GSM Cellular System

Cellular structure

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• Frequency reuse

• Area divided into small zones (cells).

• Cell shape.

Cell shape

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• Cells grouped into cluster.

• This gives less power & enables frequency reuse.

Cell Sectorization

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• Co-channel interference

• Adjacent channel interference.

Network architecture

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Actual coverage

Cell types

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• Macro cell

• Microcell

• Pico cell

Cell splitting

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GSM network architecture

Network architecture

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Network architecture

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• Switching System SS: responsible for performing all processing and subscribe related function.

• Base Station System: performs all radio-related function.

• Operation and Maintains Centre OMC: monitoring network traffic and network alarms.

• Mobile System: terminal equipment.

Mobile System MS

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Mobile Equipment ME

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• IMEI: 15 –digit number

• First 6 digits type approval code.

• Next 2 digits assemble code.

• Next 6 digits S/N.

• Last digit spare.

Subscribe Identity Module SIM

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• SIM : an electronic microchip for storing information.

• Contains: CPU, Memories (RAM, ROM and EPROM).

• Small computer!!

Subscribe Identity Module SIM

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• SIM : stores information:

Subscriber identification.

Charging

Security.

Identity numbers

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• IMEI

• Mobile Station ISDN number (MSISDN): 15 digit

• International Mobile Subscriber Identity (IMSI):

Identity numbers

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• Temporary Mobile Subscriber Identity (TMSI): use instead of IMSI

• Mobile Station Roaming Number (MSRN)

Network architecture

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Base Station Subsystem BSS

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• Base Transceiver Station BTS

• Base Station Controller BSC

Base Transceiver Station BTS

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• Ericsson calls it RBS Radio Base Station.

• Contains RF transmission equipment.

• Each BTS consists from one or more Transceiver TRU.

• Performs channel coding, ciphering and modulation.

Base Station Controller BSC

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• It carries all control function in BSS

• Paging

• Channel allocation

• Dynamic power control

• Handover

• Frequency hopping

Connecting BTSs with BSC

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• A link between the BTS and BSC is required to carry the Traffic and the signalling.

• Usually microwave links are used to connect BTSs with BSC.

• Any other type of connection can be used. (Optical fiber ).

BSS link configuration

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• Cascade

BSS link configuration

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• Loop ring

BSS link configuration

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• Star

Transcoding and rate adaptation TRA

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• In the middle between BSC & MSC.

Network architecture

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Switching System

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•MSC: The MSC performs the telephony switching functions for the mobile network. It controls calls to and from other telephony and data systems, such as the Public Switched Telephone Network (PSTN), Integrated Services Digital Network (ISDN), public data networks, private networks and other mobile networks.

•GMSC: Gateway functionality enables an MSC to interrogate a network’s HLR in order to route a call to a Mobile Station (MS). Such an MSC is called a Gateway MSC (GMSC).

Home Location Register HLR

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•HLR: The HLR is a centralized network database that stores and manages all mobile subscriptions belonging to a specific operator. The information stored includes:

Subscriber identity (IMSI, TMSI, MSISDN)

Subscriber supplementary services

Subscriber location information

Subscriber authentication information

• The HLR can be implemented in the same network node as the MSC or as a stand-alone database. If the capacity of a HLR is exceeded by the number of subscribers, additional HLRs may be added.

Visitor Location Register VLR

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• It contains almost the same information as HLR.

• When user moves from MSC to another MSC, the new MSC registers the user in VLR.

Authentication Center AUC

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• The main function of the AUC is to authenticate the subscribers attempting to use a network.

• The AUC is a database connected to the HLR which provides it with the authentication parameters and ciphering keys used to ensure network security.

Authentication Center AUC

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Equipment Identity Register EIR

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• Because SIM and ME are separated in GSM, a separate authentication process for ME is needed.

• EIR is centralized database for IMEI.

• EIR contains:

White list (valid ME equipment).

Black list (stolen ME).

Gray list (faulty software).

Operation & Maintenance Center OMC

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• Radio parts: BSC, BTS,….

• Switching parts: optimization, MSC,……