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GSM Introduction

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The global system for mobile communications (GSM) is a set of recommendations and specifications for a digital cellular telephone network (known as a Public Land Mobile Network, or PLMN). These …

The global system for mobile communications (GSM) is a set of recommendations and specifications for a digital cellular telephone network (known as a Public Land Mobile Network, or PLMN). These recommendations ensure the compatibility of equipment from different GSM manufacturers, and interconnectivity between different administrations, including operations across international boundaries
The GSM network is comprised of the following components:
Network Elements
The GSM network incorporates a number of network elements to support mobile equipment. They are listed and described in the GSM network elements section of this chapter.
GSM subsystems
In addition, the network includes subsystems that are not formally recognized as network elements but are necessary for network operation. These are described in the GSM subsystems (non-network elements) section of this chapter.
Standardized Interfaces
GSM specifies standards for interfaces between network elements, which ensure the connectivity of GSM equipment from different manufacturers. These are listed in the Standardized interfaces section of this chapter.
Network Protocols
For most of the network communications on these interfaces, internationally recognized communications protocols have been used
These are identified in the Network protocols section of this chapter.

GSM Frequencies
The frequency allocations for GSM 900, Extended GSM and Digital Communications Systems are identified in the GSM frequencies section of this chapter.

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  • Transcript

    • 1. 05/31/13Tempus Telcosys 1ADA CELLWORKS PVT LTD
    • 2. INTRODUCTION The global system for mobile communications (GSM)is a set of recommendations and specifications for adigital cellular telephone network (known as a PublicLand Mobile Network, or PLMN). Theserecommendations ensure the compatibility of equipmentfrom different GSM manufacturers, and interconnectivitybetween different administrations, including operationsacross international boundaries.05/31/13Tempus Telcosys 2
    • 3. THE GSM NETWORK The GSM network is comprised of the following components: Network Elements The GSM network incorporates a number of network elements tosupport mobile equipment. They are listed and described in the GSMnetwork elements section of this chapter. GSM subsystems In addition, the network includes subsystems that are not formallyrecognized as network elements but are necessary for networkoperation. These are described in the GSM subsystems (non-networkelements) section of this chapter. Standardized Interfaces GSM specifies standards for interfaces between network elements,which ensure the connectivity of GSM equipment from differentmanufacturers. These are listed in the Standardized interfaces section ofthis chapter.05/31/13Tempus Telcosys 3
    • 4. THE GSM NETWORK - CONTINUED Network Protocols For most of the network communications on these interfaces,internationally recognized communications protocols have been used These are identified in the Network protocols section of this chapter. GSM Frequencies The frequency allocations for GSM 900, Extended GSM and DigitalCommunications Systems are identified in the GSM frequencies sectionof this chapter.05/31/13Tempus Telcosys 4
    • 5. DIGITAL NETWORKS GSM networks are digital and can cater forhigh system capacities. They are consistentwith the world wide digitization of thetelephone network, and are an extension ofthe Integrated Services Digital Network(ISDN), using a digital radio interfacebetween the cellular network and the mobilesubscriber equipment.05/31/13Tempus Telcosys 5
    • 6. INCREASED CAPACITY The GSM system provides a greater subscriber capacity thananalogue systems. GSM allows 25 kHz. Per user, that is, eightconversations per 200kHz. Channel pair (a pair comprising onetransmit channel and one receive channel). Digital channel codingand the modulation used makes the signal resistant to interferencefrom the cells where the same frequencies are re-used (co-channelinterference); a Carrier to Interference Ratio (C/I) level of 9 dB isachieved, as opposed to the 18 dB typical with analogue cellular.This allows increased geographic reuse by permitting a reduction inthe number of cells in the reuse pattern. Since this number is directlycontrolled by the amount of interference, the radio transmissiondesign can deliver acceptable performance.05/31/13Tempus Telcosys 6
    • 7. CGI : CELL GLOBAL IDENTITY05/31/13Tempus Telcosys 7MCC MNC LAC CILAICGIMCC = Mobile Country CodeMNC = Mobile Network CodeLAC = Location Area CodeCI = Cell Identity
    • 8. MSISDN05/31/13Tempus Telcosys 8CC NDC SN98 XXX 12345CC = Country CodeNDC = National Destination CodeSN = Subscriber Number
    • 9. MSISDN The Mobile Subscriber ISDN (MSISDN)number is the telephone number of the MS.This is the number a calling party dials toreach the subscriber. It is used by the landnetwork to route calls towards the MSC.05/31/13Tempus Telcosys 9
    • 10. IMSI IMSI (International Mobile SubscriberIdentity) Network Identity Unique To A Sim.05/31/13Tempus Telcosys 10MCC MNC MSIN404 XX 12345..10SIM = Subscriber Identity ModuleMCC = Mobile Country CodeMNC = Mobile Network CodeMSIN = Mobile Subscriber Identity Number
    • 11. IMEI IMEI : Serial number unique to each mobile05/31/13Tempus Telcosys 11TAC FAC SNR SP6 2 6 1IMEI = International Mobile Equipment IdentityTAC = Type Approval CodeFAC = Final Assembly CodeSNR = Serial NumberSP = Spare
    • 12. SUBSCRIBER IDENTIFICATION International Mobile Subscriber Identity (IMSI) Just the IMEI identifies the mobile equipment, other numbers areused to identify the mobile subscriber. Different subscriber identitiesare used in different phases of call setup. The International MobileSubscriber Identity (IMSI) is the primary identity of the subscriberwithin the mobile network and is permanently assigned to thatsubscriber. Temporary Mobile Subscriber Identity (TMSI) The GSM system can also assign a Temporary Mobile SubscriberIdentity (TMSI). After the subscriber’s IMSI has been initialized on thesystem, the TMSI can be used for sending backward and forward acrossthe network to identify the subscriber. The system automaticallychanges the TMSI at regular intervals, thus protecting the subscriberfrom being identified by someone attempting to monitor the radiochannels. The TMSI is a local number and is always transmitted withthe Local numbers and is always transmitted with the Location AreaIdentification (LAI) to avoid ambiguities.05/31/13Tempus Telcosys 12
    • 13. SUBSCRIBER IDENTIFICATION MODULE(SIM) By making a distinction between the subscriber identity and themobile equipment identity, a GSM PLMN can route calls andperform billing based on the identity of the subscriber rather thanthe mobile equipment being used. This can be done using aremovable Subscriber Information Module (SIM). A ”smart card” isone possible implementation of a SIM module. IMSI. This is transmitted at initialization of the mobile equipment. TMSI This is updated periodically by the PLMN MSISDN This is made up of a country code, a national code and asubscriber number. Location Area Identity (LAI) This identified the current location ofthe subscriber. Subscriber Authentication Key (KI) This is used to authenticatethe SIM.05/31/13Tempus Telcosys 13
    • 14. EQUIPMENT IDENTITY NUMBER International Mobile station Equipment Identity (IMEI) Each MS is identified by an International Mobile station EquipmentIdentity (IMEI) number which is permanently stored in the mobileequipment. On request, the MS sends this number over thesignalling channel to the MSC. The IMEI can be used to identify MS,sthat are reported stolen or operating incorrectly. Equipment Identity Register ( EIR ) A listing of the allowed IMEI is maintained by the PLMN’s in theEquipment Identity Register (EIR) to validate the mobile equipment.05/31/13Tempus Telcosys 14
    • 15. Frequency BandsUplink 890 – 915 MHz 25 MHz05/31/13Tempus Telcosys 15Downlink 935 – 960 MHz 25 MHz100 KHz 200 KHz 100 KHz1 43 1242 …………….A 200 KHz carrier spacing has been chosen. Excluding 2x100 KHz edges ofthe band, this gives 124 possible carriers for the uplink and downlink. Theuse of carrier 1 and 124 are optional for operators.
    • 16. GSM Network Architecture05/31/13Tempus Telcosys 16BTSBTSBTSBTSBTSBSCBSCTRAUMSCHLRAUCVLREIRPSTNSMSC
    • 17. MS – Mobile Station Mobile station provides user access to GSM networkfor voice and data All GSM mobiles comply to GSM standards Subscriber data is read from a SIM card that plugsinto ME05/31/13Tempus Telcosys 17SIM MEMS
    • 18. MS (cont..) Each MS has a unique number called as IMEInumber, which is stored in EIR forauthentication purposes Mobile camps on to the GSM networkthrough the BTS serving the cell Mobile also scans neighboring cells andreports signal strengths Mobile transmits and receives voice at 13 kb/sover the air interface05/31/13Tempus Telcosys 18
    • 19. Mobile Station Output Power CLASS 1 20 watts Vehicle and Portable CLASS 2 8 watts Portable and Vehicle CLASS 3 5 watts Hand-Held CLASS 4 2 watts Hand-Held (GSM) CLASS 5 0.8 watts Hand-Held (DCS1800) Output power determines: Accessibility in areas of coverage Talk Time and Standby time05/31/13Tempus Telcosys 19
    • 20. Mobile Station Identities CC – Country Code NDC – National Destination Code SN – Serial Number05/31/13Tempus Telcosys 20MSISDN : Mobile Station ISDN NumberIt is the human identity used to call a MobileStationCC SNNDC MSISDN98 250 00134
    • 21. IMSI (International MobileSubscriber Identity) MCC – Mobile Country Code MNC – Mobile Network Code MSIN – Mobile Subscriber Identity Number05/31/13Tempus Telcosys 21MCC MSINMNC IMSI3 2 or 3Not more than 15NMSI
    • 22. IMEI (International MobileEquipment Identity) TAC – Type Approval Code FAC – Factory Assembly Code SNR – Serial Number SP – Spare digit (usually used to specifysoftware version)05/31/13Tempus Telcosys 22TAC SPFAC IMEISNR6 162 15
    • 23. SIM ( Subscriber IdentityModule) Removable module inserted when thesubscriber wants to use the ME Two sizes: credit card size and stamp size SIM features and contents are personalized bythe Service Activator ROM – 6kb to 16 kb RAM – 128 bytes to 256 bytes EEPROM – 3kb to 8 kb05/31/13Tempus Telcosys 23Space to insert SIM photo
    • 24. Contents of SIM Serial Number IMSI, Subscriber Key Ki, Ciphering Key Kc Algorithms for authentication and ciphering Network Code PIN, PUK Charging Information Abbreviated Dialling Supplementary Features (e.g. Call barring)05/31/13Tempus Telcosys 24
    • 25. SIM Security Two level protection When mobile is turned on, it will ask for userto enter PIN (Personal Id Number) 3 tries for PIN, after that PIN locked To unblock PIN, there is PUK (Pin UnblockKey) 10 attempts of PUK allowed After that SIM is blocked05/31/13Tempus Telcosys 25
    • 26. BTS (Base Transceiver Station) BTS has a set of Transceivers (TRXs) to communicatewith mobiles in its area One BTS covers one or more than one cell The capacity of a cell depends on number oftransceivers in the cell BTS is connected to the BSC through Abis Interfacewhich is 2Mbps BTS transmits and receives voice at 13kbps over airinterface to the mobiles. BTS commands mobiles to set Tx. Power, timingadvance and Handovers05/31/13Tempus Telcosys 26
    • 27. BTS05/31/13Tempus Telcosys 27
    • 28. BSC – Base Station Controller Several BTSs are connected to the BSC BSC Manages channel allocation, handovers andrelease of channels at connected BTSs BSC connects to the BTS via the Abis interfaceand to the MSC on A interface BSC has the entire database of cell parametersassociated with the BTSs. No mobile data is stored in the BSC Less connections for MSC as intelligence is madecommon to all BTSs by the BSC05/31/13Tempus Telcosys 28
    • 29. BSC05/31/13Tempus Telcosys 29
    • 30. TRAU – Transcoder RateAdaptation Unit05/31/13Tempus Telcosys 30BTSBSC PSTN13 kbps 16 kbps 16 kbps 64 kbpsMSC and TRAU
    • 31. TRAU (cont..) The MSC is based on ISDN switching. TheFixed Network is also ISDN based. ISDN has speech rate of 64 kbps. Mobilecommunicates at 13 kbps. TRAU converts the data rates between13kbps GSM rate to 64kbps Standard ISDNrate TRAU can be collocated with the BTS, BSCor MSC or it can be a separate unit.05/31/13Tempus Telcosys 31
    • 32. Location of Transcoder Collocated with MSC, BSC, BTS Separate Unit05/31/13Tempus Telcosys 32MSCTranscoderBSC
    • 33. MSC – Mobile SwitchingCentre05/31/13Tempus Telcosys 33BSCBSCBSCBTSs PSTNHLRVLR
    • 34. MSC (cont..) Exchange where calls are established, maintained andreleased Database for all subscribers and their associatedfeatures. Communicates with the BSCs on the A interface andwith PSTN on fixed line. MSC is weighted on the number of subscribers it cansupport. E.g. an MSC of 1 lac subscribers means oneMSC is enough till subscriber base increases upto 1 lac,beyond which another MSC is required.05/31/13Tempus Telcosys 34
    • 35. Multiple MSCs When there is more capacity, there are more thanone MSCs. All MSCs have to communicate with one anotherand to the outside world. Very complicated to connect each MSC to eachother and each MSC to PSTN So there is a concept of GMSC (Gateway MSC)05/31/13Tempus Telcosys 35BSCBSCMSCMSCGMSC PSTN
    • 36. HLR – Home Location Register MSC has all subscriber database storedin HLR HLR has all permanent subscriberdatabase HLR has a database which describes thesubscriber’s profile i.e. basic featuresand supplementary services MSC communicates with the HLR to getdata for subscribers on call05/31/13Tempus Telcosys 36
    • 37. VLR – Visiting Location Register A subscription when activated is registered inVLR VLR has all the subscriber numbers which areactive. VLR has a temporary database of all activesubscribers (on/off, location information)05/31/13Tempus Telcosys 37MSC VLRVLRHLR
    • 38. VLR (cont..) MSC communicates with HLR for subscriberscoming from different MSCs. If the subscriber isfound valid, then it registers the subscriber inthe VLR05/31/13Tempus Telcosys 38MSC MSCVLRVLRHLRVLR
    • 39. AUC – Authentication Centre Authentication is a process by which a SIM isverified Secret data and the verification processalgorithm are stored in AUC AUC is the element which carries out theverification of the SIM AUC is associated with the HLR05/31/13Tempus Telcosys 39MS MSC HLR AUC
    • 40. EIR (Equipment Identity Register) EIR is the Mobile Equipment Databasewhich has a series of IMEIs MSC asks the Mobile to send its IMEI MSC then checks the validity of IMEI withthe EIR All IMEIs are stored in EIR with relevantclassifications05/31/13Tempus Telcosys 40EIRMSC
    • 41. Classification of IMEIs05/31/13Tempus Telcosys 41White list: This contains the IMEI oftype approved mobilesBlack List: List of IMEIs which should bebarred because either they are stolen orare not functioning properlyGrey list: List of IMEIs which are to beevaluated before they are put in black list
    • 42. Billing Centre (BC) BC Generates the billing statement for eachsubscriber BC may be directly connected to the MSC orthrough a mediation device MSC sends CDRs (Call Detail Records) to the BC According to the template of pulse rates andunits set, BC creates a bill according to thedestination called and the call duration05/31/13Tempus Telcosys 42
    • 43. Billing Centre (BC) (cont..)05/31/13Tempus Telcosys 43CDRsTemplates for unit costs
    • 44. OMC – Operations andMaintenance Centre Also called the NOC (Network Operationscentre) It is the central monitoring and remotemaintenance centre for all network elements OMC has links to BSCs and MSCs05/31/13Tempus Telcosys 44
    • 45. OMC – Operations andMaintenance Centre Also called the NOC (Network Operationscentre) It is the central monitoring and remotemaintenance centre for all network elements OMC has links to BSCs and MSCs05/31/13Tempus Telcosys 45
    • 46. OMC05/31/13Tempus Telcosys 46OMC SystemBSCBSCBSCBTSsBTSsBTSsOMC Terminals
    • 47. 05/31/13Tempus Telcosys 47GSM Channels
    • 48. GSM Channels Physical Channel One time slot on one carrier is called physicalchannel. Logical Channel Information carried by physical channels is calledlogical Channels. Logical channels are mapped on physicalchannels.05/31/13Tempus Telcosys 48
    • 49. Logical Channels Traffic channels: Used for speech and data Full Rate(TCH/F) Half Rate(TCH/H) Control channels: Used for signaling .i.e.setting up a radio connection, call or controllingan MS during conversation BCH(Broadcast channels) CCCH(common control channels) DCCH(dedicated control channels)05/31/13Tempus Telcosys 49
    • 50. Traffic Channels(TCH)05/31/13Tempus Telcosys 50TCH/F(full Rate)TCH/H(half Rate)Traffic Channels(TCH)
    • 51. Control Channels(CCH)05/31/13Tempus Telcosys 51CCH(Control Channel)BCH CCCH DCCHCCH RACH CBCH SDCCH ACCHSynch.ChanelsSACCHFACCHPCH/AGCHFCCHSCH
    • 52. BCH(Broadcast Channels) BCCH(Broadcast Control Channels) Downlink Only. Broadcast information of the serving cell (SystemInformation). Transmitted on timeslot zero of BCCH carrier. Reads only by idle mobile at least once every 30secs.05/31/13Tempus Telcosys 52
    • 53. BCH(Broadcast Channels) cont’d SCH(Synchronisation Channels) Downlink Only Carries information for frame synchronisation. Contains frame number and BSIC(Base StationIdentity Code).05/31/13Tempus Telcosys 53
    • 54. BCH(Broadcast Channels) cont’d FCCH(Frequency Correction Channels) Downlink Only. Enable MS to synchronies to the frequency.05/31/13Tempus Telcosys 54
    • 55. CCCH(Common ControlChannel) RACH(Random Access Channel) Uplink only. Used by the MS when making its first access tothe Network. The reason for access could be initiation of a callor a page response.05/31/13Tempus Telcosys 55
    • 56. CCCH(Common Control Channel)cont’d AGCH(Assess Grant Channel) Downlink only. Used for acknowledgement of the access attemptsent on RACH. Used by the network to assign a signaling cannelupon successful decoding of access bursts.05/31/13Tempus Telcosys 56
    • 57. CCCH(Common Control Channel)cont’d PCH(Paging Channel) Downlink only. The network will page the MS ,if there is aincoming call or a short Message. It contains the MS identity number, the IMSI orTMSI.05/31/13Tempus Telcosys 57
    • 58. DCCH(Dedicated ControlChannel) SDCCH (Stand-alone Dedicated ControlChannel) Uplink and Downlink. Used for call setup, authentication, cipheringlocation update and SMS.05/31/13Tempus Telcosys 58
    • 59. DCCH(Dedicated ControlChannel) cont’d SACCH(Slow Associated Control Channel) Downlink and Uplink. Used to transfer signal while MS have ongoingconversation on traffic or while SDCCH is beingused. On the forward link, the SACCH is used to sendslow but regularly changing control information toeach mobile on that ARFCN, such as powercontrol instructions and specific timing advanceinstructions05/31/13Tempus Telcosys 59
    • 60.  SACCH(Slow Associated Control Channel)cont’d The reverse SACCH carries information aboutthe received signal strength and quality of theTCH, as well as BCH measurement resultsfrom neighboring cells.05/31/13Tempus Telcosys 60
    • 61. DCCH(Dedicated ControlChannel) cont’d FACCH(Fast Associated Control Channel) Downlink and uplink. Associate with TCH only. It is used to send fast message like hand overmessage. Work by stealing traffic bursts.05/31/13Tempus Telcosys 61
    • 62. Mapping on PhysicalChannels The Logical channels are mapped on thephysical channels. The TDMA frames are grouped together intomulti-frame. 26 TDMA multi-frame for Traffic. 51 TDMA multi-frame for control signal.05/31/13Tempus Telcosys 62
    • 63. Channel Combination Combined All the controlling signals are in the time slot 0 ofthe Multi-frame. Non Combined Dedicated controlling signals are in time slot 1 ofthe Multi-frame.05/31/13Tempus Telcosys 63
    • 64. Combined Cell with single carrier. Timeslot 0 :BCCH+CCCH+SDCCH. Timeslot 1-7 :TCH/FACCH+SACCH.05/31/13Tempus Telcosys 64
    • 65. Non Combined Cell with Two carrier Timeslot 0 (of carrier 1) BCCH+CCCH. Timeslot 1 (of carrier1) SDCCH+SACCH. Timeslot 2-7 & 0-7(of both carriers)TCH/FACCH+SACCH.05/31/13Tempus Telcosys 65
    • 66. BROADCAST MESSAGES System information 5 and 6 sent on the SACCHimmediately after Handover or whenever nothing else isbeing sent. Downlink SACCH is used for system informationmessages while uplink SACCH is used for measurementreports. System Information types 7 and 8 (optional) are anextension to type 4 and broadcast on the BCCH.05/31/13Tempus Telcosys 66
    • 67. SYSTEM INFORMATION05/31/13Tempus Telcosys 67
    • 68. SYSTEM INFORMATION 1 When frequency hopping is used in cell MS needs toknow which frequency band to use and what frequencywithin the band it should use in hopping algorithm. Cell channel descriptionCell Allocation Number(CANO)-Informs the bandnumber of the frequency channels used.00-Band 0(current GSM band)Cell Allocation ARFCN(CA ARFCN):- ARFCN’sused for hopping.It is coded in a bitmap of 124 bits.05/31/13Tempus Telcosys 68
    • 69. SYTEM INFORMATION 105/31/13Tempus Telcosys 69124 123 122 121024 023 022 021 020 019 018 017016 015 014 013 012 011 010 009008 007 006 005 004 003 002 001
    • 70. SYSTEM INFORMATION 1 RACH Control ParametersAccess Control Class(ACC) :-Bitmap with 16 bits.All MS spread out on class 0 –9 . Priority groups useclass 11-15. A bit set to 1 barred access for that class.Bit 10 is used to tell the MS if emergency call is allowedor not.0 – All MS can make emergency call.1 - MS with class 11-15 only canmake emergency calls.Cell barred for access(CB):-0- Yes1- No05/31/13Tempus Telcosys 70
    • 71. SYSTEM INFORMATION 1 RACH Control ParametersRe-establishment allowed(RE):-0- Yes1- NoMax_retransmissions(MAXRET):-Number of timesthe MS attempts to access the Network [1,2,4 or 7].Tx-integer(TX):- Number of slots to spread accessretransmissions when a MS attempts toaccess the system.Emergency call allowed:- Yes/No.05/31/13Tempus Telcosys 71
    • 72. SYSTEM INFORMATION 2 System Information Type 2 message consists ofthe Double BA list which defines the BCCHfrequencies used in the neighboring cells. The Double BA list provides the MS withdifferent frequencies on which to measure,depending on whether the MS is in idle or activemode. In active mode, the MS should measure on areduced number of frequencies in order toimprove the accuracy of measurements.05/31/13Tempus Telcosys 72
    • 73. SYSTEM INFORMATION 2 In Idle mode,the MS should measure on largernumber of frequencies, so that the time requiredfor the MS to access the network after power onis reduced. The MS is also informed which PLMN’s it mayuse. As well as System Information Type 2,it is alsopossible to have System Information Type 2 Bisand System information Type 2 Ater, dependingon the size of the BA List. System Information Type 2 Bis/Ter are optional.05/31/13Tempus Telcosys 73
    • 74. SYSTEM INFORMATION 2 Neighbor Cell Description:-BA Indicator(BA IND):- Allows to differentiatemeasurement results related to different list of BCCHfrequencies sent to MS.BCCH Allocation number(BANO):-Band 0 is used. PLMN Permitted(NCCPERM):-This the PLMNcolor codes permitted and tells the MS which networkcolor codes(NCC) on the BCCH carriers it is allowed tomonitor when it is in this cell..05/31/13Tempus Telcosys 74
    • 75. SYSTEM INFORMATION 2 RACH Control ParametersAccess Control Class(ACC) :-Bitmap with 16 bits.All MS spread out on class 0 –9 . Priority groupsuse class 11-15. A bit set to 1 barred access forthat class. Bit 10 is used to tell the MS if emergencycall is allowed or not.0 – All MS can make emergency call.1 - MS with class 11-15 only canmake emergency calls.Cell barred for access(CB):-0- Yes1- No05/31/13Tempus Telcosys 75
    • 76. SYSTEM INFORMATION 2Re-establishment allowed(RE):-0- Yes1- NoMax_retransmissions(MAXRET):-Number of timesthe MS attempts to access the Network [1,2,4 or 7].Tx-integer(TX):- Number of slots to spread accessretransmissions when a MS attempts toaccess the system.Emergency call allowed:- Yes/No.05/31/13Tempus Telcosys 76
    • 77. SYSTEM INFORMATION 2BCCH ARFCN Number(BAIND):- ARFCN’s used for ina Bitmap of 124 bits05/31/13Tempus Telcosys 77124 123 122 121024 023 022 021 020 019 018 017016 015 014 013 012 011 010 009008 007 006 005 004 003 002 001
    • 78. SYSTEM INFORMATION 3 The System Information Type 3 contains information onthe identity of the current LA and cell identity, because achange means that the MS must update the network. System Information 3 also as Control ChannelDescription parameters used to calculate the Paginggroup. When the MS is in idle mode it decides which cells to lockto. Information needed by the MS for cell selection is alsobroadcast in the Type 3 information.05/31/13Tempus Telcosys 78
    • 79. SYSTEM INFORMATION 38 7 6 5 4 3 2 11 1 1 1LACLOCATION AREA IDENTITTY(LAI)MCC DIG 1MCC DIG 2MCC DIG 1MNC DIG 1MNC DIG 2CICICELL IDENTITYLAC05/31/13Tempus Telcosys 79
    • 80. SYSTEM INFORMATION 3 Control Channel DescriptionAttach / Detach(ATT):-0 = Allowed1 = Not Allowedbs_agblk:-Number of block reserved for AGCH [0-7]Ba_pmfrms:-Number of 51 frame multi-framesbetween transmission of paging messages to MS ofthe same groupT3212:- Periodic location update timer .[1-255 deci hours].05/31/13Tempus Telcosys 80
    • 81. SYSTEM INFORMATION 3cch_conf Physical channels combined No. of CCH0 1 timeslot(0) No 91 1 timeslot(0) Yes 32 2 timeslot(0,2) No 184 3 timeslot(0,2,4) No 276 4 timeslot(0,2,4,6) No 3605/31/13Tempus Telcosys 81
    • 82. SYSTEM INFORMATION 3 Cell optionsDTX:-Whether Discontinuous Transmissionused or not.PWRC:-Power control on the downlink.0 = Not used.1 = Used.Radio link timeout(RLINKT):-Radio link time-out is the time before an MSdisconnects due to failure in decoding SACCHmessage. Sets the timer T100 in the MS.05/31/13Tempus Telcosys 82
    • 83. SYSTEM INFORMATION 3 Cell Selection ParametersRxlev_access_min:- Minimum received signal levelat the MS for which it is permitted to access thesystem.0-63 = -100 dBm to –47 dBm.Mx_txpwr_cch:- Maximum power the MS will usewhen accessing the system.Cell_reselect_hysteresis:- Used for cell reselection. RACH Control Parameters.05/31/13Tempus Telcosys 83
    • 84. SYSTEM INFORMATION 4 Location Area Identification. Cell Selection ParametersRxlev_access_min:- Minimum received signal levelat the MS for which it is permitted to access thesystem.0-63 = -100 dBm to –47 dBm.Mx_txpwr_cch:- Maximum power the MS will usewhen accessing the system.Cell_reselect_hysteresis:- Used for cell reselection.05/31/13Tempus Telcosys 84
    • 85. SYSTEM INFORMATION 4 RACH Control Parametersmax_retransmissions(MAXRET)tx_integer(TX)Cell barred for access(CB).Re-establishment allowed(RE)Emergency Call AllowedAccess Control Class (ACC)05/31/13Tempus Telcosys 85
    • 86. SYSTEM INFORMATION 4 CBCH Description(Optional) :CHN:- This is the channel number for CBCH. It iscontrolled internally in BSC.TSC:- Training Sequence Code. Base Station ColorCode(BCC) part of BSIC is used.CBCHNO:- Absolute RF channel number of CBCH.MAC:- Mobile Allocation in the cell, describes thefrequencies to be used in the hopping sequence iffrequency hopping is used.05/31/13Tempus Telcosys 86
    • 87. SYSTEM INFORMATION 4Hopping Channel(H):-Informs if CBCH Channel ishopping or single.ARFCN:- If H=0;MAIO:- If H=1, informs the MS where tostart hopping.Values [0-63].HSN:- If H=1, informs the MS in what orderthe hopping should take place. Values[0 –63].HSN=0 Cyclic Hopping.MA:-Indicates which RF Channels are usedfor hopping. ARFCN numbers coded inbitmap.05/31/13Tempus Telcosys 87
    • 88. SYSTEM INFORMATION 5 Sent on the SACCH on the downlink to the MS indedicated mode. On SAACH, the MS also receives information about theBCCH carrier in each neighboring cell. This may differfrom those sent in System information type 2. It is also possible to have system Information Type 5 Bisand System Information Type 5Ter, depending on thesize of the BA list.05/31/13Tempus Telcosys 88
    • 89. SYSTEM INFORMATION 5 Neighbor Cell Description:-BA-IND:-Used by the Network to discriminatemeasurements results related to different lists ofBCCH carriers sent by the MS(Type 2 or 5).Values 0 or 1(different from type 2).BCCHAllocation number:-00-Band 0(current GSM band).05/31/13Tempus Telcosys 89
    • 90. SYSTEM INFORMATION 5BCCH ARFCN:-Neighboring cells ARFCN’s. Sent as abitmap.0-Not used1-Used.124 123 122 121024 023 022 021 020 019 018 017016 015 014 013 012 011 010 009008 007 006 005 004 003 002 00105/31/13Tempus Telcosys 90
    • 91. SYSTEM INFORMATION 6 Ms in dedicated mode needs to know if the LA haschanged.If so, it must perform location updating whenthe call is released. MS may change between cells with different Radio linktimeout and DTX. Cell Identity. Location Area Identification. PLMN permitted.05/31/13Tempus Telcosys 91
    • 92. SYSTEM INFORMATION 6 Cell options:DTXPWRCRadio Link timeout.05/31/13Tempus Telcosys 92
    • 93. SYSTEM INFORMATION 7/8 System Information Types 7 and 8 contain CellReselect parameters. Their function is tosupplement System Information Type 4.05/31/13Tempus Telcosys 93
    • 94. GSM Interfaces (Um) Air interface - MS to BTS A bis interface - BTS to BSC A Interface - BSC to MSC B Interface - MSC to VLR C interface - MSC to HLR05/31/13Tempus Telcosys 94
    • 95. MSCBSCVLRHLRAUCEIRGMSCMSA InterfaceA bis InterfaceAir InterfaceB InterfaceC InterfaceF InterfaceD InterfaceH InterfaceTo otherNetworks05/31/13Tempus Telcosys 95
    • 96. GSM Interfaces The interfaces between MSC and MS is called A,Abis and Um interfaces. On these interfaces only three layers aredefined.They are not corresponding to the OSI(Open System Interconnection) model.05/31/13Tempus Telcosys 96
    • 97. A Interface A interface between the BSC and the MSC The A interface provides two distinct types ofinformation, signalling and traffic, between theMSC and the BSC. The speech is transcoded in the TRC and the SS7(Signalling system) signalling is transparentlyconnected through the TRC or on a separate linkto the BSC.05/31/13Tempus Telcosys 97
    • 98. Abis Interface The A-bis interface responsible for transmitting trafficand signalling information between the BSC and theBTS. The transmission protocol used for sending signallinginformation on the A-bis interface is Link AccessProtocol on the D Channel (LAPD)05/31/13Tempus Telcosys 98
    • 99. (Um) Air Interface This is the interface between the mobile station and theBase station. The Air interface uses the Time Division Multiple Access(TDMA) technique to transmit and receive traffic andsignalling information between the BTS and MS. The TDMA technique is used to divide each carrier intoeight time slots.These time slots are then assigned tospecific users,allowing up to eight conversations to behandled Simultaneously by the same carrier.05/31/13Tempus Telcosys 99
    • 100. 7 56 34 12 01 2 43 5 76Down LinkUp Link 0Time Slot05/31/13Tempus Telcosys 100• This interface is the radio interface between themobile station and the network and uses layerThree messages.• On Layer three messages we have the divisionof message types into CM (communicationManagement), MM (Mobility Management), andRR (Radio Resource Management).
    • 101. Connection Management(CM)There are three entities within CM: Call Control(CC) – Which handles the proceduresconcerning call control. e.g. setup,Change of bearerservice. Supplementary Service (SS) – Which handles such as callbearing, call waiting , call forwarding etc. Short Message Service (SMS) – Enables the MS to handleshort message transfer to and from the network.05/31/13Tempus Telcosys 101
    • 102. Mobility Management (MM) Mobility management handles functions forauthentication, location updating, identification andothers concerning the mobility of the mobile station.05/31/13Tempus Telcosys 102
    • 103. Radio Resource Management(RR) It contains the functions concerning the radio link. Herewe find the capability to establish,maintain and releasethe radio connection between the network and themobile station, which includes the handover procedure.05/31/13Tempus Telcosys 103
    • 104. B Interface The B interface between the MSC and the VLR uses theMAP/TCAP protocol. Most MSCs are associated with a VLR, making the Binterface "internal". Whenever the MSC needs access to data regarding a MSlocated in its area, it interrogates the VLR using theMAP/B protocol over the B interface.05/31/13Tempus Telcosys 104
    • 105. C Interface The C interface is between the HLR and a MSC. Each call originating outside of GSM (i.e., a MSterminating call from the PSTN) has to go through aGateway to obtain the routing information required tocomplete the call, and the MAP/TCAP protocol over theC interface is used for this purpose. Also, the MSC may optionally forward billing informationto the HLR after call clearing.05/31/13Tempus Telcosys 105
    • 106. D Interface The D interface is between the VLR and HLR. It uses the MAP/TCAP protocol to exchange the datarelated to the location of the MS and to the managementof the subscriber.05/31/13Tempus Telcosys 106
    • 107. E Interface The E interface interconnects two MSCs. The E interface exchanges data related to handoverbetween the anchor and relay MSCs using the-MAP/TCAP+ISUP/TUP protocol.05/31/13Tempus Telcosys 107
    • 108. F Interface The F interface connects the MSC to the EIR. It uses the MAP/TCAP protocol to verify the status of theIMEI that the MSC has retrieved from the MS.05/31/13Tempus Telcosys 108
    • 109. G Interface The G interface interconnects two VLRs of differentMSCs. It uses the MAP/G protocol to transfer subscriberinformation, during e.g. a location update procedure.05/31/13Tempus Telcosys 109
    • 110. 05/31/13Tempus Telcosys 110
    • 111. Topics for discussion Speech Encoding Data Encoding Interleaving for Voice,Control and Datasignals05/31/13Tempus Telcosys 111
    • 112. Speech Encoding We shall start with a raw voice signal fed intothe microphone, travel through the variousstages involving vocoding, channel coding etctill it reaches the final burst format on the AirInterface.05/31/13Tempus Telcosys 112
    • 113. Speech Encoding ckt05/31/13Tempus Telcosys 113VoiceEncodingChannelcodinginterleavingRF ModulationRawVoicesignal
    • 114. Speech Encoding ckt The voice is sampled at the rate of 50 samplesper second. This results in 20 msec blocks of speech Each of this 20 msec block is passed on to the13Kbps vocoder. There are 260 information bits from theoutput of the vocoder for every 20 msec inputi.e.; 13Kbps *20msec = 260 bits.05/31/13Tempus Telcosys 114
    • 115. Voice Encoding ckt05/31/13Tempus Telcosys 115Vocoder I/p20 msec speechblocks13Kbps Vocoder Vocoder O/p260 bits
    • 116. Channel coding Channel Coding is done to protect the logicalchannels from transmission errors introducedby the radio path. The coding schemes depend on the type ofthe logical channels, hence the coding candiffer from speech, control and data .05/31/13Tempus Telcosys 116
    • 117. Channel Coding for speech05/31/13Tempus Telcosys 117Class class 1b class 21a50 3 132 4 tailBits parity bitsConvolutional coder½ coder, k=5456 bits=378 bits from Convolution coder + 78 class 2 bits260 bits
    • 118. Channel coding for Speech The 260 bits of speech info from the vocoder isbroken down into three parts. Class 1a- 50 bits , these represent the filtercoefficients of the speech and are the mostimportant for proper detection of the speech atthe receiver and hence are given maximumprotection. 3 additional parity bits are derivedfrom the class 1a bits for cyclic redundancy check(CRC).05/31/13Tempus Telcosys 118
    • 119. Channel coding for Speechcont’d Class 1b - 132 bits are not parity checked butare fed into the convolutional coder alongwith 4 tail bits which are used to set theregisters in the receiver to a known state fordecoding purpose. Class 1b- 78 bits, these are not so importantand are not protected but are combined withthe output of the convolution coder.05/31/13Tempus Telcosys 119
    • 120. Convolutional coder CC The Convolutional coder is a series of shiftregisters implemented using logic gates, wherefor every one input bit we get 2 output bits.Hence it is called ½ coder. Here k=5 is the constraint length, it means thereare 5 shift register and each bit has memorydepth of 4 , meaning it can influence the outputof up to four next successive bits. This is usefulduring reception as bits can be derived even if afew consecutive bits are lost due to errors orcorruption.05/31/13Tempus Telcosys 120
    • 121. ½ Convolutional coder05/31/13Tempus Telcosys 121R1 R2 R3 R5R4++C0outputC1output0110..Input bits+ EX-ORR=register
    • 122. Convolutional coder cont’d The output of the CC* is now 378 bits.(50+3+132+4)*2=378The total number of bits now is 378+78=456 bits.*Note : The bit rate from the vocoder was 13Kbpsfor the 20 msec speech block, but after CC the bitrate increases to 22.8Kbps.456 bits *20msecs=22.8Kbps* CC = Convolutional Coder.05/31/13Tempus Telcosys 122
    • 123. Control Channel Coding05/31/13Tempus Telcosys 123184 bitsControl data184 40 4 tailFire coded parity bits½ Convolutional Coder456 bits output
    • 124. Control Channel Coding The control information is received in blocks of184 bits. These bits are first protected with a cyclic codecalled as Fire code, which is useful in correctionand detection of burst errors. 40 Parity bits are added, along with 4 tail bits. These 228 bits are given to the CC whose outputis again 456 bits at a bitrate of 22.8Kbps. The control channels include the RACH, PCH,AGCH etc.05/31/13Tempus Telcosys 124
    • 125. Data Channel Coding05/31/13Tempus Telcosys 125240 bits 4 tailData bits½ Convolutional CoderOutput= 488 bitsAfter PuncturingOutput=456 bits
    • 126. Data Channel Coding The data bits are received in blocks of 240 bits.These are directly convolution coded afteradding 4 tail bits. The output of the CC is now 488 bits, whichactually increases the bitrate to 24.4 Kbps. To keep the bitrate constant on the air interfacewe need to puncture the output of the CC.Hence, we have a final bitrate of 22.8 Kbps again.05/31/13Tempus Telcosys 126
    • 127. Channel Coding cont’d The above explanation was given keeping inview a full rate Traffic, Control, or Datachannel. For Half rate or Lesser rates the sameprinciple of channel coding holds good, withslight differences in the encoding process.05/31/13Tempus Telcosys 127
    • 128. Interleaving Having encoded the logical channelinformation, the next step is to build its bitstream into bursts that can be transmittedwithin the TDMA frame structure. This is thestage where the interleaving process iscarried out. Interleaving spreads the content of oneinformation block across several TDMAtimeslots or bursts.05/31/13Tempus Telcosys 128
    • 129. Interleaving cont’d The following interleaving depths are used : Speech – 8 blocks Control – 4 blocks Data – 22 blocks The interleaving process for a speech block isshown wherein which a 456 bit speech block isdivided into 8 blocks of 57 bits each and each ofthese odd and even 57 bit blocks are interleaveddiagonally on to alternate bursts on the TDMAframe.05/31/13Tempus Telcosys 129
    • 130. Speech Interleaving05/31/13Tempus Telcosys 1308* 57 bits each = 456 bitsOf Speech block N57EvenOf N-157EvenOf NSpeech blockN-157oddOf N-157oddOf NThe speech is spread over 8 such normal burstsEach normal burst consists of two blocks of 57 bit speechfrom different 20msec blocks (say N, N-1) along with26 bit training sequence T and 2 flag F plus 6 start stop bits .T+FT+FT+F456 bit speech data
    • 131. Control Data Interleaving05/31/13Tempus Telcosys 131114 114 114 114456 bits control dataThe control data is spread over 4 blocks using rectangularinterleaving instead of diagonal interleaving as inspeech the receiver will have to wait for at least2 multiframes before being able to decode the controlmessageTDMABurst blocks
    • 132. Data Interleaving05/31/13Tempus Telcosys 132114 114 114 114Burst 1 Burst 22Burst 2 Burst 3 Burst 4 Burst 19First 6bitsFirst 6bitsLast 6bitsLast 6bits456 bit data block
    • 133. Data Interleaving cont’d Here the data block of 456 bits is divided into 4blocks of 114 bits each. The first 6 bits from each of the 114 bit blocks isinserted in to each frame, the second 6 bits fromeach of the 114 bits into the next frame and so onspreading each 114 block over 19 TDMA burstswhile the entire 456 bits is spread over 22 TDMAbursts. Thus the data interleaving is said to have a depthof 22 bursts.05/31/13Tempus Telcosys 133
    • 134. Data Interleaving cont’d The reason why data is spread over such alongperiod of time is that if data burst is corrupted orlost, only a small part of it is lost which can bereproduced at the receiver. This wide interleaving depth does produce atime delay during transmission but that isacceptable since it does not affect the datasignal quality at the receiver, unlike speechwhere delay could result in bad quality of signalto the subscriber. *Note – The interleaving used in data is diagonalinterleaving.05/31/13Tempus Telcosys 134
    • 135. Before Deinterleaving3 successive bursts corruptedAfter DeinterleavingThe corrupted bursts are spread over a length equal to theinterleaving depth so that the effect of the errors isminimized.05/31/13Tempus Telcosys 135Interleaving Advantage
    • 136. Air Interface Bitrate The information which is now coded andinterleaved at 22.8 Kbps now has to betransmitted over the Air interface to the BTS. The information burst is not sent directly , but issent in ciphered form within a burst envelope.This ciphering is done using ciphering keys andalgorithms known both by the mobile and theBSS.05/31/13Tempus Telcosys 136
    • 137. Air Interface Bitratecont’d The Kc is the ciphering key and A5 algorithmare applied to the information(speech ordata) which increases the bitrate to a finalrate of 33.8 Kbps from/to each mobile. If we assume all 8 timeslots of the cell to beoccupied then the bitrate of the Air interfacecomes to 33.8 * 8= 270.4 Kbps/channel.05/31/13Tempus Telcosys 137
    • 138. Air Interface Bitratecont’d05/31/13Tempus Telcosys 138A5 AlgorithmKc InformationBlock 22.8 KbpsSent on Air interfaceCiphered information burst33.8 Kbps
    • 139. Air Interface Bitratecont’d05/31/13Tempus Telcosys 1391 2 3 4 5 6 7 8MobileTx’s at33.8 KbpsCell rx’s 8*33.8KBps = 270.4 KbpsPer TDMA frameCell coverage areaTDMA Fn TDMA Fn+1
    • 140. Decoding and Deinterleaving atthe Receiver At the receiver the reverse process ofDeinterleaving and decoding have to take placerespectively, so as to recover the informationfrom the signal. After Deinterleaving the signal will be decodedwhich is the reverse process of the Convolutionalcoding, using Viterbi decoders. The decoder can recover lost or corrupted dataup to 4 successive bits, because the memorydepth of the CC is 4(for k=5).05/31/13Tempus Telcosys 140
    • 141. Channelization Frequency band has several applicationsegments Certain blocks of the Band are reserved forcertain applications by regulating authorities Technologies have decided their frequencybands E.g. AMPS/DAMPS: 824-894 MHz05/31/13Tempus Telcosys 141
    • 142. Channelization methodsChannelization can be done primarily by threemethods: FDMA (Frequency Division Multiple Access) TDMA (Time Division Multiple Access) CDMA (Code Division Multiple Access)05/31/13Tempus Telcosys 142
    • 143. FDMA E.g. AMPS band is divided into 30 KHz channels(1666 Freq. channels) Television Channels (Star, Zee, Sony,..)05/31/13Tempus Telcosys 143FrequencyTimePower
    • 144. TDMA E.g. AMPS has 3 timeslots on each 30 KHzchannel05/31/13Tempus Telcosys 144FrequencyTimePower
    • 145. CDMA Frequency channel is divided into codechannels E.g. in IS-95 CDMA, 1.228 MHz channel isdivided into 64 Code Channels Each user has a particular code Codes are orthogonal to each other, do notinterfere with each other05/31/13Tempus Telcosys 145
    • 146. Duplex Access Methods Frequency Division Duplex (FDD) Transmit on one frequency and receive onanother frequency05/31/13Tempus Telcosys 146F1 F2 FrequencyAmplitudeTimeTx Rx
    • 147. Time Division Duplex Time division duplex Tx and Rx is on the same frequency but ondifferent times05/31/13Tempus Telcosys 147F1 FrequencyAmplitudeTimeTxRx
    • 148. GSM Air Interface Separate Bands for Uplink and Downlink Downlink: 935-960Mhz (EGSM: 925-960MHz) Uplink: 890-915 MHz (EGSM: 880-915 MHz)05/31/13Tempus Telcosys 148• TDMA and TDMA Multiplex– 124 Frequency Channels (ARFCN) forGSM900– 1 to 124 fro current band– 975 to 1023 for E-GSM– 200kHz Channels– 8 Mobiles share ARFCN by TDMA
    • 149. GSM Air interface (1800) 1800: Downlink: 1805-1880 MHz 1800: Uplink: 1710-1785 MHx 374 ARFCNs Separation of 95 MHz ARFCNs are numbered from 512 to 885inclusive05/31/13Tempus Telcosys 149
    • 150. The GSM Burst05/31/13Tempus Telcosys 1503 357 261 571 8.25Tail BitsDataControlBitMidambleControlBitDataTail BitsGuardPeriod
    • 151. Speech Coder RPE/LTP coder (RegularPulse excitation/Long termPrediction) Converts 64 kbps speechto 13 kbps At the end we get 13kbpsspeech i.e. 260 bits in 20ms05/31/13Tempus Telcosys 15120 ms blocksSpeech CoderBits Ordered50 veryimportantbits132importantbits78 otherbits
    • 152. Error Correction05/31/13Tempus Telcosys 152Type 1a 50 3(CRC)Type 1b 132 Type II 78Reordering25 66366 25 4 Type II 78Type 1aType 1b Type 1bType 1aTailHalf rate convolutional code378 Type II 78456 bits from 20 ms of speech
    • 153. Diagonal Interleaving Traffic channel (TCH) bursts carry two 57 bit blocks(114) Each 120 ms of speech = 456*6 = 2736 bits2736/114 = 24 bursts i.3. 24 framesMultiframe has 26 frames in 120ms.There are 2 spare frames .. 1 SACCH, 1 Idle05/31/13Tempus Telcosys 153456 bits from 20ms of speech 456 bits from 20ms of speech57 57575757575757 57 5757575757575757 57 57 5757 5757 5757 5757 5757 5757 57
    • 154. Convolutional Coding andInterleaving Bits to be Tx ed: HELLO Convolutionally encoded: HHEELLLLOO Interleaved: EE HH LL LL OO Bits Rx ed: EE HH LL LL OO De-Interleaved: HHEELLLLOO Viterbi Decoded: HELLO05/31/13Tempus Telcosys 154
    • 155. Speech Coding Process05/31/13Tempus Telcosys 15520 msSpeech Coder260 bits 13 kbps50 1a 132 1b 78 IIChannel Coder456 bits 22.8 kbpsTransceiver (BTS)Transcoder Handler260 bits456 bits16 kbpsTRAU frame260 + 60 = 320 bitsAbis13 kbps
    • 156. TRAU frame 260 bits info + 60 TRAU bits = 320 bits/20ms =TRAU frame 60 bits contain frame Information data whichindicates speech, data, O&M, full rate/halfrate 60 bits = 35 synchronization + 21 control + 4timing05/31/13Tempus Telcosys 156
    • 157. Midamble or Training Bits 8 midamble patterns (Colour codes) of 26 bits (BSIC) RACH and SCH have longer 41 and 64 bit Midambles Equalizer estimates channel impulse response frommidamble Mathematically construct inverse filter Uses inverse to decode bits05/31/13Tempus Telcosys 1573 357 261 571 8.25Tail BitsDataControl BitMidambleControl BitDataTail BitsGuardPeriod
    • 158. Downlink and Uplink Uplink lags downlink by 3 timeslots Uplink and downlink use same timeslot number Uplink and downlink use same channel number(ARFCN) Uplink and downlink use different bands (45MHz apart for GSM 900)05/31/13Tempus Telcosys 158
    • 159. Measurements made by MS andBTS05/31/13Tempus Telcosys 159 RxQual0 < 0.2% 1 0.2 – 0.4 %3 0.4 – 0.8 % 4 0.8 – 0.16 %5 1.6 – 3.2 % 6 3.2 – 6.4 %7 6.4 – 12.8 %Uplink RXLEV (-48 to -110 dbm)Uplink RXQUAL (0-7)Uplink RXLEV (-48 to -110 dbm)Uplink RXQUAL (0-7)
    • 160. Mobile Power Control05/31/13Tempus Telcosys 160 Mobile is commanded to change its TransmitPower Change in Power is proportionate to the PathLoss Change in Power is done in steps of 2 dbsPath LossPower Command
    • 161. Timing Advance TDMA approach requires signals to arrive atBTS at the correct time A mobile at 30 km will be late by 100microseconds Timing advance is in the range of 0-62 One unit is 550m So maximum cell size is 63*0.55 = ~35 kms05/31/13Tempus Telcosys 161
    • 162. Concepts of Channels in GSM A company vehicle is used for several purposes in aday Similarly in GSM, the timeslots are used for differentpurposes at different times05/31/13Tempus Telcosys 162
    • 163. Frames and Multiframes05/31/13Tempus Telcosys 1630 654321 73 Data 1Midamble1 Data 3 8.25 bits156.25 bits 576.92 micro sec4.615 msTimeSlotFrame0 50 0 25Control ChannelMultiframeTraffic ChannelMultiframe
    • 164. GSM Operations Location Update MobileOriginated Call MobileTerminated Call Handover SecurityProcedures Cell Barring DTX Cell Broadcast Short MessageService Emergency calls SupplementaryServices Roaming05/31/13Tempus Telcosys 164
    • 165. Mobile Turn On Mobile Searches for BroadcastChannels (BCH) Synchronizes Frequency and Timing Decodes BCH sub-channels (BCCH) Checks if Network Allowed by SIM Location Update Authentication05/31/13Tempus Telcosys 165
    • 166. Location Area05/31/13Tempus Telcosys 166Location Area 1Location Area 1LocationArea 2LocationArea 2BTSBTSBTSBTSBTSBTSBTSBTSBSCBSCBSCMSC
    • 167. Location Area Identity Location area is the area covered by oneor more BTSs where a mobile can movefreely without updating the system One Location area can be covered by oneor more BSCs, but ony one MSC.05/31/13Tempus Telcosys 167MCC LACMNC
    • 168. Importance of Location Area Reduce Paging load Resource PlanningSmaller Location Areas – Location updateincreasesLarger Location Areas – Paging load increases05/31/13Tempus Telcosys 168
    • 169. What is Location Update? MSC should know the location of theMobile for paging Mobile is continuously changinglocation area Mobile when changes Location Areainforms the MSC about its new LA Process of informing MSC about newLocation area is Location Update05/31/13Tempus Telcosys 169
    • 170. Types of Location Updates1. Normal LocationUpdate2. IMSI Attach3. Periodic LocationUpdate05/31/13Tempus Telcosys 170Hi,I am in Location areaxxx
    • 171. IMSI Attach Mobile turns off and sends an IMSI Detachto MSC Mobile turns on again and compares LAI If same, sends an IMSI attach to MSC05/31/13Tempus Telcosys 171Is the receivedLAI same asbeforeIf same,SendsIMSIattach
    • 172. Normal Location Update Mobile Turns on Power Reads the new LAI If different, does a Location Update05/31/13Tempus Telcosys 172Is the receivedLAI same asbeforeIf different,doesLocationUpdate
    • 173. Periodic Location Update The periodic location Update time is setfrom OMC/MSC After the periodic location update timerexpires, the mobile has to do a locationupdate05/31/13Tempus Telcosys 173
    • 174. What happens at LocationUpdate? Mobile changes location area Reads the new Location Area fromBCCH Sends a RACH (request for channel) Gets a SDCCH after AGCH Sends its IMSI and new and old LAI in aLocation Update request to MSC onSDCCH05/31/13Tempus Telcosys 174
    • 175. What happens at locationupdate cont..….. . . MSC starts Authentication If successful, Updates the new Location areafor the Mobile in the VLR Sends a confirmation to the Mobile Mobile leaves SDCCH, and comes to idle mode05/31/13Tempus Telcosys 175
    • 176. Mobile Originated Call05/31/13Tempus Telcosys 176Channel RequestImmediate AssignService RequestCall ProceedingSet UpCipheringAuthenticationAlertingAssignmentConnection
    • 177. Mobile Terminated Call05/31/13Tempus Telcosys 177PagingChannel RequestImmediate AssignSet UpCipheringAuthenticationPaging ResponseAssignmentCall ConfirmedAlertingConnection
    • 178. Security Features Authentication Process to verify Authenticity of SIM Mobile is asked to perform an operationusing identity unique to SIM05/31/13Tempus Telcosys 178• Ciphering–Process of coding speech forsecrecy–The speech bits are EXORed withbit stream unique to MS
    • 179. Security Features (TMSIReallocation)05/31/13Tempus Telcosys 179GSMInfrastructureMobileLocation UpdateTMSI AllocationCall SetupTMSI ReallocationTMSI- Temporary Mobile Subscriber Identity
    • 180. Security Features(Identity Check)05/31/13Tempus Telcosys 180EIRSends IMEIIdentity CheckWhite listed /Grey Listed/ BlackListed mobiles
    • 181. Handover05/31/13Tempus Telcosys 181Cell 1 Cell 2Handover is a GSM feature by which thecontrol/communication of a Mobile is transferredfrom one cell to another if certain criteria’s aremet. It is a network initiated process.
    • 182. Criteria for Handover Receive Quality (RXQUAL) on uplink anddownlink Receive Signal Strength (RXLEV) on uplinkand downlink Distance (Timing Advance) Interference Level Power Budget05/31/13Tempus Telcosys 182
    • 183. Handover Decision BSC process the measurements reported by Mobileand the BTS05/31/13Tempus Telcosys 183BTSBTSBTSBTSBTSBTSMobile has measurements of six neighbors
    • 184. Handover Decision (cont..) BSS performs averaging function on thesemeasurements every SACCH frame (480ms) Handover Decision algorithm is activated after aset number of SACCH frame periods bycomparison against thresholds05/31/13Tempus Telcosys 184
    • 185. Types of Handovers INTRA-CELL HANDOVERS INTER-CELL HANDOVERS INTRA-BSC HANDOVERS INTER-BSC HANDOVERS INTER-MSC HANDOVERS05/31/13Tempus Telcosys 185
    • 186. INTRA-CELL HANDOVER05/31/13Tempus Telcosys 186C0C1Handover between timeslots of same frequencyHandover between different frequencies of the same cell(to reduce interference)MSC is not aware about this
    • 187. Inter-cell Handover05/31/13Tempus Telcosys 187Handover between cells of the same BTSBTSCell 1 Cell 2
    • 188. Inter-cell Handover (cont..) MSC is told about HO BTS -> BSC -> MSC Why MSC is informed? In case of change of LA, MSC may need LAC forpaging. As MS is busy, a link already exists. So, MSCcan send a tone in case of call waiting, and does notneed to page again. This is needed also for billing and call tracing05/31/13Tempus Telcosys 188
    • 189. INTRA-BSC Handover05/31/13Tempus Telcosys 189MSC BSCBTSBTSThis HO takes place if the cell to which handoveris to be done belongs to the same BSC
    • 190. Inter BSC Handover05/31/13Tempus Telcosys 190MSCBSC BTSBTSBSCThe MSC is completely involved in this Handover
    • 191. Inter MSC Handover05/31/13Tempus Telcosys 191BSCBSCMSCMSCBTSBTSGMSC/PSTN/BackboneIn this case the handover takes place through theinterconnecting element which can be GMSC orPSTN or private Backbone between the MSCs
    • 192. Cell Barring05/31/13Tempus Telcosys 192BTSCell Barring is a GSM feature by which certainmobiles could be barred access to certain cellsCell barring is activated/deactivated at BTS levelCell barring is done for mobile categories andpriorities
    • 193. Cell Barring Every mobile has an access class The access class is stored in the SIM Classes 0-9 are termed normal calsses Classes 11-15 are emergency classes05/31/13Tempus Telcosys 193• Every cell has a set parameter whichdefines which access classes arebarred for the particular cell. Thisparameter is broadcasted on theBCCH
    • 194. What is DTX? DTX (Discontinous Transmission) Each direction of Transmission is only 50% Transmitter is switched ON for usefulinformation frames05/31/13Tempus Telcosys 194Need for DTX•To increase battery life•To reduce the average interferencelevelDTX is done by DTX handlers which
    • 195. VAD (Voice ActivityDetector) Senses for speech in 20ms blocks Removes stationary noise VAD is an energy detector Compares Energy of filtered speech threshold It determines which 20ms blocks containspeech and it only forwards those frames05/31/13Tempus Telcosys 195
    • 196. Evaluation of Background Noise Background noise is always present withspeech DTX cuts off this noise with speech Gives an uncomfortable feeling to the listener VAD takes care of this by inserting comfortnoise at the receiving end when speechdiscontinues.05/31/13Tempus Telcosys 196
    • 197. Emergency Calls GSM specs define 112 as an emergencynumber ‘112’ is accessible with or without SIM Without SIM it is sent on the bestchannel Mobile on sensing ‘112’ sets theestablishment cause to emergency call inthe RACH Routing of this call be done to a desiredlocation defined in the switch05/31/13Tempus Telcosys 197
    • 198. Cell (Re)selection Cell reselection is done using C1 path losscriterion. The purpose is to ensure that the MS iscamped on to the cell with the besttransmission quality. The MS will camp on to the cell with thehighest C1 value if C1 > 0.05/31/13Tempus Telcosys 198
    • 199. The following parameters are used tocalculate the C1 criterion The received signal at the MS side. Rxlev_access_min - broadcast on the BCCH -The minimum received level at the MSrequired for access to the network. Ms_txpwr_max_cch - the maximum powerthat an MS may use when initially accessingthe network. The maximum power of the MS05/31/13Tempus Telcosys 199
    • 200. C1 = A - Max(B,0) A = Received level Average -Rxlev_access_min. B = MS_txpwr_max_cch - maximum outputpower of the MS05/31/13Tempus Telcosys 200
    • 201. Cell Reselect Hysteresis Cell reselection on the border of two location areas resultin a location update. When an MS moves on the borderof two location areas lots of location updates take place.To avoid these location updates, the reselect hysteresisis introduced. A location update is performed only if: The C1 value of the new location area is higher thanthe C1 value in the current location area and The received signal strengths have at least adifference of the reselect hysteresis.05/31/13Tempus Telcosys 201
    • 202. Cellular concept05/31/13Tempus Telcosys 202
    • 203. Why to use the cellularconcept ? Solves the problem of Spectral congestionand user capacity by means of frequencyreuse. Offers high capacity in a limited spectrumallocation. Offers system level approach, using lowpower transmitters instead of a single, highpower transmitter (large cell) to cover largerarea.05/31/13Tempus Telcosys 203
    • 204.  A portion of the total channels available isallocated to each base station. Neighboring base stations are assigneddifferent groups channels, in order tominimize interference.05/31/13Tempus Telcosys 204
    • 205. Cell shape05/31/13Tempus Telcosys 205
    • 206. 05/31/13Tempus Telcosys 206
    • 207. 1-Omni-directional cell-site (Omni-directionalantenna).2-Rhombus-shaped sectors (Directive antenna).3-Hexagonal shaped sectors (Directiveantenna).05/31/13Tempus Telcosys 207
    • 208. Cell sizeLarge cell : (up to 70km in diameter)It exists where :1-Radio waves are unobstructed.2-Transmission power can cover the area.3-low subscriber density.Small cell : (up to 2km in diameter)It exists where :1-Radio waves are obstructed.2-Low transmission power to decrease interference.3-High subscriber density.05/31/13Tempus Telcosys 208
    • 209. Types of cells1-Macro-cells 2-Micro-cells.3-Pico-cells. 4-Umbrella-cells.05/31/13Tempus Telcosys 209
    • 210. What is a cluster ? A cluster is a group ofcells. No channels arereused within acluster. It is the unit ofdesign.05/31/13Tempus Telcosys 210
    • 211. Cluster size Definition : It is The number of cells perclusterN = i^2 + ij + j^2Where :i = 0, 1, 2….& j = 0,1,2…. etc.N = 1 , 3 , 4 ,7, 9 , 12 ,……05/31/13Tempus Telcosys 211
    • 212. Types of clusters1-N=7 omni frequency plan (2-directional).2-N=7 trapezoidal frequency plan(1-directional).3-N=9 omni frequency plan.4-Tricellular plansa) N=3 tricellular plan (3/9).b) N=4 tricellular plan (4/12).05/31/13Tempus Telcosys 212
    • 213. Channel assignmentstrategies Considerations :1) Max. capacity.2) Min interference.3) Perfect handover. Types of assignment strategies :1) Fixed : Each cell has permanent predetermined set of voicechannels. New calls served by unused channels of this cell. Borrowing strategy if all channels are occupied. High probabiltity that call is Blocked if channels areoccupied.( disadv.)05/31/13Tempus Telcosys 213
    • 214. 2) Dynamic : Channels are not allocated to different cellspermanently. Each new call BTS requests new channel fromMSC. MSC allocate a channel, by using an algorithmthat takes into account:1- Frequency is not already in use.2- Min. reuse distance to avoid co-channelinterference.05/31/13Tempus Telcosys 214
    • 215.  Adv. of dynamic assignment strategy :1) Increase channel utilization( Increase trunking efficiency ).2) Decrease probability of a blocked call.05/31/13Tempus Telcosys 215
    • 216. Frequency reuseConcept05/31/13Tempus Telcosys 216
    • 217. 05/31/13Tempus Telcosys 217
    • 218. Reuse cluster05/31/13Tempus Telcosys 218
    • 219. Co-channel Reuse ratio(Q) : R : cell radius. D : reuse distance. Q = D/R. =sqrt(3N).Where :N : cluster size05/31/13Tempus Telcosys 219
    • 220. Handover05/31/13Tempus Telcosys 220
    • 221. Definition : procedure that allows MS tochange the cell or time-slot to keep as goodlink as possible during all the call.05/31/13Tempus Telcosys 221
    • 222. Types of handover IntraCell : bet. 2 channels of same cell. InterCell : bet. 2 channels of 2 different cell &same BTS. InterBTS (intra BSC) : 2 cells of different BTSSame BSC. InterBSC : bet. 2 cells of different BSC’s & sameMSC.05/31/13Tempus Telcosys 222
    • 223. Measurements beforehandover1- Measurements from MS to BSC :a) Strength of BTS signal.b) Quality of BTS signal.c) Signal strength of 6 neighbor BTS’s.2-Measurements from BTS to BSC :a) Strength of MS signal.b) Quality of MS signal.c) Distance between serving BTS & MS.05/31/13Tempus Telcosys 223
    • 224. Different causes of handover05/31/13Tempus Telcosys 224Better cell HOEmergency HOLevel QualityPBGTTraffic causesInterferenceDistanceDifferent causes ofHandover
    • 225. Basic handoveralgorithmsa)“Min. acceptable performance” algorithm:MS power is increased when quality deceasestill handover is the only way.b) “Power budget “ algorithm:Prefer direct handover when quality deceaseswithout increasing MS power first .05/31/13Tempus Telcosys 225
    • 226. Handover priority1) UL quality cause (or interference).2) DL quality cause (or interference).3) UL level cause.4) DL level cause.5) Distance cause.6) Better cell cause.05/31/13Tempus Telcosys 226
    • 227. Interference05/31/13Tempus Telcosys 227
    • 228. Sources of interferenceinclude:1) Another mobile in the same cell.2) A call in progress in the neighboringcell.3) Other BTS’s operating in the samefrequency band.05/31/13Tempus Telcosys 228
    • 229. Interference effects : In voice channel causes crosstalk In control channels it leads missed andblocked calls due to errors in the digitalsignaling.05/31/13Tempus Telcosys 229
    • 230. Main types ofinterference :1) Co-channel interference.2) Adjacent channel interference.05/31/13Tempus Telcosys 230
    • 231. 1) Co-channel interference Source : Near cell using same frequency.It is a function of reuse distance(D/R). General rule :io = No. of co-channel interfering cells.S = Signal power from a desired BS.Ii = interference power caused by the ithinterfering co-channel cell BS.05/31/13Tempus Telcosys 231
    • 232.  Another form :C/I = 10 log {(1/n)(D/R)*m}Where :m = propagation constant(dep’s on nature of environment)n = number of co-channel interferers.Can be minimized by :Choosing minimum reuse distance= (2.5….3)(2R).05/31/13Tempus Telcosys 232
    • 233. 2) Adjacent channelinterference Source : A cell using a frequency adjacent to theone in another cell due to imperfect reciever’sfilter.05/31/13Tempus Telcosys 233
    • 234. Can be minimized by :1-careful filtering2-careful channel assignments3-Directional antenna. General rule : ACI= -10 Log[(d1/d2)*m] – Adj chisolation.Where :d1: distance between MS & proper BTs d2:dist. Bet MS & adj BTS causinginterference.Adj ch isolation = Filter isolation = -26db.05/31/13Tempus Telcosys 234
    • 235. Traffic engineeringtheory05/31/13Tempus Telcosys 235
    • 236. Why do we need toknow traffic? The amount of traffic during peak hours allowsus to dimension our wireless system for a certainGOS. GOS : probability of having a call blockedduring busy hour (block rate).05/31/13Tempus Telcosys 236
    • 237. Traffic intensity (E) Erlang : A unit of traffic intensity measure. 1 Erlang = 1 circuit in use for 1 hour. T ( in Erlangs) = [No. of calls per hour*averagecall holding time(sec.)] / [3600]05/31/13Tempus Telcosys 237
    • 238. Typical traffic profile05/31/13Tempus Telcosys 238
    • 239. Traffic tablesErlang BTableBlocked calls are notheldErlang CTableBlocked calls are held inthe queue indefinitelyPoissonTableBlocked calls are held inthe queue for a time =the mean holding time05/31/13Tempus Telcosys 239
    • 240. Erlang – B table P(N;T) = [ (T^N)*exp(-T) ] / N!N GOS1%GOS2%2 0.153 0.2234 0.869 1.09310 4.46 5.08420 12.0 13.18240 29.0 30.99705/31/13Tempus Telcosys 240
    • 241. Trunking Sharing channel among several users. Trunking efficiency (nT) : Measures the numberof subscribers that each channel in every cell canaccommodate.nT = (traffic in Erlangs / no. of channels)*100.05/31/13Tempus Telcosys 241
    • 242. Trunking efficiencyin presence of oneoperator :N = 7 , 312 one directionvoice channelsNo. of channels / cell = 312 /7 = 44 ch./cell.From Erlang-B table @GOS2%,this’s equivalent to 35ErlangsnT = 35 / 44 = 79.55.Trunking efficiencyin presence of twooperators :N = 7 , 312 / 2 = 156 onedirection voice channel foreach operator.No. of channels / cell = 156 /7 = 22 ch./cell.From Erlang-B table@GOS 2%,this’sequivalent to 15 Erlangs.nT = 15 / 22 = 68.18.05/31/13Tempus Telcosys 242
    • 243. System capacity05/31/13Tempus Telcosys 243
    • 244.  S : total duplex channels available for use = k*NWhere:N : cluster size.k : No. of channels / cell. C : total No. of duplex channels in system;C = M*k*N.Where :M : No. of times the cluster is repeated.05/31/13Tempus Telcosys 244
    • 245. Improving systemcapacity Cell splitting. Sectoring.05/31/13Tempus Telcosys 245
    • 246. Cell splitting05/31/13Tempus Telcosys 246
    • 247. Sectoring We use directional antennas instead of beingomnidirectional05/31/13Tempus Telcosys 247
    • 248. What does sectoringmean? We can now assign frequency sets to sectorsand decrease the re-use distance to fulfill :1) More freq reuse.2) Higher system capacity.3) Improve S/I ratio ( better signal quality ). How S/I ratio is improved?-e.g. In 120 degree sectoring there’s only2 interferers instead of 6 incase of omnidirectional N=7cluster.05/31/13Tempus Telcosys 248
    • 249. 05/31/13Tempus Telcosys 249
    • 250. 05/31/13Tempus Telcosys 250
    • 251. Directional frequency reuse Here we use 7/21pattern for frequencyallocation.05/31/13Tempus Telcosys 251
    • 252. Comparisonbetween varioustypes of clusters05/31/13Tempus Telcosys 252
    • 253. N = 7 omni frequencyplan : n = 6 , m = 4. D / R = 4.583. 1) Co-channelinterference ratio :C / I = 18.6 dB. 2) Adjacent channelinterference :ACI = -26 dB @ d1= d2.05/31/13Tempus Telcosys 253
    • 254. N = 7 trapezoidalfrequency plan n = 2 , m = 4. D / R = 6.245. 1) Co-channel interferenceratio :C / I = 28.8. 2) Adjacent channelinterference : disappearsbecause the channels areassigned alternatively to thecells.05/31/13Tempus Telcosys 254
    • 255.  Trunking efficiency : 312 one direction voice channelsN = 7 312 / 7 = 44.57 ~ 44 ch./cell. From Erlang-B table @ GOS = 2%T = 35 E. nT = 35 / 44 = 79.55 %.05/31/13Tempus Telcosys 255
    • 256. N = 9 omni frequency plan n = 4 , m = 4. D / R = sqrt ( 3 * 9 ) = 5.2. 1) Co-channelinterference :C / I = 22.6 dB. 2) Adjacent channelinterference :ACI = -38 dB @ d2 = 2(d1).05/31/13Tempus Telcosys 256
    • 257.  Trunking efficiency : 312 one direction voice channelsN = 9 312 / 9 = 34.67 ~ 34 ch./cell. From Erlang-B table @ GOS = 2%T = 25.529 E. nT = 25.529 / 34 = 75.085 %.Conclusion : nT 7 > nT 9But C/I 7 > C/I 9ACI 7 > ACI 905/31/13Tempus Telcosys 257
    • 258. 4 / 12 cell pattern n = 1 , m = 4. D / R = sqrt (3* 4) = 3.732. C / I = 22.87 dB. Trunking efficiency : No. of channels/cell= 312 / 12 = 26 ch./cell. From Erlang-B table @GOS = 2 %. T = 18.4 E/cell. nT = 18.4 / 26= 70.77%.05/31/13Tempus Telcosys 258
    • 259. 3 / 9 cell pattern n = 1 , m = 4. D / R = sqrt (3* 3) = 3. C / I = 19.1 dB. Trunking efficiency : No. of channels/cell=312 / 9 = 34 ch./cell. From Erlang-B table @ GOS= 2 %. T = 25.5 E/cell. nT = 25.5 / 24 = 75 %.05/31/13Tempus Telcosys 259
    • 260. 120 degree cell sectoring n = 2 , m = 4. D / R = sqrt(3 * 7) = 4.583. Co-channel interference :C / I = 23.436 + 6dB(due toisolation) = 29.436 dB. Trunking efficiency : No. of channels/cell = 312 / 21 =14.857. From Erlang-B @ GOS=2% T=8.2003. nT = 8.2003 / 14.857=56.216%.05/31/13Tempus Telcosys 260
    • 261.  References : Motorola CP02 NOKIA SYSTRA05/31/13Tempus Telcosys 261
    • 262. If any QueryContact9903867731TempusTelcosys@gmail.com05/31/13Tempus Telcosys 262