit rates.
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Iu-CS Interface
ALCAP
Control Plane
Transport NetworkControl Plane
User planeRadioNetworkLayer
Transport NetworkUser Plane
TransportNetworkLayer
A B
RANAP
AAL2 PATH
ATM
Physical Layer
SAAL NNI
SCCP
MTP3-B
Iu UP
SAAL NNI
MTP3-B
Transport NetworkUser Plane
� Protocol Structure for Iu CS
� The Iu CS overall protocol structure is depicted in above slide. The three
planes in the Iu interface share a common ATM (Asynchronous Transfer
Mode) transport which is used for all planes. The physical layer is the
interface to the physical medium: optical fiber, radio link or copper
cable. The physical layer implementation can be selected from a variety
of standard off-the-shelf transmission technologies, such as SONET,
STM1, or E1.
� Iu CS Control Plane Protocol Stack
� The Control Plane protocol stack consists of RANAP, on top of
Broadband (BB) SS7 (Signaling System #7) protocols. The applicable
layers are the Signaling Connection Control Part (SCCP), the Message
Transfer Part (MTP3-b) and SAAL-NNI (Signaling ATM Adaptation Layer
for Network to Network Interfaces).
� Iu CS Transport Network Control Plane Protocol Stack
� The Transport Network Control Plane protocol stack consists of the
Signaling Protocol for setting up AAL2 connections (Q.2630.1 and
adaptation layer Q.2150.1), on top of BB SS7 protocols. The applicable
BB SS7 are those described above without the SCCP layer.
� Iu CS User Plane Protocol Stack
� A dedicated AAL2 connection is reserved for each individual CS service.
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Iu-PS Interface
Control Plane User planeRadioNetworkLayer
Transport NetworkUser PlaneTransport
NetworkLayer
Transport NetworkUser Plane
C
RANAP
ATM
SAAL NNI
SCCP
MTP3-B
Iu UP
AAL Type 5
IP
UDP
GTP-U
Physical Layer
� Protocol Structure for Iu PS
� The Iu PS protocol structure is represented in above slide. Again, a
common ATM transport is applied for both User and Control Plane.
Also the physical layer is as specified for Iu CS.
� Iu PS Control Plane Protocol Stack
� The Control Plane protocol stack consists of RANAP, on top of
Broadband (BB) SS7 (Signaling System #7) protocols. The applicable
layers are the Signaling Connection Control Part (SCCP), the Message
Transfer Part (MTP3-b) and SAAL-NNI (Signaling ATM Adaptation Layer
for Network to Network Interfaces).
� Iu PS Transport Network Control Plane Protocol Stack
� The Transport Network Control Plane is not applied to Iu PS. The
setting up of the GTP tunnel requires only an identifier for the tunnel,
and the IP addresses for both directions, and these are already included
in the RANAP RAB Assignment messages.
� Iu PS User Plane Protocol Stack
� In the Iu PS User Plane, multiple packet data flows are multiplexed on
one or several AAL5 PVCs. The GTP-U (User Plane part of the GPRS
Tunneling Protocol) is the multiplexing layer that provides identities for
individual packet data flow. Each flow uses UDP connectionless
transport and IP addressing.
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Iub Interface
ALCAP
Control Plane
Transport NetworkControl Plane
User planeRadioNetworkLayer
Transport NetworkUser Plane
TransportNetworkLayer
Transport NetworkUser Plane
NBAP
AAL2 PATH
ATM
Physical Layer
SAAL UNI
Iub FP
SAAL UNI
NCP CCP
� The Iub interface is the terrestrial interface between NodeB and RNC. The Radio
Network Layer defines procedures related to the operation of the NodeB. The
Transport Network Layer defines procedures for establishing physical
connections between the NodeB and the RNC.
� The Iub application protocol, NodeB application part ( NBAP ) initiates the
establishment of a signaling connection over Iub . It is divided into two
essential components, CCP and NCP.
� NCP is used for signaling that initiates a UE context for a dedicated UE or
signals that is not related to specific UE. Example of NBAP-C procedure are cell
configuration , handling of common channels and radio link setup
� CCP is used for signaling relating to a specific UE context.
� SAAL is an ATM Adaptation Layer that supports communication between
signaling entities over an ATM link.
� The user plane Iub Frame Protocol ( FP ), defined the structure of the frames
and the basic in band control procedure for every type of transport channel.
There are DCH-FP, RACH-FP, FACH-FP, HS-DSCH FP and PCH FP.
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Iur Interface
ALCAP
Control Plane
Transport NetworkControl Plane
User planeRadioNetworkLayer
TransportNetworkLayer
A B
RNSAP
AAL2 PATH
ATM
Physical Layer
SAAL NNI
SCCP
MTP3-B
Iur Data Stream
SAAL NNI
MTP3-B
Transport NetworkUser Plane
Transport NetworkUser Plane
� Iur interface connects two RNCs. The protocol stack for the Iur is shown in
above slide.
� The RNSAP protocol is the signaling protocol defined for the Iur interface.
WCDMA RAN Fundamental
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Page27Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Contents
1. 3G Overview
2. CDMA Principle
3. WCDMA Network Architecture and protocol structure
4. WCDMA Wireless Fundamental
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Processing Procedure of WCDMA System
Source
CodingChannel Coding& Interleaving
Spreading Modulation
Source
DecodingChannel Decoding& Deinterleaving
Despreading Demodulation
Transmission
Reception
chipmodulated signal
bit symbol
ServiceSignal
Radio
Channel
Service
Signal
Receiver
� Source coding can increase the transmitting efficiency.
� Channel coding can make the transmission more reliable.
� Spreading can increase the capability of overcoming interference.
� Through the modulation, the signals will transfer to radio signals from digital signals.
� Bit, Symbol, Chip
� Bit : data after source coding
� Symbol: data after channel coding and interleaving
� Chip: data after spreading
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WCDMA Source Coding
� AMR (Adaptive Multi-Rate) Speech
� A integrated speech codec with 8
source rates
� The AMR bit rates can be controlled by
the RAN depending on the system load
and quality of the speech connections
� Video Phone Service
� H.324 is used for VP Service in CS
domain
� Includes: video codec, speech codec,
data protocols, multiplexing and etc.
5.15AMR_5.15
4.75AMR_4.75
5.9AMR_5.90
6.7 (PDC EFR)AMR_6.70
7.4 (TDMA EFR)AMR_7.40
7.95AMR_7.95
10.2AMR_10.20
12.2 (GSM EFR)AMR_12.20
Bit Rate (kbps)CODEC
� AMR is compatible with current mobile communication system (GSM, IS-95, PDC and
so on), thus, it will make multi-mode terminal design easier.
� The AMR codec offers the possibility to adapt the coding scheme to the radio channel
conditions. The most robust codec mode is selected in bad propagation conditions.
The codec mode providing the highest source rate is selected in good propagation
conditions.
� During an AMR communication, the receiver measures the radio link quality and must
return to the transmitter either the quality measurements or the actual codec mode
the transmitter should use during the next frame. That exchange has to be done as
fast as possible in order to better follow the evolution of the channel’s quality.
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Processing Procedure of WCDMA System
Transmitter
Source
CodingChannel Coding& Interleaving
Spreading Modulation
Source
DecodingChannel Decoding& Deinterleaving
Despreading Demodulation
Transmission
Reception
chipmodulated signal
bit symbol
ServiceSignal
Radio
Channel
Service
Signal
Receiver
� Source coding can increase the transmitting efficiency.
� Channel coding can make the transmission more reliable.
� Spreading can increase the capability of overcoming interference.
� Scrambling can make transmission in security.
� Through the modulation, the signals will transfer to radio signals from digital signals.
� Bit, Symbol, Chip
� Bit : data after source coding
� Symbol: data after channel coding and interleaving
� Chip: data after spreading
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WCDMA Block Coding - CRC
� Block coding is used to detect if there are any uncorrected
errors left after error correction.
� The cyclic redundancy check (CRC) is a common method of
block coding.
� Adding the CRC bits is done before the channel encoding and
they are checked after the channel decoding.
� During the transmission, there are many interferences and fading. To guarantee
reliable transmission, system should overcome these influence through the channel
coding which includes block coding, channel coding and interleaving.
� Block coding: The encoder adds some redundant bits to the block of bits and the
decoder uses them to determine whether an error has occurred during the
transmission. This is used to calculate Block Error Ratio (BLER) used in the outer loop
power control.
� The CRC (Cyclic Redundancy Check) is used for error checking of the transport blocks
at the receiving end. The CRC length that can be inserted has four different values: 0,
8, 12, 16 and 24 bits. The more bits the CRC contains, the lower is the probability of
an undetected error in the transport block in the receiver.
� Note that certain types of block codes can also be used for error correction, although
these are not used in WCDMA.
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WCDMA Channel Coding
� Effect
� Enhance the correlation among symbols so as to recover the signal when
interference occurs
� Provides better error correction at receiver, but brings increment of the delay
� Types
� No Coding
� Convolutional Coding (1/2, 1/3)
� Turbo Coding (1/3)
Code Block of N Bits
No Coding
1/2 Convolutional Coding
1/3 Convolutional Coding
1/3 Turbo Coding
Uncoded N bits
Coded 2N+16 bits
Coded 3N+24 bits
Coded 3N+12 bits
� UTRAN employs two FEC schemes: convolutional codes and turbo codes. The idea is
to add redundancy to the transmitted bit stream, sO that occasional bit errors can be
corrected in the receiving entity.
� The first is convolution that is used for anti-interference. Through the technology,
many redundant bits will be inserted in original information. When error code is
caused by interference, the redundant bits can be used to recover the original
information. Convolutional codes are typically used when the timing constraints are
tight. The coded data must contain enough redundant information to make it possible
to correct some of the detected errors without asking for repeats.
� Turbo codes are found to be very efficient because they can perform close to the
theoretical limit set by the Shannon’s Law. Their efficiency is best with high data rate
services, but poor on low rate services. At higher bit rates, turbo coding is more
efficient than convolutional coding.
� In WCDMA network, both Convolution code and Turbo code are used. Convolution
code applies to voice service while Turbo code applies to high rate data service.
� Note that both block codes and channel codes are used in the UTRAN. The idea
behind this arrangement is that the channel decoder (either a convolutional or turbo
decoder) tries to correct as many errors as possible, and then the block decoder (CRC
check) offers its judgment on whether the resulting information is good enough to be
used in the higher layers.
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WCDMA Interleaving
� Effect
� Interleaving is used to reduce the probability of consecutive bits error
� Longer interleaving periods have better data protection with more delay
1110
1.........
............
...000
0100
0 0 1 0 0 0 0 . . . 1 0 1 1 1
1110
1.........
............
...000
00100 0 … 0 1 0 … 1 0 0 … 1 0 … 1 1
Inter-column permutation
Output bits
Input bits
Interleaving periods:
20, 40, or 80 ms
� Channel coding works well against random errors, but it is quite vulnerable to bursts
of errors, which are typical in mobile radio systems. The especially fast moving UE in
CDMA systems can cause consecutive errors if the power control is not fast enough to
manage the interference. Most coding schemes perform better on random data errors
than on blocks of errors. This problem can be eased with interleaving, which spreads
the erroneous bits over a longer period of time. By interleaving, no two adjacent bits
are transmitted near to each other, and the data errors are randomized.
� The longer the interleaving period, the better the protection provided by the time
diversity. However, longer interleaving increases transmission delays and a balance
must be found between the error resistance capabilities and the delay introduced.
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Processing Procedure of WCDMA System
Source
CodingChannel Coding& Interleaving
Spreading Modulation
Source
DecodingChannel Decoding& Deinterleaving
Despreading Demodulation
Transmission
Reception
chipmodulated signal
bit symbol
ServiceSignal
Radio
Channel
Service
Signal
Receiver
� Source coding can increase the transmitting efficiency.
� Channel coding can make the transmission more reliable.
� Spreading can increase the capability of overcoming interference.
� Scrambling can make transmission in security.
� Through the modulation, the signals will transfer to radio signals from digital signals.
� Bit, Symbol, Chip
� Bit : data after source coding
� Symbol: data after channel coding and interleaving
� Chip: data after spreading
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Page35Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Correlation
� Correlation measures similarity between any two arbitrary signals.
� Identical and Orthogonal signals:
Correlation = 0Orthogonal signals
-1 1 -1 1⊗⊗⊗⊗
-1 1 -1 1
1 1 1 1
+1
-1
+1
-1
+1
-1
+1
-1
Correlation = 1Identical signals
-1 1 -1 1⊗⊗⊗⊗
1 1 1 1
-1 1 -1 1
C1
C2+1
+1
C1
C2
� Correlation is used to measure similarity of any two arbitrary signals. It is computed by
multiplying the two signals and then summing (integrating) the result over a defined
time windows. The two signals of figure (a) are identical and therefore their
correlation is 1 or 100 percent. In figure (b) , however, the two signals are
uncorrelated, and therefore knowing one of them does not provide any information
on the other.
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Orthogonal Code Usage - Coding
UE1: ++++1 ----1
UE2: ----1 ++++1
C1 : ----1 ++++1 ----1 ++++1 ----1 ++++1 ----1 ++++1
C2 : ++++1 ++++1 ++++1 ++++1 ++++1 ++++1 ++++1 ++++1
UE1××××c1:::: ----1 ++++1 ----1 ++++1 ++++1 ----1 ++++1 ----1
UE2××××c2:::: ----1 ----1 ----1 ----1 ++++1 ++++1 ++++1 ++++1
UE1××××c1++++ UE2××××c2:::: ----2 0 ----2 0 ++++2 0 ++++2 0
� By spreading, each symbol is multiplied with all the chips in the orthogonal sequence
assigned to the user. The resulting sequence is processed and is then transmitted over
the physical channel along with other spread symbols. In this figure, 4-digit codes are
used. The product of the user symbols and the spreading code is a sequence of digits
that must be transmitted at 4 times the rate of the original encoded binary signal.
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Orthogonal Code Usage - Decoding
UE1××××C1++++ UE2××××C2: ----2 0 ----2 0 ++++2 0 ++++2 0
UE1 Dispreading by c1: ----1 ++++1 ----1 ++++1 ----1 ++++1 ----1 ++++1
Dispreading result: ++++2 0 ++++2 0 ----2 0 ----2 0
Integral judgment: ++++4 (means++++1) ----4 (means----1)
UE2 Dispreading by c2: ++++1 ++++1 ++++1 ++++1 ++++1 ++++1 ++++1 ++++1
Dispreading result: ----2 0 ----2 0 ++++2 0 ++++2 0
Integral judgment: ----4 (means----1) ++++4 (means++++1)
� The receiver dispreads the chips by using the same code used in the transmitter.
Notice that under no-noise conditions, the symbols or digits are completely recovered
without any error. In reality, the channel is not noise-free, but CDMA system employ
Forward Error Correction techniques to combat the effects of noise and enhance the
performance of the system.
� When the wrong code is used for dispreading, the resulting correlation yields an
average of zero. This is a clear demonstration of the advantage of the orthogonal
property of the codes. Whether the wrong code is mistakenly used by the target user
or other users attempting to decode the received signal, the resulting correlation is
always zero because of the orthogonal property of codes.
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Spectrum Analysis of Spreading & Dispreading
Spreading code
Spreading code
Signal Combination
Narrowband signalf
P(f)
Broadband signal
P(f)
f
Noise & Other Signal
P(f)
f
Noise+Broadband signal
P(f)
f
Recovered signal
P(f)
f
� Traditional radio communication systems transmit data using the minimum bandwidth
required to carry it as a narrowband signal. CDMA system mix their input data with a
fast spreading sequence and transmit a wideband signal. The spreading sequence is
independently regenerated at the receiver and mixed with the incoming wideband
signal to recover the original data. The dispreading gives substantial gain proportional
to the bandwidth of the spread-spectrum signal. The gain can be used to increase
system performance and range, or allow multiple coded users, or both. A digital bit
stream sent over a radio link requires a definite bandwidth to be successfully
transmitted and received.
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Spectrum Analysis of Spreading & Dispreading
Max allowed interference
Eb/No
Requirement
Power
Max interference caused by
UE and others
Processing Gain
Ebit
Interference from
other UE Echip
Eb / No = Ec / No ×PG
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Process Gain
� Process Gain
� Process gain differs for each service.
� If the service bit rate is greater, the process gain is smaller, UE
needs more power for this service, then the coverage of this
service will be smaller, vice versa.
)rate bit
rate chiplog(10Gain ocessPr =
� For common services, the bit rate of voice call is 12.2kbps, the bit rate of video phone
is 64kbps, and the highest packet service bit rate is 384kbps(R99). After the spreading,
the chip rate of different service all become 3.84Mcps.
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Spreading Technology
� Spreading consists of 2 steps:
� Channelization operation, which transforms data symbols into chips
� Scrambling operation is applied to the spreading signal
scramblingchannelization
Data
symbol
Chips after
spreading
� Spreading means increasing the bandwidth of the signal beyond the bandwidth
normally required to accommodate the information. The spreading process in UTRAN
consists of two separate operations: channelization and scrambling.
� The first operation is the channelization operation, which transforms every data
symbol into a number of chips, thus increasing the bandwidth of the signal. The
number of chips per data symbol is called the Spreading Factor (SF). Channelization
codes are orthogonal codes, meaning that in ideal environment they do not interfere
each other.
� The second operation is the scrambling operation. Scrambling is used on top of
spreading, so it does not change the signal bandwidth but only makes the signals
from different sources separable from each other. As the chip rate is already achieved
in channelization by the channelization codes, the chip rate is not affected by the
scrambling.
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WCDMA Channelization Code
� OVSF Code (Orthogonal Variable Spreading Factor) is used as
channelization code
SF = 8SF = 1 SF = 2 SF = 4
Cch,1,0 = (1)
Cch,2,0 = (1,1)
Cch,2,1 = (1, -1)
Cch,4,0 = (1,1,1,1)
Cch,4,1 = (1,1,-1,-1)
Cch,4,2 = (1,-1,1,-1)
Cch,4,3 = (1,-1,-1,1)
Cch,8,0 = (1,1,1,1,1,1,1,1)
Cch,8,1 = (1,1,1,1,-1,-1,-1,-1)
Cch,8,2 = (1,1,-1,-1,1,1,-1,-1)
Cch,8,3 = (1,1,-1,-1,-1,-1,1,1)
Cch,8,4 = (1,-1,1,-1,1,-1,1,-1)
Cch,8,5 = (1,-1,1,-1,-1,1,-1,1)
Cch,8,6 = (1,-1,-1,1,1,-1,-1,1)
Cch,8,7 = (1,-1,-1,1,-1,1,1,-1)
……
� Orthogonal codes are easily generated by starting with a seed of 1, repeating the 1
horizontally and vertically, and then complementing the -1 diagonally. This process is
to be continued with the newly generated block until the desired codes with the
proper length are generated. Sequences created in this way are referred as “Walsh”
code.
� Channelization uses OVSF code, for keeping the orthogonality of different subscriber
physical channels. OVSF can be defined as the code tree illustrated in the following
diagram.
� Channelization code is defined as Cch SF, k,, where, SF is the spreading factor of the
code, and k is the sequence of code, 0≤k≤SF-1. Each level definition length of code tree is SF channelization code, and the left most value of each spreading code
character is corresponding to the chip which is transmitted earliest.
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WCDMA Channelization Code
� SF = chip rate / symbol rate
� High data rates → low SF code
� Low data rates → high SF code
16Data 128 kbps DL8Data 128 kbps UL
32Data 64 kbps DL16Data 64 kbps UL
8Data 384 kbps DL4Data 384 kbps UL
16Data 144 kbps DL8Data 144 kbps UL
128Speech 12.2 DL64Speech 12.2 UL
SFRadio bearerSFRadio bearer
� The channelization codes are Orthogonal Variable Spreading Factor (OVSF) codes. They are used to preserve orthogonality between different physical channels. They also increase the clock rate to 3.84 Mcps. The OVSF codes are defined using a code
tree.
� In the code tree, the channelization codes are individually described by Cch,SF,k, where
SF is the Spreading Factor of the code and k the code number, 0 ≤ k ≤ SF-1.
� A channelization sequence modulates one user’s bit. Because the chip rate is constant, the different lengths of codes enable to have different user data rates. Low SFs are
reserved for high rate services while high SFs are for low rate services.
� The length of an OVSF code is an even number of chips and the number of codes (for
one SF) is equal to the number of chips and to the SF value.
� The generated codes within the same layer constitute a set of orthogonal codes. Furthermore, any two codes of different layers are orthogonal except when one of the
two codes is a mother code of the other. For example C4,3 is not orthogonal with C1,0and C2,1, but is orthogonal with C2,0.
� SF in uplink is from 4 to 256.
� SF in downlink is from 4 to 512.
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Purpose of Channelization Code
� Channelization code is used to distinguish different physical
channels of one transmitter
� For downlink, channelization code ( OVSF code ) is used to
separate different physical channels of one cell
� For uplink, channelization code ( OVSF code ) is used to separate
different physical channels of one UE
� For voice service (AMR), downlink SF is 128, it means there are 128 voice services
maximum can be supported in one WCDMA carrier;
� For Video Phone (64k packet data) service, downlink SF is 32, it means there are 32
voice services maximum can be supported in one WCDMA carrier.
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Purpose of Scrambling Code
� Scrambling code is used to distinguish different transmitters
� For downlink, scrambling code is used to separate different cells in
one carrier
� For uplink, scrambling code is used to separate different UEs in
one carrier
� In addition to spreading, part of the process in the transmitter is the scrambling
operation. This is needed to separate terminals or base stations from each other.
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Scrambling Code
� Scrambling code: GOLD sequence.
� There are 224 long uplink scrambling codes which are used for
scrambling of the uplink signals. Uplink scrambling codes are assigned
by RNC.
� For downlink, 512 primary scrambling codes are used.
� Different scrambling codes will be planned to different cells in downlink.
� Different scrambling codes will be allocated to different UEs in uplink.
� The scrambling code is always applied to one 10 ms frame.
� In UMTS, Gold codes are chosen for their very low peak cross-correlation.
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Primary Scrambling Code Group
Primary
scrambling
codes for downlink
physical
channels
Group 0
…
Primary scrambling code 0
……
Primary scrambling code
8*63
……
Primary scrambling code
8*63 +7512 primary
scrambling
codes
…………
Group 1
Group 63
Primary scrambling code 1
Primary scrambling code 8
64 primary
scrambling code
groups
Each group consists of 8
primary scrambling codes
� There are totally 512 primary scrambling codes defined by 3GPP. They are further
divided into 64 primary scrambling code groups. There are 8 primary scrambling codes
in every group. Each cell is allocated with only one primary scrambling code.
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Code Multiplexing
� Downlink Transmission on a Cell Level
Scrambling code
Channelization code 1
Channelization code 2
Channelization code 3
User 1 signal
User 2 signal
User 3 signal
NodeB
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Code Multiplexing
� Uplink Transmission on a Cell Level
NodeB
Scrambling code 3
User 3 signal
Channelization code
Scrambling code 2
User 2 signal
Channelization code
Scrambling code 1
User 1 signal
Channelization code
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Processing Procedure of WCDMA System
Source
CodingChannel Coding& Interleaving
Spreading Modulation
Source
DecodingChannel Decoding& Deinterleaving
Despreading Demodulation
Transmission
Reception
chipmodulated signal
bit symbol
ServiceSignal
Radio
Channel
Service
Signal
Receiver
� Source coding can increase the transmitting efficiency.
� Channel coding can make the transmission more reliable.
� Spreading can increase the capability of overcoming interference.
� Scrambling can make transmission in security.
� Through the modulation, the signals will transfer to radio signals from digital signals.
� Bit, Symbol, Chip
� Bit : data after source coding
� Symbol: data after channel coding and interleaving
� Chip: data after spreading
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Modulation Overview
1 00 1
time
Basic steady radio wave:
carrier = A.cos(2 ππππFt+φφφφ)
Amplitude Shift Keying:
A.cos(2 ππππFt+φφφφ)
Frequency Shift Keying:
A.cos(2 ππππFt+φφφφ)
Phase Shift Keying:
A.cos(2 ππππFt+φφφφ)
Data to be transmitted:Digital Input
� A data-modulation scheme defines how the data bits are mixed with the carrier signal,
which is always a sine wave. There are three basic ways to modulate a carrier signal in
a digital sense: amplitude shift keying (ASK), frequency shift keying (FSK), and phase
shift keying (PSK).
� In ASK the amplitude of the carrier signal is modified by the digital signal.
� In FSK the frequency of the carrier signal is modified by the digital signal.
� The PSK family is the most widely used modulation scheme in modern cellular systems.
There are many variants in this family, and only a few of them are mentioned here.
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Modulation Overview
� Digital Modulation - BPSK
1
t
1 10
1
t-1
NRZ coding
fo
BPSK
Modulated
BPSK signal
Carrier
Information signal
φφφφ=0 φφφφ=ππππ φφφφ=0
1 102 3 4 9875 6
1 102 3 4 9875 6
Digital Input
High FrequencyCarrier
BPSK Waveform
� In binary phase shift keying (BPSK) modulation, each data bit is transformed into a
separate data symbol. The mapping rule is 1 −> + 1 and 0 − > − 1. There are only two possible phase shifts in BPSK, 0 and π radians.
� NRZ means none return zero.
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Modulation Overview
� Digital Modulation - QPSK
-1 -1
1 102 3 4 9875 6
1 102 3 4 9875 6
NRZ Input
I di-Bit Stream
Q di-Bit Stream
IComponent
QComponent
QPSK Waveform
1
1
-1
1
-1
1
1
-1
-1
-1
1 1 -1 1 -1 1 1 -1
� The quadrature phase shift keying (QPSK) modulation has four phases: 0, π/2, π, and 3π/2 radians. Two data bits are transformed into one complex data symbol; A symbol is any change (keying) of the carrier.
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Modulation Overview
NRZ coding
90o
NRZ coding
QPSK
Q(t)
I(t)
fo
±±±±A
±±±±A ±±±±Acos( ωωωωot)
±±±±Acos( ωωωωot + ππππ/2)
φφφφ
1 1 ππππ/4
1 -1 7ππππ/4
-1 1 3ππππ/4
-1 -1 5ππππ/4
)cos(2: φω +oAQPSK
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Demodulation
� QPSK Constellation Diagram
1 102 3 4 9875 6
QPSK Waveform
1,1
-1,-1
-1,1
1,-1
1 -11 -1 1 -1-11-1 1
-1,1
NRZ Output
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WCDMA Modulation
� Different modulation methods corresponding to different
transmitting abilities in air interface
HSDPA: QPSK or 16QAMR99/R4: QPSK
� The UTRAN air interface uses QPSK modulation in the downlink, although HSDPA may
also employ 16 Quadrature Amplitude Modulation (16QAM). 16QAM requires good
radio conditions to work well. As seen, with 16QAM also the amplitude of the signal
matters.
� As explained, in QPSK one symbol carries two data bits; in 16QAM each symbol
includes four bits. Thus, a QPSK system with a chip rate of 3.84Mcps could
theoretically transfer 2 × 3.84 = 7.68 Mbps, and a 16QAM system could transfer 4 ×3.84 Mbps = 15.36 Mbps. In 3GPP also the usage of 64QAM with HSDPA has been
studied.
WCDMA RAN Fundamental
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Processing Procedure of WCDMA System
Source
CodingChannelCoding
Spreading Modulation
Source
DecodingChannel
DecodingDespreading Demodulation
Transmission
Reception
chipmodulated signal
bit symbol
ServiceSignal
Radio
Channel
Service
Signal
Transmitter
Receiver
� Source coding can increase the transmitting efficiency.
� Channel coding can make the transmission more reliable.
� Spreading can increase the capability of overcoming interference.
� Scrambling can make transmission in security.
� Through the modulation, the signals will transfer to radio signals from digital signals.
� Bit, Symbol, Chip
� Bit : data after source coding
� Symbol: data after channel coding and interleaving
� Chip: data after spreading
WCDMA RAN Fundamental
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Wireless Propagation
ReceivedSignal
TransmittedSignal
Transmission Loss:Path Loss + Multi-path Fading
Time
Amplitude
� A mobile communication channel is a multi-path fading channel and any transmitted
signal reaches a receive end by means of multiple transmission paths, such as direct
transmission, reflection, scatter, etc.
WCDMA RAN Fundamental
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Propagation of Radio SignalSignal at Transmitter
Signal at Receiver
-40
-35
-30
-25
-20
-15
-10
-5
dB
0
0
dBm
-20
-15
-10
-5
5
10
15
20
Fading
WCDMA RAN Fundamental
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Fading Categories
� Fading Categories
� Slow Fading
� Fast Fading
� Furthermore, with the moving of a mobile station, the signal amplitude, delay and
phase on various transmission paths vary with time and place. Therefore, the levels of
received signals are fluctuating and unstable and these multi-path signals, if overlaid,
will lead to fast fading. Fast fading conforms to Rayleigh distribution. The mid-value
field strength of fast fading has relatively gentle change and is called “slow fading”.
Slow fading conforms to lognormal distribution.
WCDMA RAN Fundamental
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Diversity Technique
� Diversity technique is used to obtain uncorrelated signals for
combining
� Reduce the effects of fading
� Fast fading caused by multi-path
� Slow fading caused by shadowing
� Improve the reliability of communication
� Increase the coverage and capacity
� Diversity technology means that after receiving two or more input signals with
mutually uncorrelated fading at the same time, the system demodulates these signals
and adds them up. Thus, the system can receive more useful signals and overcome
fading.
WCDMA RAN Fundamental
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Diversity
� Time diversity
� Channel coding, Block interleaving
� Frequency diversity
� The user signal is distributed on the whole bandwidth frequency
spectrum
� Space diversity
� Polarization diversity
� Diversity technology is an effective way to overcome overlaid fading. Because it can be
selected in terms of frequency, time and space, diversity technology includes
frequency diversity, time diversity and space diversity.
� Time diversity: Channel coding
� Frequency diversity: WCDMA is a kind of frequency diversity. The signal energy is
distributed on the whole bandwidth.
� Space diversity: using two antennas
WCDMA RAN Fundamental
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Principle of RAKE Receiver
Receive set
Correlator 1
Correlator 2
Correlator 3
Searcher correlator Calculate the
time delay and
signal strength
CombinerThe combined
signal
tt
s(t) s(t)
RAKE receiver help to overcome on the multi-path fading and enhance the receive
performance of the system
� The RAKE receiver is a technique which uses several baseband correlators to
individually process multipath signal components. The outputs from the different
correlators are combined to achieve improved reliability and performance.
� When WCDMA system is designed for cellular system, the inherent wide-bandwidth
signals with their orthogonal Walsh functions were natural for implementing a RAKE
receiver. In WCDMA system, the bandwidth is wider than the coherence bandwidth of
the cellular. Thus, when the multi-path components are resolved in the receiver, the
signals from different paths are uncorrelated with each other. The receiver can then
combine them using some combining schemes. So with RAKE receiver WCDMA
system can use the multi-path characteristics of the channel to get signal with better
quality.
WCDMA RAN Fundamental
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Summary
� In this course, we have discussed basic concepts of WCDMA:
� Spreading / Despreading principle
� UTRAN Voice Coding
� UTRAN Channel Coding
� UTRAN Spreading Code
� UTRAN Scrambling Code
� UTRAN Modulation
� UTRAN Transmission/Receiving
WCDMA RAN Fundamental
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