mobile cellular networks

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Mobile Cellular Networks. Evolution 1st generation, 1980s analogue voice 2nd generation 1990s digital Voice, fax data 95% coverage of UK by 1991 3rd generation - within 10 years digital anywhere, anytime, anything Most significant development in telecommunications in recent years. - PowerPoint PPT Presentation


  • Mobile Cellular NetworksEvolution1st generation, 1980s analoguevoice2nd generation 1990sdigitalVoice, fax data95% coverage of UK by 19913rd generation - within 10 yearsdigitalanywhere, anytime, anythingMost significant development in telecommunications in recent years

  • Mobile Cellular NetworksCellular principleProposed as a solution to the bandwidth problemRestrict the radio range of Base Station (transmitter)Can now reuse BS frequency in other parts of the networkTaking this one step furthertessellate network coverage area with cell reuse pattern (cluster)Each cell in cluster operates on a different frequencyCluster sizes of 4,7,9 etc are commonResult - increase in capacity of network in terms of max number of simultaneous calls the network can support

  • Mobile Cellular NetworksCellular principleCells are hexagonal shapeBase station located in middleRadius of cell is governed by power of Base StationIncreasing the power increases geographical size of cellSmaller sizes automatically increase the network capacitybut can also increase interference

  • Mobile Cellular Networks

  • Mobile Cellular NetworksCellular principleTrend is to have sophisticated cell structuresessentially overlay large cells on smaller cellsCommon cell sizesPico cells floor of a buildinga few metresMicro cells Street10 -400 metresBase station mounted below roof levelStreet canyonsMacro cells5 kmsspecial masts erected for Base stationPico cells give large capacity for a small areaMacro cells give small capacity for a large area

  • Mobile Cellular NetworksGlobal System for Mobility (GSM)Small amount of radio spectrum allocated for cellular networksFor GSM890-915MHz uplink (Mobile station to Base station)935-960Mhz downlinkEach call requires a dedicated full duplex channel (circuit switched)Typically a network provider is allocated a subset of these for operationNote Mobile station must operate across all frequencies

  • Mobile Cellular Networks

  • Mobile Cellular NetworksNetwork ComponentsMobile StationMobile Equipment (e.g. phone)antennaSubscriber Identity Module (SIM)Smart cardSIM must be inserted into ME before ME will workEssentially personalises MEContains subscription informationOther information - subscribers short dialing codesCan make emergency codesFuture is multi-media mobile stations

  • Mobile Cellular NetworksNetwork ComponentsBase Station SystemBase Transceiver StationAntennaInterfaces to MSAble to transmit /receive signals on many channels simultaneouslyBase Station ControllerControls a number of Base Transceiver StationsEssentially a concentrator (multiplexer)Multiplexes Base Transceiver Stations onto high speed linkUndertakes some radio management taskspasses Location Area Code to Base Transceiver Station for broadcasting to MSs Also translates 13kbps speech from radio channels to 64Kbps PCM for transmission on fixed network

  • Mobile Cellular NetworksNetwork ComponentsMobile Switching Centre (MSC)ISDN switch enhanced to operate in mobile networkIn addition to switchingmanages calls for all MSs within its domainBillingHandoverAuthentication

  • Mobile Cellular NetworksNetwork ComponentsIntelligence (databases) in NetworkEquipment Identity Register (EIR)Stores information on lost or stolen MSsEach MS has a unique International Mobile Equipment Identifier (IMEI)Network can refuse access id IMEI is stored on EIR.Authentication Centre (AuC)provides access security for network

  • Mobile Cellular NetworksNetwork ComponentsIntelligence (databases) in NetworkHome Location Register (HLR)One logical HLR in networkContains an entry for every subscriberStores fairly static information about subscriberservices subscribed toBut also location information to allow mobilityLocation Area Code where MS is currently operating

  • Mobile Cellular NetworksNetwork ComponentsIntelligence (databases) in NetworkVisitor Location Register (VLR)One VLR for every Location Area in networkTypically an Mobile Switching Centre covers a location area In this instance VLR is integrated with MSCVLR contains information on every subscriber (visitor) currently operating in the domain of VLR Entries are added when visitors enter VLR domainEntries are deleted when visitors leave VLR domainHLR and VLR jointly facilitate mobility

  • Mobile Cellular Networks

  • Mobile Cellular NetworksRadio InterfaceTraffic channelsFull duplex, circuit switchedControl channels for signallingBroadcaste.g. Broadcast Control Channel (BCCH)Gives Location Area Code Privatee.g. Fast Associated Control Channel (FACCH)Used during call establishment, for handover etc.Other Interfaces - very like N-ISDN

  • Mobile Cellular NetworksMobilityTerminal Mobility (1st generation systems)Keeps track of MSMS / subscriber more or less the same entityOne-to-one relationship between subscriber and MSGive your MS to someone else, they will receive your callsNot unlike the fixed network

  • Mobile Cellular NetworksMobilityPersonal mobility in GSM (2nd generation systems)More flexible than terminal mobilitySubscriber can receive calls on any MSprovided their SIM card is insertedOne-to-many relationshipSeparated MS from subscriber

  • Mobile Cellular NetworksMobilityFull personal mobility (3rd generation systems)MS can be used by many subscribersSubscriber can be registered to receive calls on any MSMany-to-many relationship

  • Mobile Cellular NetworksMobility Management (Network Mobility)Needed to deliver Incoming callsVarious ApproachesNetwork doesnt keep track of subscribers movesTo deliver an incoming call need to broadcast to every cell in the networkImplications of extending this to an international level

  • Mobile Cellular NetworksMobility Management Another approach (used by 2nd generation systems)Network keeps track of subscribers movesHLR and VLR used for this purposeTwo operations involvedUpdate (location update)Find (finding subscriber to deliver an incoming call)

  • Mobile Cellular Networks

    if subscriber highly mobile (frequent updates) if subscriber receives many calls (frequent finds) location update approach is best else subscriber receives few calls ..............

    else (subscriber is stationary) if subscriber receives many calls .............. else subscriber receives few calls ..............

  • Mobile Cellular NetworksMobility managementUpdate - when a subscriber moves to a new location area i.e. comes under the domain of a new VLRMS detects it has roamed into a new location areaMS requests a location update from new MSCNew MSC enters subscribers details in associated (new) VLRNew VLR forwards location update to HLRHLR is updated with new VLR addressHLR requests old VLR to delete subscribers entry

  • Mobile Cellular Networks

  • Mobile Cellular NetworksMobility managementFind (mobile subscriber)HLR is used to find the subscribers current location (VLR) HLR requests a temporary roaming number from VLRVLR returns roaming number to HLRHLR returns roaming number to call sourceCall may now be routed (to VLR)VLR meanwhile will be alerting MS that a call is expected

  • Mobile Cellular Networks

  • Mobile Cellular Networks

  • Mobile Cellular NetworksMobility ManagementRoaming Agreements

  • Mobile Cellular Networks

  • Mobile Cellular Networks


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