1.3.1 GSM

NTUEE Mobile Communications KC Chen 1

GSM, GPRS, and EDGE

Prof. Kwang-Cheng ChenInstitute of Communications Engineering

National Taiwan UniversityFAX: (02) 2368 3824

email: [email protected]

mailto:[email protected]


Outlinesq Introductory System Constructionq GSM Architecture and Principlesq Physical Layerq Data Link Layerq Network Layerq Testing


GSM Phase 1 Services

TelephonyEmergency callsShort-message: point-to-

point and cell broadcastTelefaxAsynchronous dataSynchronous dataAsynchronous PAD

access (packet switched)Alternate speech/dataCall forwardingCall barring

Teleservices

Bearerservices

Supplement-ary services

Full-rate 13 kbps

Alphanumericalinformation

Group 3300-9.6 kbps

Category Services Comments


GSM Phase 2 Services

TelephonyShort-message servicesSynchronous dedicated

packet data accessCalling/connected line

identity presentationCalling/connection line

identity restrictionCall waitingCall holdMultiparty comm.Closed user groupAdvice of chargeOperator barring

Teleservices

Bearerservices

Supplement-ary services

Half-rate 6.5 kbps

2.4-9.6 kbps

Conference call

On-line information

Category Services Comments


GSMp GSM stands for Global System for Mobile.p GSM (group special mobile) was first

developed by the CEPT.p GSM services follow ISDN and are classified

as teleservices and data services.p Subscriber Identity Module (SIM) is a memory

device storing ID, networks or countries for services, privacy keys, etc.


Further Standardization (I)p New bearer services and data-related

improvementsüHSCSD (high-speed circuit-switched data)ü14.4 kbps (single-slot) dataüGPRS (general packet radio service)üEDGE (enhanced data rates for global evolution)

p Speech-relatedüEFR (enhanced full-rate) speech codecüAMR (adaptive multi-rate) codecüTFO (tandem free operation)


Further Standardization (II)p Mobile station (MS) positioning relatedüCell identityüUplink time of arrival (TOA) and enhanced

observed time difference (E-OTD)üGPS and A-GPS

p Frequency band-relatedüGSM-400/700/850

p Supplementary, billing, relatedp Service platformsüSIM application toolkitüCustomized applications for mobile network

enhanced logic (CAMEL)


GSM System Architecture

BTS

BTSBSC

BTS

BTSBSC

HLR VLR AUC

MSC

OMC

PSTNISDNDatanet.

Base StationSubsystem Network Switching Subsystem

SS7A

Abis

Air


Registrationp When a mobile station is on, a scanning

algorithm scans the whole GSM frequency band.

p If a network is detected, mobile station reads system information from (forward) base channel.

p If current location is not the same as it was when the mobile station off, registration procedure starts.


MS BTS BSC (G)MSC VLR HLR Actionchannel requestchannel activationactivation knowledgechannel assignmentlocation updateauthetication requestauthetication responsecomparison of authet.assignment of new

area and TMSIack. of area and TMSIentry area & ID into

VLR & HLRchannel release

Registration in Network


MS BTS Actionchannel requestchannel assignmentcall establishment requestauthentication requestauthentication responseciphering commandciphering complete and in functionsetup messagecall proceedingassignment of a traffic channelassignment complete & all messages on channelalerting (ringing)connect (call party accepted the call)connect ack. (two-way call)speech data

MobileOriginatedCall Establishment


MS BTS Actionpaging mobile stationchannel requestchannel assignmentanswer to paging & on the assigned channelauthentication requestauthentication responserequest to transmit in the ciphered modeack. of ciphered modesetup msg. for the incoming callconfirmationassignment of a traffic channelack. of traffic channelalerting (caller getting ringing sound)connect when mobile off-hookacceptance of connected msg.exchange of speech data

MobileTerminated CallEstablishment


Handoff in Analog Systemsp Base station monitors the quality of link

between a mobile station and itself. If the quality degraded, it requests adjancent cells to report power level for the mobile. Network decides the frequency to use in the new cell and eventually command change.

p Mobile station is passive and cell sites are equipped with measuring receiver.


Handover in GSM

p The mobile station monitors the perceived power levels of neighboring cells that are provided by the base station. Measurement report is periodically sent back to the base station that might conduct measurements too. In case necessity of a handover, it can be performed without delay.

p GSM distinguished different types of handovers.


Types of GSM Handover

p In case a handover is performed within the area of a BSC, BSC handles this simple handover and MSC is just informed.

p In case a mobile crossing boundary of a BSC, MSC has to control the handover.

p For a handover between 2 MSCs, the first MSC still has to maintain control of call managment, though 2nd MSC will handle evantually.


GSM Authentication

authenticationalgorithm

Mobile StationUm

Interface Network

= ?SRES

KEY (in SIM) RAND (generatedrandom number)

(SRES)

A set of (RAND,SRES) are stored in the HLR & VLR for theuse of authentication center.


Cipheringp The ciphering algorithms are usually based

on certain one-way function.p If a ciphering algorithm A5 is used to encipher

a data stream in GSM system, the same algorithm is used to decipher.

p In current system, only A5/1 algorithm is used. But for non-COCOM countries, a simpler A5/2 is used. Both algorithms can coexist in western European countries.


Dynamic CipheringMS Um Network

Kc

Ki RAND

A8

A5 A5

CipheringCommand

DATA DATACipheredData


Temporary Mobile Subscriber Identity (TMSI)

p To prevent an intruder from identifying a GSM user IMSI, TMSI is assigned to each subscriber using the network during the location updating and is used for reporting, calling, paging as long as remaining activities.

p The assignment, administration, updating of TMSI is performed by the VLR. When MS off, it is stored on the SIM card.


Handset HW

BasebandProcessor

RF PA

Antenna

MultimediaCo-Processor

Memory

Power/Battery ManagementIrDA

BluetoothWLANWiMAXUWBFM

DVB/DAB-TDVB-HDSC

SD/MSMP3

MPEG, H.264LCD Driver

LCD Controller

SIM


Handset SW

BasebandProcessor

RF PA

Antenna

MultimediaCo-Processor

Memory

Power/Battery Management IrDABluetooth

WLANWiMAXUWBFM

DVB/DAB-TDVB-HDSC

SD/MSMP3

LCD DriverLCD Controller

SIMLayer 1/2/3

MMI, drivers,Middleware,

Appl. SW


Physical Layer- Layer 1


GSM Frame Structure...Superframe

6.12 sec51 Multiframe

... 26 Frames120 msec

8 Time Slots4.615 msec 0 7

0.57692 msec156.25 bits

Tail Bit

3 57 1 1 326 57 8.25

Stealing Flag Guard Period

Coded Data Midamble


GSM Radio Subsystem

p GSM uses a combination of TDMA and FHMA, and FDD.

p 200 kHz wide channels called ARFCNs (absolute radio frequency channel numbers)

p Each ARFCN pair is separated by exactly 45 MHz with 3 time slots spacing.

p channel data rate 270.833 kbps using BT=0.3 GMSK.


GSM Traffic CHannels (TCH)

p full rate speech at 13 kbps with channel coding added to 22.8 kbps

p full rate data for 9600/4800/2400 bps. With FEC, data is sent at 22.8 kbps.

p half-rate speech at 6.5 kbps and can carry up to 11.4 kbps

p half-rate data at 4800/2400 bps.


GSM Control Channels (CCH)

p Broadcast Channels (BCH): broadcast control channel (BCCH), frequency correction channel (FCCH), synchronization channel (SCH).

p Common Control Channels (CCCH): paging channel (PCH), random access channel (RACH), access grant channel (AGCH).


CCHp Dedicated Control Channel (DCCH):

stand-alone dedicated control channel (SDCCH), slow associated control channel (SACCH),

p fast associated control channel (FACCH).

p bidirectional with the same format and function on both forward and reverse links.


Frequencies: Primary GSM

p Mobile station transmits in 890-915 MHz. Base station transmits in 935-960 MHz. 125 channels are numbered from 0 to 124.

p Within the system, only the absolute radio frequency channel number (ARFCN) is used (from 1 to 124).

p Channel 0 is used as the guard band for GSM and other applications.


Frequencies: E-GSM

p Additional 10 MHz bandwidth has been added to the bottom end of the duplex bands.

p It results in 50 more channels with numbers from 974 to 1023.

p Channel number 0 is returned for use in extended GSM and channel 974 serves as the guard band.


DCS-1800 or PCNp Same signaling and messaging

techniques as GSM.üAlso known as GSM-1800

p 1710-1785 MHz for uplink and 1805-1880 MHz for downlink. Duplex spacing is 95 MHz with 374 channels.

p Channel numbers are 512 to 885.


PCS-1900/DCS-1900p Same DCS-1800 system for North

America PCS.üAlso known as GSM-1900

p Lower frequency starts from 1850 MHz with 80 MHz duplex spacing.

p Channel numbers range from 512 to 810.


Power Levels in GSMPowerClass

Max. Power of aMobile Station (dBm)

Max. Power of aBase Station (dBm)

1 20W(43) 320W(55)2 8W(39) 160W(52)3 5W(37) 80W(49)4 2W(33) 40W(46)5 0.8W(29) 20W(43)6 10W(40)7 5W(37)8 2.5W(34)


Power Levels in DCS-1800 and Phase II GSM

PowerClass

Max. Power of DCS-1800MS (dBm)

Max. Powerof DCS-1900MS (dBm)

Max. Powerof DCS-1800BTS (dBm)

Max. Powerof DCS-1900BTS (dBm)

1 1W(30) 1W(30) 20W(43) 20-40W2 0.25W(24) 0.25W(24) 10W(40) 10-20W3 2W(33) 5W(37) 5-10W4 2.5W(34) 2.5-5W


Macro-cell and Micro-cellbad coverage

hot spot


Power Levels for Micro-BTS

PowerClass

Max. Powerof GSMMicro-BTS

Max. Powerof DCS-1800Micro-BTS

Max. Powerof PCS-1900Micro-BTS

M1 0.25W 1.6W 0.5-1.6WM2 0.08W 0.5W 0.16-0.5WM3 0.03W 0.16W 0.05-0.16W


Pulse Power Profile

147 bits0.5428 msec

dB+4+1-1-6

-30

-70

10us10us8us


Time Division Duplex (TDD)in GSM

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

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

BTS transmits

MS transmtsTDMA Frame 4.615msaround 216.6 Hz effect


TDDp no need for a dedicated duplex stage

(duplexer); only requiring fast-switching synthesizer, RF filter paths, fast antenna switching

p increased battery life or lighter batteryp better quality and lower cost


Normal Burst

T3

Coded Data57

S1

TrainingSequence 26

S1

Coded Data57

T3

GP8.25

148 bits = 0.54612 msec


Tail Bits (T)p used as guard time to cover the

uncertainty during power ramping up and ramping down.

p The tail bits are always set to be zero, while the demodulation process requires initial zero bits.


Stealing Flag (S)p These two bits are an indication to the

receiver whether the incoming burst is carrying signaling data (to maintain the link) or user data (traffic).

p Indicating flag is needed since signaling data are very important and go to different places.


Training Sequencep Let radios synchronize their receivers

with burst, e.g. equalizer for multipath fading.

p 8 sequences are defined in GSM. All radios in a particular cell share the same training sequence.

p An equalizer in GSM can compensate up to 16 micro-sec path delay.


Guard Period (GP)p No data is transmitted and is just

considered as guard time, to avoid possible overlap of radiation power of two bursts.


Random Access Burst

T8

T3

SynchronizationSequence 41

Coded Data36

Guard Period68.25

88 bits = 0.32472 msec

68.25 bits = 0.252 msec which is equivalent to 75.5 kmpropagation delay.

That is, the max. allowed distance between mobile stationand BTS is 37.75 km. Based on other system parameters,the max. cell size is 35 km in GSM.


Frequency-Correction Burst

T3

T3

GP8.25

fixed bit sequence142

148 bits = 0.54612 ms

An all zeros sequence can meet the purpose of frequencycorrection due to the nature of GMSK.


Synchroniation BurstT3

T3

Coded Data39

Coded Data39

SynchronizationSeq. 64

GP8.25

148 bitsAt beginning of mobile communicating to network, it only detectsthe frequency of base channel and needs to know the training seq.and system parameters. This is done by the synchronization burst.In this kind of burst, in addition to a longer synchronization seq.,coded data contains the BSIC (base station information code)including BCC (BS color code) and NCC (national color code),and shortened TDMA frame number.


Logical Channelsp A logical channel carries signaling data or

user data. It can be mapped into any physical channel (frequency and time slot).

p Once a physical channel is assigned to carry the content of a logical channel, the assignment shall not change.

p 7 combinations of logical channels.p GSM distinguishes between traffic channels

and control channels.


Traffic Channels

p TCH/FS (traffic channel/full-rate speech): 13 kbps net speech rate.

p TCH/HS (traffic channel/half-rate speech): future application without speech quality degradation.

p TCH/F9.6/4.8/2.4: data transmission at rates of 9.6/4.8/2.4 kbps.

p TCH/H4.8/2.4:


Control Channelsp braodcast channelsp common control channelsp dedicated control channelsp associated control channels


Broadcast Channels (BCH)

BCHs are only transmitted by the base station and provide information for MSs to synchronize with the network. Three types of BCH:

p broadcast control channel (BCCH)p frequency-correction channel (FCCH)p synchronization channel (SCH)


Common Control Channels (CCCH)

p CCCH support the establishment of a dedicated link between a mobile and a BTS. CCCH provides tools for call setups and can originate from the network or mobiles.

p Three types of CCCH.


Common Control Channels (CCCH): continued

p random access channel (RACH): to request a dedicated channel and only used by mobiles.

p paging channel (PCH): BTS calls individual MSs within its cell.

p access grant channel (AGCH): where MS gets information from BTS on which dedicated channel for its immediate needs.


Dedicated Control Channels (DCCH)

used for message transfers between network and MS, not for traffic, and also used for low-level signaling messages among radios.

p standalone dedicated control channel (SDCCH)

p slow associated control channel (SACCH): carrying control and measurement parameters/routine data to maintain a link.


Fast Associated Control Channel (FACCH)

p In downlink, a BTS transmits a reduced set of system parameters to keep mobile up to date on the latest changes in the system. In uplink, MS reports the measurement results.

p FACCH can carry the same information as SDCCH but FACCH replaces all/part of a traffic channel.


Logical Channels and Directions

Logical Channel MS BTSTCH <----->FACCH <----->BCCH <-----FCCH <-----SCH <-----RACH ----->PCH <-----AGCH <-----SDCCH <----->SACCH <----->


Channel Combinations1. TCH/FS+FACCH/FS+SACCH/FS2. TCH/HS(0,1)+FACCH/HS(0,1)

+SACCH/HS(0,1)3. TCH/HS(0)+FACCH/HS(0)+SACCH/HS(0)

+TCH/HS(1)+FACCH/HS(1)+SACCH/HS(1)4. FCCH+SCH+CCCH+BCCH5. FCCH+SCH+CCCH+BCCH+SDCCH/4

+SACCH/46. CCCH+BCCH7. SDCCH/8+SACCH/8


Multiframe Structurep Each channel combination requires one

single physical channel. Multiframe structure made of a fied number of TDMA fames allows logial channels to be ordered into time slots.

p 26-multiframe structure is used for the traffic channel combinations and 51-multiframe structure is used for signaling combinations.


Traffic Channel Frame Structure (26-Multiframe)

p For combination I (TCH/FS), the first 12 fames for traffic data (speech & data), 13rd frame for SACCH, another 12 frames for traffic, and the last frame idle for MS to measure etc.

p 120 ms totally.


Traffic Channel Frame Structure

(26-Multiframe): continuedp For combination II or III (TCH/HS), 2 half-rate

speech channels are packed onto one 26-multiframe structure. One logical channel uses every other TDMA frame. Frame 13 for SACCH1 and 26 for SACCH2.

p Combination II for one half-rate channel and III for two half-rate channels.

p FACCH may take a position of traffic channel if necessary.


Signaling Frame Structure(51 Multiframe)

p NOT carrying any user data.p more complex as incorporating 4

different channel combinations and structures.


Combination IV (downlink):FCCH+SCH+CCCH+BCCCH

F0

S1

BCCH2-5

CCCH6-9

CCCH12-19

CCCH22-29

CCCH32-39

CCCH42-49

I50

FCCH

SCH

idle

CCCH includes PCH and AGCH

235.38 ms


Combination IV (uplink):

R0

R1

BCCH2-5

CCCH6-9

CCCH12-19

CCCH22-29

CCCH32-39

CCCH42-49

R50RACH

• This combination is normally used for cells with severalcarriers and a large amount of traffic on CCCH.

• It can be transmitted on any frequency available in timeslot 0. The frequency here is a reference for neighboringcells.


Combinations V VI VIIp Combination V is the minimum for smaller

cells with only one or two transceivers. It may assign up to 4 DCCHs.

p Combination VI is similar to IV but without FCCHs and SCHs for cases with a huge number of transceivers.

p Combination VII is to provide routine signaling. 8 DCCHs may be used to servce 8 parallel signaling links on one physical channel.


Cell Broadcast Channel (CBCH)

p CBCH supports a part of the group of short message services (point-to-omnipoint). An operator is thus able to transmit messages to its subscribers.

p CBCH is always mapped on the 2nd subslot of SDCCH independently for channel combination V and VII.

p CBCH only in downlink and no ack.


Block and Convolutional Coding of Full-Rate Speech

Class Ia50 bits

Class Ib132 bits

Class II78 bits

block codingof clas Ia bits

with3 CRC bits adding 4 bits

of zeros toreset codec

378 coded bits 78 bits

convolutional code r=1/2 K=5


Coding for 9.6 kbps Data Transmission

p 9.6 kbps coding in terminal equipment => 240 bits a frame (at 12 kbps)

p By adding 0000, 244 bits.p By r=1/2 K=5 convolutional code, 488

coded bits.p Puncturing 32 coded bits, 456 coded

bits.


Coding for 2.4 kbps Datap 2.4 kbps at terminal equipment => 72

bits (at 3.6 kbps)p By adding 0000, 76 bitsp By r=1/6 K=5 convolutional code, 456

coded bits.


Coding for Signaling Channel

signaling information184 bits

parity40 bits

0000

Fire Code

convolutional code r=1/2 K=5

456 coded bits


Speech Coding for Mobile Communications


Speech Coders

Waveform Coders Source Coders

Time Domain Frequency Domain

Nondifferential Differential

LPC

VocodersSBC

ATCPCMDELTA

CVSDM

ADPCM

APC


ADPCM for CT-2

+4-bit adaptivequantizer

adaptive scalingfactor generator

inverse adaptivequantizer

adaptivepredictor

+

-

inputanalogwaveform

output


Channel Vocoder: Speech Generation Model

Anaylzer Transmission

NoiseSource

PulseSource

VocalTractFilter

secondary source

speechoutput

speech


Linear Predictive Coders (LPC)

The LPC system models the vocal tract as an all-pole linearfilter with transfer function

H z G b zkk

Mk( ) / ( )= +

=

−∑11


LPC Coding System

Buffer

LPCFilter

Voiced/UnvoicedDecision

PitchAnalysis

Encoder

Encoder

Encoder

CHANNEL

Decoder

Decoder

Decoder

SYNTHESIZER

Excitation


Code-Excited LPC (CELP)p Coder and decoder have a predetermined

code book of stochastic (zero-meam white Gaussian) excitation signals.

p Transmitter searches its codebook for best perceptual match and the corresponding index is transmitted.

p The receiver uses the index for synthesizer.p CELP coders are extremely complicated.


GSM cellular RPE-LTP 13CD-900 cellular SBC 16IS-54 cellular VSELP 8IS-95 cellular CELP 8IS-95 PCS PCS CELP 14.4PDC cellular VSELP 4.5/6.7/11.2CT-2 cordless ADPCM 32DECT cordless ADPCM 32PHS cordless/PCSADPCM 32DCS-1800 PCS RPE-LTP 13PACS PCS ADPCM 32

Standards Service Speech Coder Bit Rate (kbps)

Speech Coders Used in Various Mobile Radio Systems


GSM Codecp regular pulse excited long term

prediction (RPE-LTP)p combination of RELP (France) and

MPE-LTP (Germany)p 13 kbpsp complicated and power hungry


GSM Speech EncoderHammingWindow

Segmentation

Pre-emphasis

LPCInverseFilter

STPAnalysisFilter

+ LPFGridSelection M

UX

LTPAnalysisFilter

Pre-processing STP LTP RPE


GSM Speech Decoder

DEMUX

GridPosition/RPEDecoding

LTPSynthesisFilter

STPSynthesisFilter

Post-Processing

output


Transmissionp Speech coder issues 260 bits every 20 msec.p 50 bits out of 260 bits describe filter coef.,

block amplitude, LTP parameters and are class Ia under channel coding protection.

p 132 bits describe RPE pointers, RPE pulses, some LTP parameters and are class Ib.

p 78 bits contain RPE pulse and filter parameters and are class II.


Discontinuous Transmission (DTX)

p When a pause is detected by speech transcoder, we discontinue/suspend radio tx. for the duration of pause, 50% duty cycle.

p Voice activitiy detection (VAD) determines the presence/absence of speech, even under strong background noise.

p Every 480 ms, a silence descriptor (SID) frame is transmitted to yield presence.


Adaptive Multi-rate Codec (AMR)p 1999, ETSI approved AMR codec by

Ericsson, Nokia, Siemens.ü3GPP adopted AMR laterüAMR contains a set of fixed-rate speech, channel

codecs, fast in-band signaling, link adaptation.• Operating at full-rate (22.8K bps) and half-rate (11.4K

bps)• Ability to adapt to radio channel and traffic load

conditions, to select optimal channel mode (HR/FR) and codec mode

• Tradeoff between speech and channel coding to deliver best possible combination of speech quality and system capacity


AMR Speech & Channel Codingp AMR (and EFR) utilizes algebraic code

excitation linear prediction (ACELP)p A combination of 8 speech codecsü12.2, 10.2, 7.95, 7.4, 6.7, 5.9, 5.15, 4.75 kbps

• All for full-rate codec• Lower 6 rates for half-rate codec

üAMR NB (narrow band) with GMSK in rel’98üError correction is based on recursive systematic

convolutional (RSC) coding with puncturingü6-bit CRC is used for detecting bad frames


AMR In-band Signaling & Link Adaptationp Both MS and BS perform channel quality

measurementüCodec mode command (up link) or codec mode

request (down link) is sent over radio interface in in-band messages

p The receiving end uses information to select the best codec mode for prevailing channel conditionüCodec mode indicator is sent over radioüCodec mode might be different in up/down links

but the channel mode (FR/HR) must be the sameüNetwork controls codec/channel mode, and MS

followsüAMR contains voice activity detection (VAD) and

DTX


Link adaptation

Speechin

Speechout

Multi-rate

SpeechEncoder

Multi-rate

ChannelEncoder

Multi-rate

SpeechDecoder

Multi-rate

ChannelDecoder

MIu

SMIu

SMRd

ModeRequest

Generator

DownlinkQualityMeas.

MCu

SMIu

MCu

Link

ada

ptat

ion

QIu

MRd

Mobile station (MS)

Radio Channel(uplink)

Radio Channel

(downlink)

MIu

SMRd

Multi-rate

ChannelDecoder

MIu

S

MRd

Downlinkmode

control

Uplinkmode

control

Multi-rate

ChannelEncoder

MCu

SMId

SMId

MCu

QIu

UplinkQualityMeas.

MCd

Abis/ter

Abis/ter

MIu

S

Multi-rate

speechdecoder

Multi-rate

speechencoder

SMId

MCd

Speechout

Speechin

Base transceiver station (MS) Transcoder (TC)

S- Speech QI- quality indicator MC- codec mode command (inband signaling)MR- codec mode request (inband signaling)MI- codec mode indicator (inband signaling)

U=UplinkD=Downlink

AMR Codec System


Bit Allocation of AMR Codec(Kbps) LPC LTP FCB Gains Total12.2 38 30 140 36 24410.2 26 26 124 28 2047.95 27 28 68 36 1597.4 26 26 68 28 1486.7 26 24 56 28 1345.9 26 24 44 24 1185.15 23 20 36 24 1034.75 23 20 36 16 951.75 29 0 0 6 35

FCB: fixed codebook ACB: adaptive codebook


Data Link Layer - Layer 2


Layer 2 GSM Signalingp Protocol used for signaling transfer

between a MS and a BTS is link access procedure for the Dm-channel (LAPDm).

p It is adapted from link access protocol data (LAPD) in ISDN networks.

p LAPD is used in GSM on Abis interface between BTS and BSC.


Principle of Link Controlp Similar to ARQüStop-and-wait

• Transmitter waits until acknowledgement• Low efficiency

üSelective• Resend only those with errors• Memory size

üGo-back-N• Transmitting N packets then waiting for

acknowledgement• Widely used in link control protocols


Tasks of Data Link LayerThe data link layer is responsible for the correct and completetransfer of information blocks between layer 3 entities over GSMair interface. The protocol have the following functions:

• organization of layer 3 information into frames• peer-to-peer transmission of signaling data in defined formats• recognition of frame formats• establishment, maintainance/supervision, termination of one or

parallel data links on signaling channels• acknowledgement of transmission and reception of numbered

information frames (I-frames)• unacknowledged transmission and reception of unnumbered

infromation frames (UI-frames)


Frame Format A

addressfield

controlfield

length indicatorfield

fill bits

1 octet

variable length


Frame Format B

addressfield

controlfield

length indicatorfield

information field& fill bits

1 octet

variable length


Frame Formats A & Bp Frame format A is used when no signaling but

wanting to keep the signaling channel.p When signaling is ready for transmission,

frame format B is used, which contains an information field. Such a frame is called an I-frame.

p When numbered I-frames are transmitted, it is referred as the acknowledged mode and the procedure called multi-frame operation.


Frame Formats Abis and Bbis

Abis Length IndicatorField

Fill Bits

Length IndicatorField

Information Field& Fill Bits

Bbis

Formats Abis and Bbis are equivalent to formats A and Bbut they are only used in the unacknowledged mode ofsignaling data transfer.


Address Fieldp In GSM control channels, the address field is

fixed at one octet.p It is primarily used to addressed the service

access point (SAP), a defined interaface which provides services to a layer 3 entity.

p GSM provides two SAPs on radio interface: for signaling and for short message.


Address Field: continued

8 7 6 5 4 3 2 1

X LPD SAPI C/RE/A

LPD=00 for link protocol discriminatorSAPI=000 for layer 3 signaling

011 for short messagesC/R=0 for mobile sending a command

1 for mobile sending a responseE/A=0 for next octet is a part of address E/A=1 for GSM control channels


Control FieldIt consists of only one octet and is only in frame formats A & B. 3 types:

p I-frame: numbered and carrying numbered layer 3 information

p S-frame: control functions like I-frame ack., requests for repartitions, intermittent suspension of numbered information transfers.

p U-frame: unnumbered type frames offering additional data link functions.


Control Field: continued8 7 6 5 4 3 2 1

8 7 6 5 4 3 2 1

8 7 6 5 4 3 2 1

N(R) P N(S) 0

N(R) P/F

P/FU U U U U 1 1

1S S 0

I-frame

S-frame

U-frame


I-frame: This type of frames are numbered and carrynumbered Layer 3 information.

S-frame: Supervisor frames are control function like(a) I-frame ack. with fill frame (Format A)(b) request for repetitors(c) intermittent suspension of numbered informationtransfers

U-frame: The unnumbered frames offer additional datalink functions for Layer 2 and allow for the transfer of unnumbered and unack. information frames on controlchannels.


Control Field Parametersp N(S) Transmitter Send Sequence

Number: modulo-8 counterp N(R) Transmitter Receive Sequence

Number: also a modulo-8 counterp Poll/Final Bit: Poll bit is set when a

response is requested; final bit is set when a response to a command is sent back.


Control Field Parameters: Supervisor and Unnumbered

Bitsp Receive Ready RR frame, SS=00, has 3

functions: a data link entity is ready to receive an I frame; ack. reception up to N(R)-1 frames; reset Layer 2 in case not ready

p Receive Not Ready, RNR frame, SS=01: can not receive I-frame

p Reject, REJ frame, SS=10: reception of one or more frames is required.


Control Field: U Framep SABM Command, UUUUU=00111: Set

asynchronous balanced mode starts the modulo-8-counted I-frame transmissions.

p DISC Command, UUUUU=01000: Disconnect ends a multi-frame operation session.

p UA Response, UUUUU=01100: Unnumbered ack. is set to ack. an SABM or DISC.

p UI Command, UUUUU=00000: transmission of unnumbered information within the frame.

p DM Response, UUUUU=00011: sent from a data link layer entity when multiframe operation is not allowed.


Length Indicator Field

8 7 6 5 4 3 2 1L M EL

One octet is sufficient for GSM signaling.

L stands for the length of Information Fieldin the remainder of the frame.M=0 either an entire layer 3 message included

or the last part of segmented messageM=1 another part of message followingEL=1 the last octet in the length indicator fieldEL=0 not the last octet


Network Layer - Layer 3


Layer 3p The network layer of GSM, also referred

as signaling layer, uses a protocol to establish, maintain, terminate mobile connections.

p Three sublayer defined for Layer 3 (network layer): radio resource management (RR), mobility management (MM), connection management (CM).


RR Sublayerp responsible for management of

frequency spectrum, system reaction to radio environment changes, maintaining of a clear channel between PLMN and MS.

p including channel assignment, power control, time alignment, handover, etc.


RR Sublayer Proceduresp channel assignment procedurep channel releasep channel change and handover proceduresp change of frequencies, hopping sequences or

algorithms, frequency tablesp measurement report from mobilesp power control and timing advancep modification of channel modesp cipher mode setting


MM Sublayerp support of user mobility, registration,

management of mobile datap checking user & equipment identityp checking allowed services for usersp support of confidentiality (e.g. TMSI)p user securityp provision of MM connection, based on

RR, to CM


MM Sublayer Procedures

p location updatep periodic updatingp authenticationp IMSI attachp IMSI detachp TMSI reallocationp indentification


CM Sublayerp managing all functions necessary for

circuit switching call control in GSM PLMN

p call control responsibilities, which are amost identical to a fixed ISDN network,

p call control entity in GSM establishing, maintaining,and releasing call connection for communication links.


CM Sublayer Proceduresp mobile-originated call establishmentp mobile-terminated call establishmentp changes of transmission mode during

an ongoing callp call re-establishment after interruption of

an MM connectionp dual-tone multi-frequency (DTMF)

control for DTMF transmissions


Structure of Layer 3 Message

8 7 6 5 4 3 2 1

TI ProtocolDiscriminator

TIflag

0 Message Type

Information Elementsmandatory

Information Elementsoptional


Transaction Identifierp TI is a pointer to distinguish multiple

parallel CM connections and various simultaneous transactions.

p For RR & MM, TI is not relevant, TI=0000.

p TI flag indicates originator of a CM connection. It is set 0 by the originator and 1 when sent back.


Protocol Discriminatorp PD links Layer 3 protocol to the

addressed entity and identifies 6 protocols: radio resource management (0110), mobility management (0101), call control (0011), short message services (1001), supplementary service (1011), test procedure (1111).


Information Elementsp Mandatory IEs have a reserved place in

structure of message; optional IEs carry information element identifier (IEI) telling receiver the purpose of information contained.

p 4 possible IE types: mandatory fixed length (MF), mandatory variable length (MV), optional fixed length (OF), optional variable length (OV).


Testing GSM


First Generation GSM Radio Test

SC

ENC

HWC

DEC

BDM

RF/SYNTH

MOD

O-att

I-att

DEMOD

PersonalComputer

RF-out

RF-in


Transmitter Measurementsp RF powerp frequency error and phase errorp special transmitter power measurements:

peak power, power-time template, burst timing

p measurements in spectrum: due to modulation, due to switching transients, spurious emissions, intermodulation attenuation


Measurements on Digital Receivers

p BER, residual BER, frame erasure ratep sensitivity p cochannel rejectionp adjacent channel rejectionp intermodulation rejectionp blocking & spurious response rejection


Test of Layer 1p synchronization and timingp power controlp radio channel management


Fading Environmentsp rural area (RA)p hilly terrain (HT)p typical urban (TU)p equalizer (EQ)


Test of Layer 2p establishment of an acknowledged data linkp error control during data link establishmentp seq. counting during ack. block transferp segmentation and concatenationp loss of I-framep reaction to erroneous C/R in address fieldp reaction to erroneous values in control fieldp reaction to invalid frames


Block Diagram of Mobile Station

antennacombiner

VCO &synthesizer

controlsignaling

unit

channelcodec

speechcodec

A/DD/A

receivingcircuits

transmittingcircuits

A/D

D/A

equalizerdemodulatordemultiplexer

burst building unitmultiplexermodulator telephone


Additional RF Tests on a MSp bad-frame indication performancep intermodulation rejectionp transceiver test for spurious emission

measurement in active & idle states.


Signaling Test of Layer 1p downlink power controlp correction of burst timingp report of actual timing advance & power

levels (uplink SACCH)p measurement report


Block Diagram of Base Station

VCO &synthesizer

controlsignaling

unit

channelcodec

speechcodec

receivingcircuits

transmittingcircuits

A/D

D/A

equalizerdemodulatordemultiplexer

burst building unitmultiplexermodulator

speechcodec

signaling

Abis

64 kbps

64 kbps

A-law

64 kbps

13 kbps

16 kbps

3 kbps in-bandsignaling

BTS BSC


Iridium:Satellite Mobile Using GSM


Briefingp 66 LEO (low-earth-orbit) satellites in 6 polar

orbital planes which 780 km above sea-surface. Each has 48 L band beams for subscriber coverage.

p Constellation of satellites is controlled by the system control segment (SCS). SCS also decides frequency planning and routing information.

p It is a packet switching network.


Gateway

Internationalswitching

center

PSTN

SystemControl

Segment

K-band

L-band K-bandL-band

Iridium System Overview

ISU


Iridium Gateway

InternationalSwitch &PSTN

MOC GMS

MSC

HLRVLREIR

ETC

MOC: message origination controllerGMS: gateway management systemETC: earth station controllerEIR: equipment identity register


INMARSATp The only commercial satellite mobile

communication systemü3 geo-stationary satellites over Pacific,

Indian, Atlantic oceansüSupporting speech, data, video trafficüSmall VSAT and portable terminalsüOriginally for marine-time applications


General Packet Radio Services: GPRS


What Is GPRS?Conventional Way: Circuit Switched Data

A

HLR

PSTN

Data overVoiceC

IRC

UIT

SW

ITC

HE

D MSC/VLR

GSMBTS

BSC


What Is GPRS?Packet Switched Technology on GSM

Internet

GbA

PSDN

HLR

PSTN

MSC/VLR

PAC

KE

TSW

ITC

HE

D

GGSN

SGSNBSC

GSMBTS

Packet Data

GGSN: Gateway GPRS Support Node

SGSN: Serving GPRSSupport Node


What Is GPRS?GPRS VS Circuit Switched Data

TS1TS1TS2TS2TS3TS3

Circuit Switched DataCircuit Switched Data

TS1TS1GPRSGPRS

TimeTime

Stochastic Multiplexing


0 1 2 3 4 5 6 7 0 1

5 6 7 0 1 2 3 4 5 6

0 1 2 3 4 5 6 7 0 1

0 1 2 3 4 5 6 7 0 1

5 6 7 0 1 2 3 4 5 6

5 6 7 0 1 2 3 4 5 6

3 slots: 4th slot: 5th slot:

Downlink

Uplink

Monitor

Downlink

Uplink

Monitor

Downlink

Uplink

Monitor

1-slot

2-slot

3-8-slot

GPRS Multi-slot Capabilities


What Is GPRS?GPRS Network Seen by IP Network

Subnetwork191.200.44.xxx

Host155.222.33.55

Source: Nokia


Why GPRS?Operator’s Viewp First attractive data service for GSM.p Optimal support for packet switched traffic.p First step to the 3rd generation.p The possibility to offer new services.p Better network efficiency.p Higher revenue.


Why GPRS?User’s View

p A global and wireless access to the Internet !p All existing TCP/IP applications can be used.p New and attractive services.p Users stay on the line long but only pay for the

capacity used.p Data rate from 9.05 kbps up to 171.2 kbps.ü 9.05 kbps per channel by CS-1 (Channel Coding Scheme 1).ü 13.4 kbps by CS-2, 15.6 kbps by CS-3, and 21.4 kbps by CS-

4.

ü Maximum date rate: 21.4 x 8 = 171.2 kbps.


Services on GPRSGPRS is only a bearer!p E-mailp File transferp Shopping and ticket salesp Banking and finance managementp Newsp Webp Traffic informationp Stock pricesp And many others...

GPRS Logical Architecture

New Interface ( IP/X.25 )New Interface ( FR )

SGSN: Serving GPRS Support NodeGGSN: Gateway GPRS Support Node

New Interface ( IP )

New Interface ( SS7 )

SGSN GGSN

SGSN


pp SGSNSGSNüSame level as the MSC/VLR.üConnected to the BSS with Frame Relay.üDetects new GPRS MSs in its service area.üRecords location of MSs in its service area.üSends/Receives data packets to/from the MSs.

pp GGSNGGSNüProvides interworking with the PDN (e.g., the

Internet).üLooks like a router, when seen by the Internet.üConnected to the SGSN via an IP-based backbone.

New Elements for GPRS


Enhanced Elements for GPRSpp HLRHLRüEnhanced with GPRS subscriber data and

routing information.pp MSC/VLRMSC/VLRüEnhanced for co-ordination of GPRS and Circuit

Switched services (e.g., combined location update, paging for circuit-switched calls via the SGSN ).

pp BSSBSSüSupports flexible radio channel allocation, and

supports a new interface to the SGSN.pp SMSSMS--GMSC and SMSGMSC and SMS--IWMSCIWMSCüSupports SMS transmission via the SGSN.


Internet

IP based backbone

Illustration - GPRS Attach

GGSN

SGSN

BSS

HLR

GGSN

SGSN

BSSAttach


Internet

IP based backbone

Illustration - Activate an IP Address

GGSN

SGSN

BSS

HLR

GGSN

SGSN

BSSActivate


Internet

IP based backbone

Illustration - Intra SGSN Routing Area (RA)

Update

GGSN

SGSN

BSS

HLR

GGSN

SGSN

BSSRA Update


Internet

IP based backbone

Illustration - Inter SGSN RA Update

GGSN

SGSN

BSS

HLR

GGSN

SGSN

BSSRA Update


Internet

IP based backbone

Illustration - Data Routing from the Internet to

the MS

GGSN

SGSN

BSS

HLR

GGSN

SGSN

BSS


Internet

IP based backbone

Illustration - Data Routing from the MS to the

Internet

GGSN

SGSN

BSS

HLR

GGSN

SGSN

BSS


Internet

IP based backbone

Illustration - MS to MS Routing via the same

GGSN

GGSN

SGSN

BSS

HLR

GGSN

SGSN

BSS


Internet

IP based backbone

Illustration - MS to MS Routing via Different

GGSNs

GGSN

SGSN

BSS

HLR

GGSN

SGSN

BSS


Illustration - Data Routing for Roaming MS

HLR

Operator 2backbone

Internet

Operator 1 backbone

GGSN

SGSN

BSS

SGSNBG

Inter-operatorbackbone

BG

GGSN

Transmission plane


Transmission plane ( continued )

üGTP: GPRS Tunneling Protocolü IP: Internet ProtocolüUDP: User Data ProtocolüTCP: Transmission Control ProtocolüSNDCP: Subnetwork Dependent Convergence

ProtocolüLLC: Logical Link ControlüBSSGP: BSS GPRS ProtocolüNS: Network ServiceüRLC: Radio Link Control functionüMAC: Medium Access Protocol



p GPRS Tunneling ProtocolüBy GTP, many packet data protocol ( e.g., IP, X.25

) can be supported, even if the protocol is not supported by all SGSNs.üGTP header contains an IMSI (International Mobile

Subscriber Identifier) and an NSAPI (Network Service Access Point Identifier) .üBelow GTP, IP ( V4 or V6 ) is used as a backbone

network protocol. Ethernet, ISDN, or ATM may be used below IP.üTCP carries GTP protocol data unit for X.25, UDP

carries GTP protocol data unit for IP.



p Subnetwork Dependent Convergence ProtocolüMultilplexing, segmentation, and compression.

TLLI: Temporary Logical Link Identifier



p RLC/MAC



p RLC/MAC (uplink)üThe access to the uplink uses a Slotted-Aloha

based reservation protocol.



p RLC/MAC (uplink)üA selective ARQ protocol that provides

retransmission of erroneous RLC data blocks.



p RLC/MAC (downlink)üThe network initiates packet to an MS that is in

Standby state by sending a Packet Paging Request.



p RLC/MAC (downlink)



p LLCüProvides a reliable logical link between the MS

and its SGSN.üAcknowledged mode for Packet Data Unit.üUnacknowledged mode for signaling and SMS.

p BSS GPRS ProtocolüConveys routing information between SGSN and

BSS.p Network ServiceüFrame Relay.


Signaling plane: MS-SGSN

p GMM: GPRS Mobility Managementp SM: Session Management


Signaling plane: SGSN-HLR

p MAP: with enhancement for GPRS


Signaling plane: SGSN-MSC/VLR

p BSSAP+: A subset of Base Station System Application Part ( BSSAP ) . It supports signaling for “Mobility Management Functionality” ( e.g. combined RA/LA update )


Signaling plane: GSN-GSN

p GTP: GPRS Tunneling Protocolp UDP: User Datagram Protocol


Signaling plane: GGSN-HLR-based on MAP

p MAP: Supports signaling for “Network-Requested PDP ( Packet Data Protocol ) Context Activation Procedure”


Signaling plane: GGSN-HLR-based on GTP and MAP

p Interworking: between GTP and MAP


Referencesp CHT Labs. Presentationp GSM 03.60 Version 6.3.2 ( 1999-07 )p GSM 03.64 Version 6.2.0 ( 1999-05 )p Nokia’s White Paper on GPRSp http://www.nokia.comp http://www.ericsson.comp http://www.motorola.comp http://www.alcatel.comp http://www.nortelnetworks.com

http://www.nokia.com

http://www.ericsson.com

http://www.motorola.com

http://www.alcatel.com

http://www.nortelnetworks.com


EDGE

EDGE: Enhanced data rate for GSM evolutionECSD: Enhancement of HSCSDEGPRS: Enhancement of GPRS for through per time slot


Logical architecture


Transmission Plane

Note: Data flow is not simple at all.


Network architecture for supporting HSCSD (High Speed

Circuit-Switched Data)


Multiplexing of network protocols


EGPRSp EGPRS is built on top of GPRS with major

impacts onüRFüPHYüRLC/MAC with inclusion of type II hybrid ARQ

• Information is first sent with an initial code rate (i.e. rate 1/3 punctured with PS 1 of selected MCS). If RLC data block is received in error, additional coded bits (i.e. output of rate 1/3 encoded data that is punctured with PS 2 of prevailing MCS) are sent and decoded together with already received code words until successful decoding.

• If is possible to use incremental redundancy mode called MSC-5-7 or MCS-6-9.

• With higher coding schemes, RLC window size is increased from 64 to 128.


Modulation & Coding Scheme (MCS)

p MCS-1 to MCS-9üRLC/MAC header is strongly coded.

p 8-PSKü270.833 ksps (as GMSK)ü3 bits/symbolüPayload per burst: 342 bits (vs 114 bits)üGross rate per time slot: 68.4 kbps (vs 22.8

kbps)


EGPRS MCSMCS Code Rate Modulation Data Rate / time

slot (kbps)Family

9 1.0 8-PSK 59.2 A

8 0.92 54.4 A

7 0.76 44.8 B

6 0.49 29. A

5 0.37 22.4 B

4 1.0 GMSK 17.6 C

3 0.8 14.8 A

2 0.66 11.2 B

1 0.53 8.8 C


EGPRS coding and puncturing example

USF RLC/MACHdr. HCS E FBI Data=592 bits BCS TB E FBI Data=592 bits BCS TB

36 bits 135 bits 1836 bits 1836 bits

Rate 1/3 convolutional coding Rate 1/3 convolutional coding

36 bits 124 bits 612 bits

Puncturing

SB=8 612 bits 612 bits 612 bits 612 bits 612 bits

PuncturingPuncturing

P1 P2 P3 P1 P2 P3

1392 bits

3 bits 45 bits 612 bits 612 bits

(MCS-9: uncoded 8-PSK, two RLC blocks per 20ms)


Network architecture

(a) 57.6 kbps non-transparent service

(b) 56.0 / 64.0 kbps transparent service

1.3.1 GSM

Documents

Transcript of 1.3.1 GSM