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Basic Telecom concepts
Various Wireless Technologies
Cellular concepts & Principal of cellular Comm.
GSM Network Architecture
GSM channel Architecture
Call Flows in GSM
GSM Planning steps (Nominal Plan & RF surveys)
Alternative means of wireless communication
Walkie - Talkie
Trunked private radios

Mobile Phone - the magic technology that enables everyone to communicate anywhere with anybody.

Till 1982 Cellular Systems were exclusively Analog Radio Technology.
Advanced Mobile Phone Service (AMPS)
U.S. standard on the 800 MHz Band
Total Access Communication System (TACS)
U.K. standard on 900 MHz band
Nordic Mobile Telephone System (NMT)
Scandinavian standard on the 450 & 900 MHz band

Published in: Education, Business, Technology


  1. 1. Telecom TutorialsFriday, June 21, 2013www.tempustelcosys.comGSM Fundamentals & RF Survey
  2. 2. Basic Telecom conceptsVarious Wireless TechnologiesCellular concepts & Principal of cellular Comm.GSM Network ArchitectureGSM channel ArchitectureCall Flows in GSMGSM Planning steps (Nominal Plan & RF surveys)Friday, June 21,
  3. 3. Friday, June 21,•Signaling•Traffic•Off Hook•Dial Tone•Dialing Digits•RBT•ConversationSWITCH / EXCHANGE•Ring•Off Hook &Conversation
  4. 4. Alternative means of wireless communicationWalkie - TalkiePagersTrunked private radiosMobile Phone - the magic technology that enableseveryone to communicate anywhere with anybody.Friday, June 21,
  5. 5. Friday, June 21, 2013www.tempustelcosys.comBTS BTSMSC
  6. 6. Till 1982 Cellular Systems were exclusively Analog Radio Technology.Advanced Mobile Phone Service (AMPS)U.S. standard on the 800 MHz BandTotal Access Communication System (TACS)U.K. standard on 900 MHz bandNordic Mobile Telephone System (NMT)Scandinavian standard on the 450 & 900 MHz bandFriday, June 21,
  7. 7. GSM - 900The term GSM-900 is used for any GSM system which operates in any 900 MHz band.P-GSM - 900P-GSM-900 band is the primary band for GSM-900 Frequency band for primary GSM-900 (P-GSM-900) : 2 x 25MHz890 – 915 MHz for MS to BTS (uplink)935 – 960 MHz for BTS to MS (downlink)E-GSM - 900In some countries, GSM-900 is allowed to operate in part or in all of the following extension band. E-GSM-900(Extended GSM-900) band includes the primary band (P-GSM-900) and the extension band :880 – 890 MHz for MS to BTS (uplink)925 – 935 MHz for BTS to MS (downlink)R-GSM-900R-GSM-900 (Railway GSM-900) band includes the primary band (P-GSM-900) and the following extension band:876 – 890 MHz for MS to BTS (uplink)921 – 935 MHz for BTS to MS (downlink)GSM-1800Frequency band: 2 x 75 MHz1710 – 1785 MHz for MS to BTs (uplink)1805 – 1880 MHz for BTS to MS (downlink)Friday, June 21,
  8. 8. Telecom Service Providers/OperatorsGSMCDMABasic-WLLInternet ServicesLong DistanceVendorTelecom ConsultancyFriday, June 21,
  9. 9. End of 1980‟s Analog Systems unable to meet continuing demandsSeverely confined spectrum allocationsInterference in multipath fading environmentIncompatibility among various analog systemsInability to substantially reduce the cost of mobile terminals andinfrastructure requiredFriday, June 21,
  10. 10. Spectrum space - most limited and precious resourceSolution - further multiplex traffic (time domain)Can be realized with Digital Techniques onlyFriday, June 21,
  11. 11. 1979 Europe wide frequency band reservedfor Cellular1982 “Groupe Speciale Mobile” created within CEPT1986 GSM had full time in Paris1988 ETSI takes over GSM Committee1990 The phase 1 GSM Recommendationsfrozen1991 GSM Committee renamed “Special MobileGroup” and GSM renamed as “GlobalSystem for Mobile Communication”1992 GSM launched for commercialoperationsFriday, June 21,
  12. 12. A cellular system links Mobile subscribers to PublicTelephone System or to another Mobile subscribers.It removes the fixed wiring used in a traditionaltelephone installation.Mobile subscriber is able to move around, perhaps cantravelin a vehicle or on foot & still make & receive call.Friday, June 21,
  13. 13. Friday, June 21,
  14. 14. CONSIDERATIONS - FREQUENCY SUBSCRIBER DENSITY COVERAGEFriday, June 21, 2013www.tempustelcosys.comBase StationBase StationBase StationBase StationBase StationBase Station
  15. 15.  Cellular Radio involves dividing a large service area into regions called“cells.” Each cell has the equipment to switch, transmit and receive calls. Cells - Reduce the need of High powered transmission Cells - Conventionally regarded as being hexagonal, but in reality they areirregularly shaped. Cell shape is determined by the nature of the surroundingarea e.g. Hills , tall building etc.Friday, June 21,
  16. 16. Friday, June 21, 2013www.tempustelcosys.comLarge Cells35 KmRemote AreasHigh Transmission PowerFew subscribers Small Cells Near about 1 KM Urban Areas Low Transmission Power Many Subscribers
  17. 17.  Coverage› Percentage of the geographical area covered bycellular service where mobile telephony isavailable Capacity -› Number of calls that can be handled in a certainarea within a certain period of time.› Capacity can also refer to the probability thatusers will be denied access to a system due tothe simple unavailability of radio channels.Friday, June 21,
  18. 18.  Each Cell in the Cellular Network consists of one or more RFcarriers. An RF carrier is a pair of radio frequencies› One used in upward direction by MS - Uplink› Other used in downward direction by BTS - Downlink› The transmit and receive frequencies are separated by agap of 45 MHz in GSM of 75 MHz in DCS. There are 124 carries in GSM Band. With each carrier carrying7 timeslots, only 124 x 7 = 868 calls can be made! Frequency Reuse is the solutionFriday, June 21,
  19. 19. Friday, June 21, 2013www.tempustelcosys.comFul(n) = 890.0 + (0.2) *n MHzFdl(n) = Ful + 45 MHzwhere n =ARFCN ; 1  n  124
  20. 20. Friday, June 21, 2013www.tempustelcosys.com1710 1785 1805 1880duplex distance: 95 MHz890 915 935 960duplex distance: 45 MHz
  21. 21. Friday, June 21,
  22. 22. Friday, June 21, 2013www.tempustelcosys.comPowerTDMAPowerFDMAPowerCDMAFDMA: AMPS & NAMPS•Each user occupies a private Frequency,protected from interference through physicalseparation from other users on the samefrequency•TDMA: IS-136, GSM•Each user occupies a specific frequency butonly during an assigned time slot. Thefrequency is used by other users duringother time slots.•CDMA•Each user occupies a signal on a particularfrequency simultaneously with many otherusers, but is uniquely distinguishable bycorrelation with a special code used only bythis user
  23. 23. Three types of frequency reuse patterns7 Cell reuse pattern4 cell reuse pattern3 cell reuse patternFriday, June 21,
  24. 24. Friday, June 21, 2013www.tempustelcosys.comc2c1c3a1a3b1b2b3Cell Re-use
  25. 25. Friday, June 21, 2013www.tempustelcosys.com24567D
  26. 26.  Omni Directional Cells 120 degree Sectors 60 Degree sectors› Each Sector in a Site has its own allocation of RadioCarriers Advantage› By frequent reuse of frequency more capacity can beachievedFriday, June 21,
  27. 27. Friday, June 21, 2013www.tempustelcosys.comOMNI CELL1 ANTENNAb1b2b3120O CELLS3 ANTENNAS60O CELLS6 ANTENNASa1 a3a4a6a5a2
  28. 28. Friday, June 21, 2013www.tempustelcosys.comHard HandoffAnalog, TDMA and GSMSoft HandoffCDMABreak before Make Make before Break
  29. 29. CompatibilityNoise RobustIncreased Capacity & FlexibilityUse of Standard Open InterfacesImproved Security & ConfidentialityCleaner HandoversSubscriber IdentificationISDN CompatibilityEnhanced Range of ServicesFriday, June 21,
  30. 30. Friday, June 21, 2013www.tempustelcosys.comMSISDN : Human Identity used to call a Mobile StationIMEI: Serial number unique to every Mobile StationIMSI : Network Identity unique to a SIM3digits2digits10digits TMSI : Identity unique in a LAIMSRN : Mobile Station RoamingNoCC NDC SN98 XXX 12345MCC MNC MSIN404 XX 12345TAC FAC SNR S6 digits 2 digits 6 digits 1 digit
  32. 32. Mobile Station consists of two parts-Mobile Equipment (ME)Subscriber Identity Module (SIM)MEHardware e.g. Telephone, Fax Machine, Computer.SIMSmart Card which plugs into the ME.Friday, June 21,
  33. 33. Class Power O/p1 20 W2 8 W3 5 W4 2 W5 0.8 WFriday, June 21, 2013www.tempustelcosys.comTypicalSettings
  34. 34. IMSI(International Mobile Subscriber Identity)Transmitted over Air Interface on initializationPermanently stored on SIM card15 digit DecimalFriday, June 21,
  35. 35. MSISDN10 digit number to which a subscriber is being called.PIN (Personal Identification Number)Four digit PINAn internal security to Protect the SIM from illegal use.Card blocks itself after three wrong entriesFriday, June 21,
  36. 36. Temporary Mobile Subscriber IdentityPeriodically changed by the System Management oninstances like location update etc.Reason for use of TMSITo prevent a possible intruder from identifying GSM users,TMSI is usedManagementAssignment, Administration & Updating is performed by VLR.Friday, June 21,
  37. 37. BSS (Base Station System)BSC (Base Site Controller)BTS (Base Transceiver Station)XCDR (Transcoder)Friday, June 21, 2013www.tempustelcosys.comNetworkSwitchingSystem(NSS)XCDRBSCBTS
  38. 38. Converts 64 Kbps PCM circuits from MSC to 16 Kbps BSS circuits.Each 30 channel 2 Mbps PCM link can carry 120 GSM - specified voicechannels.Friday, June 21,
  39. 39. BSCConveys information to/from BTSConnects terrestrial circuits & Air Interface ChannelsControls handovers between BTSs under itselfBTSContains RF HardwareLimited control functionality1 - 6 carriers in a BTS Cabinet7 - 48 simultaneous calls per BTSFriday, June 21,
  40. 40. Collocated BTSRemote BTSStar ConfigurationDaisy Chain BTS Loop ConfigurationFriday, June 21, 2013www.tempustelcosys.comBSCBTSBTSBTSAllBTSon1E1BSCBTSBTSBTSBTS
  41. 41. NSS (Network Switching System)MSC (Mobile Switching Centre)HLR (Home Location Register)VLR (Visitor Location Register)EIR (Equipment Identity Register)AUC (Authentication Centre)IWF (Interworking Function)EC (Echo Canceller)Friday, June 21,
  42. 42. MSCCall SwitchingOperation & Management SupportInternetwork InterworkingCollects call billing dataGateway MSCMSC which provides interface between PSTN & BSS‟s in the GSM Network.Friday, June 21,
  43. 43. Reference database for the Subscriber profiles-Subscriber ID (IMSI & MSISDN)Current VLR AddressSupplementary Services subscribedSupplementary Service InformationSubscriber Status (Registered/deregistered)Authentication Key and AUC functionalityTMSIMSRNFriday, June 21,
  44. 44. Temporary Data, which exists as long as the subscriber isactive in a particular Coverage area.Contains the following-Mobile Status (Busy/ Free/ No Answer/etc.)Location Area Identity (LAI)TMSIMSRN (Mobile Station Roaming Number)Friday, June 21,
  45. 45. Friday, June 21,
  48. 48. Access NetworkMicrowave 15 /23 GHzBackbone NetworkMicrowave 7 GHzOptical FibersLeased Line( From Dot or any other service provider on any media)Friday, June 21,
  49. 49. Physical ChannelLogical ChannelPhysical ChannelPhysical channel is the medium over which the information iscarried.Logical ChannelLogical channels consists of the information carried over thePhysical Channel.Friday, June 21,
  50. 50. Friday, June 21, 2013www.tempustelcosys.com0 1 2 3 4 5 6 7357encrypted57encrypted26training1S1S3T8.25GP3T577STDMA Frame
  51. 51. Friday, June 21,
  52. 52. Friday, June 21, 2013www.tempustelcosys.comDCCH(Dedicated Channels)Downlink & UplinkCCCH(Common Control Chan)Downlink & UplinkSynch.ChannelsRACHRandomAccess ChannelCBCHCell BroadcastChannelSDCCHStandalonededicatedcontrol channelACCHAssociatedControl ChannelsSACCHSlow associatedControl ChannelFACCHFast AssociatedControl ChannelPCH/AGCHPaging/Access grantFCCHFrequencyCorrection channelControl ChannelsBCH ( Broadcast channels )Downlink onlyBCCHBroadcastcontrol channelSCHSynchronizationchannel
  53. 53. BCH channels are all downlink and are allocated to timeslot zero.Channels are:• FCCH: Frequency control channel sends the mobile a burst of all „0‟bits which allows it to fine tune to the downlink frequency• SCH: Synchronization channel sends the absolute value of the framenumber (FN), which is the internal clock of the BTS, together with the BaseStation Identity Code (BSIC)• BCCH: Broadcast Control Channel sends radio resourcemanagement and control messages, Location Area Code and so on.Some messages go to all mobiles, others just to those that are in theidle stateFriday, June 21,
  54. 54. •CCCH contains all point to multi-point downlink channels (BTS toseveral MSs) and the uplink Random Access Channel:• CBCH: Cell Broadcast Channel is an optional channel for generalinformation such as road traffic reports sent in the form of SMS• PCH: Paging Channel sends paging signal to inform mobile of a call• RACH: Random Access Channel is sent by the MS to request achannel from the BTS or accept a handover to another BTS.A channel request is sent in response to a PCH message.• AGCH: Access Grant Channel allocates a dedicated channel(SDCCH) to the mobile• NCH: Notification Channel informs MS about incoming group orbroadcast callsFriday, June 21,
  55. 55. SDCCH( Standalone Dedicated Control Channel )Uplink and DownlinkUsed for call setup, location update and SMS.SACCH( Slow Associated Control Channel )Used on Uplink and Downlink only in dedicated mode.Uplink SACCH messages - Measurement reports.Downlink SACCH messages - control info.FACCH( Fast Associated Control Channel )Uplink and Downlink.Associated with TCH only.Friday, June 21,
  56. 56. The Time Slots are arranged in a sequence , conventionally numbered 0to 7.Each repetition of this sequence is called a TDMA Frame.The information content carried in one time slot is called a “burst”.Friday, June 21,
  57. 57. Friday, June 21, 2013www.tempustelcosys.com0 1 2 3 4 5 6 7 2 4 5 6 730 1FRAME 1 FRAME 2Training SequenceInformation InformationGUARDPERIODGUARDPERIODTAIL BITS TAIL BITS
  58. 58. Friday, June 21, 2013www.tempustelcosys.com0 7TDMA frame = 4.615 ms= BURST PERIOD0
  61. 61. Various steps are listed belowCW surveyModel TuningNominal PlanningRF site SurveysRealized PlanningFrequency PlanningImplementationOptimizationDrive TestingPerformance AnalysisFriday, June 21,
  62. 62. It consists of planning a set of sites on planning tool so as to predict thecoverage of the target areaTool needs to be made intelligent so as to predict the coverage as close aspossible to actual coverageCoverage plots are based on customer intension of providing indoor andoutdoor coverageFriday, June 21,
  63. 63. It consists of planning a set of sites on planning tool so as to predict thecoverage of the target areaTool needs to be made intelligent so as to predict the coverage as close aspossible to actual coverageCoverage plots are based on customer intension of providing indoor andoutdoor coverageFriday, June 21,
  64. 64. Clutter typesDense UrbanUrbanSub UrbanRuralWaterVegetationIndustrialForestFriday, June 21,
  65. 65. Each nominal has a search ring defined by the RF PlannerCandidates needs to be identified as close as possible to thenominal within the search ringHeight, orientations & antenna placement at site are the key RFparameter which are based upon the coverage requirement in theareaMajor obstructions and clutter type in various directions to beobserved on RF surveyFriday, June 21,
  66. 66. Equipment required for RF SurveyGPSDigital CameraBinocularsMagnetic CompassMeasuring TapeThere might be 3 or more candidates surveys for onesiteEach candidate would have an RF survey form andpanoramic associated with itFriday, June 21,