Intro to GSM - Slides (Rev 1).pptx

7/29/2019 Intro to GSM - Slides (Rev 1).pptx

1/71

ECE DepartmentFlorida Institute of Technology

ECE 5221 Personal Communication Systems

Introduction to GSM


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ECE DepartmentFlorida Institute of TechnologyPage 2

Course Outline

Part 1: Introduction

o Historical overview

o Elements of network architecture

o Elements of air interface

Part 2: Signal processing and network features

o Voice processing

o GSM Network features

Part 3: Network design

o Coverage planning

o Capacity planning

o Migration towards 3G and beyond

The GSM logo used on numerous

handsets and by carries who wish to

identify a GSM product
http://upload.wikimedia.org/wikipedia/en/5/5d/GSMLogo.svg


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History

Driving Factors:

Incompatibility of the European analog cellular systems

Reaching of capacity limits

Costs of the equipment

1982, Conference of European Post and Telecommunications formed Group Speciale Mobile (GSM)

1987, 15 operators from 13 countries signed Memorandum of Understanding (MoU)

1991, Finlands operator Radiolinia launched first GSM network in July 1991

1992, Massive deployment of GSM started

By 2000 GSM became the most popular 2G technology worldwide

GSM standard still evolving and enriched with new features and services

GSM = Global System for Mobile communications

(GSM: originally from Groupe Spcial Mobile)


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Deployment worldwide

930 networks in 222 countries and regions

More than 3 billion subscribers worldwide

More than 80% worldwide market share

Worldwide map of GSM coverage (source www.gsmworld.com)


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GSM in the USA

1994, US FCC auctioned large blocks ofspectrum in 1900MHz

GSM started deployment in PCS band

1995, American PersonalCommunications launched first GSMnetwork

In 2002, 850 band opened for GSM

Currently there are ~ 95M GSMsubscribers

Largest GSM operators ATT

T-Mobile

ATT coverage map

T-Mobile coverage map


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GSM Standards

Divided into 12 series

Standardization efforts coordinatedby ETSI

www.etsi.org

Specifications available onlinefree of charge

Standardization and publicavailability of specification - one offundamental factors of GSMsuccess

Series Specifications area

01 General

02 Service aspects

03 Network aspects04 MS-BS interface and protocol

05 Physical layer and radio path

06 Speech coding specification

07 Terminal adapter for MS

08 BS-MSC interface

09 Network internetworking10 Service internetworking

11 Equipment and type approval specification

12 Operation and maintenance

GSM Standard
http://www.etsi.org/http://www.etsi.org/


7/71ECE DepartmentFlorida Institute of Technology

Page 7

GSM Network Layout

GSM system layout is standardized

o Standardization involves:

Elements of the network

Communication Interfaces

o Standard layout allows for the use of equipment from different suppliers

MSCArea

HLR

MSCArea

VLR

MSCTRAUBSC

BTS

BTS

BSS

MSC Area

BSS

BSSBTS

PSTN

PLMN - Public Land Mobile Network

GatewayMSC

NSS



Page 8

GSM Components and Interfaces

Network has many functional components

Components are integrated through a network protocol MAP

Standardized interfaces

Um (air interface)

A GERAN interface

A-Bis (somewhat standardized)



Page 9

Mobile Station (MS)

Two functional parts

o HW and SW specific forGSM radio interface

o Subscriber IdentityModule (SIM)

SIM detaches user identityfrom the mobile

o Stores user information

o Without SIM onlyemergency calls

Functional diagram of GSM mobile

SIM card

Most popular GSM phone

Nokia 1100 200M+ sold

Keyboard

Control

Display

Transmit AudioSignal

Processing

Receive AudioSignal

Processing

ChannelDecoding

DeinterleavingMessage

Regenerator

ChannelEncoding

InterleavingMessageGenerator

Ciphering

Ciphering

RFProcessing

RFProcessing

SIM

Duplexer

Antenna

ANTENNAASSEMBLY

TRANSMITTER

RECEIVER

TRANSCEIVER UNITCONTROLSECTION
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Base Transceiver Station (BTS)

BTS is a set of transceivers (TX/RX).

GSM BTS can host up to 16 TX/RX.

In GSM one TX/RX is shared by 8 users.

The main role of TX/RX is to provide

conversion between traffic data on the

network side and RF communication on

the MS side.

Depending on the application, it can be

configured as macrocell, microcell, omni,

sectored, etc.

Typical BTS installation

BTS antenna system

Macrocell BTS radio

cabinet hosts TX/RX

Femto-cell


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BSC plays a role of a small digital exchange.

It can be connected to many BTSs and it offloads a great deal ofprocessing from MSC

One BSC connects to several tens to couple of hundred BTS

Some of BSC responsibilities:

o Handoff management

o MAHO management

o Power control

o Clock distribution

o Operation and maintenance TRAU is responsible for transcoding the user data from 16Kb/sec

to standard ISDN rates of 64Kb/sec.

It can physically reside on either BSC side or MSC side. If it resides on the MSC side, it provides substantial changes in

the backhaul 4 users over a single T-1/E-1 TDMA channel.

TRAU, BSC and BTSs form Base Station Subsystem (BSS

Base Station Controller (BSC) and TRAU

Typical BSC

TRAU = Transcoding and Rate Adaptation Unit


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Responsible for connecting the mobile to the

landline side

GSM MSC is commonly designed as a regular

ISDN switch with some added functionality for

mobility support

GSM Network can have more than one MSC

One of the MSC has an added functionality for

communication with public network Gateway

MSC (GMSC)

All calls from the outside networks are routedthrough GMSC

Mobile Switching Center (MSC)


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Registry HLR/VLR

HLR Home Location Registry

Database for permanent or semi-

permanent data associated with the user

Logically, there is only one HLR per

network

Typical information stored in HLR:International Mobile Service Identification

Number (IMSI), service subscription

information, supplementary services,

current location of the subscriber, etc.

HLR is usually implemented as an

integral part of MSC

VLR Visitor Location registry

Temporary database that keeps the

information about the users within the

service area of the MSC

Usually there is one VLR per MSC

The main task of the VLR is to reduce

the number of queries to HLR. When

the mobile, registers on the system its

information is copied from HLR to VLR

VLR is usually integrated with the switch


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AUC/EIR

AUC Authentication center Integral part of HLR

GSM specifies elaborateencryption

Three levels

o A5/1 USA + Europe

o A5/2 COCOM country list

o No encryption rest of theworld

EIR Equipment Identity Registry

Responsible for tracking equipmentand eligibility for service

Maintains three lists

o White list approved mobiletypes

o Black list barred mobile types

o Gray list tracked mobiletypes

Over years many other vendor specific features added to the system


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GSM Air Interface - Um

Interface between the MS and the GSM network

Subject to rigorous standardization process

We examine:

o Channelization

o Multiple access scheme

o Interface organization:

On the physical level

On the logical level


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Frequency allocation

For PCS-1900 band

o ARFCNul = (Fc-1850)/0.2+511; ARFCNdl = (Fc-1930)/0.2+511

For GSM-850

o ARFCNul = (Fc-824)/0.2+127; ARFCNdl = (Fc-969)/0.2+127

Mapping formulas

GSM is FDD technology


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TDMA Access Scheme

Multiple users operate on the same

frequency, but not at the same time.Advantages of TDMA:

o Relatively low complexity

o MAHO

o Different user rates can beaccommodated

o Easier integration with thelandline

Disadvantages:

o High sync overheado Guard times

o Heavily affected by themultipath propagation

Uplink ( From MS to BS)

Wireless Comm unication Channel

Downlink ( From BS to MS )

Base Station

fu0,

s1

fd0,

s1, s

2, ...,s

8

S1

S2

S3

.... S8 s1

s7 s8.... s1 s2 s3

fu0,

s2

fu0,

s8

TDMA = Time Division Multiple Access


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GSM as a TDMA system

GSM is acombination ofFDMA and TDMA

TDMA supports:

o Up to 8 full rateusers

o Up to 16 half rateusers

GSM uses

Frequency DivisionDuplexing

BTS

USER 1 USER 2 .... USER 8

U SER 6 U SER 7 U SER 8 U SER 1

USER 1,

ARFCN1

USER 2,

ARFCN1

USER 8,

ARFCN1

USER 9,

ARFCN2

USER 10,

ARFCN2

USER 16,

ARFCN2

ARFCN1

ARFCN2


19/71


GSM bursts

Data sent over one time slot =burst

Five types: normal, frequencycorrection, synchronization,dummy, access

Format of a burst defied by itsfunction

DL: normal, frequency correction,synchronization, dummy

UL: normal, access

Time/Frequency/Amplitude diagram for GSM

normal burst


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Normal Burst

Used to carry information on both control and traffic channels

Mixture of data and overhead

GSM defines 8 training sequences assigned in color code mode

Both on the forward and reverse link

Total of 114 encoded user information bits

Total of 34 overhead bits

Tail Traffic/Signaling Flag Training Sequence Flag Traffic/Signaling Tail

3 57 1 26 1 57 3

Normal burst


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Frequency Correction Burst

Sometimes referred to as the F-burst

Provides mobile with precise reference to the frequency of the broadcast controlchannel

Inserting the F-bursts on the control channel produces spectral peak 67.7 KHzabove the central frequency of the carrier

Only on the forward link

Spectral characteristics of the control

channel.

The peak in the spectrum allows for

easier MS network acquisition

Format of the F-burst

Fixed sequence consists of all zeros

fc fc+67.7 KHz frequency

Power Spectrum Density

BW = 200KHz

Tail Fixed Bit Sequence (All zeros) Tail

3 3142

Frequency correction burst


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Synchronization Burst

Facilitates the synchronization of the MS to the network at the base band

Commonly referred to as S-burst


The same sync sequence is used in all GSM networks

Tail Synchronization Training Sequence Synchronization Tail

3 33939 64

Synchronization burst


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Dummy Burst

Supports MAHO

Used to ensure constant power level of the broadcast

control channel


Tail Predefined Bit Sequence Tail

3 3142

Dummy burst


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Access Burst

Used when the MS is accessing the system

Shorter in length burst collision avoidance

Extended synchronization sequence

Used only on the reverse link

GSM mobiles use slotted ALOHA to access the system

In the case of collision a hashing algorithm is provided

Tail Synchronization Access Bits Tail

8 41 36 3

Access burst


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GSM Time Division Duplex

Communication on the forward and reverse link does not

happen simultaneously

Delay of three slots between TX and RX

Time division duplexing avoids RF duplexer at the RF stage

o Reduces the cost of mobile

o Saves battery

0

1 2 3 4 5 6 7 00

1 2 3 4 5765

Forward Link - BTS Transmits

Reverse Link - MS T ransmits


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GSM Logical Channels

GSM Logical

Channels

TCH

TCH/F TCH/H

CCH

BCH CCCH DCCH

CBCH

ACCH SDCCH

FACCHSACCH

FCCH

SCH

BCCH

PCH

AGCH

RACH

TCH - Traffic Channel

TCH/F - Traffic Channel (Full Rate)

TCH/H - Traffic Channel (Half Rate)BCH - Broadcast Channels

FCCH - Frequency Correction Channel

SCH - Synchronization Channel

BCCH - Broadcast Control Channel

CCCH - Common Control Channels

PCH - Paging Channel

AGCH - Access Grant Channel

RACH - Random Access Channel

DCCH - Dedicated Control Channels

SDCCH - Stand-alone DedicatedControl Channel

ACCH - Associated Control Channels

SACCH - Slow Associated Control

Channel

FACCH - Fast Associated Control

Channel

CCH - Control Channel

CBCH - Cell Broadcast Channel


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Traffic channel carries speech and user data in both directions

o Full rate ~ 33.85 Kb/sec

o Half rate ~ 16.93 Kb/sec

o Full rate uses 1 slot in every frame

o Half rate uses 1 slot in every other frame

Data rates differ due to differences in Error Control Coding

Traffic Channels (TCH)

Full Rate TCH can carry:

Voice (13 Kb/sec)

Date at rates:

-9.6 Kb/sec-4.8 Kb/sec

-2.4 Kb/sec

Half Rate TCH can carry:

Voice (6.5 Kb/sec)

Date at rates:

-4.8 Kb/sec-2.4 Kb/sec


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Control Channels

GSM Defines 3 types of Control Channels:1. Broadcast Channels (BCH)

Broadcast information that helps mobilesystem acquisition, frame synchronization,etc. They advertise properties andservices of the GSM network.

Forward link only

2. Common Control Channels (CCCH)

Facilitate establishment of the link betweenMS and system

Both forward and reverse link

3. Dedicated Control Channels (DCCH)

Provide for exchange the controlinformation when the call is in progress

Both forward and reverse in bandsignaling

CCH

BCH

CCCH

DCCH


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Broadcast Channels (BCH)

Three types of BCH:

1. Synchronization channel (SCH)

Provides a known sequence that helps mobilesynchronization

at the baseband

Communicates with S-burst

Broadcasts Base Station Identity Code (BSIC)

2. Frequency Correction channel (FCH)

Helps mobile tune its RF oscillator

Communicates with F-burst

3. Broadcast Control Channel (BCCH) Provides mobile with various information

about network, its services, accessparameters, neighbor list, etc.

BCH

SCH

FCH

BCCH


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Broadcast Channels (BCH) contd.

In general, the information sent over BCCH can be grouped into four categories:

1) Information about the network

2) Information describing control channel structure

3) Information defining the options available at the particular cell

4) Access parameters

Some BCCH messages


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Common Control Channel (CCCH)

Three types of CCCH:

1. Random Access Channel (RACH)

Used by mobile to initialize communication

Mobiles use slotted ALOHA

Reverse link only

2. Paging Channel (PCH)

Used by the system to inform the mobile

about an incoming call

Forward link only

GSM Supports DRX

3. Access Grant Channel (AGC)

Used to send the response to the mobiles

request for DCCH

Forward link only

CCCH

RACH

PCH

AGC


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Dedicated Control Channels (DCCH)

Three types of DCCH:

1. Stand Alone Dedicated Control Channel(SDCCH)

Used to exchange overhead informationwhen

the call is not in progress

2. Slow Associated Control Channel (SACCH)

Used to exchange time delay tolerantoverhead

information when the call is in progress

3. Fast Associated Control Channel (FACCH)

Used to exchange time critical information

when the call is in progress

DCCH

SDCCH

SACCH

FACCH


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Logical Channels - Summary

UL - Uplink DL - Downlink

Channel UL only DL only UL/DL Point topoint

Broadcast Dedicated Shared

BCCH X X X

FCCH X X X

SCH X X X

RACH X X X

PCH X X X

AGCH X X X

SDDCH X X X

SACCH X X X

FACCH X X X

TCH X X X


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Timing Advance

Mobiles randomlydistributed in space

Timing advanceprevents burst collisionon the reverse link

Maximum

advancement is 63bits

BTS

SLOT 0 SLOT 1 SLOT 2 SLOT 3 SLOT 4 SLOT 5

MS2

MS1

d2, Slot 2

d1, Slot 1

d1 > d2MS2

MS1

T1

T2

Collision

T1

- Delay of MS 1Signal

T2

- Delay of MS2

Signal

SLOT 7SLOT 6

km35bit

s10693.3bit63

s

m103

2

1max 68

D

Signal Processing


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Signal ProcessingFrom Voice to Radio Waves

Sampling,Quantization and

source encoding

ChannelEncoding

(Error Correction

Coding)

InterleavingBurst

Formating

Mapping

De-

Ciphering

Modulation

De-Modulation

Ciphering

Burst

Formating

Mapping

De

-Interleaving

Channel

Decoding

(Error Correction )

Source Decoding

and Waveform

Generation

Um

Interface

VoiceSignal

Voice

Signal

Transmit Side

Receive Side

As a digital TDMA technology GSM implements extensivesignal processing


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Sampling and Quantization

Sampling

o Sampling theoremspecifies conditions fordiscretization of bandlimited analog signals

o Voice needs to besampled at the samplingrate greater then

8000Hz

Quantization

o Discrete valuesassigned to continuoussamples

o Quantization noise

o In GSM, voice issampled at 8 Ksamples/sec andquantized with 8192levels (13 bit words)

111 +3V

110 +2V

101 +1V

0V

001 -1V

010 -2V

011 -3V

111 +3V

110 +2V

101 +1V

0V

001 -1V

010 -2V

011 -3V

Analog Signal

Sampling Pulse

PAM

101 110 101 100 010 010 010 100 111 111PCM


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Speech Source Encoding

Speech coder reduces the data rateneeded for voice signal representation

GSM specifies operation of:

o Full rate vocoder

13Kb/sec

o Half rate vocoder 5.6Kb/sec

o Enhanced Full Rate (EFR)

12.2Kb/sec

o AMR (Adaptive multi rate)

AMR-FR (4.75-12.2Kb/sec)

AMR-HR (4.75-7.95Kb/sec)

AMR rate - function of C/I

BPF A/Dconverter

SPEECH

ENCODER

CHANNEL

CODING

TO

MODULATOR

MICROPHONE

BAND-PASS

300 Hz-3.4 kHz

SPEECH

DECODER

CHANNEL

DECODERLP

LOW-PASS

4 kHz

D/Aconverter

Vocoders enable efficient channel

utilization

Performance comparison of some


39/71


Performance comparison of somecommercial vocoders

Mean Opinion Scores (MOS) - Voice Quality

source IIR. The First Annual CDMA Congress

London, Oct. 29-30, 1997

0

0.5

1

1.5

2

2.5

33.5

4

4.5

Clean Speech 20dB SNR

Babble

20dB SNR

Car

15dB SNR

Street

Mu-PCM

8Kb/s EVRC(CDMA)

13Kb/s CELP

(CDMA)

IS-136 ACELP

GSM EFR


40/71


Error control coding (ECC) increases the robustness of thesignal

ECC increases the overhead and reduces the efficiency of thecommunication

In GSM, the ECC increases the overhead per user by 57%

Channel Encoding

TYPE IaBITS

TYPE IIBITS

TYPE IbBITS

CONVOLUTIONAL

ENCODER

r=1/2

K=5

MUX

ERROR DETECTING CODE50

132

78

3

4

189

189

378

456

0TO

INTERLEAVER

FROM

VOCODER


41/71


Interleaving

In mobile

communications, the

errors are bursty

Optimal performance

from ECC is obtained for

uniform error

distribution

Interleaving increases

the performance of ECC

in mobile environment

252015105

24191494

23181383

22171272

21161161

bbbbb

bbbbb

bbbbb

bbbbb

bbbbb

Data is written

column-wise

Data is read

row-wise

Interleaver

b1

b2

b3

b4b

5b

6b

7b

8b

9b

10b

11b

12b

13b

14b

25b

16b

17b

18b

19b

20...

b1

b6

b11

b16

b21

b2

b7

b12

b17

b22

b3

b8

b13

b18

b23

b4

b9

b14

b19

b24

..

Burst Error

Caused by

Rayleigh Fading

Errors are spread over the bit stream


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Modulation: GMSK (Gaussian MSK)

GMSK has excellent spectralcharacteristics

o Low sidelobes

o Robust to non- linearities

Price paid is in the increasedInter Symbol Interference (ISI)

Simplified GMSK block diagram

MSK

Filtered MSKGMSK

(f-fo) / Rb0 1 2 3

-80

-60

-40

-20

0

POWER SPECTRALDENSITY

dBSpectral

characteristics

of GMSK


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Tail Traff ic /Si gnali ng Flag Tra in ing Sequence Flag Traffi c/Si gnali ng Tai l

3 57 1 26 1 57 3

Sequence used for equalizer training

Equalization

Necessary due to the multipathpropagation

Needs to have :

o Fast convergence

o Low complexity

Two modes of operation

1. Training

2. Equalization

GSM equalizer capable of equalizing fortwo equal multi paths separated by 16microseconds

Introduces overhead of about 18%

RF

Processing

Adaptive

Equalizer

Equalization

AlgorithmExtraction of

Synchronization

Bits

Unequalized

Data

Equalized

Data


44/71


GSM Network Features

Mobile Assist Handoff (MAHO)

Discontinuous Transmission (DTX)

Dynamic Power Control (DPC)

Frequency Hopping (FH)

Intercell Handoff


45/71


Mobile Assisted Handoff (MAHO)

GSM ImplementsMAHO

In the process ofevaluating handoffcandidates, GSMsystems evaluatemeasurementsperformed by both the

MS and BTS

There are three typesof measurements:

1. Signal StrengthMeasurements

2. Signal Quality

Measurements

3. Timing Advance

Measurements

Measurement

type

Link Cell DTX Measurement

Source

RSL Downlink Serving Cell Full Set Mobile

RSL Downlink Serving Cell Subset Mobile

RSL Downlink Neighbors N/A Mobile

Quality Downlink Serving Cell Full Set Mobile

Quality Downlink Serving Cell Subset Mobile

RSL Uplink Serving Cell Full Set BTS

RSL Uplink Serving Cell Subset BTS

RSL Uplink Neighbors Full Set BTS

RSL Uplink Neighbors Subset BTS

Quality Uplink Serving Cell Full Set BTS

Quality Uplink Serving Cell Subset BTS

Timing Advance Uplink Serving Cell N/A BTS

Measurement

type

Link Cell DTX Measurement

Source

RSL Downlink Serving Cell Full Set Mobile

RSL Downlink Serving Cell Subset Mobile

RSL Downlink Neighbors N/A Mobile

Quality Downlink Serving Cell Full Set Mobile

Quality Downlink Serving Cell Subset Mobile

RSL Uplink Serving Cell Full Set BTS

RSL Uplink Serving Cell Subset BTS

RSL Uplink Neighbors Full Set BTS

RSL Uplink Neighbors Subset BTS

Quality Uplink Serving Cell Full Set BTS

Quality Uplink Serving Cell Subset BTS

Timing Advance Uplink Serving Cell N/A BTS

Measurement

type

Measurement

type

LinkLink CellCell DTXDTX Measurement

Source

Measurement

Source

RSLRSL Downlink Downlink Serving CellServing Cell Full SetFull Set MobileMobile

RSLRSL Downlink Downlink Serving CellServing Cell SubsetSubset MobileMobile

RSLRSL Downlink Downlink NeighborsNeighbors N/AN/A MobileMobile

QualityQuality Downlink Downlink Serving CellServing Cell Full SetFull Set MobileMobile

QualityQuality Downlink Downlink Serving CellServing Cell SubsetSubset MobileMobile

RSLRSL Uplink Uplink Serving CellServing Cell Full SetFull Set BTSBTS

RSLRSL Uplink Uplink Serving CellServing Cell SubsetSubset BTSBTS

RSLRSL Uplink Uplink NeighborsNeighbors Full SetFull Set BTSBTS

RSLRSL UplinkUplink NeighborsNeighbors SubsetSubset BTSBTS

QualityQuality Uplink Uplink Serving CellServing Cell Full SetFull Set BTSBTS

QualityQuality Uplink Uplink Serving CellServing Cell SubsetSubset BTSBTS

Timing AdvanceTiming Advance UplinkUplink Serving CellServing Cell N/AN/A BTSBTS


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MAHO - Signal Strength Measurements

Performed on uplink and downlink

Reported as a quantized value RXLEV:

RXLEV = RSL[dBm] + 110

Minimum RXLEV:

-110, MAX RXLEV = -47

On the downlink, measurementperformed for both serving cell and up

to 32 neighbors

Up to 6 strongest neighbors are

reported back to BTS through SACHH

Example measurement report


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MAHO - Signal Strength Measurements

Measurements of theneighbors are performed onthe BCCH channels notaffected by the DTX

Measurements on the servingchannel affected by theDTX.

Perform over a subset ofSACCH that guaranteestransmission even in the caseof active DTX

Before processing, the RXLEVmeasurements are filtered to

prevent unnecessary handoffs

-100

-90

-80

-70

-60

-50

-40

0 500 1000 1500 2000

Measurement

RXLEV(dBm)

510

520

530

540

550

560

570

580

BCCHARFCN

RX LEV (dBm) BCCH

Example RSL measurement


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MAHO Signal Quality Measurements

Performed on uplink and downlink

Only on the serving channel Reported as a quantized value RXQUAL

For a good quality call RXQUAL < 3

Measurements are averaged before thehandoff processing

If DTX is active, the measurements areperformed over the subset of SACCH that

guarantees transmission

RXQUAL BER

0 Less than 0.1

1 0.26 to 0.30

2 0.51 to 0.64

3 1.0 to 1.3

4 1.9 to 2.7

5 3.8 to 5.4

6 7.6 to 11.0

7 Above 15

RXQUAL BER

0 Less than 0.1

1 0.26 to 0.30

2 0.51 to 0.64

3 1.0 to 1.3

4 1.9 to 2.7

5 3.8 to 5.4

6 7.6 to 11.0

7 Above 15

RXQUALRXQUAL BERBER

00 Less than 0.1Less than 0.1

11 0.26 to 0.300.26 to 0.30

22 0.51 to 0.640.51 to 0.64

33 1.0 to 1.31.0 to 1.3

44 1.9 to 2.71.9 to 2.7

55 3.8 to 5.43.8 to 5.4

66 7.6 to 11.07.6 to 11.0

77 Above 15Above 15

RXQUAL mapping table

RXQUAL

measurements

Measurement report


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Performed on uplink (BTS)

Only on the serving channel

Used by the BTS to estimatedistance to the MS

Expressed in number of bitsof TX advancement

Can be between 0 and 63

TA

MAHO Time Alignment Measurement


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Discontinuous Transmission (DTX)

Typical voice activity is around 60%

DTX discontinues transmission duringsilent periods

Benefits of DTX

o Uplink:

System interference reduction

Lower battery consumption

o Downlink

System interference reduction

Reduction of the intermodulationproducts

Lower power consumptions

Downsides of DTX usage:

o MAHO measurements are less accurate

o Voice quality is degraded due to

slowness of VAD

Mobile station Environment Typicalvoice

activityHandset Quiet location 55%

Handset Moderate office noisewith voice interference

60%

Handset Strong voiceinterference (ex. airport,

railway station)

65-70%

Hands free /handset

Variable vehicle noise 60%


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There are three reasons for DPC:

1. Reduction of battery consumption2. Elimination of near-far problem

3. Reduction of system interference

Power Class GSM (900MHz)

[W]

PCS-1900 / GSM1800

[W]

1 20(1) 1

2 8 0.24

3 5 Not Defined

4 2 Not Defined

5 0.8 Not Defined

Power Class GSM (900MHz)

[W]

PCS-1900 / GSM1800

[W]

1 20(1) 1

2 8 0.24

3 5 Not Defined

4 2 Not Defined

5 0.8 Not Defined

Power ClassPower Class GSM (900MHz)

[W]

GSM (900MHz)

[W]

PCS-1900 / GSM1800

[W]

PCS-1900 / GSM1800

[W]

11 20(1)20(1) 11

22 88 0.240.24

33 55 Not DefinedNot Defined

44 22 Not DefinedNot Defined

55 0.80.8 Not DefinedNot Defined

(1) Not available commercially


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DPC for MS

o Depending on its power class, MS can adjust its power between the max and min

value in 2dB steps

o MS can perform 13 adjustments every SACCH period, i.e., 480ms

o Large adjustments > 24 dB will not be completed before the arrival of new

command

o Commonly implemented as BSC feature. Many vendors are moving it at the BTS

level DPC for BTS

o Vendor specific

o Based on MAHO reports


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Hierarchical Cell Structure (HCS)

Incorporates various cell sizes into

layers of RF coverage

Three common layers:

1. Umbrella cells (HL = 0)

2. Macrocells (HL = 1)

3. Microcell (HL = 2)

HCS provides a way to assignpreference levels between the cells

Very effective way for capacity andinterference management

SignalStrength

ReselectionPoints

Select Micro-Cell

SS_SUFF

Macrocel

Preferred

Micro-Cell

Distance

HL = 1

HL = 2


54/71

ECE DepartmentFlorida Institute of Technology Page 54

Handling of Fast Moving Mobiles

If the mobile is moving at a high speed, it will

spend a short time in the coverage area of the

microcell

To prevent excessive handoffs, a temporal

GSM introduces temporal penalty preventsimmediate handoff initialization

If the duration of mobile stay within the

coverage area is shorter than the temporal

penalty, it will never initialize handoff

F H i (FH)


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Frequency Hopping (FH)

FH - multiple carriers used over the course of radio transmissiono There are two kinds of FH:

1. Slow Hopping change of carrier frequency happens at the rateslower than the symbol rate

2. Fast Hoping carrier frequency changes faster than the symbol

rate

o GSM implements slow FH Scheme

o Carrier frequency is changed once per time slot

o There are two reasons for frequency hopping

1. Frequency Diversity

2. Interference avoidance

F Di i f FH


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Frequency Diversity of FH

Mobile environment ischaracterized with smallscale fading

The depth of signal fadeis a function frequency

If two signals aresufficiently separated infrequency domain theyfade independently

Frequency diversity gaindiminishes for fast

moving mobiles

I f A id f FH


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Interference Avoidance of FH

FH averages interference

Allows for tighter reuse of frequencies

Increases the capacity of the system

User 1

User 2

User 3

User 4

User 5

f1

f4

f1

f1

f1

f1

f1

f2

f2

f2

f2

f3

f4

f1

f1

f2

f3

f3

f4

f1

f4

f3

f1

f3

f4

4TT 2T 3T 5T

4TT 2T 3T 5T

4TT 2T 3T 5T

4TT 2T 3T 5T

4TT 2T 3T 5T

B b d FH i GSM


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Baseband FH in GSM

Each radio operates on a

fixed frequency The bursts are routed to

individual radios inaccordance to their hoppingsequence

Advantages of baseband hopping

No need to real time retune simpler

radios

More efficient combiners

Disadvantage of baseband hopping

Number of hopping frequencies limited

by the number of radios

TX/RX

TX/RX

TX/RX

Carrier

Freuqnacy

f1

CombinerCarrier

Freuqnacy

f2

Carrier

Freuqnacy

fn

1

2

n

Bus for Routingand Switchning

S th i d FH i GSM


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Synthesized FH in GSM

Each radio is hopping in anindependent way

Radios retunereal time

Advantages of synthesized hopping:

Set of the hopping frequencies can be assigned in

an arbitrary way

Disadvantage of synthesized hopping:

Need for expensive and lossy combiners

TX/RX

TX/RX

TX/RX

Carrier

Freuqnacyf0,f

1,...,f

m

Broadband

Combiner

1

2

n

CarrierFreuqnacyf0,f

1,...,f

m

CarrierFreuqnacy

f0,f

1,...,f

m

FH Al ith


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FH Algorithms

Random Hopping

Implemented in a pseudo random way

Uses one of 63 available pseudorandom sequences

The actual frequency is obtained as a modulo operation withnumber of available frequencies in allocation list (FH group)

,,,,,,, 3214321 fffffff

,,,,,,, 3234421 fffffff

Cyclic Hoppingo Frequencies are used in the consecutive order

o If the radio is performing cyclic FH the order of frequencies in thesequence goes from the lowest ARFCN to the highest ARFCN

I t ll H d ff


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Intracell Handoff

High Interference

Measurement indicates:

o Poor RXQUAL

o Good RXLEV

There is high probability that the call will improve with the handoff to

different carrier within the same cell

To avoid unnecessary handoffs, system introduces maximum number

of intercell handoffs

GSM RF Pl i / D i


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GSM RF Planning / Design

Link Budget and Nominal Cell Radius Calculation

Receiver Sensitivity

Required C/I ratio

Mobile Transmit Power

Examples of Link Budget

Calculation of a Nominal Cell Radius

Frequency Planning and Reuse Strategies

Frequency Planning Using Regular Schemes

Automatic Frequency Planning

Capacity of GSM Networks

GSM Mi ti T d 3G


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Migration:

1. High speed circuits

switched data

(HSCSD)

2. Packet switched data

(GPRS,EDGE)

3. Integrated packet

services possibly

under different access

scheme (UMTS)

GSM Migration Towards 3G

GSM 2+

9.6 Kb/sec

HSCSD

64 Kb/sec

GPRS

114 Kb/sec

EDGE

384 Kb/sec

UMTS

2Mb/sec

1999 1Q2000

2Q2000

3Q2001

4Q2002

Timeline

Data Rate

HSCSD - High Speed Circuit Switched Data

GPRS - General Packet Radio System

EDGE - Enhanced Data GSM Environment

UMTS - Universal Mobile Telephone Service

GSM 2 Data Services


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GSM 2+ Data Services

GSMs traffic channel can support the data transfer of a bit rate up to9.6Kb/sec

o This data rate can be used for:

Short messages

Fax services

E-mail, etc.

o Circuit switched data services

o Not suitable for Internet

Too slow

Too costly (user would pay for the circuit even if there is notraffic exchanged

High Speed Circuit Switched Data (HSCSD)


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High Speed Circuit Switched Data (HSCSD)

HSCSD is using existing GSM organization to provide dataservices of a somewhat higher data rates

It can combine several existing traffic channels into a singleconnection, i.e., it allows for mobiles multislot operation

HSCSD can be implemented through software upgrades onexisting networks and no hardware upgrades are needed

Seems to be less accepted by the service providers

General Packed Radio Data (GPRS)


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GPRS is another new transmission capability for GSM that will be especiallydeveloped to accommodate for high-bandwidth data traffic

GPRS will handle rates from 14.4Kbps using just one TDMA slot, and up to

115Kbps and higher using all eight time slots

It introduces packet switching - can accommodate the data traffic

characteristics

General Packed Radio Data (GPRS)

GPRS Network architecture


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GPRS Network architecture

New type ofnode:

GPRS ServiceNode (GSN)

BSC

BSC

MSC

VLR

HLR

AUC

EIR

BTS

BTS

BTS

BTS

BTS - Base Station

BSC - Base Station Contoller

MSC - Mobile Switching Center

VLR - Visitor Location Register

HLR - Home Location Register

AUC - Authentification Center

EIR - Equipment Identity Register

Um

Interface

A-Bis

Interface

A

Interface

D

C

PSTN

B

B,C,D,E,F - MAP

Interfaces

SGSN

GGSN

SGSN - Service GPRS Support Node

GGSN - Gateway GPRS Support Node

Gn

Interface

Gr

Outside

Packet

Network

GPRS Call routing


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GPRS Call routing

SGSN

GGSN

GGSN

SGSN

BTS

BTS

GPRS - PDN

GPRS - PDN

Routing is performed parallel to the GSM network

Enhanced Data GSM Environment (EDGE)


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Packet switched

Upgrades the modulation schemeo From GMSK to 8-PSK

o Maximum speed ~59 Kb/sec per time slot, ~473.6 Kb/sec for all 8 time slots

o Variable data rate depending on the channel conditions

Defines several different classes of service and mobile terminals

Enhanced Data GSM Environment (EDGE)

EDGE enabled data mobile

Practically achievable data rates


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Theoretical rates are constrained by mobilepower and processing capabilities

Most mobiles support less than the maximumallowed by standard


Universal Mobile Telephone Service (UMTS)


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UMTS 3G cellular service

Provides data rates up to 2Mb/sec

Possibly standardized as W-CDMA

Universal Mobile Telephone Service (UMTS)

Outline of UMTS(WCDMA) network

Documents

Intro to GSM - Slides (Rev 1).pptx