book for basics-1

8/3/2019 Book for BASICS-1

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Generation of wireless Network

Technologies used in 1G/2G/2.5G/3G/4G


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Analog and Digital Signals

Analog Signals


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Advantage of Analog Signals


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Digital Signals


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Advantage of Digital Signals


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Analog and Digital Clocks


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Analog to digital Transmission

Digital transmission involves sending a series of symbols, ones and

zeros; from one point to another. Because speech is analogue, that

is, a continuous wave form; it must be converted to digital signals

before it can be transmitted. This process is called analogue to

digital conversion (A/D conversion).


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The A/D conversion is performed by using a process called Pulse

Code Modulation (PCM). PCM is a common method used in

telecommunication systems. It involves the three main steps

described below:

Sampling

Quantization

Coding


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SAMPLING

Sampling involves measuring the analogue signal at specific time

intervals. Each measurement is called a sample and the sampling

time interval is defined as Ts [s]. The accuracy of describing the

analogue signal in digital terms depends on how often the analogue

signal is sampled, among other things. This is expressed as thesampling frequency: fs=1/Ts [Hz].


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According to the Sampling principle:

Normal speech mainly contains frequency components lower than

3000 Hz. Higher components have quite low energy and may be

omitted without affecting the speech quality very much. Applying

the sampling principle when sampling analogue speech signals, the

sampling frequency,fs, should be at least 2 x 3 kHz = 6 kHz.Telecommunication systems use a sampling frequency of 8 kHz,

which is acceptable based on the Sampling principle.


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QUANTIZATION

In order to limit the number of values transmitted, the amplitude

level is divided into a finite set of levels. Each sample within a

certain interval is represented by one of these levels. Figure 6.6

shows the principle of quantization applied to the analogue signal -

the actual sample and the quantified value. The figure shows the

principle ofUniform Quantization used in the GSM system. In

uniform quantization, the distance between two levels is constant.


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CODING

Every quantified value is represented by a binary code. In order to

obtain the 256 levels, 8 bits are used (2^8 = 256). In GSM, 13 bits

are used to obtain the 8192 levels (2^13 = 8192). The process of

PCM, including sampling at 8 kHz and performing quantization and

coding using 8 bits; produces a bit rate of 8000 x 8 = 64 kbit/s. Adigital link used to transmit these bits is called a PCM link.


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In order to use the link more efficiently several channels are

multiplexed onto the same link. The technique used is called Time

Division Multiple Access (TDMA) and it means that several channels

share the same link. Each channel uses the link during a certain

amount of time called a time slot. Figure 6.7 shows how 32

channels are multiplexed onto one PCM link, forming a first order

PCM system. The bit rate on such a link is 32 x 8 x 8000 = 2048

kbit/s called as E1 Link

Multiplexing 32 channels into one PCM link.


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There is also a solution where 24 channels are multiplexed ontoone PCM link. The bit rate for this solution is 24 x 8 x 8000 = 1544

kbit/s. This type of link is preferable in the US Called as T1 Link.

The result from the process of A/D conversion is 8,000 samples per

second of 13 bits each. This is a bit rate of 104 kbits/s. When it isconsidered that 8 subscribers use one radio channel, the overall bit

rate would be 8 x 104 kbits/s = 832 kbits/s. Recalling the general

rule of 1 bit per Hertz, this bit rate would not fit into the 200 kHz

available for all 8 subscribers. The bit rate must be reduced

somehow - this is achieved using segmentation and speech coding.


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Modulation

Modulation is the Process of Varying the Characteristics of high

Signal(Carrier) in accordance with instantaneous Value of low

signal(modulating Signal).

Signals are of low amplitude Strength with low frequency (20 Hz to

20 KHz).

To send signal up to longer distance Modulation is Required


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Types of Modulation

Three types of Digital Modulation Technique

Amplitude Shift Keying Modulation

Frequency Shift Keying Modulation

Phase Shift Keying Modulation

The Modulation used in GSM is Gaussian Minimum Shift

Keying(GMSK), a kind of Phase frequency Shift Keying.


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GMSK(Gaussian Minimum Shift Keying )

In GSM, the carrier bandwidth is 200 kHz. As a general rule, usingsimpler modulation techniques, 1 bit/s can be transmitted within1 Hz. Using this method, only 200 kbits/s could be transmittedwithin 200 kHz. However, more advanced modulation techniquesare available which can transmit more bits/s within 1 Hz. The

modulation technique used in GSM is Gaussian Minimum ShiftKeying (GMSK).

GMSK enables the transmission of 270kbit/s within a 200 kHzchannel. The channel capacity in GSM does not compare favorablywith other digital mobile standards, which can fit more bits/s into

a channel. In this way the capacity of other mobile standards ishigher. However, GSMs GMSK offers more tolerance ofinterference. This in turn enables the tighter re-use of frequencies,which leads to an overall gain in capacity which out-performs thatof other systems.


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GMSK Diagram


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Multiple Access Technology

Multiple Access Technique is achieved by dividing the available radio

frequency spectrum, So that multiple users can be given at the

same time.

Frequency division multiple access (FDMA)( eg.GSM each user frequency channel is 200Hz )

Time division multiple access (TDMA)( eg.GSM each frequency channel is divided into 8 time slots )

Code division multiple access (CDMA)( eg.IS 95- Each user data is coded with unique code)


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Frequency division multiple access (FDMA)

Frequency division multiplexing is used to allow multiple user to share aphysical communication channel , It is called frequency division multiple

access (FDMA)

Time division multiple access (TDMA)TDMA is a channel access method for shared medium network . It allowsseveral user to share the same frequency channel by dividing the signal intodifferent time slots . he user transmit in rapid success in ,one after the other ,

each using his own time slot.

Code division multiple access (CDMA)

CDMA is a channel access method used by various radio communication

technologies .


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Duplex Technology

Types of Duplexing Technology

Frequency division duplex (FDD)( eg; In GSM the up link and down link of a user is separated by 45

MHz)

Time division duplex (TDD)

( eg; In GSM the up link and down link of a user will be the

same frequency but at different Time)


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Duplex Technology


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FREQUENCY CONCEPTS

The following table summarizes the frequency-related specifications ofeach of the GSM systems. The terms used in the table are explained in the

remainder of this section.


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FREQUENCY

An MS (Mobile Station) communicates with a BTS by transmitting orreceiving radio waves, which consist of electromagnetic energy. Thefrequency of a radio wave is the number of times that the waveoscillates per second. Frequency is measured in Hertz (Hz), where 1

Hz indicates one oscillation per second. Radio frequencies are usedfor many applications in the world today. Some common usesinclude:

Television: 300 MHz approx.

FM Radio: 100 MHz approx.

Mobile networks: 300 - 2000 MHz approx.

The frequencies used by mobile networks vary according to thestandard being used. An operator applies for the availablefrequencies


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UPLINK AND DOWNLINK

The MS to the network is referred to as uplink. The direction from thenetwork to the MS is referred to as downlink.

Logic question

Why uplink band consists of lower range of frequency?

Because it requires less power to transmit a lower frequency overa given distance , uplink frequency in mobile system are always the

lower band of frequency- this saves a valuable battery power of theMS


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Wave Length

There are many different types of electromagnetic waves. These

electromagnetic waves can be described by a sinusoidal function,which is characterized by wavelength. Wavelength is the length ofone complete oscillation and is measured in meters (m). Frequencyand wavelength are related via the speed of propagation, which forradio waves is the speed of light (3 x108 m/s).

The wavelength of a frequency can be determined by using the

following formula:

Wavelength = Speed/Frequency


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Thus, for GSM 900 the wavelength is:

Wavelength = 3 x 108m/s/900 MHz

Wavelength = 300,000,000 m/s/900,000,000

Wavelength = 0.33 m (or 33 cm)

From this formula it can be determined that the higher thefrequency, the shorter the wavelength. Lower frequencies, with

longer wavelengths, are better suited to transmission over large

distances, because they bounce on the surface of the earth and in

the atmosphere. Television and FM radio are examples of

applications, which use lower frequencies.


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Higher frequencies, with shorter wavelengths, are bettersuited to transmission over small distances, because they are

sensitive to such problems as obstacles in the line of the

transmission path. Higher frequencies are suited to small areas of

coverage, where the receiver is relatively close to the transmitter.

The frequencies used by mobile systems compromise between the

large-coverage advantages offered by lower frequencies and the

closeness-to-the-receiver advantages offered by use of higher

frequencies.


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Module B;Overview of GSM


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What is GSM?

Global System for Mobile (GSM) is a second

generation cellular standard developed to

cater voice services and data delivery using

digital modulation


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Evolution of GSM

GSM in world


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GSM in INDIA


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Fundamentals of GSM

The Global System for Mobile Communications (GSM) is a set ofrecommendations and specifications for a digital cellulartelephone network (known as a Public Land Mobile Network, orPLMN).

These recommendations ensure the compatibility of equipmentfrom different GSM manufacturers, and interconnectivity betweendifferent administrations, including operation across internationalboundaries.

GSM networks are digital and can cater for high system capacities.

They are consistent with the world-wide digitization of the telephone

network, and are an extension of the Integrated Services DigitalNetwork (ISDN), using a digital radio interface between the cellularnetwork and the mobile subscriber equipment.


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CELLULAR TELEPHONYCELLULAR TELEPHONY

A cellular telephone system links mobile subscribers into the public

telephone system or to another cellular subscriber.

Information between the mobile unit and the cellular network

uses radio communication. Hence the subscriber is able to move

around and become fully mobile.

The service area in which mobile communication is to be provided

is divided into regions called cells. Each cell has the equipment to transmit and receive calls from any

subscriber located within the borders of its radio coverage area.

Mobile subscriber

RadioCell


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GSMGSM FREQUENCIESFREQUENCIES

GSM systems use radio frequencies between 890-915 MHz for receive and

between 935-960 MHz for transmit.

RF carriers are spaced every 200 kHz, allowing a total of 124 carriers for

use.

An RF carrier is a pair of radio frequencies, one used in each direction.

Transmit and receive frequencies are always separated by 45 MHz.

960935890 915

UPLINK AND DOWNLINK FREQUENCY SEPARATED BY 45MHZ

UPLINK FREQUENCIES DOWNLINK FREQUENCIES


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ExtendedExtended GSMGSM (EGSM)(EGSM)

EGSM has 10MHz of bandwidth on both transmit and receive.Receive bandwidth is from 880 MHz to 890 MHz.

Transmit bandwidth is from 925 MHz to 935 MHz.

Total RF carriers in EGSM is 50.


880 880 925 935 960



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DCSDCS18001800 FreqencyFreqency

DCS1800 systems use radio frequencies between 1710-1785 MHz for receive

and between 1805-1880 MHz for transmit.RF carriers are spaced every 200 kHz, allowing a total of 373 carriers.

There is a 100 kHz guard band between 1710.0 MHz and 1710.1 MHz and

between 1784.9 MHz and 1785.0 MHz for receive, and between 1805.0

MHz and 1805.1 MHz and between 1879.9 MHz and 1880.0 MHz for

transmit.

Transmit and receive frequencies are always separated by 95 MHz.

1805 MHz1710 MHz 1785 MHz



1880 MHz1805 MHz


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GSM STRUCTURE


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GSM Architecture

OMC

Home Location Register

AuC

Equipment ID

Network

Management

Center

BT

S

BT

S

BT

S

ME

ME

ME

Subscriber

Identity

Module

SubscriberIdentity

Module

Subscriber

Identity

Module

Base stationcontroller

PSTN

Mobile

switching

center

Data

communication

network

BTS = Base Transceiver Station

AuC = Authentication Center

OMC = Operation and Maintenance Center

PSTN = Public Switched Telephone Network

ME = Mobile Equipment

Source: Stallings, 313

Source: Mehrotra, 27

Visitor LocationRegister


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INTERFACE NAMESINTERFACE NAMES

Each interface specified in GSM has a name associated with it


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GSM System Architecture

Mobile Station (MS)Mobile Equipment (ME)

Subscriber Identity Module (SIM)

Base Station Subsystem (BSS)

Base Transceiver Station (BTS)Base Station Controller (BSC)

Network Switching Subsystem(NSS)

Mobile Switching Center (MSC)

Home Location Register (HLR)Visitor Location Register (VLR)

Authentication Center (AUC)

Equipment Identity Register (EIR)

Operational support Subsystem(OSS)


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Mobile Station(MS)

The Mobile Station is made up of two entities:

1. Mobile Equipment (ME)2. Subscriber Identity Module (SIM)


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Mobile Equipment

Portable, vehicle mounted, hand held device

Uniquely identified by an IMEI (International Mobile EquipmentIdentity)

Voice and data transmission

Monitoring power and signal quality of surrounding cells foroptimum handover

Power level : 0.8W 20 W

160 character long SMS.


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Subscriber Identity Module (SIM)

Smart card contains the International Mobile SubscriberIdentity (IMSI)

Allows user to send and receive calls and receive other

subscribed services Encoded network identification details

- Key Ki,Kc and A3,A5 and A8 algorithms

Protected by a password or PIN

Can be moved from phone to phone contains key informationto activate the phone


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International Mobile Subscribers IdentityInternational Mobile Subscribers Identity -- IMSIIMSI

Network Identity Unique to a MS

The International Mobile Subscriber Identity (IMSI) is the

primary identity of the subscriber within the mobile network

and is permanently assigned to that subscriber.

The IMSI can be maximum of 15 digits.

404 XX 12345..10

MCC MNC MSIN

MCC

MNC

MSIN

= Mobile Country Code ( 3 Digits )

= Mobile Network Code ( 2 Digits )

= Mobile Subscriber Identity Number

Mobile Station International SubscribersMobile Station International Subscribers DiallingDialling


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Mobile Station International SubscribersMobile Station International Subscribers DiallingDiallingNumberNumber (MSISDN ) :(MSISDN ) :

Human identity used to call a MS

The Mobile Subscriber ISDN (MSISDN) number is the telephonenumber of the MS.

This is the number a calling party dials to reach the subscriber.

It is used by the land network to route calls toward the MSC.

CC= Country codeNDC= National Destination CodeSN= Subscriber Number

98 XXX 12345

CC NDC SN


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TemporaryTemporary MobileMobile SubscribersSubscribers IdentityIdentity (( TMSITMSI )) ::

The GSM system can also assign a Temporary Mobile Subscriber Identity

(TMSI).

After the subscriber's IMSI has been initialized on the system, the TMSI

can be used for sending messages backwards and forwards across the

network to identify the subscriber.The system automatically changes the TMSI at regular intervals, thus

protecting the subscriber from being identified by someone attempting

to monitor the radio channels.

The TMSI is a local number and is always allocated by the VLR.

The TMSI is maximum of 4 octets.


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Base Station Subsystem (BSS)

Base Station Subsystem is composed of two parts that

communicate across the standardized Abis interface allowing

operation between components made by different suppliers

1. Base Transceiver Station (BTS)

2. Base Station Controller (BSC)


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Base Station Controller (BSC)

Manages Radio resources for BTS

Assigns Frequency and time slots for all MSs in its area

Handles call set up

Transcoding and rate adaptation functionality

Handover for each MS Radio Power control

It communicates with MSC and BTS


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Structure of Base Station Controller(BSC)

BBase Station Controller (Base Station Controller (BSCSC)) Siemens BSCSiemens BSC


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Network Switching Subsystem(NSS)

Mobile Switching Center (MSC)

Heart of the networkManages communication between GSM and other networksCall setup function and basic switchingCall routingBilling information and collectionMobility management

- Registration- Location Updating- Inter BSS and inter MSC call handoff

MSC does gateway function while its customer roams to othernetwork by using HLR/VLR.


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Structure ofMobile Switching Centre(MSC)

MMobileobile SSwitchingwitching CCentre (MSC)entre (MSC) Lucent MSCLucent MSC


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Home Location Registers (HLR)

- permanent database about mobile subscribers in a largeservice area(generally one per GSM network operator)

database contains IMSI ,MSISDN ,prepaid/postpaid ,roamingrestrictions ,supplementary services.

Visitor Location Registers (VLR)

Temporary database which updates whenever new MS entersits area, by HLR database

Controls those mobiles roaming in its area

Reduces number of queries to HLR

Database contains IMSI ,TMSI ,MSISDN ,MSRN ,Location Area ,authentication key


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Authentication Center (AUC)

Protects against intruders in air interface

Maintains authentication keys and algorithms and providessecurity triplets ( RAND ,SRES ,Kc)

Generally associated with HLR

Equipment Identity Register (EIR)

- Database that is used to track handsets using the IMEI(International Mobile Equipment Identity)

Made up of three sub-classes: The White List, The Black Listand the Gray List

Only one EIR per PLMN


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Operational support Subsystem(OSS) OROR

Operation And Maintenance Centre For RadioOperation And Maintenance Centre For Radio

((OMCOMC--RR))The OMC controls and monitors the Network elements within a

region.

The OMC also monitors the quality of service being provided by

the Network.The following are the main functions performed by the OMC-R

The OMC allows network devices to be manually removed for

or restored to service. The status of network devices can be

checked from the OMC and tests and diagnostics invoked.


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The alarms generated by the Network elements are reported

and logged at the OMC. The OMC-R Engineer can monitorand analyze these alarms and take appropriate action like

informing the maintenance personal.

The OMC keeps on collecting and accumulating traffic

statistics from the network elements for analysis.

Software loads can be downloaded to network elements oruploaded to the OMC.

Operation And Maintenance CentreOperation And Maintenance Centre


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Operation And Maintenance CentreOperation And Maintenance Centre

For Radio (For Radio (OMCOMC--RR))


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BBase Station Identity Codease Station Identity Code

BSIC allows a mobile station to distinguish between neighboringbase stations.

It is made up of 8 bits.

NCC = National Colour Code( Differs from operator to operator )

BCC = Base Station Colour Code, identifies the base station to help

distinguish between Cells using the same BCCH frequencies


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Cell Global Identity (CGI)Cell Global Identity (CGI)


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GSM CHANNELCONCEPTGSM CHANNELCONCEPT

PhysicalPhysical channelchannel - Each timeslot on a carrier is referred to as aphysical channel. Per carrier there are 8 physical channels.

LogicalLogical channelchannel - Variety of information is transmitted between the

MS and BTS. There are different logical channels depending on the

information sent. The logical channels are of two types Traffic channel

Control channel


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GSM Traffic ChannelsGSM Traffic Channels

GSM C t l Ch lGSM C t l Ch l


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GSMControl ChannelsGSMControl Channels


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BCHChannelsBCHChannels

BCCH( Broadcast Control Channel )BCCH( Broadcast Control Channel )

Downlink only Broadcasts general information of the serving cell called System

Information

BCCH is transmitted on timeslot zero of BCCH carrier

Read only by idle mobile at least once every 30 secs .

SCH( Synchronization Channel )SCH( Synchronization Channel ) Downlink only

Carries information for frame synchronization. Contains TDMA

frame number and BSIC.

FCCH( Frequency Correction Channel )FCCH( Frequency Correction Channel )

Downlink only.

Enables MS to synchronize to the frequency.

Also helps mobiles of the n cells to locate TS 0 of BCCH carrier.


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CCCHChannelsCCCHChannels

RACH( Random Access Channel)RACH( Random Access Channel)

Uplink only

Used by the MS to access the Network.

AGCH( Access Grant Channel )AGCH( Access Grant Channel ) Downlink only

Used by the network to assign a signaling channel upon

success full decoding of access bursts.

PCH( Paging Channel )PCH( Paging Channel )

Downlink only.

Used by the Network to contact the MS.


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DCCH ChannelsSDCCH( Standalone Dedicated Control Channel )SDCCH( Standalone Dedicated Control Channel )

Uplink and Downlink Used for call setup, location update and SMS.

SACCH(SACCH( Slow Associated Control Channel )Slow Associated Control Channel )

Used on Uplink and Downlink only in dedicated mode.

Uplink SACCH messages - Measurement reports. Downlink SACCH messages - control info.

FACCH( Fast Associated Control Channel )FACCH( Fast Associated Control Channel )

Uplink and Downlink.

Associated with TCH only. Is used to send fast messages like handover messages.

Works by stealing traffic bursts.


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Traffic Channel

TCH carries the Voice data

one TCH is allocated for every active call

Full Rate

used 22.8kbps/s

used for Speech at 13 kbps/sor Sending data at 9.6 kbps/s

Half rate

used for Speech at 6.5 kbps/s

or Sending data at 4.8 kbps/s


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TS 0 TS 1 TS 2 TS 3 TS 4 TS 5 TS 6 TS 7

FACCH

SCH

BCCH

PCH

RACH

AGCH

SDCCH

SACCH

CBCH

TCH

SACCH

FACCH

TCH

SACCH

FACCH

TCH

FACCH

SACCH

TCH

SACCH

FACCH

TCH

SACCH

FACCH

TCH

SACCH

FACCH

O.577 ms

1 TDMA FRAME

2OO kHZ

4.615 ms

TDMA Frame Structure in GSM


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Absolute Radio Frequency Channel


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Absolute Radio Frequency Channel

Number (ARFCN)

The ARFCN is a number that describes a pair of frequencies, one

uplink and one downlink. The uplink and downlink frequencies each

have a bandwidth of 200 kHz. The uplink and downlink have a

specific offsetthat varies for each band. The offset is the frequency

separation of the uplink from the downlink. Every time the ARFCN

increases, the uplink will increase by 200 khz and the downlink also

increases by 200 khz.


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Therefore 124 channels available for each UL and DL in GSM 900 and

374 channels available in GSM 1800

GSM 900= 1 to 124GSM 1800= 512 to 885

To calculate actual frequency;

For GSM 900 Band

UL freq-Fu(n)=890+0.2(1


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Call Flow in GSM

Mobile OriginatedCall

Mobile Terminated Call


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Mobile OriginatedCall


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Mobile TerminatedCall

RADIO INTERFACE


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RADIOINTERFACE


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INTERFERENCE

What is interference

Interference is the sum of the all signalscontributions that are neither noise not the wanted signal.


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Source of interference

Another mobile in the same cell.

A call in process in the neighbor cell.

Other base station operating on the same frequency.

Two types ofInterferenceCo Channel Interference

Adjacent Channel Interference


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Co Channel Interference

This type of Interference is due to frequency reuse, eg Several cellsuse the same set of frequency .

These cells are called Co Channel Interference

Co Channel Interference cannot be combated by increasing the power ofthe transmitter .This is because an increase in carrier transmit power

increases the Interference to neighbor co-channel cells.

To reduce Co Channel Interference , Co Channel cells must bephysically separated by a minimum distance to provide sufficientisolation due to propagation or reduce the foot print of cell .


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Adjacent Channel Interference

Interference resulting from signal which are adjacent in frequency

to the desired signal is called Adjacent Channel Interference.

Adjacent Channel Interference results from imperfect receiver filters

which are near by frequency to leak into the baseband.

Adjacent Channel Interference can be minimized through careful

filtering and channe3 assignments.By keeping the frequency separation between each channel in a given

cell as large as possible, the adjacent interference may be reduced

considerably.


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FREQUENCY HOPPING


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Frequency Hopping

Frequency Hopping is sequential change of carrier frequency on

the radio link between BS and MS.

Can be used to improve the quality of the network

Also can be used to increase the capacity of the Network therebyreducing the number of sites required for CAPACITY.

The way it works

Each burst is transmitted on a different frequency

Both mobile and base station follow the same hopping sequence


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TYPESTYPES OFOF HOPPINGHOPPING

BaseBase BandBand HoppingHopping (BBH)(BBH)

SynthesiserSynthesiser FrequencyFrequency HoppingHopping (SFH)(SFH)

HoppingHopping ParametersParameters


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pp gpp g

For frequency hopping operability, GSM defines the

following set of parameters: Mobile Allocation (MA): Set of frequencies the mobile is

allowed to hop over. MA is a subset of all the frequencies allocated

by the system operator to the cell (cell allocation) although it can

be the same. Eg:- If the operator has frequencies from 1 -32, then

he can use 1-15 for BCCH and 17-32 for hopping ( MA).

Hopping Sequence Number (HSN): Determines the hoppingorder used in the cell. 64 different HSNs can be assigned, where

HSN = 0 provides a cyclic hopping sequence and HSN = 1 to 63

provide various pseudorandom hopping sequences.

Mobile Allocation IndexOffset ( MAIO): Determines inside thehopping sequence which frequency the mobile starts to transmit

on.


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Short Message Services (SMS)

Short Message Services(SMS) is the text communication services

component of phone ,web or mobile communication system ,

using standardized communications protocols that allow the

exchange of short message between f5xed line 6r mobile phone

devices .


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SMS Applications

SMS up to 160 alphabets characters.

Alert services (MT-SMS)

voice message alert

FAX/Telex Message Alert

E-mail system Alert

Information Services

Financial Services (stock market queries and alerts)

Weather OR traffic information (eg; from TV/Radio station

data feeds)


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Concept of GPRS/EDGE


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GPRS(General Packet Radio Services )General Packet Radio Services (GPRS) is a packet based wireless

communication service that promises data rates from 56 up to 114 kbpsand continuous connection to the Internet for mobile phone and

computer users. The higher data rates allow users to take part in video

conferences and interact with multimedia Web sites and similar

applications using mobile handled devices as well as notebook

computers.GPRS is based on Global System for Mobile(GSM) communication and

complements existing services such circuit Switch cellular phone

connections and the Short Message Service (SMS).

GPRS packet-based services cost users less than circuit-switched

services since communication channels are being used on a shared-use,

as-packets-are-needed basis rather than dedicated to only one user at a

time.


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GPRS Network

GPRS network provide the mobility management ,session

management , transport for internet protocol packet services in

GSM network

GPRS support node(GSN)-It is node which support use of GPRS in

GSM network .there are 2 key variant

GGSN(Gateway GPRS Support Node)SGSN(Serving GPRS Support Node)

Benefits of GPRS network;

High speed data rate 14.4-115 kbps.

Efficient use of BandwidthCircuit Switching and Pocket Switching are used in parallel.

Constant Connectivity


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Comparison of GSM and GPRS

EDGE (Enhanced Data GSM Environment)


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EDGE (Enhanced Data GSM Environment)

EDGE (Enhanced Data GSM Environment)EDGE (Enhanced Data GSM Environment) is a faster version

the Global System for Mobile (GSM) wireless service designed to deliver

data at rates up to 384 kbps and enable the delivery of multimedia and

other broad band applications to mobile phone and computer users.

The EDGE standard is built on the existing GSM standard, using thesame time-division multiple access (TDMA) frame structure and existing

cell arrangements.

EDGE is particular used as a GPRS solution for large data services ,Such

as Streaming Video and Video Conferencing.


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HANDOVERHANDOVER


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HAND OVER

The changing to a new traffic channel , During call setup or busy

state is called Handover. he network makes the decision about the

change .After receiving the information about the signal strength

and quality the BSC ranks the neighbour BTSs using through

information.

HANDOVERHANDOVER CONDITIONSCONDITIONS


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Handover is done on five conditions

Interference

RXQUAL

RXLEV

Distance or Timing Advance

Power Budget


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Interference - If signal level is high and still there is RXQUAL

problem, then the RXQUAL problem is because of interference.

RXQUAL - It is the receive quality. It ranges from 0 to 7 , 0 being thebest and 7 the worst

RXLEV - It is the receive level. It varies from -47dBm to -110dBm.

Timing Advance - Ranges from 0 to 63.

Power budget - It is used to save the power of the MS.

HANDOVERHANDOVER


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HANDOVERHANDOVERHANDOVER TYPESHANDOVER TYPES

IntraIntra--Cell HandoverCell Handover

Handover takes place in the same cell from one timeslot toanother timeslot of the same carrier or different carriers( but thesame cell).

Intra-cell handover is triggered only if the cause is interference.

Intra-cell handover can be enabled or disabled in a cell.

HANDOVERHANDOVER


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HANDOVERHANDOVER

HANDOVER TYPESHANDOVER TYPES

InterInter--BSCHandoverBSCHandover

Handover takes place between different cell which are controlled by

the different BSC.

HANDOVERHANDOVER


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HANDOVERHANDOVERHANDOVER TYPESHANDOVER TYPES

InterInter--MSCHandoverMSCHandover

Handover takes place between different cell which are controlled by the

different BSC and each BSC is controlled by different MSC


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Uses of Handover

To keep a continuous communication with a moving MS

To improve network service performance

To reduce the call drop rate

To reduce the congestion rate


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Cell Selection

When the mobile is turned on , it ill try to contact o public GSMPLMN , so the MS ill select a proper cell and extract from the cell

the control channel parameters and system message .This selection

process is called cell selection .the quality of radio channel is

important factor cell selection , GSM specification defines the path

loss rule C1.For the so- called proper cell,C1>0 must be ensured

ll l


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Cell Reselection

Cell Reselection (C2) is a process ,when MS change its service cell

idle mode.

When the MS selects a cell it will begin to measure the signal levels

of the BCCH TRX of its adjacent cells , record the Adjacent cells

whose signal levels are the strongest and extract from them varioustypes of strongest and extract from them various types of system

message and control message of each adjacent cell.

When given conditions are met ,the MS will move from the current

cell into another one . This process is called Cell reselection.

Pilot Pollution in Network


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Pilot Pollution in NetworkThe number of strong cells Exide more than then number of

active cells called Pilot Pollution .

Overshooting in Network

The another site signal strength is strong than the active cellsite is called Overshooting .

eg; Adjacent Site Signal is Stronger than our current site

signal

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