BASIC GSM Training Material

BASIC GSM Training MaterialContents:Introduction of GSM.GSM Network Architecture.Access Mode of GSM.Logical Channels in GSM.GSM Cell Structure.GSM Bands.Coding's in GSM.Call Originating.INTRODUCTION OF GSMBASIC WIRELESS COMMUNICATIONThere are TWO major parts of wireless communication: TRANSMITTER (Tx) RECEIVER (Rx)TRANSMITTERMICMODULATORRF AMPLIFIERLOCAL OSC.RECEIVERBAND PASS FILTERMIXERLOCAL OSCILLATORDEMODULATORAUDIO AMPLIFIERIF OUTTYPES OF CALLSMOBILE to LL Mobile - BTS - BSC - PSTN - LLLL to MOBILE LL - PSTN - BSC - BTS - MobileMOBILE to MOBILE Mobile - BTS - BSC - BTS - Mobile ( If it is same Network) Mobile - BTS - BSC1 - PSTN - BSC2 - BTS - Mobile ( If it is different Network with same SP or different SP)GSM means Global System for Mobile communications.Developed in 1982.Most popular of cellular technologies.GSM Only Handsets belong to 2G and 2.5G.In GSM just like FM Radio channels users are identified by different frequencies, with assigned time slots.Has mainly four frequency bands of operation.(850/900/1800/1900).5/17/2013TELECOM/MOBILE/MSS8124578*0369#GSM5/17/2013TELECOM/MOBILE/MSS91st Generation Mobile Communication2nd Generation Mobile Communication2.5th Generation Mobile Communication3rd Generation Mobile Communication3G and aboveMobile Technology EvolutionEmerging Technologies1G-First GenerationExample-AMPSAnalog2 way radio w/transmitter/receiverVoice service onlyFDM5/17/2013TELECOM/MOBILE/MSS10Emerging Technologies2G-Second GenerationExample-DAMPSTDM Digital transmission over same frequency BW3-10 times more capacity as 1GEnhanced featuresMessaging on handsetsBetter securityDigital data is scrambled when multiplexedExample-GSMSame as DAPMS + International MobilitySIM in handset5/17/2013TELECOM/MOBILE/MSS11Emerging Technologies2G-2.5 GenerationExample EDGE (Enhanced data rate for GSM evolution) Wireless data @ 384Kbps GPRS (General Packet radio service) 115KbpsPacket over circuit overlay NW based on IPBoth wireless voice and wireless data More capabilities than 2G but less than 3GTDMA/GSM type of NWs can upgrade to it2G to 3G is expensive2.5 G is a cost effective alternative for higher wireless speeds5/17/2013TELECOM/MOBILE/MSS123G-Third GenerationExample-UMTS (Universal Mobile Telephone System)Also Known as W-CDMACDMA is a spread spectrum technology. Each conversation is spread over multiple frequencies as it it sent.This is accomplished via a set of 40 codes that is assigned to each transmission. These are called walesh codes. Having a unique code assigned to each conversation allows multiple users to share spectrumHigher speeds than ever before for wireless transmissionEvolution Path from 2G, 2.5GHigh MobilityInternational RoamingHigh Speed Internet Access-IP connectivityHigh SecurityInteroperability between 2G, 2.5G, 3G HandsetsIssues2G (Mostly TDMA) to 3G(Mostly CDMA) is expensive-New InfrastructureHandsets-Mini Computers-High Power consumption5/17/2013TELECOM/MOBILE/MSS133 G GSM NETWORK ARCHIETECTUREGSM NETWORK ARCHITECTUREMSMS BTSBTS BTSBSBSMSCMSCMSCMSCVLRVLRHLR HLREIRAuCOSBSCBTSBTS BTSBSC124578*0369#Interface to other networks5/17/2013TELECOM/MOBILE/MSS16GSM NETWORK ARCHITECTUREMobile Station (MS)Mobile Equipment (ME)Subscriber Identity Module (SIM)Base Station Subsystem (BBS)Base Transceiver Station (BTS)Base Station Controller (BSC)Network SubsystemMobile Switching Center (MSC)Home Location Register (HLR)Visitor Location Register (VLR)Authentication Center (AUC)Equipment Identity Register (EIR5/17/2013TELECOM/MOBILE/MSS17GSM SYSTEM ARCHITECTURE5/17/2013TELECOM/MOBILE/MSS18 Mobile Equipment Fixed Portable International Mobile Equipment Identity (IMEI) number Subscriber Identity Module (SIM) Personal Identification Number (PIN) International Mobile Subscriber Identity (IMSI) number Enables access to subscribed services Smart cardMOBILE STATION GSM NETWORKThe GSM system contains The Mobile Stations (MS).both the hand held (portables) & Traditional mobiles in a car.Base Station System (BSS).The BSS Consist of a Base Transceiver Station (BTS) and Base Controller System (BSC).Mobile Switching Center (MSC).Each MSC Will have a Visitors Location Register (VLR), Home Location Register (HLR), Authentication Center (AUC), Equipment Identity Register (EIR).28/07/09DIAGNOSTIC CHENNAIGSM NETWORKThere are also facilities within the system for Operations and Maintenance (OMC) & Network Management (NMC) organizations.The MSC also has the interface to other networks such as Private Land Mobile Networks (PLMN) and Public Switched Telephone Networks (PSTN) and ISDN.28/07/09DIAGNOSTIC CHENNAIMobile Station - MSA GSM MS comprises an ME and a SIM.SIM is the removable part identified by a unique 15 digit IMSI.ME is the handheld radio equipment operating in GSM frequenciesMS is capable of initiating and receiving voice calls and SM ME is identified by a unique 15 Digit IMEIMS is capable of initiating an emergencycall without a SIMDIAGNOSTIC CHENNAI28/07/09Base Station Subsystem - BSS28/07/09DIAGNOSTIC CHENNAIBase Station Subsystem - BSSThe BSS is responsible for managing the radio network and it is controlled by an MSC. Typically one MSC contains several BSSs. A BSS itself may cover a considerably large geographical area consisting of many cells . The BSS consists of the following elements :BSC Base Station ControllerBTS Base Transreceiver StationTC Transcoder28/07/09DIAGNOSTIC CHENNAIBase Transreceiver Subsystem - BTSThe BTS handles the radio interface to the mobile station.The BTS is the radio equipment (transceivers and antennas) needed to service each cell in the network. A group of BTSs are controlled by a BSC1 frequency with 8 timeslots is allocated per transceiverCommunicates with MS on Um interfaceConnected to BSC on Abis interfaceCiphering is done in BTS.28/07/09DIAGNOSTIC CHENNAIBase Station Controller - BSCThe BSC provides all the control functions and physical links between the MSC and BTS. It is a high-capacity switch that provides functions such as handover, cell configuration data, and control of radio frequency (RF) power levels in base transceiver stations. A number of BSCs are served by an MSC.BSC communicates with MSC on A interface.28/07/09DIAGNOSTIC CHENNAITranscoder & Rage Adapter Unit - TRAUPart of the BTS/BSC used for conversion between 64 Kbps PCM speed and 13Kbps Speech.TRAU is usually remotely located at BSC or MSC siteTRAU frames transfer information between channel codec unit of BTS and the remote TRAUTRAU frames can be speech, Data, O&M or Idle28/07/09DIAGNOSTIC CHENNAINetwork Switching Subsystem - NSS28/07/09DIAGNOSTIC CHENNAIMobile Service Switching Centre - MSCCalls are established, supervised and release by MSC.All MO & MT calls are routed & connected by MSC.Charging information is generated and transferred to Billing Centre.Communicates with BSCs on A interface.Communicates with HLR, VLR, EIR & SMSC using MAPDIAGNOSTIC CHENNAI28/07/09Home Location Register - HLRThe HLR is a database used for storage and management of subscriptions.The HLR is considered the most important database, as it stores permanent data about subscribers, including a subscriber's service profile, location information, and activity status.When an individual buys a subscription from one of the PCS operators, he or she is registered in the HLR of that operatorDIAGNOSTIC CHENNAI28/07/09Visitor Location Register - VLRThe VLR is a database that contains temporary information about subscribers that is needed by the MSC in order to service visiting subscribers. The VLR is always integrated with the MSC. When a mobile station roams into a new MSC area, the VLR connected to that MSC will request data about the mobile station from the HLR. Later, if the mobile station makes a call, the VLR will have the information needed for call setup without having to interrogate the HLR each time.28/07/09DIAGNOSTIC CHENNAIAuthentication Centre - AUCA unit called the AUC provides authentication and encryption parameters that verify the user's identity and ensure the confidentiality of each call. The HLR communicated with AUC for authenticating SIMThe AUC protects network operators from different types of fraud found in today's cellular world.Data generated by AUC and the SIM using authentication algorithms is compared in the HLR.28/07/09DIAGNOSTIC CHENNAIEquipment Identity Register - EIRThe EIR is a database that contains information about the identity of mobile equipment that prevents calls from stolen, unauthorized, or defective mobile stations. The AUC and EIR are implemented as stand-alone nodes or as a combined AUC/EIR nodeWhite, grey & black are mandatory lists.MSC communicates with EIR for equipment identification.28/07/09DIAGNOSTIC CHENNAIShort Message Service Centre - SMSCSMS is a service that allows a mobile to exchange text messages with other entities.Messages can be upto 160characters.SMSC serves to store and relay the messages from different entities to MSSMSC communicates with MSC on MAP for relaying messages.28/07/09DIAGNOSTIC CHENNAIVoice Mail Service Centre - VMSVoice Mail Service is like an answering machine service offered tomobile subscribers.VMS contains the subscription data for all voice mail subscribersVMS also stores voice messages for subscribers.VMS is connected to the MSC.28/07/09DIAGNOSTIC CHENNAIOperation & Maintenance CentreThe operations and maintenance center (OMC) is connected to all equipment in the switching system and to the BSC. The implementation of OMC is called the operation and support system (OSS). The OSS is the functional entity from which the network operator monitors and controls the system. The purpose of OSS is to offer the customer cost-effective support for centralized, regional, and local operational and maintenance activities that are required for a GSM network. An important function of OSS is to provide a network overview and support the maintenance activities of different operation and maintenance organizations 28/07/09DIAGNOSTIC CHENNAI5/17/2013TELECOM/MOBILE/MSS36International Mobile Equipment Identity ( IMEI )TAC = Type Approval CodeFAC = Final Assembly CodeSNR = Serial NumberSP = SpareIMEI=TAC+FAC+SNRSP+6 digits2 digits6 digits1digit5/17/2013TELECOM/MOBILE/MSS37IMEI5/17/2013TELECOM/MOBILE/MSS38International Mobile Subscriber Identity ( IMSI )IMSI=MCC+MNC+MSINNMSI3 digits2 digitsNot more than 15 digitsMCC = Mobile Country CodeMNC = Mobile Network CodeMSIN = Mobile Station Identification NumberNMSI = National Mobile Subscriber Identity5/17/2013TELECOM/MOBILE/MSS39Subscriber Identity Module ( SIM )SIM contains ( at least ) following information : SIM’s Serial Number ID - key K1 Encryption key Kc IMSI (International Mobile Subscriber Identification) TMSI (Temporary Mobile Subscriber Identification) LAI (Location Area Identification) PIN (Personal Identification Number) PUK (Personal Unblock Code) A3 A8Smart card containing the International Mobile Subscriber Identity (IMSI)Allows user to send and receive calls and receive other subscribed servicesEncoded network identification detailsProtected by a password or PINCan be moved from phone to phone – contains key information to activate the phone5/17/2013TELECOM/MOBILE/MSS40SIM SIM CardSIM Card comes in two Sizes :Standard (Credit Card Size)Micro (Postage Stamp Size)SIM’s (Subscriber Identification Modules) plug into the GSM Mobile.The SIM Holds all the information related to a subscriber. For example:Unique Subscriber number or IMSI (International Mobile Subscriber Identification)Any other user specific information like speed dial numbers and memories.K(i) – Secret key for authentication (Stores in SIM)Stores information on Last Location.Stores user information : Speed Dial Lists, Memories etc.28/07/09DIAGNOSTIC CHENNAIGSM ACCESS MODESVarious Access MethodFrequency multiplexSeparation of the whole spectrum into smaller frequency bandsA channel gets a certain band of the spectrum for the whole timeAdvantages:no dynamic coordination necessaryworks also for analog signalsDisadvantages:waste of bandwidth if the traffic is distributed unevenlyinflexibleguard spacesk2k3k4k5k6k1ftcftck2k3k4k5k6k1Time multiplexA channel gets the whole spectrum for a certain amount of timeAdvantages:only one carrier in themedium at any timethroughput high even for many usersDisadvantages:precise synchronization necessaryfTime and Frequency MultiplexCombination of both methodsA channel gets a certain frequency band for a certain amount of timetck2k3k4k5k6k1GSM FDMA and TDMAEach band is divided into 200KHz slots called ARFCN’s (Absolute Radio Frequency Channel Numbers). The ARFCN is also divided intime into 8 Timeslots (TS), each TS being used in turn by a different MS. The 8 TS’s together are known as a Frame.Each one of the Traffic Channel uses a particular ARFCN and Timeslot. The Combination of a TS number and ARFCN is called a Physical Channel.28/07/09DIAGNOSTIC CHENNAIfTime and Frequency MultiplexExample: GSM Advantages:Better protection against tappingProtection against frequency selective interferenceHigher data rates compared tocode multiplexBut: precise coordinationrequiredtck2k3k4k5k6k1Code MultiplexEach channel has a unique codeAll channels use the same spectrum at the same timeAdvantages:Bandwidth efficientNo coordination and synchronization necessaryGood protection against interference and tappingDisadvantages:Lower user data ratesMore complex signal regenerationImplemented using spread spectrum technologyk2k3k4k5k6k1ftcChannel UtilizationDIAGNOSTIC CHENNAIExample of the TDMA being used in combination with CDMA28/07/09DIAGNOSTIC CHENNAIDownlink and UplinkUplink lags downlink by 3 Timeslot periodsUplink and Downlink use same Timeslot NumberUplink and Downlink use same channel number (ARFCN)Uplink and Downlink use different bands (45MHz apart for GSM900)28/07/09DIAGNOSTIC CHENNAITime Division Multiple Access (TDMA)5/17/2013TELECOM/MOBILE/MSS535670123456701342577us4.6msMS Only transmits at its own timeslot ONON5/17/2013TELECOM/MOBILE/MSS54Time Frame012345674.615 ms156.25 Bits0.577ms3311575726TrainingDataData148 BitsBurstBurst StructureTDMA Frame Structure Uplink & Downlink5/17/2013TELECOM/MOBILE/MSS55Downlink / MS Receive5670123456701342067012345671342Uplink / MS Transmit556TELECOM/MOBILE/MSS5/17/20135. Power controlIssues / important concepts: Near-far problem Uplink SIR expression; what means Target SIR? Open loop power control Inner loop (closed loop) power control Outer loop (closed loop) power control5/17/2013TELECOM/MOBILE/MSS57Handoff :Cellular system tracks mobile stations in order to maintain their communication links.When mobile station goes to neighbor cell, communication link switches from current cell to the neighbor cell.Hard Handoff :In FDMA or TDMA cellular system, new communication establishes after breaking current communication at the moment doing handoff. Communication between MS and BS breaks at the moment switching frequency or time slot.POWER CONTROL58TELECOM/MOBILE/MSS5/17/2013MS2MS1power controlcommands to the mobilesP1P2nearfarPower ControlThe base station performs frequent estimates of the received signal-to-interference ratio (SIR) and then compares it to a target SIR.If the measured SIR is higher than the target SIR, the BS will command the MS to lower the power.If the measured SIR is lower than the target SIR, the BS will command the MS to increase the power.5/17/2013TELECOM/MOBILE/MSS59Closed-Loop Power ControlLOGICAL CHANNELS IN GSMLOGICAL CHANNELSTRAFFICSIGNALLINGFULL RATE 22.8 Kb/SHALF RATE 11.4 Kb/SBROADCASTCOMMON CONTROL DEDICATED CONTROLFCCHSCHBCCHPCHRACHAGCHSDCCHSACCHFACCHFCCH -- FREQUENCY CORRECTION CHANNELSCH -- SYNCHRONISATION CHANNELBCCH -- BROADCAST CONTROL CHANNELPCH -- PAGING CHANNELRACH -- RANDOM ACCESS CHANNELAGCH -- ACCESS GRANTED CHANNELSDCCH -- STAND ALONE DEDICATED CONTROL CHANNELSACCH -- SLOW ASSOCIATED CONTROL CHANNELFACCH -- FAST ASSOCIATED CONTROL CHANNELDOWN LINK ONLYUPLINK ONLYBOTH UP & DOWNLINKSGSM Broadcast ChannelBroadcast Control Channel (BCCH) - DOWNLINK All BTS produce a Broadcast Channel (BCH). The BCH is like a lighthouse or beacon. It’s on all the time and allows mobile to find the GSM network. The network for a variety of user functions also uses the BCH signal strength. It’s a useful way of telling which is the closest BTS to the mobile. It also has information coded onto it, such as the identity of the network, paging messages for any mobiles need bug to accept a phone call, and a variety of other information. Each mobile will monitor the power of adjacent cell BCH’s to aid the network in making hand-off decisions. This channel contains system parameters needed to identify the network and gain access. These parameters include the Location Area Code (LAC), the Mobile Network Code (MNC), the frequencies of neighboring cells, and access parameters28/07/09DIAGNOSTIC CHENNAIGSM Traffic ChannelMobiles on a call use a Traffic Channel (TCH). The TCH is a two way channel used to exchange speech information between the mobile and base-station. It’s interesting to note that while the TCH uses a frequency channel in both the uplink and downlink, the BCH occupies achannel in the downlink band only. The corresponding channel in the uplink is effectively left clear. The mobile can use this for unscheduled or Random Access Channels (RACH). Traffic Channels are used to carry two types of information to and from the user:Encoded SpeechData28/07/09DIAGNOSTIC CHENNAIGSM Traffic ChannelThere are two basic types of Encoded Speech channelsEncoded Speech - Encoded speech is voice audio that is converted into digital form and compressed.     Full Rate Speech TCH (TCH/FS) - 13 kb/sHalf Rate Speech TCH (TCH/HS) - 5.6 kb/s28/07/09DIAGNOSTIC CHENNAIGSM Traffic Channel28/07/09DIAGNOSTIC CHENNAIGSM Traffic ChannelData - Data refers to user data such as text messages, picture messages, internet browsing, etc. It includes pretty much everything except speech. Full rate Data TCH (TCH/F14.1) - 14.4 kb/sFull rate Data TCH (TCH/F9.6) - 9.6 kb/sFull rate Data TCH (TCH/F4.8) - 4.8 kb/sHalf rate Data TCH (TCH/F4.8) - 4.8 kb/sFull rate Data TCH (TCH/F2.4) - ≤2.4 kb/sHalf rate Data TCH (TCH/H2.4) - ≤2.4 kb/s28/07/09DIAGNOSTIC CHENNAIHandoff67GSM Hand-OffHandover (handoff) is switching of an on-going call to a differentchannel or cell.There are four types of handoversSwitching channels in the same cell.Switching cells under control of the same Base Station Controller (BSC)Switching cells under the control of different BSCs, but belonging to the same Mobil service Switching Center (MSC)Switching cells under control of different MSCs28/07/09DIAGNOSTIC CHENNAIGSM Hand-OffThe first two types of handover, called internal because they involveonly BSC, and MSC is notified only on completion of the handover.The last two types of handover, called external because they involve MSC. Handover may be initiated by MSC (traffic balancing) or by mobile unit. The mobile unit always scans Broadcast Control Channel of up to 16 neighboring cells, and forms a list of the six best candidates for possible handover. This information is transmitted to current Base Station at least once per second. BSC and MSC use this information for handover algorithm. 28/07/09DIAGNOSTIC CHENNAIGSM Hand-OffOne of the problems while making handover decision is whether the poor signal quality is due to physical interference or mobile having moved to another cell. There are two basic algorithms for making handover decision:Minimum acceptable performance. If signal degrades beyond some point, then transmission power is increased. If power increase does not lead to improve then handover is performed. Disadvantages: increasing transmission power may cause interference with neighbor cell.Power budget. Uses handover to improve transmission quality in the same or lower power level. This method avoids neighbor cell interference, but is quite complicated. 28/07/09DIAGNOSTIC CHENNAIGSM CELL STRUCTURE GSM Cell PlanGSM uses a number of channe