introduction to gsm

Cellular MobileCellular Mobile Communications-Communications-IIIIIIIntroduction to GSMIntroduction to GSM

Dr. Nasir D. Dr. Nasir D. GoharGohar

T.S. Rappaport Ch 11T.S. Rappaport Ch 11 NDG NotesNDG Notes 22

AN INTRODUCTION TO GSMAN INTRODUCTION TO GSM

Second Generation Cellular Mobile Radio Systems-Second Generation Cellular Mobile Radio Systems-Digital Cellular Telephony:Digital Cellular Telephony: Main Advantages of Digital Cellular NetworksMain Advantages of Digital Cellular Networks

Higher Spectrum EfficiencyHigher Spectrum Efficiency Speech Encoding Speech Encoding Better Access Technologies: TDMA and CDMABetter Access Technologies: TDMA and CDMA

Higher System CapacityHigher System Capacity Aggressive Frequency ReuseAggressive Frequency Reuse

Low Infra-Structure and Terminal CostLow Infra-Structure and Terminal Cost Application of VLSI/VVLSI ChipsApplication of VLSI/VVLSI Chips Many Traffic Channels per Carrier Channel [Transceivers are shared Many Traffic Channels per Carrier Channel [Transceivers are shared

among several users)among several users) Low S/I Ratio (SIR) Allowing Smarter EquipmentLow S/I Ratio (SIR) Allowing Smarter Equipment

Better Integration with Digital PSTN [ISDN]Better Integration with Digital PSTN [ISDN]New Services such as Data Communications, Fax, and SMSNew Services such as Data Communications, Fax, and SMSBetter Privacy due to EncryptionBetter Privacy due to Encryption


AN INTRODUCTION TO GSMAN INTRODUCTION TO GSM Digital Cellular StandardsDigital Cellular Standards

Why So Many Standards?Why So Many Standards?

Region Standard Developing Organization Remarks

Europe GSM ETSI Harmonized European Standard

DCS-1800 ETSI GSM Varient for 1800 MHz Band

USA D-AMPS, D-AMPS 1900 TIA [IS-54B, IS-136] Digital AMPS works in 800 MHZ and 1900 MHz Bands

IS-95 CDMA TIA/QualComm[IS-95] Downward Compatible with AMPS, later modified to work with 1900 MHz Band

PCS-1900 ETSI GSM Vairent to work with 1900 MHz Band

Japan PDC NTT Works both in 800 MHz and 1500 MHz

Table-L13.1: Overview of Second Generation Standards



Digital Cellular Standards Digital Cellular Standards

Standard Forward Ch. Reverse Ch.

0.8 W MAHOTDMA, 3

Slots, later 6 Slots

25 KHz 42 kbpsVSELP, 11.2

kbps

810-826/1477-1489 + 1501-

1513800-1500

940-956/1429-1441 + 1453-

1465130/48

0.2 WSoft

HandoverCDMA 1.25 MHz

1.2 to 14.4 Kbps

Transmitted at 1.339

Mchips/s

QSELP, 1.2 to 8 kbps

800/1900869-894/1930-

1970824-849/1850-

189045/80

1.2 W MAHOTDMA, 3 Slots 30 KHz 48.6 KpbpsVSELP, 7.95

kpps800/1900

869-894/1930-1970

824-849/1850-1890

45/80

2W/1W/1W MAHOTDMA, 8 Time

Slots, Later 16 Time Slots

200 KHz 271 Kbps LPC,13 kbps900/1800

/1900

935-960/1805-1880/1930-

1970

890-915/1710-1785/1850-

189045/95/80

H/O

Table-L13.2: Overview of Important Technical Parameters of Digital Cellular Standards

Channel BW Mod. RateSpeech

EncodingTx Power of

MSFrequency band(Mhz)

Air InterfaceDuplex

SeparationAccess Tech.

GSM/DCS-1800/PCS-1900

D-AMPS

IS-95 CDMA

PDC

Standard

Parametrs



Overview of GSM MilestonesOverview of GSM Milestones 19821982 GSM Group, set up by CEPT, started Investigation to reserve a GSM Group, set up by CEPT, started Investigation to reserve a Spectrum in 900 MHz band for Pan-European Cellular Digital Spectrum in 900 MHz band for Pan-European Cellular Digital TelephonyTelephony 19861986 Two 25 MHz frequency Blocks [890-915 MHz, 935-960 MHz] Two 25 MHz frequency Blocks [890-915 MHz, 935-960 MHz] reserved by EC, July 01, 1991 set as Introduction date.reserved by EC, July 01, 1991 set as Introduction date.

Choice of Digital and Narrow band [Approx. 200 KHz] Choice of Digital and Narrow band [Approx. 200 KHz] TDMA made.TDMA made.

19871987 13 Operators from 12 European Countries signed MOU to 13 Operators from 12 European Countries signed MOU to Support GSM Support GSM

19891989 ETSI established which took over GSM from CEPTETSI established which took over GSM from CEPT 19921992 Introduction of first Commercial GSM NetworkIntroduction of first Commercial GSM Network 19941994 51 Commercial Networks Established51 Commercial Networks Established 19961996 More Than 20 Million Subscribers in 191 Networks, More than More Than 20 Million Subscribers in 191 Networks, More than

Double of all Subscribers of other Digital Systems [D- Double of all Subscribers of other Digital Systems [D-AMPS, AMPS,

PDC, IS-95 CDMA]PDC, IS-95 CDMA] 20062006 More than 2 billion subscribers (30% of world population More than 2 billion subscribers (30% of world population

and and 82% of cellular market)82% of cellular market)


AN INTRODUCTION TO GSMAN INTRODUCTION TO GSM Implementation Phases of GSMImplementation Phases of GSM

Phase-1: Phase-1: Most Essential Services [Voice, Data, SMS] Implemented. Most Essential Services [Voice, Data, SMS] Implemented. Mostly all Current GSM Systems belong to this Phase. Mostly all Current GSM Systems belong to this Phase.

Phase-2:Phase-2: Half-Rate Speech Encoding, Doubling the System Capacity, Half-Rate Speech Encoding, Doubling the System Capacity, Several Encryption Algorithms, Conference Call Several Encryption Algorithms, Conference Call

Facility[ up to 5 Facility[ up to 5

Participants] ,Participants] ,Call Waiting Facility, Call Waiting Facility,

Information on Call Charges, Calling or Called Part etc.,Information on Call Charges, Calling or Called Part etc.,

Cell-Broadcast [Point to Multi-Point SMS].Cell-Broadcast [Point to Multi-Point SMS].

Many of the Phase-2 Facilities have already been Implemented by some Manufacturers.Many of the Phase-2 Facilities have already been Implemented by some Manufacturers.

Phase-2 +Phase-2 + GPRS[General Packet radio Service] for Packet Switched GPRS[General Packet radio Service] for Packet Switched

Data Transmission to Support LAN and Internet Traffic. Data Transmission to Support LAN and Internet Traffic. [Considerably Delayed due to Lack of Interest on part of Network [Considerably Delayed due to Lack of Interest on part of Network

Operators due to Large Investment required for Infra-Structure and MS Operators due to Large Investment required for Infra-Structure and MS

Modifications]Modifications]

GSM 3G…..GSM 3G…..


AN INTRODUCTION TO GSMAN INTRODUCTION TO GSM2G EVOLUTION TO 3G2G EVOLUTION TO 3G


AN INTRODUCTION TO GSMAN INTRODUCTION TO GSMGSM EVOLUTIONGSM EVOLUTION



MSMSSIM CardSIM CardEIN/ESNEIN/ESN

Base Station Base Station Subsystem (BSS)Subsystem (BSS)Several Dozens of BTS Several Dozens of BTS

under one BSCunder one BSCEach BTS has 3-5 Carrier Each BTS has 3-5 Carrier

ChannelsChannels Network &Switching Network &Switching

SubsystemSubsystemMTX [up to 1 M users]MTX [up to 1 M users]Call set up , all Other Call set up , all Other

FunctionsFunctions

GSM SYSTEM ARCHITECTUREGSM SYSTEM ARCHITECTURE

•GMTX: An Interface to Other Networks•HLR: Keeps Record of System’s Own Users•VLR: Keeps Temporary Record of Visitors / Roamers [SID, ST,SVCES]

•Au C/EIR: Manages the Sub. Authentication and Encryption Data

MTX

HLRHLR = Home Location Register

GMTX/IWF To Other Networks

VLRVLR = Visitor Location Register

GMTX = Gateway MTXIWF = Inter Working Function

BTS = Base Transceiver StationBSC = base Station Controller

BTS

BTS

BTSBSC

BTS

BTS

BTSBSC

MS BASE STATION SUBSYSTEM[BSS] NETWORK & SWITCHING SUBSYSTEM

Cost Management Performance Management

Fault Management Config. Management Security Management

MANAGEMENT SUBSYSTEM



Management Management Subsystem Subsystem [Operation [Operation Subsystem (OSS)]Subsystem (OSS)]Directly or Indirectly Directly or Indirectly

Connected to all Other Connected to all Other SubsystemsSubsystems

Fault ManagementFault ManagementSystem ConfigurationSystem ConfigurationPerformance Performance

ManagementManagementCost ManagementCost ManagementSecurity ManagementSecurity Management

MTX

HLRHLR = Home Location Register

GMTX/IWF To Other Networks

VLRVLR = Visitor Location Register

GMTX = Gateway MTXIWF = Inter Working Function

BTS = Base Transceiver StationBSC = base Station Controller

BTS

BTS

BTSBSC

BTS

BTS

BTSBSC

MS BASE STATION SUBSYSTEM[BSS] NETWORK & SWITCHING SUBSYSTEM

Cost Management Performance Management

Fault Management Config. Management Security Management

MANAGEMENT SUBSYSTEM

GSM SYSTEM ARCHITECTURE-2GSM SYSTEM ARCHITECTURE-2



GSM InterfacesGSM InterfacesRadio Interface: Radio Interface:

Describes Data Describes Data Interchange between Interchange between MS and BSSMS and BSS

Abis Interface: Abis Interface: Describes Data Describes Data Communications Communications between BTS and BSC, between BTS and BSC, allows Various allows Various Manufacturers Manufacturers EquipmentEquipment

A Interface: Describes A Interface: Describes Data Interchange Data Interchange between BSS and NSS between BSS and NSS

GSM SYSTEM ARCHITECTURE-3GSM SYSTEM ARCHITECTURE-3


AN INTRODUCTION TO GSMAN INTRODUCTION TO GSM LOGICAL CHANNELSLOGICAL CHANNELS


AN INTRODUCTION TO GSMAN INTRODUCTION TO GSMControl Channels

Control channels fall into three categories:Broadcast:: BCCH, FCCH, SCH

One way, from base to mobile

Common Control: RACH, AGCH, PCHOne way, some from base to mobile and some from

mobile to the base

Dedicated: SDCCH, SACCG, FACCHTwo-way, stand-alone or embedded in the traffic

channels

All signaling channels share one carrier in a cellthe dedicated control channels may be transmitted

on traffic carriers


AN INTRODUCTION TO GSMAN INTRODUCTION TO GSMBroadcast Channels

Frequency Correction Channel (FCCH)Carries information for frequency correction

Synchronization Channel (SCH)Carries information for frame synchronization and for

identification of the BTS

Broadcast Control Channel (BCCH)Broadcasts general information on the BTSBroadcasts cell-specific information, e.g. Control

channel organization, frequency hopping sequences, cell identification, etc.



Common Control Channels Paging Channel (PCH) - downlink only

for paging purposes Random Access Channel (RACH) - uplink only

used by any MS to request allocation of a signaling channel (SDCCH)

a slotted Aloha protocol is used, so collisions among MSs may happen

Access Grant Channel (AGCH) - downlink onlyused to allocate a SDCCH or a TCH

Notification Channel (NCH) - downlink onlynotify MS of voice group and voice broadcast call (ASCI

feature)



Dedicated Control ChannelsStand Alone Dedicated Control Channel (SDCCH)

used for call setup (authentication, signaling,, traffic channel assignment), location updates and SMS

Slow Associated Control Channel (SACCH)always coupled with a SDCCH or TCHfor communicating measurement data and control

parametersFast Associated Control Channel (FACCH)

to respond to increased signaling demand, e.g. during handover

bandwidth (bit slots) are stolen from the associated TCH (traffic data are preempted)



Traffic ChannelsGSM support two types of traffic channels

full rate (TCH/F): 22.8 kbpshalf rate (TCH/H): 11.4 kbps

Mapping to physical channelfull rate traffic channel - 1 timeslothalf rate traffic channel - 1 timeslot in alternating

framesFull rate channel may carry

13 kbps speech or data at 2.4, 4.8 or 9.6 kbpsHalf rate channel may carry

6.5 kbps speech or data at 2.4 or 9.6 kbps



Channel Usage & MS Terminating Calls


GSM Call Setup ProcedureGSM Call Setup Procedure Locating the SubscriberLocating the Subscriber

HLR HLR keeps record of the MSC area which the Subscriber last keeps record of the MSC area which the Subscriber last registeredregistered

VLRVLR keeps record of the keeps record of the Location Area[LA]Location Area[LA] in which Subscriber in which Subscriber last registeredlast registered

Location AreaLocation Area: A Group of Neighboring Cells having the same : A Group of Neighboring Cells having the same LACLAC

LAC:LAC: Each Cell in the Area Broadcasts this Code Each Cell in the Area Broadcasts this CodeEach Mobile itself periodically registers itself with MSCEach Mobile itself periodically registers itself with MSC

Paging and Random Access Procedure [RAP]Paging and Random Access Procedure [RAP]GMSC GMSC interrogates HLR for MSC the Subscriber last registeredinterrogates HLR for MSC the Subscriber last registeredCall is Switched to that MSCCall is Switched to that MSCVLR tells about the LA the user last registeredVLR tells about the LA the user last registeredMSC arranges a Paging in all the Cells in the LAMSC arranges a Paging in all the Cells in the LA



GSM Call Setup Procedure-2GSM Call Setup Procedure-2 Paging and Random Access Procedure[RAP]-Cont’dPaging and Random Access Procedure[RAP]-Cont’d

The Mobiles listen to the Paging Channels for their NumberThe Mobiles listen to the Paging Channels for their NumberIf received a Paging Message, the Mobile starts a RAPIf received a Paging Message, the Mobile starts a RAP

It sends a Random Number [RN] + Brief Guide to describe the It sends a Random Number [RN] + Brief Guide to describe the PurposePurpose

The System [MSC] responds to it by repeating the RN and providing The System [MSC] responds to it by repeating the RN and providing the decided Channel the decided Channel

The Mobile listens to this RN, if it is the same, it gets hold of the The Mobile listens to this RN, if it is the same, it gets hold of the allocated Channelallocated Channel

Reconfirmation is done by the System by sending again the Mobile Reconfirmation is done by the System by sending again the Mobile Number [in case some other Mobile has also sent the same RN at the Number [in case some other Mobile has also sent the same RN at the same time]same time]

If the Mobile hears its own number, it responds to the System and If the Mobile hears its own number, it responds to the System and thus it gets connected to the incoming Call, thus it gets connected to the incoming Call,

If it was a wrong number [other than its own number] it must leave If it was a wrong number [other than its own number] it must leave that Channel.that Channel.

In case, a Mobile listens no same RN from the System, it may repeat In case, a Mobile listens no same RN from the System, it may repeat RAP at some time later randomly.RAP at some time later randomly.



AN INTRODUCTION TO GSMAN INTRODUCTION TO GSMCALL PROCESSING & MOBILE TERMINATING CALLS


AN INTRODUCTION TO GSMAN INTRODUCTION TO GSMCALL PROCESSING & MOBILE ORIGINATING


GSM Handover and RoutingGSM Handover and Routing Handover Handover

The Mobile keeps updating MSC about the RSS levels from the The Mobile keeps updating MSC about the RSS levels from the neighboring Cells.neighboring Cells.

MSC, while looking at the quality of the existing link, decides whether a MSC, while looking at the quality of the existing link, decides whether a Handoff/ Handover is necessary or not.Handoff/ Handover is necessary or not.

If yes, it asks the Candidate Cell to prepare the Channel [ GSM uses If yes, it asks the Candidate Cell to prepare the Channel [ GSM uses Fixed Channel Assignment]Fixed Channel Assignment]

When Channel is allocated, it tells the Mobile to move to that ChannelWhen Channel is allocated, it tells the Mobile to move to that ChannelWhen Mobile has moved, it deactivates the old ChannelWhen Mobile has moved, it deactivates the old Channel

RoutingRoutingGMSC interrogates HLR to locate the Subscriber by telling the MSC GMSC interrogates HLR to locate the Subscriber by telling the MSC

where the Mobile last registered.where the Mobile last registered.PROBLEM: Call originated from PSTN in CANADA for a US Mobile PROBLEM: Call originated from PSTN in CANADA for a US Mobile

roaming in CANADA will result in two International Callsroaming in CANADA will result in two International Calls


“TROMBONE PROBLEM”????

[Don’t Worry, Be Happy, Other People will Take Care of this Problem]


AN INTRODUCTION TO GSMAN INTRODUCTION TO GSMHANDOVER TYPESHANDOVER TYPES

Intra-BSCOld and new BTSs are controlled by the same BSCThe MSC is not involved

Intra-MSCOld and new BTSs are attached to different BSCsThe BSCs are attached to the same MSC

Inter-MSCHandover to a new MSCServing MSC becomes anchor MSCIMT (Inter Machine Trunk) is required


GSM Numbering Scheme and Spectrum EfficiencyGSM Numbering Scheme and Spectrum Efficiency GSM Numbering Scheme GSM Numbering Scheme

Each GSM Mobile has at least three NumbersEach GSM Mobile has at least three Numbers:: MSISDN [Mobile Station Integrated Services Digital Network] stored MSISDN [Mobile Station Integrated Services Digital Network] stored

in in SIM CardSIM Card SIM Card SIM Card holds Subscriber ID[MSISDN, holds Subscriber ID[MSISDN, IMSIIMSI], some Extra Memory to store ], some Extra Memory to store

phone numbers and Encryption Algorithmsphone numbers and Encryption Algorithms IMSI[International Mobile Subscriber Identity] not known to the User, IMSI[International Mobile Subscriber Identity] not known to the User,

HLR does translation between MSISDN to IMSI and vice versa.HLR does translation between MSISDN to IMSI and vice versa. ESN or IMEI:Permanently stored/wired in the Mobile Station ESN or IMEI:Permanently stored/wired in the Mobile Station

Spectrum EfficiencySpectrum EfficiencyTDMA, 200 KHz Channel BW, 8-Time Slots per Carrier ChannelTDMA, 200 KHz Channel BW, 8-Time Slots per Carrier ChannelRadio Spectrum = 2 x 25 MHz bands can support 125[124] Duplex Carrier Radio Spectrum = 2 x 25 MHz bands can support 125[124] Duplex Carrier

Channels and 1000 Traffic Channels [1000 Simultaneous Calls].Channels and 1000 Traffic Channels [1000 Simultaneous Calls].A typical GSM System Cluster Size = 12, so each Cell have Approx. 10 A typical GSM System Cluster Size = 12, so each Cell have Approx. 10

Carrier Channels and a Capacity of 80 Simultaneous Call [Traffic Carrier Channels and a Capacity of 80 Simultaneous Call [Traffic Channels]Channels]

In case of half-rate Coder, Spectrum Efficiency will be Doubled.In case of half-rate Coder, Spectrum Efficiency will be Doubled.



Technical Realization of GSM Technical Realization of GSM GSM Speech CommunicationsGSM Speech Communications

User Speech is Digitized using Adaptive PCMUser Speech is Digitized using Adaptive PCMSpeech Encoding using Linear Predictive Coding [LPC]Speech Encoding using Linear Predictive Coding [LPC]User data flow = 13 kbps [ 6.5 kbps in case of half-rate coding]User data flow = 13 kbps [ 6.5 kbps in case of half-rate coding]Adding an overhead of 9.8 kbps[for error detection, error correction, and Adding an overhead of 9.8 kbps[for error detection, error correction, and

synchronization], we get an over all user data flow of 22.8 kbps.synchronization], we get an over all user data flow of 22.8 kbps.This user data flow is subdivided into This user data flow is subdivided into short data blocks each of 456 bits, short data blocks each of 456 bits,

which is divided into 8 sub-blocks, each of 57 bits, 2 such sub-blocks are used which is divided into 8 sub-blocks, each of 57 bits, 2 such sub-blocks are used to make a burst [to fit into a time slot of 0.58 ms]. to make a burst [to fit into a time slot of 0.58 ms]. See frame structureSee frame structure. .

These bursts from a user are interleaved over 8 time slots spread over 8 These bursts from a user are interleaved over 8 time slots spread over 8 frames.frames.

TDMA/FDMA MechanismTDMA/FDMA Mechanism Each Carrier Channels carries data burst of eight (8) users, each in its Each Carrier Channels carries data burst of eight (8) users, each in its

allocated time slot in the frame.allocated time slot in the frame. Time slots are transmitted on several Channels [Carrier Channel or Time slots are transmitted on several Channels [Carrier Channel or

Frequency] Frequency] Each Carrier Channel transmits the data of 8 users at 271 kbpsEach Carrier Channel transmits the data of 8 users at 271 kbps..



Technical Realization of GSM [ Cont’d]Technical Realization of GSM [ Cont’d] GSM Speech Communications-2GSM Speech Communications-2

GSM Carrier Frequencies are numbered 1-124 Channels[Duplex]GSM Carrier Frequencies are numbered 1-124 Channels[Duplex]Forward Channel = 935.2 MHz + (n-1) * 200 KHzForward Channel = 935.2 MHz + (n-1) * 200 KHz

Reverse Channel = 890.2 MHz + (n-1) * 200 KHzReverse Channel = 890.2 MHz + (n-1) * 200 KHz

Due to slightly more than 200 KHz bandwidth of the modulated Due to slightly more than 200 KHz bandwidth of the modulated signal, Consecutive Frequencies are not used in the same Systemsignal, Consecutive Frequencies are not used in the same System

Also, 1 and 124 Channels are generally not used.Also, 1 and 124 Channels are generally not used.The Spectrum of 124 Channels is generally not allotted to one The Spectrum of 124 Channels is generally not allotted to one

Service Provider.Service Provider.Separation between two Duplex paired Channels is 45 MHz.Separation between two Duplex paired Channels is 45 MHz.Each user’s bursts are transmitted every 4.6ms apart.Each user’s bursts are transmitted every 4.6ms apart.


979695949392

1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8

Fre

qu

ency

TimeFrame [4.6ms]


AN INTRODUCTION TO GSMAN INTRODUCTION TO GSMSPEECH PROCESSINGSPEECH PROCESSING



SPEECH CODINGSPEECH CODING

SPEECH ENCODERSPEECH ENCODER



SPEECH DATA SPEECH DATA PROCESSINGPROCESSING



CHANNEL ENCODINGCHANNEL ENCODING



INTERLEAVINGINTERLEAVING


AN INTRODUCTION TO GSMAN INTRODUCTION TO GSMVOICE TRANSMISSION PATHVOICE TRANSMISSION PATH


Technical Realization of GSM [ Cont’d]Technical Realization of GSM [ Cont’d] GSM Framing StructureGSM Framing Structure


Hyper Frame 3 Hrs 28 Min

1 2048

1 511 26

Super Frame 6.12 Sec

1 26 1 51

Multi-Frame 120 ms Multi-Frame 235 ms

One Super Frame Occurs whenwhen the Speech and Control Channel restart at the same time.

SpeechTraffic

ControlTraffic

26 x Frames 4.61 ms 1 8 Each Frame is sub-divided into 8 time-slots 0.58 ms

3 57 bits User Speech Data 26 bits

Preamble

57 bits User Speech Data 3GuardTime

Time Slot 0.58 ms

1 8 1 8 1 8 1 8 1 8 1 8 1 8 1 8

Blocked User SignalInter-Leaved into 8 Time Slots over 8 Frames

Block = 456 Bits

1 2 8. .

8 sub-blocks 57 bits each

8 x Frames 4.61 ms, Slot-2 of each Frame is Allocated to the User


AN INTRODUCTION TO GSMAN INTRODUCTION TO GSM TIME-SLOT STRUCTURETIME-SLOT STRUCTURE


AN INTRODUCTION TO GSMAN INTRODUCTION TO GSM FRAME HIERARCHYFRAME HIERARCHY


AN INTRODUCTION TO GSMAN INTRODUCTION TO GSM BURSTBURST



Five different types of burstsNormal burst

Traffic and control payloadFrequency correction burst

All zeroes sequenceSynchronization burst

A special fixed sequenceRandom access burst

Extended guard period of 68.25 bitts (252 μs)Dummy burst

TYPES OF BURSTTYPES OF BURST


AN INTRODUCTION TO GSMAN INTRODUCTION TO GSMBURST STRUCTURESBURST STRUCTURES


Technical Realization of GSM [ Cont’d]Technical Realization of GSM [ Cont’d] GSM Modulation SchemeGSM Modulation Scheme

Gaussian Minimum Shift Keying [GMSK]Gaussian Minimum Shift Keying [GMSK] (For Detail (For Detail see Ch-5 of the see Ch-5 of the Text Book)Text Book)

No Speech, No TransmissionNo Speech, No Transmission Saves Energy in MS, Reduces Ave. InterferenceSaves Energy in MS, Reduces Ave. Interference Comfort Noise added for the Listener’s Pleasure.Comfort Noise added for the Listener’s Pleasure.

GSM MS Power ClassesGSM MS Power ClassesClass 1: 20 W Class 1: 20 W Not (yet) AvailableNot (yet) AvailableClass 2: 8 WClass 2: 8 W Car PhoneCar PhoneClass 3: 5 WClass 3: 5 W --Class 4: 2 WClass 4: 2 W Normal Pocket PhoneNormal Pocket PhoneClass 5: 0.8 WClass 5: 0.8 W Limited Coverage Phone [Urban Areas Only]Limited Coverage Phone [Urban Areas Only]

Maximum Cell Size: Maximum Cell Size: Depends on Max. Permitted Delay, 35 km.Depends on Max. Permitted Delay, 35 km. Maximum Mobile Speed:Maximum Mobile Speed: 250 km/hr 250 km/hr



Technical Realization of GSM [ Cont’d]Technical Realization of GSM [ Cont’d] GSM SMSGSM SMS

Individual Messages:Individual Messages: up to 160 Characters long can be sent and received by MS up to 160 Characters long can be sent and received by MS SMS uses Signaling Channel, thus, it can be received during SMS uses Signaling Channel, thus, it can be received during

current Communication Session current Communication Session Max. rate 600 bpsMax. rate 600 bps

Cell Broadcast:Cell Broadcast: up to 93 Character long message can be sent to all users in a up to 93 Character long message can be sent to all users in a

given area [Cells].given area [Cells]. Uses Communication Channel, so, can’t be received during current Uses Communication Channel, so, can’t be received during current

Communication SessionCommunication Session Neither Addressed Nor EncryptedNeither Addressed Nor Encrypted

Applications of SMS:Applications of SMS: .Network Operator Messages, Third .Network Operator Messages, Third Party Messages, Public Interest Information MessagesParty Messages, Public Interest Information Messages

SMS Cost: SMS Cost: Differs from Operator to Operator and depends on Differs from Operator to Operator and depends on type of Applicationtype of Application



Technical Realization of GSM Technical Realization of GSM [ Cont’d][ Cont’d] GSM Security AspectsGSM Security Aspects

GSM provides security about GSM provides security about the identity of MSthe identity of MS

Guards against Guards against Eavesdropping Eavesdropping

ImplementationImplementationUser Authentication [A3 User Authentication [A3

Algorithm]:Algorithm]: 128 bit Secret 128 bit Secret Number, Ki, assigned to each Number, Ki, assigned to each User, stored in SIM Card as User, stored in SIM Card as well as AuC, is used to create well as AuC, is used to create SRES using Ki and 128 bit SRES using Ki and 128 bit RAND number from the RAND number from the network, if SRES of MS network, if SRES of MS matches with SRES of the matches with SRES of the network, the MS is accepted.network, the MS is accepted.



AN INTRODUCTION TO GSMAN INTRODUCTION TO GSMData Encryption [A8+A5 Algorithm]:Data Encryption [A8+A5 Algorithm]:

Frame # + (RAND+Ki(Alg-A8))(Alg-A5) -> 144 bit Code Train Frame # + (RAND+Ki(Alg-A8))(Alg-A5) -> 144 bit Code Train bit user Data Train -> [Network] bit user Data Train -> [Network] Frame # + Frame # + (RAND+Ki(Alg-A8))(Alg-A5) ->Original Message(RAND+Ki(Alg-A8))(Alg-A5) ->Original Message


Technical Realization of GSM [Cont’d]Technical Realization of GSM [Cont’d] GSM Inter-Connection with Other Networks:GSM Inter-Connection with Other Networks:

PSTN/ISDN for VoicePSTN/ISDN for Voice GSM Speech data is Digital and CompressedGSM Speech data is Digital and Compressed Converted into audio of 3.1 KHz BWConverted into audio of 3.1 KHz BW

PSTN/ISDN for DataPSTN/ISDN for Data For Data Interconnection, Modem Pools are used in GSM For Data Interconnection, Modem Pools are used in GSM

Network. Many Telephone Modems at GMSC/IWF supporting all Network. Many Telephone Modems at GMSC/IWF supporting all the important telephone modem standards V.21[0.3 kbps, AS], the important telephone modem standards V.21[0.3 kbps, AS], V.22[1.2 kbps, AS and S], V.32 [4.8 kbps, S] etc.V.22[1.2 kbps, AS and S], V.32 [4.8 kbps, S] etc.

PSDN (Basic PAD or Dedicated PAD) for DataPSDN (Basic PAD or Dedicated PAD) for Data 300 bps to 9600 bps on AS/S links 300 bps to 9600 bps on AS/S links



NEW DEVELOPMENTS IN GSMNEW DEVELOPMENTS IN GSM Frequency Shortage and Extended GSM BandFrequency Shortage and Extended GSM Band

In some European countries, up to half GSM band is occupied by In some European countries, up to half GSM band is occupied by Interim Systems; NMT, ETACS etc. Interim Systems; NMT, ETACS etc.

Additional frequencies adjacent to GSM band is recommended by Additional frequencies adjacent to GSM band is recommended by ERO[1996], new terminals for this extended band are not available in ERO[1996], new terminals for this extended band are not available in bulkbulk

New Encoding TechniquesNew Encoding Techniques Half-Rate Speech EncodingHalf-Rate Speech Encoding

Instead of 13 kbps only 6.5 kbps will be required for the same speech Instead of 13 kbps only 6.5 kbps will be required for the same speech qualityquality

Standardized in early 1995, but, only few manufacturers have implementedStandardized in early 1995, but, only few manufacturers have implemented lack of interest on part of system supplierslack of interest on part of system suppliers fear of investment decrease in network expansion [uCell]fear of investment decrease in network expansion [uCell]

Enhanced Full Rate [EFR]:Developed by GSM and DCS-1800 SuppliersEnhanced Full Rate [EFR]:Developed by GSM and DCS-1800 SuppliersSame 13 kbps speed, but, considerable improvement in speech qualitySame 13 kbps speed, but, considerable improvement in speech qualityMore Immunity to transmission errorsMore Immunity to transmission errors


NEW DEVELOPMENTS IN GSMNEW DEVELOPMENTS IN GSM Any Cellular Phone may have many Speech CodersAny Cellular Phone may have many Speech Coders, , including including

FR/HR/EFR, it must be able to switch, and at least support FR for roaming FR/HR/EFR, it must be able to switch, and at least support FR for roaming purpose.purpose.

Data Communications over GSMData Communications over GSMGeneral Packet Radio Service[GPRS] offers packet-switched data General Packet Radio Service[GPRS] offers packet-switched data

communications suitable for LAN and Internet Applications[PVC]communications suitable for LAN and Internet Applications[PVC]Requires GPRS enabled Handsets and Changes at BSS[addition of Packet Requires GPRS enabled Handsets and Changes at BSS[addition of Packet

Control Unit, PCU]Control Unit, PCU]Option of Upgrading of BTS to support Enhanced Data rate for GSM Option of Upgrading of BTS to support Enhanced Data rate for GSM

Evolution, EDGE [8-PSK system]Evolution, EDGE [8-PSK system] Multi-band TerminalsMulti-band Terminals

Cellular phones to support more than frequency bands [GSM and DSC-Cellular phones to support more than frequency bands [GSM and DSC-1800 or GSM and PCS-1900 or GSM/DCS/PCS or many more combinations]1800 or GSM and PCS-1900 or GSM/DCS/PCS or many more combinations]

GSM Moving into 3G ModeGSM Moving into 3G ModeGSM extends itself into 3G as Universal Mobile Telecomm. Services [UMTS]GSM extends itself into 3G as Universal Mobile Telecomm. Services [UMTS]

Radio Interface will use WCDMA technology [UMTS Terrestrial Radio Access, Radio Interface will use WCDMA technology [UMTS Terrestrial Radio Access, UTRA] in two different modes: FDD [two different frequencies for uplink and UTRA] in two different modes: FDD [two different frequencies for uplink and downlink] or TDD[same frequency for both uplink and downlink but time-downlink] or TDD[same frequency for both uplink and downlink but time-shared]shared]


The Market Share of GSM The Market Share of GSM Suppliers [1/97]Suppliers [1/97]

Networking & Switching Subsystems [NSS]Networking & Switching Subsystems [NSS] Ericsson [48 %], Siemens [21 %], Nokia [14 %], and Alcatel [10%] = 93 Ericsson [48 %], Siemens [21 %], Nokia [14 %], and Alcatel [10%] = 93

%% Others (Lucent, Motorola, Nortel, etc] = 7%Others (Lucent, Motorola, Nortel, etc] = 7%

Basestation Sub-System [BSS]Basestation Sub-System [BSS] Nokia [22%], Motorola [13%], Alcatel [10%] and Ericsson [7%] = 52%Nokia [22%], Motorola [13%], Alcatel [10%] and Ericsson [7%] = 52% Others [Italtel, Lucent, Matra, Philips etc] = 48%Others [Italtel, Lucent, Matra, Philips etc] = 48%

GSM / DCS-1800 / PCS-1900 Mobile TerminalsGSM / DCS-1800 / PCS-1900 Mobile Terminals Ericsson [25 %], Nokia [24%], MOTOROLA [20 %], SIEMENS [9%] =78 %Ericsson [25 %], Nokia [24%], MOTOROLA [20 %], SIEMENS [9%] =78 % Others [Alcatel, Panasonic, Nortel, etc.] = 22 %Others [Alcatel, Panasonic, Nortel, etc.] = 22 %

Due to Licensing Problems, Unfair and Restricted Due to Licensing Problems, Unfair and Restricted Competition in GSM MarketsCompetition in GSM Markets


GSM and Health ProblemsGSM and Health Problems

GSM Terminals Cause Interference with GSM Terminals Cause Interference with Hearing Aid DevicesHearing Aid Devices and and Pacemakers Pacemakers [Instruments used to regulate the heart [Instruments used to regulate the heart

functionality of Heart Patients], andfunctionality of Heart Patients], and Some Research show that Some Research show that GSM phones cause Brain GSM phones cause Brain

TumorsTumors * * Inherent in GSM TDMA setup to generate strongly pulsating Inherent in GSM TDMA setup to generate strongly pulsating

transmission signals [Continuously Tx is switched on and off transmission signals [Continuously Tx is switched on and off that generates LF signals 217, 434, 651 Hz]that generates LF signals 217, 434, 651 Hz]

* Extensive Research required to prove the validity of GSM * Extensive Research required to prove the validity of GSM Cellular Phones being the cause of Brain Tumors or Cancer. Cellular Phones being the cause of Brain Tumors or Cancer.


GSM Derivative Systems:GSM Derivative Systems: DCS-1800 & DCS-1800 & PCS-1900PCS-1900

Digital Cellular System[DCS]-1800Digital Cellular System[DCS]-1800 Originally started [in 1990] as a separate system, but, later on became Originally started [in 1990] as a separate system, but, later on became

just a GSM variantjust a GSM variant Main modifications were made only in Air InterfaceMain modifications were made only in Air Interface Developed [by ETSI] particularly for densely populated urban areasDeveloped [by ETSI] particularly for densely populated urban areas 1.7 - 2.3 GHZ band [ 2 x 75 MHz spectrum, 1710- 1785 + 1805-1888 MHz]1.7 - 2.3 GHZ band [ 2 x 75 MHz spectrum, 1710- 1785 + 1805-1888 MHz] Duplex separation is 95 MHz, Channel BW is 200 KHz, 374 duplex Duplex separation is 95 MHz, Channel BW is 200 KHz, 374 duplex

channelschannels Much smaller cells [cells within a building], lower power BTS and MS as Much smaller cells [cells within a building], lower power BTS and MS as

compared to GSM compared to GSM handoff problems are much cleverly settled using hierarchical Cell handoff problems are much cleverly settled using hierarchical Cell

structure structure Max Cell size 8 km with Class 1 MS [1W]Max Cell size 8 km with Class 1 MS [1W] Max Cell size with Class II[0.25W] even smaller [0.5 -4/5 km]Max Cell size with Class II[0.25W] even smaller [0.5 -4/5 km] International as well as National roaming is possible [Country to Country, International as well as National roaming is possible [Country to Country,

Network to Network, and Intra-Network]Network to Network, and Intra-Network] Half-rate speech coding is possible/EFR is more likely to prevail.Half-rate speech coding is possible/EFR is more likely to prevail.


Personal Communication Services [PCS]-1900Personal Communication Services [PCS]-1900 A GSM variant to adapt to US MarketA GSM variant to adapt to US Market Frequency band 1900 MHz [1850-1890, 1930-1970 MHz]Frequency band 1900 MHz [1850-1890, 1930-1970 MHz] 2 x 40 MHz bands with Duplex Separation of 80 MHz2 x 40 MHz bands with Duplex Separation of 80 MHz Channel BW is 200 KHz, 200 Duplex ChannelsChannel BW is 200 KHz, 200 Duplex Channels TDMA 8 time-slotsTDMA 8 time-slots EFR speech encoding is getting more Interest from US Service EFR speech encoding is getting more Interest from US Service

ProvidersProviders

GSM Derivative Systems:GSM Derivative Systems: DCS-1800 & DCS-1800 & PCS-1900PCS-1900


GSM Facing ChallengesGSM Facing Challenges Higher Costs incurred on Network Capacity IncreaseHigher Costs incurred on Network Capacity Increase Business Market Saturation Business Market Saturation

More Money on Advertisement and Subsidies/Customer More Money on Advertisement and Subsidies/Customer DiscountsDiscounts

Interconnection Costs [to PSTN/ISDN] are very highInterconnection Costs [to PSTN/ISDN] are very high Leased Line Costs to Interconnect own Infra-structural Leased Line Costs to Interconnect own Infra-structural

elements are very highelements are very high High License CostsHigh License Costs

With Implementation of With Implementation of De-regulationDe-regulation policies policies thisthis will CHANGE.will CHANGE.


REFERENCESREFERENCESwww.utdallas.edu/~nhutnn/cs6v81/LECTwww.utdallas.edu/~nhutnn/cs6v81/LECT

URE_06.pdfURE_06.pdfhttp://www.gsmworld.comhttp://www.gsmworld.comDr. Veselin Rakocevic

http://www.staff.city.ac.uk/~veselin/Wireless

Comms

http://www.utdallas.edu/~nhutnn/cs6v81/LECTURE_06.pdf

http://www.utdallas.edu/~nhutnn/cs6v81/LECTURE_06.pdf

http://www.gsmworld.com/



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