Mobile Cellular Networks

1. 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

2. Mobile Cellular Networks • Cellular principle • Proposed as a solution to the bandwidth problem • Restrict the radio range of Base Station (transmitter) • Can now reuse BS frequency in other parts of the network • Taking this one step further • tessellate network coverage area with cell reuse pattern (cluster) • Each cell in cluster operates on a different frequency • Cluster sizes of 4,7,9 etc are common • Result - increase in capacity of network in terms of max number of simultaneous calls the network can support

3. Mobile Cellular Networks • Cellular principle • Cells are hexagonal shape • Base station located in middle • Radius of cell is governed by power of Base Station • Increasing the power increases geographical size of cell • Smaller sizes automatically increase the network capacity • but can also increase interference

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5. Mobile Cellular Networks • Cellular principle • Trend is to have sophisticated cell structures • essentially overlay large cells on smaller cells • Common cell sizes • Pico cells • floor of a building • a few metres • Micro cells • Street • 10 -400 metres • Base station mounted below roof level • Street canyons • Macro cells • 5 kms • special masts erected for Base station • Pico cells give large capacity for a small area • Macro cells give small capacity for a large area

6. Mobile Cellular Networks • Global System for Mobility (GSM) • Small amount of radio spectrum allocated for cellular networks • For GSM • 890-915MHz uplink (Mobile station to Base station) • 935-960Mhz downlink • Each call requires a dedicated full duplex channel (circuit switched) • Typically a network provider is allocated a subset of these for operation • Note Mobile station must operate across all frequencies

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8. Mobile Cellular Networks • Network Components • Mobile Station • Mobile Equipment (e.g. phone) • antenna • Subscriber Identity Module (SIM) • Smart card • SIM must be inserted into ME before ME will work • Essentially personalises ME • Contains subscription information • Other information - subscriber’s short dialing codes • Can make emergency codes • Future is multi-media mobile stations

9. Mobile Cellular Networks • Network Components • Base Station System • Base Transceiver Station • Antenna • Interfaces to MS • Able to transmit /receive signals on many channels simultaneously • Base Station Controller • Controls a number of Base Transceiver Stations • Essentially a concentrator (multiplexer) • Multiplexes Base Transceiver Stations onto high speed link • Undertakes some radio management tasks • passes 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

10. Mobile Cellular Networks • Network Components • Mobile Switching Centre (MSC) • ISDN switch enhanced to operate in mobile network • In addition to switching • manages calls for all MSs within its domain • Billing • Handover • Authentication

11. Mobile Cellular Networks • Network Components • ‘Intelligence’ (databases) in Network • Equipment Identity Register (EIR) • Stores information on lost or stolen MSs • Each 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

12. Mobile Cellular Networks • Network Components • ‘Intelligence’ (databases) in Network • Home Location Register (HLR) • One logical HLR in network • Contains an entry for every subscriber • Stores fairly static information about subscriber • services subscribed to • But also location information to allow mobility • Location Area Code where MS is currently operating

13. Mobile Cellular Networks • Network Components • ‘Intelligence’ (databases) in Network • Visitor Location Register (VLR) • One VLR for every Location Area in network • Typically an Mobile Switching Centre ‘covers’ a location area • In this instance VLR is integrated with MSC • VLR contains information on every subscriber (visitor) currently operating in the domain of VLR • Entries are added when visitors enter VLR domain • Entries are deleted when visitors leave VLR domain • HLR and VLR jointly facilitate mobility

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15. Mobile Cellular Networks • Radio Interface • Traffic channels • Full duplex, circuit switched • Control channels for signalling • Broadcast • e.g. Broadcast Control Channel (BCCH) • Gives Location Area Code • Private • e.g. Fast Associated Control Channel (FACCH) • Used during call establishment, for handover etc. • Other Interfaces - very like N-ISDN

16. Mobile Cellular Networks • Mobility • Terminal Mobility (1st generation systems) • Keeps track of MS • MS / subscriber more or less the same entity • One-to-one relationship between subscriber and MS • Give your MS to someone else, they will receive your calls • Not unlike the fixed network

17. Mobile Cellular Networks • Mobility • Personal mobility in GSM (2nd generation systems) • More flexible than terminal mobility • Subscriber can receive calls on any MS • provided their SIM card is inserted • One-to-many relationship • Separated MS from subscriber

18. Mobile Cellular Networks • Mobility • Full personal mobility (3rd generation systems) • MS can be used by many subscribers • Subscriber can be registered to receive calls on any MS • Many-to-many relationship

19. Mobile Cellular Networks • Mobility Management (Network Mobility) • Needed to deliver Incoming calls • Various Approaches • Network doesn’t keep track of subscribers’ moves • To deliver an incoming call need to broadcast to every cell in the network • Implications of extending this to an international level

20. Mobile Cellular Networks • Mobility Management • Another approach (used by 2nd generation systems) • Network keeps track of subscribers’ moves • HLR and VLR used for this purpose • Two operations involved • Update (location update) • Find (finding subscriber to deliver an incoming call)

21. 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 ..............

22. Mobile Cellular Networks • Mobility management • Update - when a subscriber moves to a new location area • i.e. comes under the domain of a new VLR • MS detects it has roamed into a new location area • MS requests a location update from new MSC • New MSC enters subscribers details in associated (new) VLR • New VLR forwards location update to HLR • HLR is updated with new VLR address • HLR requests old VLR to delete subscribers entry

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24. Mobile Cellular Networks • Mobility management • Find (mobile subscriber) • HLR is used to find the subscriber’s current location (VLR) • HLR requests a temporary roaming number from VLR • VLR returns roaming number to HLR • HLR returns roaming number to call source • Call may now be routed (to VLR) • VLR meanwhile will be alerting MS that a call is expected

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27. Mobile Cellular Networks • Mobility Management • Roaming Agreements

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29. Mobile Cellular Networks