gsm overview

GSMChapter 1BASICS

Tutor: Pradyot Majumdar

Global System for MobilesGSM

TOPICSGSM CONCEPTSGSM SYSTEM ARCHITECTUREGSM CHANNELSGSM RADIO LINKMOBILITY MANAGEMENTCALL MANAGEMENTRADIO RESOURCE MANAGEMENT

Telecom BasicsCommunicationVoice and DataAnalog and DigitalCircuit Switched and Packet SwitchedMedia - Copper Wire, Co-axial cable, Air, Optical FibreNetworks -PSTN, ISDN, PDN and Mobile Networks

Background to GSM1G : Advanced Mobile Phone Service (AMPS)Analog, Circuit Switched, FDMA, FDD2G : Digital Advanced Mobile Phone Service (D-AMPS)Digital, Circuit Switched, FDMA, FDD2G : Global System for Mobile (GSM)Digital, Circuit Switched, FDMA and TDMA, FDD2G : Code Division Multiple Access (CDMA)Digital, Circuit Switched, FDMA, SS, FDD

GSM History

Development of the GSM Standard1982:Groupe Spcial Mobile (GSM) created 1984:Description of GSM features1985:List of recommendations settled1987:Initial MoU (Memorandum of Understanding) aside the drafting of technical specifications was signed by network operators of 13 countries:1988:Validation and trials, of the radio interface.1991:First system trials are demonstrated at the Telecom 91 exhibition.1992:Official commercial launch of GSM service in Europe. First Launch in Finland1993:The GSM-MoU has 62 signatories in 39 countries worldwide. 1995:Specifications of GSM phase 2 are frozen.1999:GSM MoU joins 3GPP (UMTS)GPRS Trials begins2000:480M GSM subscribers WorldwideFirst GPRS Networks roll outEnd 2002:792M GSM subscribers Worldwide

GSM Specifications

Increasing GSM Data RatesTransmission TimeGPRS = General Packet Radio ServiceHSCSD = High Speed Circuit Switched DataEDGE = Enhanced Data rate for GSM EvolutionUMTS = Universal Mobile Telecommunication System

Wireless Data Technology Optionsthroughput kbps10 k100 k64 k1 M2 M1 k19981999200020012002Time frameUMTS GPRSHSCSD9.614.4packetGPRS = General Packet Radio ServiceHSCSD = High Speed Circuit Switched DataEDGE = Enhanced Data rate for GSM EvolutionUMTS = Universal Mobile Telecommunication SystemEDGEcircuit

Circuit-Switched or Packet-SwitchedCircuit modePacket modeAFDHCGCGCGCGCGDHDHAFDHDHAFAFAF

Multiple Access TechniqueMultiple Access Achieved by dividing the available radio frequency spectrum, so that multiple users can be given access at the same time.FDMA - Frequency Division Multiple Access( eg: GSM each Frequency channel is 200KHz)TDMA - Time Division Multiple Access( eg: GSM each frequency channel is divided into 8 timeslots)CDMA - Code Division Multiple Access (eg: IS95- Each User data is coded with a unique code)

Duplex TechniqueDuplex - How the up link and Down link of a user is separatedFDD - Frequency Division Duplex(eg:In GSM the up link and down link of a user is separated by 45MHz )TDD - Time Division Duplex (the up link and down link of a user will be at the same frequency but at different Time )

GSM Concepts - Cellular StructureCellularNetworking technology that breaks geographic area into cells shaped like honey comb

Cellis the radio coverage area of one base transceiver station

What are the types in GSM Network?GSM-900 (Channels 125 operating band 900Mhz carrier spacing 200khz spacing 45Mhz)

GSM -1800 (Channels 374 spacing 95Mhz)

GSM -1900(Used in USA)

GSM Band Allocations (MHz)Carrier frequency = ARFCN = Absolute Radio Frequency Channel Number Frequencies are in MHz

GSM systemsUplinkDownlinkBandDuplex SpacingDuplex channelsGSM 450GSM 480GSM 850450.4-457.6 478.8-486 824-849460.4-467.6488.8-496869-8942x7.22x7.2 2x251010453535124GSM 900E-GSM (900)R-GSM (900)890-915 880-915 876-880935-960 925-960 921-9252x25 2x35 2x0445454112417440GSM 1800GSM 19001710-1785 1850-19101805-1880 1930-19902x75 2x609580374299

GSM Family Radio Band SpectrumUplinkDownlink8808909151710178592593596018051880MHzP-GSMGSM 1800GSM 19001850191019301990R-GSM876921960960915915E-GSM UplinkDownlink824849869894MHzGSM 850478.8486488.8496450.4457.6460.4467.6GSM 450GSM 480

Traffic/SignalingSignalingbla bla bla... RING ! riiiiingNetworkTraffic

GSM - Network StructureAuCMSMSBTSBTSBTSBSCBSCMSCMSCVLRVLRGMSCHLRPSTNEIRUmAbisAbisAAOMC ServerUmBEEX.25CFHX.25

GSM System specificationsFrequency band Uplink 890 - 915 MHz Downlink 935 - 960MHzDuplex Frequency Spacing 45MHzCarrier separation 200KHzFrequency Channels124Time Slots /Frame(Full Rate)8Voice Coder Bit Rate13KbpsModulation GMSKAir transmission rate 270.833333 KbpsAccess method FDMA/TDMASpeech Coder RPE-LTP-LPC

Paired Radio Channels in GSM Case of GSM 900890 MHz915 MHz935 MHz960 MHzUplinkDownlinkExample:Channel 48FrequencyFrequencyDuplex spacing = 45 MHzFrequency band spectrum = 2 x 25 MHzChannel spacing = 200 kHzBTS

GSM Time Division Multiplex Frame and Physical Channels

Physical ChannelMS3//ARFCN12124FDMABTSWithout FH0TDMAsTS7nn-1n+1MS2MS1timeBTSWith FH

Radio Link AspectsFrom Speech to RF SignalBlah Blah Blah...Blah... Blah... Blah...

Functions of the Radio InterfaceBTS-1BTS-2

Access TechniquesUplink 890 MHz to 915 MHzDown Link 935 MHz to 960 MHz25 MHz divided into 125 channels of 200 KHz bandwidth

Access Techniques ...Time Division Multiple AccessEach carrier frequency subdivided in time domain into 8 time slots Each mobile transmits data in a frequency, in its particular time slot - Burst period = 0.577 milli secs.8 time slots called a TDMA frame. Period is .577 * 8 = 4.616 milli secs

Fundamentals

GSM utilizes two bands of 25 MHz. 890-915 MHz band is used for uplink while the 935-960 MHz is used for downlink.The frequency bands are divided into 200 KHz wide channels called ARFCNs (Absolute Radio Frequency Channel Numbers) i.e. there are 125 ARFCNs out of which only 124 are used.Each ARFCN supports 8 users with each user transmitting / receiving on a particular time slot (TS).

960 MHz 959.8MHz200KHz935 MHz935.2 Mhz915 MHz200KHz45 MHzDownlink (TDMA frame) = 8 TSUplink (TDMA frame) DelayTS: Time slot914.8 MHz890.2 MHz890 MHzDOWNLINKUPLINKTherefore 1 TDMA frame = 156.25 x 8 = 1250 bits and has a duration of 576.92s x 8 = 4.615 msThe technology

124123. 2 1

124123. 2 1

0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7

Data burst = 156.25 bit periods = 576.9s

GSM Delays Uplink TDMA FramesDownlink TDMATTTTTTTTRTMS1RTMS2DownlinkUplinkFixed transmitdelay of threetime-slotsRR0123 4567The start of the uplink TDMAis delayed of three time-slotsBTS sideMSs sideBTSTDMA Frame (4.615 ms)

Timing Advance 1 - Propagation DelayM2M1d1>>d2d2BTS Frame reference MSs transmitPropagation Delay tp Bits Overlapping

Timing Advance2 - Without Timing Advance: CollisionPropagation DelayDD+3TSTA

Timing Advance3 - With Timing Advance: No Collision CANWHATHOWWHENWHATCANWHATHOWWHENWHATTX BTSRX BTSRX MS1TX MS1RX MS2TX MS2RX MS3TX MS3RX MS4TX MS4RX MS5TX MS5RX MS6TX MS6RX MS7TX MS7RX MS8TX MS8yesthePropagation DelayDD+3TS - TAyestheTiming Advance = 2 * Propagation DelayGSMms-isdnms-isdnGSM

GSM in comparison with other StandardsGSM gives mobility without any loss in Audio quality Encryption techniques used gives high security in the air Interface and also use of SIM.Bit Interleaving for high efficiency in Transmission.Variable Power (Power budgeting- extend battery life)Minimum Interference.Features-CCS7 Signaling SMS (Short Message Services)Emergency CallsCELL Broadcast

GSM - Network StructureAuCMSMSBTSBTSBTSBSCBSCMSCMSCVLRVLRGMSCHLRPSTNEIRUmAbisAbisAAOMC ServerUmBEEX.25CFHX.25

GSM NetworkOMCAUCHLRMSCEIRVLRBSCBTSMSExternalPSTN &PDN N/W

SSBSSSwitchingSystemBase StationSystemMS Mobile StationBTS Base transceiver SystemBSC Base Station ControllerMSC Mobile Switching CenterHLR Home Location RegisterVLR Visitor Location RegisterEIR Equipment Identity RegisterAUC Authentication Center OMC Operation And Maintenance Center

GSM ArchitectureHLRVLREIRAUCMSCBSCBSCSMSCPSTNVMSCMobileStation GSM Air interfaceOMCRTRAUBase Station SystemNetwork and switching subsystemA interface SS7 / speechSS7X.25BTSBTSBTSBTSBTSBTS Abis interface A interfaceOMCS

Mobile Equipment(ME)Frequency and Time SynchronizationVoice encoding and transmissionVoice encryption/decryption functionsPower measurements of adjacent cellsDisplay of short messagesInternational Mobile Equipment Identifier (IMEI)

SIMPortable Smart Card with memory (ROM-6KB to 16KB-A3/A8 algorithm, RAM- 128KB TO 256KB, EEPROM- 3KB to 8KB )Static InformationInternational Mobile Subscriber Identity(IMSI)Personal Identification Number (PIN)Authentication Key (Ki)Dynamic InformationTemporary Mobile Subscriber Identity(TMSI)Location Area Identity (LAI)Phone memories, billing informationAbility to store Short Messages received

SIM-Card and GSM Mobile Equipment+SIM-CardContains:- IMSI=

The SIM-Card FunctionsMicrochip with storeduser informationCredit Card SizePermanent data:Unique mobile subscriber identity through IMSI number and PIMSI for Packet ModeAuthentication parameter Ki,Authentication algorithm A3,Generating encryption key Kc algorithm A8,PIN code.Removable data:- Temporary Mobile Subscriber Number,Location Area Identification Routing Area Identification (Packet mode) SIM-Card

Subscriber IdentificationNatureInternational Mobile Subscriber Identity

Conformity with E212Mobile Station - Integrated Services Digital Network Nb

Similar to ISDN, Conformity with E164/E213Nb. digits32max 101 to 32 to 4total max 15*This code does not identify a geographical areabut an operatorMS - ISDNFormatMCCMNCMSINH1 H2 x x x ......... x x xCCNDCSNM1 M2 x x x x x x x xMeaningMobileCountryCodeMobileNetworkCodeMobile SubscriberIdent. NbH1 H2 = Identity of HLR within the home PLMNCountryCode(where subscription has been made)NationalDestinationCode *Mobile Subscriber(national definition)M1 M2 = nbr of logical HLRIMSINational Significant Mobile NumberIdentify a PLMN worldwideIdentify the subscriber of a PLMN

Description Stored in SIM CardMobile Subscriber Identification Number (MSIN)H1 H2 X X X X X X 10 digits maxLocation Area CodeLACMCC = 208 (France)234 (G-B)262 (Germany)404,405(India)MNC =71(APBSNL)72(TNBSNL)20 (Bytel)IMSI = 15 digits maxNMSILAIRouting Area CodeRACRAI

Description Stored in the NetworkCountryCode

3 digits maxNationalDestinationCode2 or 3 digitsSubscriber Number (SN)Roaming Number (RN)HO-numberMust be dialed to make a call to mobile subscriberIs a PSTN-like number to track the MS that hands over to another MSC during call-in-stateIs a PSTN-like number used to reach a roamingMSCC = 33 (France)091(India)001(US)NDC = 9448(BSNL-karnataka)9845,9880(Airtel)9886(Hutch)

= 660, 661, 618 (Bytel)M1 M2 X X X X X X X X X X X X X10 digits maxCountryCodeNationalDestinationCodeCountryCodeNationalDestinationCodeMS-ISDN (15 digits max)MSRN

Descriptor Embodied in the Mobile EquipmentType ApprovalCode TACFACSNRSPFinal AssemblyCode Serial NumbeR(SPare)TYPEAPPROVEDIMEI enables the operator to check the Mobile Equipment Identityat call setup and make sure that no stolen or unauthorized MS is used in the GSM network

International Mobile Equipment Identity (IMEI)Type ApprovalCodeTACFACSNRSPFinal AssemblyCodeSerial number(SPare)IMEI: * # 0 6 #351475 609265144

MS ClassmarkRevision levelRF powerEncryption algorithmFrequencyShort messageLoCation ServicesMS Positioning Method8-PSK modulationMulti-slot classMulti-bandClassmarkPower classesClassGSM400/850/90012345

8 W* 5 W 2 W**0.8 WGSM1800GSM19001 W**0.25 W4 W1 W**0.25 W2 W*Typical value for car mounted**Typical value for handheldClassGSM400/850/900GSM1800GSM1900E1E2E3 2 W0.5 W0.2 W 1 W 0.4 W0.16 W 1 W 0.4 W0.16 WFor GMSK modulationFor 8-PSK modulation

Base Transceiver Station (BTS)Handles the radio interface to the mobile station.Consists of one or more radio terminals for transmission and receptionEach Radio terminal represents an RF ChannelTRX and MS communicates over Um interfaceReceived data transcodingVoice encryption/decryptionSignal processing functions of the radio interfaceUplink Radio channel power measurements

Base Station Controller (BSC)Provides all the control functions and physical links between the MSC and BTS External InterfacesAbis interface towards the BTSA interface towards the MSCMonitors and controls several BTSsManagement of channels on the radio interfaceAlarm Handling from the external interfacesPerforms inter-cell HandoverSwitching from Abis link to the A linkInterface to OMC for BSS Management

Mobile Switching Center (MSC)

Performs call switching Interface of the cellular network to PSTNRoutes calls between PLMN and PSTNQueries HLR when calls come from PSTN to mobile userInter-BSC HandoverPagingBilling

Home Location Register (HLR)Stores user data of all Subscribers related to the GMSCInternational Mobile Subscriber Identity(IMSI)Users telephone number (MS ISDN)Subscription information and servicesVLR addressReference to Authentication center for key (Ki)Referred when call comes from public land network

Visitor Location Register (VLR)Database that contains Subscriber parameters and location information for all mobile subscribers currently located in the geographical area controlled by that VLR Identity of Mobile SubscriberCopy of subscriber data from HLRGenerates and allocates a Temporary Mobile Subscriber Identity(TMSI)Location Area CodeProvides necessary data when mobile originates call

Authentication Center (AuC)Stores Subscriber authentication data called Ki, a copy of which is also stored in in the SIM cardGenerates security related parameters to authorize a subscriber (SRES-Signed RESponse)Generates unique data pattern called Cipher key (Kc) for user data encryptionProvides triplets - RAND, SRES & Kc, to the HLR on request.

EIR (Equipment Identity Register)EIR is a database that contains a list of all valid mobile station equipment within the network, where each mobile station is identified by its International Mobile Equipment Identity(IMEI).EIR has three databases.,White list - For all known,good IMEIsBlack list - For all bad or stolen handsetsGrey list - For handsets/IMEIs that are on observation

Location Area IdentityLAI identifies a location area which is a group of cells.. It is transmitted in the BCCH. When the MS moves into another LA (detected by monitoring LAI transmitted on the BCCH) it must perform a LU. LAI = MCC + MNC + LAC MCC= Mobile Country Code(3 digits), identifies the countryMNC= Mobile Network Code(1-2 digits), identifies the GSM-PLMNLAC= Location Area Code, identifies a location area within a GSM PLMN network. The maximum length of LAC is 16 bits,enabling 65536 different location areas to be defined in one GSM PLMN.

Interfaces and Protocols

GSM Entities and Signaling Architecture

GSM ProtocolsCM - Connection ManagementMM- Mobility ManagementRR - Radio resource LAPDm - LAPD for mobileLAPD - Link Access Procedure for D channelBTSM- BTS Management PartBSSAP - BSS Application Part (BSC - MSC)DTAP - Direct Transfer Application Part (MS - MSC)MAP - Mobile Application PartMTP - Message Transfer part of SS7SCCP - Signalling Connection Control Part of SS7TCAP - Transaction Capabilities Application PartISUP- ISDN User Part

Functional Plane of GSMMS BTS BSC MSC/ HLR GMSC VLRMS BTS BSC MSC/VLR HLR GMSCCCMMRRTrans

Channels : differentiating between Physical and Logical channelsPhysical channels : The combination of an ARFCN and a time slot defines a physical channel. Logical channels : These are channels specified by GSM which are mapped on physical channels.

Channel conceptPhysical channel:One timeslot of a TDMA-frame on one carrier is referred to as a physical channel. There are 8 physical channels per carrier in GSM,channel 0-7(timeslot 0-7)

Logical channel:A great variety of information must be transmitted between BTS and the MS,for e.g. user data and control signaling.Depending on the kind of information transmitted we refer to different logical channels.These logical channels are mapped on physical channel.

Logical Channels on Air interfaceLOGICALCHANNELSCOMMONCHANNELSDEDICATED CHANNELSBROADCAST CHANNELSCOMMONCONTROLCHANNELSDEDICATED CONTROL CHANNELS TRAFFIC CHANNELSFCCHBCCHSCHSDCCHSACCHFACCHPCHAGCHRACHTCH/FTCH/EFRTCH/H

Logical channelsFCCH

Broadcast channels BCH Broadcast Channel-BCH Alloted one ARFCN & is ON all the time in every cell. Present in TS0 and other 7 TS used by TCH.Frequency correction channel-FCCH To make sure this is the BCCH carrier.Allow the MS to synchronize to the frequency.Carries a 142 bit zero sequence and repeats once in every 10 frames on the BCH.Synchronization Channel-SCHThis is used by the MS to synchronize to the TDMA frame structure within the particular cell.Listening to the SCH the MS receives the TDMA frame number and also the BSIC ( in the coded part- 39 bits).Repeats once in every 10 frames.

Broadcast channels BCH ...BCCHThe last information the MS must receive in order to receive calls or make calls is some information concerning the cell. This is BCCH.This include the information of Max power allowed in the cell.List of channels in use in the cell.BCCH carriers for the neighboring cells,Location Area Identity etc.BCCH occupies 4 frames (normal bursts) on BCH and repeats once every Multiframe.This is transmitted Downlink point to multipoint.Cell Broadcast Channel - CBCHUsed for the Transmission of generally accessible information like Short Message Services(SMS)

Common Control Channels CCCHCCCH- Shares TS-0 with BCH on a Multiframe.Random access channel-RACH:Used by Mobile Station for requesting for a channel. When the mobile realizes it is paged it answers by requesting a signaling channel (SDCCH) on RACH. RACH is also used by the MS if it wants to originate a call.Initially MS doesnt know the path delay (timing advance), hence uses a short burst (with a large guard period = 68.25 bits).MS sends normal burst only after getting the timing advance info on the SACCH.It is transmitted in Uplink point to point.

Common Control Channels CCCH ..Access Grant Channel-AGCHOn request for a signaling channel by MS the network assigns a signaling channel(SDCCH) through AGCH. AGCH is transmitted on the downlink point to point.Paging Channel-PCHThe information on this channel is a paging message including the MSs identity(IMSI/TMSI).This is transmitted on Downlink, point-to-multipoint.

Dedicated Control Channels-DCCHStand alone dedicated control channel(SDCCH)AGCH assigns SDCCH as signaling channel on request by MS.The MS is informed about which frequency(ARFCN) & timeslot to use for traffic. Used for location update, subscriber authentication, ciphering information, equipment validation and assignment of TCH.This is used both sides, up and Downlink point-point.

Dedicated Control Channels-DCCHSlow associated control channel-SACCHTransmission of radio link signal measurement, power control etc.Average signal strengths(RXLev) and quality of service (RXQual) of the serving base station and of the neighboring cells is sent on SACCH (on uplink).Mobile receives information like what TX power it has to transmit and the timing advance. It is associated with TCH or SDCCHFast associated control channel-FACCHUsed for Hand over commands and during call setup and release. FACCH data is sent over TCH with stealing flag set

Traffic Channels-TCHTCH carries the voice data.Two blocks of 57 bits contain voice data in the normal burst.One TCH is allocated for every active call.Full rate traffic channel occupies one physical channel(one TS on a carrier) and carries voice data at 13kbpsTwo half rate (6.5kbps) TCHs can share one physical channel.

GSM Channels GSM ChannelsControl ChannelsTraffic Channels(TCHs)FullrateHalfrateDedicated ControlChannels(DCCHs)SlowFastDownlinkBroadcastChannels(BCHs)Common ControlChannels(CCCHs)DownlinkUplinkTCH /FTCH /HFCCHSCHBCCHPCHCBCHRACHAGCHSDCCHSACCHFACCHTraffic MultiframingSignaling MultiframingTraffic Multiframing(down uplink)

The Logical Channels on Radio Interface

Logical Channel Description (1/2)

Logical Channel Description (2/2)

GPRS Channels GPRSCORENETWORKBSCPCUSNPDCH = Packet Data CHannelPPCHPAGCHPNCHPDTCHPACCHPTCCHPDTCHPACCHPTCCHPBCCHPRACHDLPacket Common Control CHannelsPacket Traffic CHannelsPBCCH

Traffic and Control Multiframing01234212223242501234464748495026 traffic frames = 120 ms1 Hyperframe = 2,715,648 frames= 3h 28 min. 53 s 760 ms0123520422043204420452046204741326 framesTS0TS1TS2TS3TS5TS6TS7TS0TS1TS2TS3TS4TS5TS6TS7TS0TS1TS2TS3TS4TS5TS6TS7TS4TS0TS1TS2TS3TS4TS5TS6TS7TS0TS1TS2TS3TS4TS5TS6TS7Frame4.615 msControl channelTraffic channel51 x 26 traffic frames = 6.12 s26 x 51 control frames = 6.12 s

Logical Channel Mapping1 - Traffic Channel CombinationT: TCHA: SACCH: IDLETi: TCH sub-channel no. iAi: SACCH sub-channel no. itime 26 frames = 120 ms T0A0T0T0T0T0T0T0T0T0T0T0T0T1T1T1T1T1T1T1T1T1T1T1T1A1timeTATTTTTTTTTTTTTTTTTTTTTTT 26 frames = 120 ms

Logical Channel Mapping2 - Dedicated Signaling Channel CombinationA: SACCHD: SDCCH: IDLE 51 frames = 235 ms A1A2A3A0D7D6D5D4D3D2D1D0A5A6A7A4D7D6D5D4D3D2D1D0time 51 frames = 235 ms time

Logical Channel Mapping3 - Common Channel Combination 51 frames = 235.38 ms time 51 frames = 235.38 ms timeB: BCCHS: SCH F: FCCH: IDLE: PCH /AGCHCR: RACHBTSMSPhysical ChannelARFCN (n) TS (s) FCCHSCHBCCHPCH/AGCHFrames repeat continuouslyMultiframe m+1Multiframe m-1Multiframe m

Logical Channel Mapping4 - Common Channel CombinationA3A2A1D3D2D3D2D1D1D0D0 FS FS FSCCC FSB FS FS FS FSCCC FS 51 frames = 235 ms A0timeDownlinkRRRRD2D2D1D1D0D0A1A3A0A2RRRRD3D3 51 frames = 235 ms timeRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRA: SACCHD: SDCCH: IDLEB: BCCHS: SCH F: FCCH: AGCH/PCHCR: RACH

Why 26 and 51 Frames per Multiframe?Downlink messageUplink messageNeighboring BTS(downlink) Measurement WindowsCCFSCCFSCCFSCCCFS 0 1 12 25 0 1 12 250 1 10 20 30 40 50 0 1Mobile activity Rx Rx Tx Rx Rx Tx Rx Rx Tx (n) (n) (n)

From Speech to Radio TransmissionSpeechSourcedecodingChanneldecodingDe-interleavingBurst deformattingDecipheringDemodulationequalizationDigitizing andsource codingChannelcodingModulationCipheringBurst formattingInterleavingStep 1Step 2Step 3Step 4TransmissionStep 5Step 6Diversity

GSM Radio LinkSpeech Coding -Done at Transcoder of BSC and MSThe Linear Predictive Coder uses RPE-LTP(Regular Pulse Excitation- Long Term Prediction)Converts 64kbps voice to 13kbps(260 bits every 20ms)Channel Coding - Done at BTS and MSUses Convolution Coding and CRC (Cyclic Redundancy Check)Converts 13 kbps to 22.8 kbps (456 bits per 20ms)

GSM Radio LinkBit Interleaving - Done at BTS and MSEncryption - Done at BTS and MS EX OR data with cipher block, which is generated by applying A5 Algorithm to the Ciphering Key(Kc)Multiplexing - Done at BTS Modulation - Done at BTS and MS GMSK(Gaussian filtered Minimum Shift Keying)Phase change of +90 for 0 and -90 for 1

Why Digitizing and Coding the Speech?SPEECHTRANSMISSIONBETWEEN MOBILEAND NETWORKBSSMSSPEECH MUST BE DIGITIZED AND CODED64 kbit/sBetter QualityLower Rate

Speech Quality Source CodingCodec Type Mean Opinion ScoreRate (kb/s)(MOS)

PCM A law4.2564GSM EFR4.212.2CDMA 134.213D-AMPS48GSM FR3.813CDMA 83.48 QualityMOS Listening Effort Required

Excellent5 Complete relaxation possible, no effort. Good4 Attention necessary, no appreciable effort. Fair3 Moderate effort. Poor2 Considerable effort. Bad1 No meaning understood with feasible effort.

Speech CodingBPA/DSPEECHENCODERCHANNEL CODINGLPD/ASPEECHDECODERCHANNEL DECODINGBAND PASS300 Hz - 3.4 kHZEvery 125 s value issampled from analog signal and quantised by 13 bit wordData rate = 13/125*10 -6 = 104 kbpsEvery 20ms 160 samples takenData rate = 160 * 13/20ms = 104 kbpsLinear Predictive Coding & Regular Pulse Excitation Analysis1. Generates 160 filter coeff2. These blocks sorted in 4 sequence 1,5,9,37 / 2,6,10----38/ 3,7,1139/8,12,16403. Selects the sequence with most energy

So data rate = 104/4 = 26 kbpsLong term prediction analysis1. Previous sequences stored in memory2. Find out the correlation between the present seq. And previous sequences3. Select the highest correlation sequence4. Find a value representing the differencebetween the two sequences.

Reduces data rate = 26 kbps/2 = 13 kbpsie 260 bits in 20ms50132781A1B21A = Filter Coeff block ampl, LTP params1B = RPE pointers &pulses2 = RPE pulse & filterparams50313243 crc bitsFour 0 bits for codec378 coded bitsConv coding rate = 1/2 delay = 478456 bits in 20 ms = 22.8 kbps57 x 8 = 456To modulator

Channel Processing in GSMOverview for Full Rate8 Bursts8 Sub blocks of 57 bits Source codingChannel codingInterleavingNormal burstSpeech blocks

Channel Processing in GSMOverview for Half Rate4 Bursts4 Sub blocks of 57 bits Source codingChannel codingInterleavingSpeech blocks

Interleaving: TCH Full Rate0 1 2 3 4 5 6 7 8 ......452 453 454 45501234567 8 9101112131415 44844945045145245345445557 RowsDivide 456 bits in 8 sub-blocks7654321076540123reordering&partitioningoutdiagonalinterleaving456coded bitsburstb0b1b56b1b56b0bitinterleaving

Burst FormattingNormal Burst1 frame:4.615 ms01234567Guard572657DATA156.25 bits duration(0.577 ms)Trainingsequence3DATA8.25SSGuardBandBurst148 bits

Burst Formats

Burst FormatsAccess BurstDummy BurstNormal Burst

CipheringPlain data:0 1 1 1 0 0 1 0.....Ciphering sequence:0 0 0 1 1 0 1 0.....XOR:Ciphered data (transmitted):0 1 1 0 1 0 0 0.....Ciphered sequence: 0 0 0 1 1 0 1 0..... XOR: Recovered data:0 1 1 1 0 0 1 0.....DataSSDataBurst to betransmittedDataSSTrainingsequenceDataReceived burst

Interleaving5757575757575757575757575757575757575757575757575757575757575757575757575757575757575757575757575757575757575757Encoded speech blocks - Diagonal InterleavingEven bitsOdd bitsTb 3Coded Data 57F 1Training Sequence26F 1Coded Data 57Tb 3Gp8.25Bn-4 Bn-3 Bn-2 Bn-1 Bn Bn+1 Bn+2 Bn+3 575757575757575757575757575757575757575757575757575757575757575757575757575757575757575757575757Encoded control channel blocks - Rectangular InterleavingEven bitsOdd bitsBn-4 Bn-3 Bn-2 Bn-1 Bn Bn+1 Bn+2 Bn+3

BurstThe information format transmitted during one timeslot in the TDMA frame is called a burst.Different Types of BurstsNormal BurstRandom Access BurstFrequency Correction BurstSynchronization Burst

Normal BurstT3Coded Data57S1T. Seq.26S1Coded Data57T3GP8.25Tail Bit(T):Used as Guard TimeCoded Data :It is the Data part associated with the burstStealing Flag:This indicates whether the burst is carrying Signaling data (FACCH) or user info (TCH).Training Seq.:This is a fixed bit sequence known both to the BTS & the MS.This takes care of the signal deterioration.

156.25 bits 0.577 ms

T3Training Sequence41Coded Data36T3GP68.25Random Access BurstT3Fixed Bit Sequence142T3GP8.25T3Coded Data39 Training Sequence64CodedData 39T3GP8.25Synchronization Burst156.25 bits 0.577 ms156.25 bits 0.577 ms156.25 bits 0.577 ms

Transmission on the radio channels A timeslot has a duration of .577 m seconds (148 Bits) 8 timeslots(8 x 0.577 = 4.62 ms) form a TDMA frame If a mobile is assigned one TS it transmits only in this time slot and stays idle for the other 7 with its transmitter off, called bursting The start on the uplink is delayed from downlink by 3 TS periods One TS = duration of 156.25 bits, and its physical contents is called a burst DownlinkBTS > MSUplinkMS > BTSOffset

Timing Advance

Frames Types On Um InterfaceTDMA Frame 8 Time slots (Burst Period)Length is 4.62 ms(8 * 0.577ms) 26-TDMA Multiframe26 TDMA Frames (24 TCH, SACCH, Idle)120 ms (26 * 4.62ms)51-TDMA Multiframe26 TDMA Frames (FCCH, SCH, BCCH, SDCCH, CCCH)235.6 ms (51 * 4.62ms)

Frames Types On Um InterfaceSuper Frame51* 26 TDMA Frames6.12 SHyper Frame2048 * 51* 26 TDMA Frames3 Hours, 28 Minutes, 53 Secs and 760 ms

Mobility ManagementMobility Management (MM)Location updating- normal,periodic, IMSI attachPagingSecurity ManagementPreventing unauthorized users- authenticationMaintaining Privacy of users- cipheringProviding roaming facilityMM functionality mainly handled by MS, HLR, MSC/VLR.

Network AttachmentCell IdentificationMS scans complete GSM frequency band for highest powerTunes to highest powered frequency and looks for FCCH. Synchronizes in frequency domainGet training sequence from SCH which follows FCCH. Synchronizes in time domain.Accesses BCCH for network id, location area and frequencies of the neighboring cells. Stores a list of 30 BCCH channels

Network Attachment..PLMN SelectionGet the operator information from SIM.Cell SelectionSelected cell should be a cell of the selected PLMNSignal strength should be above the threshold.Cell should not be barredLocation UpdateRegister with the network by means of location updation procedures.

MS Location Update (registration) MS BTS BSC (G)MSC VLR HLR Action

Security - Authentication

Authentication center provides RAND to MobileAuC generates SRES using Ki of subscriber and RANDMobile generates SRES using Ki and RANDMobile transmits SRES to BTSBTS compares received SRES with one generated by AuC

Security - Ciphering

Data sent on air interface ciphered for security A5 and A8 algorithms used to cipher dataCiphering Key is never transmitted on air

Communication Management (CM)Setup of calls between users on requestRouting function i.e. Choice of transmission segments linking usersPoint to Point Short message services

GSM ActorsPublicSwitchedTelephoneNetworkBTSBSSFixed subscriberMobile subscriberAUCHLRVLRMSCNSS

PLMN SelectionNoautomatic modeThe MS selects the first PLMN from the preferred PLMNs list (if it is not in the forbidden PLMNs list)The user selects a PLMN from the displayed PLMNsmanual modeYesYesCreation of a found PLMN listIs there an up to date found PLMNs list?End of PLMN selectionYesNo (automatic)Selection of the next preferred possible PLMNNo (manual)

PLMN SelectionConstitution of the "Found PLMN list"Listen to all the frequencies of the GSM spectrum:power level measurement and average on these measurementsSelect the best frequencies according to the power level(124 channels in GSM 900, 374 in GSM 1800and 299 in GSM 1900(30 in GSM 900 and 40 in GSM 1800)Memorize the beacon frequencies in the precedent selection => Create the Found PLMN list

Initial Cell SelectionSuitable cell:

- cell of the selected PLMN- cell not barred- C1 > 0Eligible cellList of the frequencies of the selected PLMNIMSI AttachLook for the cell with the best C1 in the suitable cells listYesSelection of another PLMNNoC1 Computation for eligible cellsYesNoRejected?YesPLMN set in the forbiddenPLMN listEnd of Cell SelectionNo

Cell SelectionBTS-2BTS-1This cellBTS-3BTS-4BTS-511112345Purpose: get synchronization with the GSM network prior establishing any communication.FCCHSCHBCCH1

Immediate AssignmentImmediate Assignment

Registration: the Very First Location UpdateLAIHLRIMSIVLR idTMSIIMSITMSIReleaseVLRIMSITMSILAIMSC245261245634TMSI5

Intra VLR Location UpdateVLRIMSITMSILAI1234 new TMSITMSI + old LAI23423TMSINew TMSINew LAIBTSBSSIMSI not Required

Inter VLR Location UpdateNew LAI newTMSITMSI + old LAITMSINew TMSIBSS12572572IMSI,TMSILAINew VLRIMSI, TMSIOld LAIOld VLRRAND, SRES, KcHLRnew VLR idsubscriberdata34665IMSI not RequiredRAND, SRES, Kc

IMSI AttachBTSBSSVLR345464AuthenticationProcedure

IMSI DetachVLR1CHANNELREQUEST

Outgoing CallFTGreat BritainFranceGermanyTelephonenetworkTerminatingMSCBTSBSSVLRGatewayMSCHLR

Mobile Originating CallACM = Address Complete Message ANM = ANswer MessageIAM = Initial Address MessageDialingRingingPathEstablishedRingingSendingNumber

Mobile Terminating Call1 - Paging PrinciplePSTNLA1LA2BTS11BTS21BTS22BTS31BTS12BTS2343512566BSC1BSC2BSC3MSC/VLRGMSC

Mobile Terminating Call2 - Detailed ProcedureIAM:Initial Address MessageMSISDN:Mobile Station Integrated Services Digital network NumberMSRN:Mobile Station Roaming NumberIMSI:International Mobile Subscriber IdentityGMSC:Gateway MSCVMSC:Visitor MSCTMSI:Temporary Mobile Subscriber IdentityMSISDN1

Mobile Terminating Call3 - End to End ProcedureDialingRingingPathEstablished

Call Release1 - Mobile Initiated

Call Release2 - PSTN InitiatedPSTNOn hookPurpose:informs the mobilethen releases radio and network resources.RELRLCBTSBSS1111233455462

Mobile Originated CallRequest for ServiceAuthenticationCipheringEquipment ValidationCall SetupHandoversCall Release

Mobile Terminated CallPagingAuthenticationCipheringEquipment ValidationCall SetupHandoversCall Release

Mobile Terminated CallAuthentication and Ciphering procedure done as seen in Location Updation

Radio Resource ManagementEstablish maintain and release stable connections between MS and MSCManage Limited Radio and Terrestrial resourcesHandover process is the sole responsibility of the RR LayerFunctions of RR layer are performed by MS and BSC and partly by MSC

Radio Resource Management

Power ControlHand over ControlDiscontinuous TransmissionFrequency Hopping

Power ControlBTS commands MS at differentdistances to use different power levelsso that the power arriving at the BTSs Rx isapproximately the same for each TS

- Reduce interference- Longer battery life

HandoverMeans to continue a call even a mobile crosses the border of one cell to another Procedure which made the mobile station really roamHandover causesRxLev (Signal strength , uplink or downlink)RxQual (BER on data)O & M interventionTiming AdvanceTraffic or Load balancing

Handover TypesInternal Handover (Intra-BSS)Within same base station - intra cellBetween different base stations - inter cellExternal Handover (Inter-BSS)Within same MSC -intra MSCBetween different MSCs - inter-MSC

Handover TypesBSCBSCBSCBSCMSCMSCGMSCC-1C-2C-3C-4

Periodic Measurement Reports (SACCH)Cell 1Cell 2BSCBTS 1BTS 2Intra BSC handover

Frequency plan and importance of BCCH B3B2B9B6B4B1Sectored antennasMS ( monitoring the broadcast radio B1 in idle mode )F0F50F2F3F4F5F10F11F1

F,S,B exist in time slot 0 of each frame

B7B8B5B10B11B12BPL frequency plan:Broadcast frequencies : 15 Broadcast channels = 48-62 15 Hopping channels = 32-46

FSBBBB..FS....I

What information does Broadcast Control channel (BCCH) contain? Serves as a Beacon for the Cell Country Code (CC) and the Network Code (NC) Location Area Identity (LAI) List of neighboring cells which should be monitored by MS List of frequencies used in the cell Cell identityBack

Location UpdatesLocation Updates can be classified into two:

Periodic Location Updates:This occurs as per the timer set by the network operator. If the MS does not perform this update the MSC marks the MS as Detached on the VLR.

Location Update on a handover:This occurs if during a handover the MS is moved into a new Location Area Code (LAC).

BackThe MS is monitoring the BCCH and has all the decoded information stored on the SIM ( including the LAC) As soon as the mobile is on a TCH it sends the signal strength indication on the corresponding SACCH The BSC monitors the signal strengths and on analysis sends a handoff request on FACCH. The handoff process is completed on the FACCH. After the completion of call, the MS starts monitoring the BCCH again. On finding the LAC (stored on SIM) and that decoded from the BCCH to be different , the MS requests a Location Update through SDCCH.

Discontinuous Transmission Discontinuous Transmission(DTX) allows the radio transmitter to be switched off most of the time during speech pauses.A Silence Indicator Block is transmitted at 500bps, which generates a comfort noiseDown Link interference is decreased.Up link battery is saved

Frequency HoppingFrequency Hopping permits the dynamic switching of radio links from one carrier frequency to another.Base Band HoppingAt the BTS each the timeslot is shifted to another transceiver, which is transmitting at the hop frequency. User will be connected to different Transceivers depending on hop sequence.Synthesis HoppingAt the BTS transceiver changes the frequencies used. The user will be connected to only one transceiver.Decreases the probability of interferenceSuppresses the effect of Rayleigh fading

Wireless Data

Coverage or Traffic LimitationsTRAFFIC-LIMITEDAREA(10000 subscribers per km2)COVERAGE-LIMITEDAREA(-75 dBm at cell edge)COVERAGE- LIMITEDAREA(-70 dBm at cell edge)

Erlang Concept Average number of busy channels during the period of observation (usually, the peak hour).Erlang is the unit of statistical resource useErlang BAt any time, more than 1 user may request the same resource simultaneously. The use of such a resource is associated with a blocking rate.

Erlang CWhen more than 1 user request at the same time, instead of rejecting the extra calls, there is a queuing system.

Different Types of CellsHigh sensitivity to interferenceRequires "secured" Frequency reuse pattern High isolation from interferencesA few Frequencies intensively reusedMACRO-CELL:antenna radiating above roofs---> Wide Coverage ( 35 km)MICRO-CELL:Antenna below the roofs---> small coveragePICO-CELL:Antenna inside building---> Very small coverageEXTENDED-CELL:macro cell with system coverageextension ( 120 km) for coasts...CONCENTRIC-CELL:macro cell with system coveragelimitation inside another macro

Cell Patterns

Cell SectorizationTRIOMNIBI

Omnidirectional Site Antennas

Bi and Trisectorial Site Antennas

Link BudgetingCalculation of the maximum coverage range of each cell in a specific environment.

Definition of planning tools parameters.

Based on the path loss calculation between the MS and the BS in both ways.

This calculation considers:RF parameters of MS and BS,system parameters (diversity gains...),propagation parameters (shadowing),physical installation parameters (antenna height),environment classification.

-What is the maximum EIRP?-What are the losses in transmission and reception?-Is diversity used?-What is the minimum equivalent sensitivity?-What is the maximum equivalent output power?-What are the body losses?-Beyond which distance the communication will cut off? -Is indoor coverage guaranteed?-Is frequency hopping used?EIRP:Equivalent Isotropic Radiated Power

Link Budget ParametersOverviewDuplexerCombinerPower AmplifierDLNA:Diversity Low Noise AmplifierSpecific Tx Cable LossesTx PA OutputPowerCombiner lossesRx SensitivityRx Diversity GainDLNA conf.Standard conf.Base StationTx PA Output PowerOther factors for MSBody LossesCommon cable lossesPropagation Parameters:- Incar, Indoor penetration factors- Frequency 900, 1800, 1900 MHz- Antenna Height- Environment

Design Parameters:Overlapping marginRx SensitivityAntenna GainMSRx SensitivityCommon cable LossesAntenna GainRadio Link

Link Budget ParametersBTS TX Power Amplifier2.5W PA25W PA35W PA20W PA30W PAGSM 900S2000LS2000ES4000 IndoorS4000 OutdoorS4000 IndoorS2000HS8000 Indoor S8000 OutdoorDCS 1800S2000LS4000 Indoor S2000E S2000H S4000 Outdoor S4000 IndoorS8000 Indoor S8000 Outdoor PCS 1900S2000LS2000E S2000H S4000 Indoor S4000 Outdoor S8000 Outdoor

Link Budget ParametersCombinersDH2DHy/22-Way Hybrid Combiner with Duplexer 4.5 dB Lossallows Synthesized Frequency Hopping4-Way Cavity Combiner with Duplexer allows Baseband Frequency Hopping4.9 dB LossCCCCDTXTXTXTXTXTX

Link Budget ParametersCable LossesAt the BS, for a 7/8 foam dielectric coaxial cable:4 dB/100 m (900 MHz),

6 dB/100 m (1800 MHz),

Common cable losses for 40 meters: 2.5 dB (900 MHz) and 3.5 dB (1800 MHz).

Jumpers (up and down the feeder)

0.5 dB (800 MHz),

1 dB (1800 MHz).

Link Budget ParametersBTS Antenna GainOmnidirectional antenna

Default 6.5 V with 11 dBi gain

Directional antenna for trisectorial site

Default 65 H / 6.5 V with 18 dBi gain

Link Budget ParametersMobile Station Parameters900 MHz1800/1900 MHzTX PA OutputPower33 dBm (2W)30 dBm (1W)RX Sensitivity-102 dBm-2 dBi for Handheld2 dBi for Car KitBody LossAntenna GainCommon CableLoss-100 dBm0 dB for Handheld2 dB for Car Kit3 dB for Handheld0 dB for Car Kit

Link Budget PresentationParameters

Frequency1800 MHzBase Height40.0 mMobile Height1.5 mEnvironmentUrbanRXTXMobileAntenna Gain-2 dB Cable Loss 0 dBOutput PowerSensitivity -100 dBm30 dBmAntenna Gain (65 ) Jumper LossFeeder Loss Sensitivity -110 dBm18 dBi3 dBOptions Rx Diversity Gain: 5 dB Overlapping Margin: 0 dB Penetration FactorBody Loss3 dB15 dB0.5 dBBase StationMax TX Output PowerRXm RXd 44.8 dBmCoupling systemTx loss4.5 dB

Link Budget CalculationExercise 1: S8000 INDOOR: OPERATING FREQUENCY 1800 MHz

FadingExample of Field Strength Variation for GSM 1800 -100-90-80-70-60-50-40-30-20-100500100015002000250030003500400045005000Distance (m)Field Strength (dBm)Zoom onShort Term FadingLong Term Fading 2 m /2

Clutters

1982: CEPT (Confrence Europenne des Administrations des Postes et Tlcommunications) decides to establish a "Groupe Spcial Mobile" (the initial origin of the Term GSM) to develop a set of common standards for a future pan-European Cellular Mobile Network.1984: Establishment of three Working Parties to define and describe GSM features:the radio interface,transmission and signaling protocols,interfaces and network architecture.1985, 1986: Discussion and adoption of a list of recommendations to be generated by the Group Spcial Mobile. A so-called permanent nucleus is established to continuously coordinate the work, which is intensely supported by industry delegates. Much thought goes into developing a radio transmission prototype.

One important question was how far GSM should go in its specification work; that is, to what degree the system had to be specified so as to be identical in all countries, and how much could be left to the operators and suppliers to agree upon.Clearly, without identical air interfaces in all networks, the subscribers were not going to have free roaming between networks. This was considered to be the absolute minimum degree of standardization, and this solution was favored. It might have been seen to be advantageous to specify everything in the system, including the hardware and the mobile station and even other parts of the system. It was agreed however that there would be no attempt to specify the system in such detail. Basically, only the functional interfaces between the major buildings blocks would be specified. This approach had several advantages, perhaps the most important of which is that for each major building block, the principle of functional specifications offers each operator, and thus the customer, the opportunity to purchase whatever make of equipment he wants, thus setting the stage for maximum competition between manufacturers. For instance the fact that an operator has purchased an exchange from a certain supplier does not force him to go on buying equipment from the same supplier.Standardized electrical interfaces as well as protocols were provided for both the fixed network and subscriber equipment. These included standardized rate adaptations compatible with conventional ISDN (Integrated Services Digital Network) definitions.GSM phase 2We can currently use a data terminal attached to an MS to connect to any standard data service provided by the PSTN, ISDN or PDN networks as long as the network accepts a data rate of 9.6 kbps and the Inter-Working Function (IWF) is installed.This includes access to the Web, e-mail, fax etc.. Use of these facilities is generally limited due to the speed of the communication. Internet use is expensive and slow due to the limited data rate and the circuit switched nature of the GSM system.The BSS provides two modes:transparent data service,non transparent data service, using RLP protocol between the MS and the IWF.GSM phase 2+A new service has been standardized in ETSI to reach 14.4 kbps user rate on one TS. This new data rate is the result of a new channel coding on the radio interface. This enhancement is a part of a global strategy aimed at offering higher data rates and called High Speed Circuit Switched Data (HSCSD). HSCSD allows 14.4 kbps in one TS and up to 56 kbps in the future, using multiple TSs. It is however, still a circuit switched system which will supply expensive connections unless the operators pricing schemes are imaginative. It will help those who use data over GSM today and encourage others to use the services but it does involve a capacity penalty for the network.Today, GSM has the capability to handle messages via the Short Message Service SMS and a 14.4 kbps circuit switched data service for data/fax calls.This maximum speed of 14.4 kbps is relatively low compared to wireline modem speeds of 34.4 and even 56 kbps.To enhance the current data capabilities of GSM, operators and infrastructure providers have specified new extensions to GSM phase 2:High Speed Circuit Switched Data (HSCSD) by using several circuit channels.General Packet Radio Service (GPRS) to provide packet radio access to external Packet Data Networks (Internet or X.25 networks).Enhanced Data rate for Gsm Evolution (EDGE), using a new modulation scheme, to allow up to three times higher throughput (for HSCSD and GPRS).Universal Mobile Telecommunication System (UMTS), a new wireless technology but utilizing new infrastructure deployment. These extensions enable:higher data throughput,better spectral efficiency,lower call setup times.The typical internet data traffic is characterized by an ON/OFF model.The user spends a certain amount of time downloading web pages in quick succession followed by indefinite periods of inactivity. During this inactivity the end-user may read the information or think or do something else. The traffic is sporadic and can be characterized as data packets of average size 16 kbytes/s with average intervals of 7 seconds.If a circuit switch connection is used to access the Internet, the bandwidth dedicated for the entire duration of the session is under-utilized.The carrier frequency is designated by the Absolute Radio Frequency Channel Number (ARFCN). If we call Fl(n) the frequency value of the carrier ARFCN n in the lower band, and Fu(n) the corresponding frequency value in the upper band, we have:GSM 450:Fl(n) = 450.6 + 0.2*(n - 259)(259 n 293)Fu(n) = Fl(n) +10,GSM 480:Fl(n) = 479 + 0.2*(n - 306)(306 n 340)Fu(n) = Fl(n) +10,GSM 850:Fl(n) = 824.2 + 0.2*(n - 128)(128 n 251)Fu(n) = Fl(n) + 45,P-GSM 900:Fl(n) = 890 + 0.2*n(1 n 124)Fu(n) = Fl(n) + 45,E-GSM 900:Fl(n) = 890 + 0.2*n (0 n 124)Fu(n) = Fl(n) + 45,Fl(n) = 890 + 0.2*(n -1024)(975 n 1023)Fu(n) = Fl(n) + 45,R-GSM 900:Fl(n) = 890 + 0.2*n(0 n 124)Fu(n) = Fl(n) + 45,Fl(n) = 890 + 0.2*(n -1024)(955 n 1023)Fu(n) = Fl(n) + 45,

DCS 1800:Fl(n) = 1710.2 + 0.2*(n-512)(512 n 885)Fu(n) = Fl(n) + 95,PCS 1900:Fl(n) = 1850.2 + 0.2*(n-512)(512 n 810)Fu(n) = Fl(n) + 80.

Frequencies are in MHz.

Following the resolution of the World Radio Communication Conference in 1978, the European Telecom Authorities primarily reserved two frequency bands of twice 25 MHz:890 MHz to 915 MHz from the mobile station to the network, 935 MHz to 960 MHz from the base stations to the mobile stations, for use by cellular systems.By 1990, a newly allocated band of twice 75 MHz (1710 MHz to 1785 MHz for the uplink and 1805 MHz to 1880 MHz for the downlink) was specified for the Digital Communication System which is a version of GSM suited to the 1800 MHz frequency band. This application was initiated in the United Kingdom.Furthermore the FCC granted bands of twice 60 MHz (1850 MHz to 1910 MHz for the uplink and 1930 MHz to 1990 MHz for the downlink) devoted to GSM networks.Two other frequency bands are supported:the Extended GSM 900 band or E-GSM = P-GSM + 2x10 MHz,the Railway GSM 900 band for Railway companies or R-GSM = E-GSM + 2x4 MHz.New frequency bands available:GSM 450 and 480 (not supported by Nortel),GSM 850.The network can carry two types of information:Traffic: this concerns all the user to user information. It can be voice as well as data.Signaling: the network also needs to carry information for its own working. The purposes of this information are numerous: traffic data routing, maintenance, security. These data are not usually visible from the users point of view.There are several signaling types:PTS (Per-Trunk Signaling): signaling and voice components are transmitted on the same facility. PTS requires the voice component to be completely built, even if the call cant be completed.CCS (Common Channel Signaling): two separate paths are used for information transfer (one for traffic, another for all related signaling information). Thus, CCS allows the voice component to be built separately, which allows resources to be saved. For instance, no voice facilities would be assigned to the call if the dialed number is busy.

GSM works with CCS (no. 7)A pair of radio channels are used for full duplex communications. Thus GSM uses both the uplink and the downlink bands of a given radio spectrum. In other words, a radio channel refers to a pair of frequencies used for a cellular radio talk path. One is used for cell site to mobile transmission while the other is used for mobile to cell site transmission.The radio spectrum is first partitioned in frequency by radio frequency channels (RFCHs) divided into bands. GSM signal defines a channel spacing (the space between two adjacent channels) of 200 kHz.A TDMA frame contains 8 successive Time-Slots (TS) with a duration of 60/13 ms or 4.615385 ms.A TS, has a duration of 15/26 ms or 0.576923 ms.A physical channel is made of the recurrence of the same TS taken from successive frames of the same channel.

A physical channel uses a combination of frequency and time division multiplexing and is defined as a sequence of radio frequency channels and time slots.An optional feature is to activate frequency hopping. Mobile radio channels suffer from frequency-selective fading due to multipath propagation phenomena. This selective frequency interference can increase with the distance from the base station, especially at the cell boundaries and under unfavorable conditions. Frequency hopping the transmission frequencies periodically and thus average the interference over the frequencies in one cell.This leads to an improvement of the Signal-to-Noise Ratio (SNR).On the emitting end, speech frames are first coded from analog to digital (source coding) then protected (channel coding). Bits are then interleaved and grouped together in sub-blocks. These sub-blocks are distributed over several bursts modulating a carrier and then transmitted.On the receiving end, the reverse operations are performed with an option on processing diversity.The radio interface in the GSM system is responsible for maintaining communication between the fixed network and mobile subscribers.The radio interface serves two major functions in the GSM system.To transport user information, either speech or data.To exchange signaling messages between the mobile station and the network (e.g. call in progress indication and preparation and execution of handovers).Signaling by borrowing the traffic channel of an existing communication.Signaling over a dedicated channel.The transmission resource used to fulfill this radio need is the channel.

The start of an uplink TDMA frame is delayed with respect to the downlink by a fixed period of three Time Slots. Why?In GSM, all radio frequency channels in a given cell are synchronized such that the frame and time slot boundaries on all downlink radio frequency channels occur at the same time. The same is true for the uplink radio frequency channels in that cell. However, the uplink frames are delayed by three time slots from the downlink frames. This prevents an MS using a single time slot in each direction from having to transmit and receive simultaneously and reduces the cost and complexity of GSM handsets.On the radio path, propagation delays cannot be ignored. Indeed, 1 km corresponds to a propagation delay of 3.33 s (compared with a bit period of 48/13 = 3.7 s).But the BTS receives continuously, and has its own scheduling. The mobile station must itself balance the propagation delay, in order to avoid overlapping in the frame received by the BTS.This is why the system takes into account these timing delays and orders the mobile station to transmit with an anticipation called the Timing Advance.On their path, radio waves propagate at the speed of light:3*10exp8 m/s.1 km corresponds to a propagation delay of 3.33 ms (compare to a bit period of 48/13 ms = 3.69 ms).Timing Advance is exchanged between BTS and MS through a number (from 0 to 63), one unit represents one bit duration: 48/13 ms, maximum value for Timing Advance is 63 or 63*48/13 ms.Timing Advance being twice the propagation delay between BTS and MS, this maximum value corresponds to [(63*48 *10-6 )/(13*2)]*3*10exp8 or 34,892 km.One unit or step in Timing Advance (TA) corresponds to: [(48 *10-6 )/(13*2)]*10exp8 or 553,84 m.The GSM committee has introduced an important powerful innovation by using a Smart Card in conjunction with a mobile telephone. Thus GSM subscribers are provided with a Subscriber Identity Module card (SIM-Card) with its unique identification at the very beginning of the service.The subscriber is identified within the system when he inserts the SIM-Card in the mobile equipment and switches it on. This provides a considerable amount of flexibility to the subscribers since they can use any GSM-specified mobile equipment.With the SIM-Card the idea of "personal communication" is already realized: the user only needs to take his smart card on a trip. You can rent a mobile equipment unit at the destination, even in another country, and insert your own SIM-Card. Any call you make will be charged to your home GSM account. Also the GSM system is able to reach you at the mobile unit you are currently using.The Mobile Station (MS) includes radio equipment and the man machine interface (MMI) that a subscriber needs in order to access the services provided by the GSM network.Mobile Stations can be installed in vehicles or can be portable or hand-held stations.The mobile station includes provisions for data communication as well as voice.Mobile Stations transmit and receive messages to and from the GSM over the air interface to establish and continue connection through the system.Each mobile station has an International Mobile Equipment Identity (IMEI) that is permanently stored in the mobile unit. Upon request, the MS sends this number over the signaling channel to the network. The IMEI is used to identify mobile units that are reported stolen or operating incorrectly.The SIM-Card is a removable smart card, the size of a credit card, and contains an integrated circuit chip with a microprocessor, random access memory, and read-only memory. It carries the subscribers unique information as well as personal directories or other information that the user might think that they are storing on their mobile.Many MSs use the SIM-Card which can be snapped out of the credit card SIM, if required.The SIM-Card is programmed somewhere between manufacture and delivery to include security attributes that allow the mobile to successfully authenticate in the network and be able to coordinate ciphered communications across the radio interface. The keys and algorithms used for authentication and ciphering are programmed in the SIM-Card.When mobile users want to make a call, they insert their SIM-Card and provide their Personal Identity Number (PIN), which is compared with a PIN stored within the SIM-CARD. The PIN can also be permanently bypassed by the subscribers if authorized by the service provider. Disabling the PIN code simplifies the call set-up but reduces the protection of the user's account in the event of a stolen SIM-Card.The International Mobile Subscriber Identity (IMSI) is the primary identification of the subscriber within the GSM network and is permanently assigned to him. It is stored in the SIM card. The IMSI consists ofMobile Country Code (MCC): 3 decimal places, internationally standardizedMobile Network Code (MNC): 2 decimal places, for unique identification for mobile networks within a countryMobile Subscriber Identification Number (MSIN): maximum 10 decimal places, identification number of the subscriber in his/her mobile home network.The Mobile Subscriber ISDN Number (MSISDN) is the real telephone number of a mobile station. It is used by the land networks to route calls toward an appropriate GSM network. The MSISDN is stored in the HLR and consists ofCountry Code (CC): up to 3 decimal placesNational Destination Code (NDC): typically 2-4 decimal placesSubscriber Number (SN): 10 decimal places.These descriptors are used in the different phases of call setup:International Mobile Subscriber Identity (IMSI) is the proprietary identifier of the mobile subscriber within the GSM network and is permanently assigned to him; it consists of an MCC, an MNC and an MSIN:Mobile Country Code (3 digits) is allocated to the operator country,Mobile Network Code (2 digits) is allocated to each operator,Mobile Subscriber Identification Number (10 digits) is allocated to each subscriber by the GSM network (HLR).The GSM network can assign a Temporary Mobile Subscriber Identity (TMSI) to identify the mobile on a local basis (within the VLR), allocated to visiting mobile subscribers and correlated with the IMSI. Location Area Identity (LAI) defines a part of a MSC/VLR service area in which a MS can move freely without updating location; it consists of an MCC, an MNC and a Location Area Code (LAC).Routing Area Identity (RAI) defines a part of a SGSN service area in which a GPRS MS can move freely without updating its routing area; it consists of an LAI and a Routing Area Code (RAC).National Mobile Subscriber Identity (NMSI) consists of the MNC and the MSIN.The Mobile Subscriber ISDN Number (MS-ISDN) is the number that the calling party dials in order to reach the GSM subscriber. It is used by the land networks to route calls toward an appropriate GSM network. The MSISDN is stored in the HLR.The Mobile Subscriber Roaming Number (MSRN) is allocated on a temporary basis when the MS roams into another numbering area.Thus the MSRN shall have the same structure as international ISDN number in the area in which it is allocated. The visited MSC allocates an MSRN upon the VLR request, which in turn was requested by the HLR.Upon reception of the MSRN, the HLR sends it to the GMSC, which can now route the call to the MSC/VLR where the called subscriber is currently registered.HO number is used for inter-MSC Handovers, to establish a circuit from the serving MSC to the new MSC.The IMEI is stored inside the Mobile Equipment.It is used instead of the IMSI or TMSI when both are unavailable (example: Emergency calls without SIM card) or when required by the network (for maintenance).It can be used for EIR database updating (when it exists):TAC = 6 digits describing the type of equipment.FAC = 2 digits for identification of the factory.SNR = 6 digits for the serial number of the device.The IMEI may be temporary stored within MSC/VLR to minimize signaling within the Network.

Stored inside the Mobile Equipment.Used to replace IMSI or TMSI when both are unavailable (example: Emergency calls without SIM-Card) or when required by the network (for maintenance).Can be used for EIR database updating (when it exists):TAC = 6 digits describing the type of equipmentFAC = 2 digits for identification of the factorySNR = 6 digits for the serial number of the device.The type of MS must be given to the NSS at the beginning of each new connection, because this type can change between calls. The subscriber may insert this SIM-Card into another Mobile Equipment (ME). There are three MS classmark types. MS Classmark parameters are:revision level: Phase 1, 2 or 2+RF power capability,encryption algorithm: A5/1, A5/2, A5/2, A5/3, A5/4, A5/5, A5/6 and A5/7,frequency capability:P-GSM (2 x 25 MHz), E-GSM (2 x 35 MHz), R-GSM (2 x 39 MHz), GSM 1800 (2 x 75 MHz), GSM 1900 (2 x 60 MHz), GSM 450 (2 x 7.2 MHz), GSM 480 (2 x 7.2 MHz), GSM 850 (2 x 25 MHz).short message (SMS) capability.LoCation Services (LCS) capability.MS Positioning Method(s) supported: MS assisted E-OTD and/or MS based E-OTD and/or MS assisted GPS and/or MS conventional GPS capabilities.8-PSK modulation capabilities.HSCSD, ECSD, GPRS and EGPRS multi-slot class: from class 1 to class 29 specifies the maximum number of supported timeslots for Rx, Tx and Sum. Example, a class 1 MS does only support 1 Rx and 1 Tx TS as a class 8 MS supports up to 8 Rx and Tx TSs.Multi-band capability.Control channels are intended to carry signaling or synchronization data. Three are defined: Broadcast Channels (BCHs), Common Control Channels (CCCHs), Dedicated Control Channels (DCCHs).Broadcast channels are point-to-multipoint unidirectional (downlink) control channels from the fixed subsystem to the mobile station. First, BCHs include a Frequency Correction Channel (FCCH) that allows an MS to accurately tune to a Base Transceiver Station (BTS).Then BCHs contain the Synchronization Channel (SCH), which provide TDMA frame-oriented synchronization data to an MS.Last, BCHs include the Broadcast Control Channel (BCCH) intended to broadcast a variety of information to MSs, including cues necessary for the MS to register in the network.Three groups of logical channels:1.Traffic channels (TCH), and associated channels (FACCH, SACCH): Number computed from Erlang B law, starting from offered traffic, according to the traffic model.2.Dedicated signaling channels (SDCCH, SACCH, CBCH): Number computed from Erlang B law, using figures given by the traffic model. The CBCH is optionally used. When activated, it permanently uses one SDCCH resource.3.Common channels (CCCH), BCCH and synchronization channels (FCCH, SCH) Theoretical studies on message exchanges on the radio interface have shown that one common channel is sufficient, whatever the offered traffic on CELL. BCCH combined: common channel pattern for small capacity cells (O1):Signaling channels SDCCH/SACCH are included in same frame as common channels:Slow Associated Control CHannel (SACCH)SACCH is a dedicated signaling channel associated with SDCCH or TCH. It is used to carry:on the uplink path: radio measurements, Layer 1 Header and Short Messages (SMS),on the downlink path: System Information type 5, 5bis, 5ter and 6, Layer 1 Header and Short Messages (SMS).These messages give information about quality of the communication (UL), Location Area Identity (DL), Cell Identity (DL), Neighboring Cells Beacon Frequencies in dedicated mode (DL), NCC permitted (DL), Cell Options (DL), Power Control (Layer 1 Header- UL/DL), Timing Advance (UL/DL).Standalone Dedicated Control CHannel (SDCCH)SDCCH is a dedicated and consequently a duplex channel. This channel transmits signaling messages for link establishment, location update, SMS, authentication of the subscriber, ciphering command and answer, and all kinds of supplementary services.Frequency Correction CHannel (FCCH)FCCH does not contain any coded information but it has an easily recognizable structure. It aims to tune the frequency of the MS to the beacon frequency of the cell in order to enable the decoding of the following information.Synchronization CHannel (SCH)After FCCH decoding, MSs decode the SCH. It gives MSs all the information needed for their synchronization and for the cell identification: framing information (Frame Number on 22 bits) and BTS identity (BSIC = Base Color Code (3 bits) + Network Color Code (3 bits)).Broadcast Control CHannel (BCCH)All the necessary information needed by the MSs in idle mode are broadcast on the BCCH.All the messages broadcast regularly on BCCH give information about cell allocation, BCCH allocation in the neighboring cells, Location Area Identity: Location Area Code + Mobile Network Code + Mobile Country Code, CCCH and CBCH management, control and selection parameters, cell options. All these information are named System Information (SI). Paging CHannel (PCH)When the network wants to reach a MS, it broadcasts the mobile identity in all the cells of a defined Location Area on PCH, in order to raise the MS, because a dedicated channel is only allocated by the network on request from a MS. The MS is identified by its TMSI (if it exists) or IMSI.GPRS uses some GSM broadcast channels for frequency tuning (FCCH) and synchronization (SCH), but for other purposes, specific packet logical channels are defined. There are two types of logical channels: traffic channels and control channels. Among the control channels, three subtypes have been defined for GPRS Broadcast, common channel and associated. In addition to the GPRS logical channels (BCCH, CCCH, RACH) are used for the MS access to the network and for the packet transfer establishment when GPRS control channels are not allocated in a GPRS cell.The different packet data logical channels are as follows:Packet Data Traffic Channel (PDTCH): The PDTCH is the channel on which the user data is transmitted during uplink or downlink packet transfer. The PDTCH can be both uplink or downlink Packet Associated Control Channel (PACCH): The PACCH is a unidirectional channel that is used to carry signaling for a given MS during uplink or downlink packet data transfer. It is always associated with one or several PDTCHs allocated to a MS.Packet Broadcast Control Channel (PBCCH): The PBCCH broadcast information on the cell the MS is camping on (the cell that is selected by the MS) and on neighbor cells. It contains the parameters needed by the mobile to access the network. When there is no PBCCH in the cell, the information is broadcasted on BCCH.Packet Common Control Channel (PCCCH): The PCCCH is a set of logical channels composed of PRACH, PPCH and PAGCH.Higher order frames, called traffic multiframes, consist of 26 TDMA frames and have a duration of 120 ms (26 x 4.615 ms). This 26 DTMA multiframe carries Traffic Channels (TCHs), Slow Associated Control Channel (SACCH), and Fast Associated Control Channel (FACCH). Similarly, a 51-frame multiframe, called a control multiframe, has a duration of 235.365 ms (51 x 4.615 ms) and supports Common Control Channels (CCCHs), Broadcast Channels (BCHs) and Stand Alone Control Channels (SDCCHs).One Superframe consists of 51 traffic multiframes or 26 control multiframes, in other words contains 51 x 26 TDMA frames with a total duration of 6.12 seconds (51 x 120 ms).The highest order frame is called a hyperframe and consists of 2,048 superframes, or 2,715,648 frames (2048 x 51 x 21). The time duration of the hyperframe is 3 hrs, 28 min., and 52.76 sec (2,715,648 x 4.615 ms). This long period of hyperframe is called the GSM time.Full rate speech transmissionWhen a Mobile Station is in communication mode, speech is coded every 20 ms in blocks. These blocks are coded in 8 half-bursts, whose information quantity is equivalent to 4 entire bursts. Then, one burst has to be delivered every 4.615 ms.So, in 26 frames lasting 120 ms, 24 bursts are used for speech transmission. One burst is used for an SACCH. The last one in the sequence is an idle burst. During this burst, the mobile is not idle, but it uses this time to monitor the neighboring cell frequencies.Half rate speech transmissionWhen the half rate speech transmission is in use, the 26 frames of a given time slot can be separated between two users, since only 12 coded speech bursts are used per user.So, in 26 frames lasting 120 ms, the odd burst numbers are restricted to one user, and the other numbers are for the other user. SACCH bursts are in the 13th and 26th positions. In this case, the monitoring is more frequent.Full rate speech: 13 kbpsHalf rate speech: 5.6 kbpsThe dedicated channels are combined into two multiframes of 51 frames. In the uplink and the downlink directions, the configuration is almost the same one, only shifted by 15 frames.The dedicated channels combination broadcasts a group of 8 SDCCH frames (2 groups of 4 consecutive SDCCH frames), each of them is associated to 4 consecutive SACCH frames. Each different group is used by a different dedicated communication. The multiframe configuration is shown on the above figure.So 8 users can use the same physical channel simultaneously, and the different communications associated to their SACCH signaling are spread on a cycle of 102 frames (2 51-multiframes). In such a multiplexing cycle, 6 frames are unused (idle TS).Downlink wayThe downlink channel is used to combine FCCH, SCH, BCCH, PCH and AGCH:FCCH and SCH are always transmitted consecutively (an SCH always follows an FCCH). Over 51 frames, the pairs are located at the 0-1, 10-11, 20-21, 30-31 and 40-41 positions.BCCH uses 4 frames per multiframe (Frame Number 2 to 5) and sometimes 4 other frames (6 to 9) for BCCH extension.PCH and AGCH form the CCCH blocks (9 groups of 4 frames). They can have different configurations, depending on the cell capacity and are dynamically defined in SI (System Information) message Type 3 (management of these channels). The 51th frame is unused.Uplink wayThe uplink direction is reserved for RACH. The configuration is simple: all the 51 frames broadcast RACH messages. So all the mobile station can request a dedicated resource to access the network on each TS 0 of a specific TDMA frame in the cell.** Nortel BTSs use TS 0 of the lowest frequency of the frequencies allocated to a BTS for their beacons. Thus, the corresponding uplink TS can contain RACHs.In the case of a low capacity cell, it is possible to combine some dedicated channels with some common control channels on the same physical channel.Their configuration is done on 2 x 51 frames and is indicated in the SI type 3.This combination contains all the channels of dedicated and common combinations: FCCH, SCH, BCCH, PCH, AGCH, SDCCH, SACCH and RACH.Downlink wayFrom a common control combination, FCCH, SCH and BCCH keep their configuration (FCCH+SCH: 0, 10, 20, 30 and 40; BCCH: 2 to 5) for both multiframes.PCH and AGCH are still dynamically configured but only on the bursts: 6-9 (except when extended BCCH are used), 12-15 and 16-19, for both multiframes.On the bursts left, 4 blocks of 4 SDCCH TSs, each of them associated with a SACCH block of 4 TSs, and one idle TS at the end of each multiframe. Each different group is used by a different sub-channel.Uplink way On 102 frames, 27 RACH frames are reserved and the other ones are replaced by 4 blocks of 4 SDCCH TSs, each of them associated with a block of 4 SACCH TSs.During a communication, the Mobile Station has to listen to the beacon frequency of the neighboring cells (which list is provided to the MS through a SACCH) in order to know synchronization values with the neighboring sites. This pre-synchronization is useful for an eventual handover, so that the mobile station can access the assigned channel. The MS can decode beacon frequency information only during the idle window of the TCH multiframe. Indeed, during data exchanges, the mobile has not enough time to decode information between reception, transmission (3 TSs later), and the next reception (5 TSs later), since it has to change frequencies and process some data. However, between transmission and reception (4 TSs), the MS has sufficient time to perform a level measurement on a neighboring cell.However, the MS must find time to decode the synchronization information broadcast on the SCH of the neighboring cells and read and decode BCCH information for new cells. For this, the MS uses the idle TS (TS 26 on the traffic multiframe) that provides a larger observation window and processing time. Since 26 and 51 have no common divider and 26*2=51+1, the idle slot of the TCH multiframe shifts forward a frame in the 51-multiframe: 0, 26, 1, 27, 2,... We are sure that the MS has been able to pre-synchronize with a neighboring site (FCCH+SCH decoding) after at most 11 successive decoding phases at the idle TS level.From a speech signal to a radio signal, several operations are performed. The reverse mechanisms are performed on the receiver side. Main operations are the following:Digitizing: Speech blocks are first digitized: one sample is coded on 8 bits and the sampling frequency is 8 kHz. This leads to a raw bit rate of 64 kbps (G.703/G.704 A or -law). On the NSS side, it is the format of the speech on the A interface (E1 or T1).Source coding uses a low bit-rate code for the air interface. Input: 20 ms of digitized speech (160 speech samples of 8 bits each rate is 64 kbps). Output: depends on speech vocoder. As an example, for full rate speech vocoder, the rate of the coded speech is 13 kbps.Channel coding uses codes enabling detection and correction of signal errors. The result is a flow of code words (456 bits long).Interleaving and burst formatting spread the bits of several code words to expand data of the same block in different bursts. The results is a succession of blocks, one block for each channel burst.Ciphering modifies the contents of these blocks through a "secret code" known only by the mobile telephone and the Base Transceiver Station, thus protecting data from eavesdropping.Speech is the most important feature that the mobile must process. The transmission path has to provide the highest speech quality possible for the user.In wireless communication, the best way to detect and correct errors introduced by the transmission path is to process a digital signal. Then, by threshold comparisons, we can recover the binary information with an acceptable quality, compared to an analog transmission.Telephony bandwidth is from 300 to 3400 Hz. The sampling frequency is 8 kHz.The perceived speech quality after coding in a GSM network shall remain as close as possible to the one perceived in the classical fixed telephony network (PSTN).Since each telecommunication system has its own intrinsic characteristics and limitations, specific voice CODECs have been designed for each system with the objective of achieving the best trade-off between voice quality, robustness to errors and network capacity. As a result, the voice quality differ from one system to another.The advent of new speech compression codecs for wireless systems has provoked intense interest in comparisons of subjective voice quality over these codecs. Estimates of subjective quality are typically given as Mean Opinion Scores (MOS) obtained from listening tests. Voice quality is a subjective parameter. By asking a group of normal telephone listeners to rate the quality of telephone speech samples, we can obtain an estimate of the quality that would be achieved on various types of connections. In particular, we use subjective listening tests to characterize the voice quality of speech compression codecs used in wireless and other systems where bandwidth efficiency is at a premium, because there are no objective measures that can estimate voice quality effectively.After having transformed speech blocks (20 ms) into digital blocks, channel coding adds redundancy.The purpose of channel coding is to improve poor transmission quality due to disturbances such as noise, interference, or multipath propagation (resulting from the reflections of the transmitted signal from buildings, etc.).Channel coding consist in adding redundant information to the source data calculated from this source information:Convolutional codes and block codes: for correction purposes.Fire code: detection and correction of bursty errors.Parity code: error detection.Each channel has its own coding and interleaving scheme.A common structure of 456 (for full rate) or 228 (for half rate) coded bit is interleaved and mapped onto bursts.The blocks are interleaved and spread into segments which are combined with flags and a training sequence to build up the burst. Ciphering is applied to the bursts, and the resulting data is used to modulate the carriers.For half rate, 20 ms of speech generate 112 bits of information (rate=5.6 kbits/s), that are coded into 228 bits (channel coding).Interleaving of these 228 bits is done on the same principle as per Full Rate but on four bursts instead of eight.After channel coding, speech coded information (TCH Full rate) are classified into 456 bits blocks. They are then spread into bursts.These 456 bits are reordered into a 8 x 57 array, line by line. The initially close bits are separated. The array is split into 8 columns of 57 bits. In this way, each 57 bits block contains bits which were all distant each other.Each 57 bits block shall be grouped with another one in order to create a burst which contains 114 information bits. Each of the 4 first blocks is grouped with each of the 4 last blocks of the previous segment. In the same way, each of the 4 last blocks is grouped with each of the 4 first blocks of the next segment.In a burst, containing 2 x 57 bits blocks, it is possible to increase bit spreading. The first block uses the even positions and the second one uses the odd positions inside the burst. The proximity of initially successive bits are now destroyed.Each speech block of 456 bits (20 ms) is so spread over 8 bursts.A basic unit of measure in transmission on a radio path is a burst, a series of 114 modulated bits of information. Bursts have a finite duration and occupy a finite part of the radio spectrum. Bursts are sent in time and frequency windows called slots.The normal burst shown in this slide is made of:Tail bits: three "0" bits at the beginning and end to help avoid loss of synchronization.Information: speech, data, and signaling.A training sequence: a list of bits known by the receiver allowing it to demodulate the burst.Stealing flags (S): indicate if information is either user's data (includes speech) or signaling data whenever the TCH has been stolen.A guard band: bits where nothing is transmitted to allow for overlap due to the variable distance from the mobile telephone to the Base Transceiver Station. This is necessary if the timing advance is not exactly right.Normal Burst bears traffic channels, its associated channel (slow and fast), Stand Alone, and the broadcast Control Channels (BCCHs).Frequency correction burstThis burst is used for the frequency synchronization of a mobile station. The repeated transmission of Frequency Bursts is also called Frequency Correction Channel (FCCH). Tail bits as well as data bits are all set to 0. This corresponds to the broadcasting of an unmodulated carrier with a frequency shift of 1625/24 kHz above the nominal carrier frequency. This signal is periodically transmitted by the base station on the BCCH carrier frequency. Depending on the stability of its own reference clock, the mobile can periodically resynchronize with the base station using the FCCH.

Synchronization BurstThis burst is used to transmit information which allows the mobile station to synchronize time-wise with the BTS. Besides a long midamble, this burst contains the running number of the TDMA frame number. Repeated broadcasting of synchronization bursts is considered as the synchronization channel.Normal burstA normal burst contains 26 bits for the training sequence, plus 2 x 58 bits for information. More precisely, there are twice x 57 information bits and two stealing flags, which indicate if information is traffic or signaling. There are also three tail bits, and 8.25 bits for the guard period.Dummy burstThe dummy burst structure is the same as for the normal burst. However, information bits are replaced by mixed bits: this burst is used to replace data if there is nothing to transmit. This is the case for BCCH and TCH filling when they are transmitted on the beacon frequency.Access burstAn access burst contains 41 bits for the training sequence, 36 bits for the information, 8 and 3 tail bits at respectively the beginning and the end of the burst. The guard period is of 68.25 bits. This burst is used for random access to the RACH without reservation. It has a guard period significantly longer then the other bursts. This reduces the probability of collisions, since the mobiles competing for the RACH are not (yet) synchronized.Ciphering, or encryption, is a procedure that provides additional security for the subscriber. Ciphering is not channel coding. It is performed after the encoding and interleaving of different channel and is done independently of whether the channel is a signaling channel or a traffic channel. Ciphering is only done on the two data segments.Ciphering is achieved by performing an exclusive OR (XOR) operation between a pseudo-random bit sequence (which was computed through the A5 algorithm by the ciphering key allocated to the user for a call and the burst number) and the 114 useful bits of a normal burst.Deciphering, in turn, applies exactly the same operation, since XOR twice with the same data leads back to the original value.Last, it is worth noting that the whole specification of the encryption algorithm (A5) is distributed under conditions by the Association of European Operators which have signed the GSM Memorandum of Understanding (MoU). GSM uses seven A5 types of algorithm:Encryption algorithm A5-1 which contains European and United States technical software that cannot directly or indirectly be exported to any embargoed or restricted country.Encryption algorithm A5-2 which contains software that does not require a license or approval.Encryption algorithms A5-3 to A5-7 not supported by Nortel.The above slides show the GSM actors that are involved in the following procedures.

Generally, a user remains in his home PLMN (HPLMN). When the MS is switched on, the selected PLMN is the nominal PLMN and the first beacon frequency found belongs to this PLMN. There is no PLMN selection procedure.When the user roams, the MS checks the beacon frequencies of the previous existing. This check fails because the detected beacon frequencies do not belong to the selected PLMN (HPLMN). The MS must select a new PLMN. This operation consists in finding the existing PLMNs. The MS does a normal selection on all the GSM frequencies, checks the beacon frequencies, and reads the PLMN number on the BCCH channel. If the MS has already done this check, the MS can try first the registered PLMN before. There are two ways to select a network in the found PLMN list:automatic mode: a list of networks classified by priority order (the preferred PLMN list) is stored in the SIM card. The list allows the MS to select the available network with the highest priority,manual mode: the MS displays the list of available networks (found PLMN list) so that a PLMN may be selected by the user.When switched on, a MS must be available as soon as possible. Therefore, the selection of a PLMN and a cell is really optimized because, during this time, the user can not use his MS. When there is no existing beacon frequencies list stored in the SIM card (neither a list of the latest neighboring cells, nor a list of found PLMNs), the MS:checks all the frequencies of the GSM spectrum (124 frequencies in GSM 900, 374 in GSM 1800, 299 in GSM 1900),measures their level (averaging done at least on 5 measurements during at least 3 seconds [GSM 05.08]),selects the 30 frequencies (in GSM 900, 40 in GSM 1800) with the highest level,selects the frequencies corresponding to a beacon frequency (FCCH and SCH channels),creates the found PLMN list (PLMN name corresponding to the beacon frequencies).Phase 1 MSThe MS searches a suitable cell in the previous list. The first beacon frequency studied is the first frequency of the list i.e. the frequency with the best level.A suitable cell is a cell:of the selected PLMN,not barred,complying with the C1 criterion (C1 > 0).When a suitable cell is found, an IMSI attach is performed if necessary.

Phase 2 MS2 lists of cells are created, according to the priority level for selection (normal/low). In both lists, the cells are classified from the best to the worst C1 received. The MS first scans the normal priority list, and if no cell is suitable, the MS considers the second list (low priority).Since a dual band MS is at least a phase 2 MS, this procedure is also used by dual band MS in dual band networks, and the MS selects the best suitable cell independently of the band.The principle applied to each list is the same as described for phase 1 MS.1-Provided a SIM card is present, immediately after tuning on power, the MS starts the search of BCCH carriers. Normally, the MS has a stored list of 32 carriers of the current network. Signal level measurements (RXLEV) are done on each of these frequencies. If no list is available, all GSM frequencies have to be measured to find potential BCCH carriers.2-After having found potential candidates based on the received signal level, each carrier is investigated for the presence of FCCH signal, beginning with the strongest signal. In the above slide, the strongest signal comes from BTS1.3-The synchronization burst of the SCH in the TDMA frame immediately following the FCCH burst has a long training sequence of 64 bits which is used for fine tuning of the frequency correction and time synchronization. This way the MS is able to read and decode the BSIC and the RFN.4-The MS can now reads data from broadcast channel (BCCH).5-The MS camps on this BCCH if it is suitable for the MS; otherwise it tries to select the next strongest beacon carrier.The Immediate Assignment procedure is always initiated by the MS and may be triggered by a Paging Request or by a Mobile Originating Service request.Procedure1- The MS sends a CHANNEL REQUEST message (RACH).2- The BTS decodes this message and indicates it to BSC through CHANNEL REQUIRED message.3- The BSC asks the BTS to activate a dedicated channel: SDCCH

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