GSM Network Components Lesson 2

GSM network consists of several functional entities.Those functions and interfaces are defined. The GSM network can be divided into following network components.

1. Mobile Station ( MS )
2. Base Transceiver Station ( BTS )
3. Base Station Controller ( BSC )
4. Mobile Switching Center ( MSC )
5. Authentication Center ( AUC )
6. Home Location Registers ( HLR )
7. Visitor Location Registers ( VLR )
8. Equipment identity Register ( EIR )

1) Mobile Station ( MS )

Mobile Station (MS) is the user equipment in GSM System. Mobile station consists of the physical equipment and hardware related software. such as the radio transmitters, display, digital signal processors, and the SIM card. It provides the air interface to the user in GSM networks.

Mobile Station consists of following components

Mobile Termination ( MT )

Mobile termination offers common functions, such as Radio signal Transmission and receiving, handover, speech encoding and decoding, Error detection and correction,signalling and access to the SIM card. The IMEI code is attached to the MT. 

Terminal Equipment (TE)

Any device connected to the MS offering services to the user.

Terminal Adapter (TA) This is provides access to the MT. Communication between the TE and MT over the TA takes place using AT commands.

Subscriber Identity module (SIM)
This is a removable subscriber identification ( SIM card ) token storing the IMSI a unique key shared with the mobile network operator. SIM Card provides personal mobility so that the user can have access to all subscribed services irrespective of both the location of the terminal and the use of a specific terminal.

2) Base Transceiver Station (BTS)

BTS is a telecommunication infrastructure used to facilitate wireless communication between subscriber device ( MS ) and Base Station Controller (BSC).

BTS consists of following parts

Transceiver (TRX)
Transceiver (TRX) which handles transmission and reception of signals sending and reception of signals to or from higher network entities. 

Combiner

Combines feeds from several TRX so that they could be sent out through a single antenna. Allows for a reduction in the number of antenna and feeders used.

Power amplifier (PA)

Power amplifier which aids in signal amplification from TRX for transmission through the antenna.

Combiner

Duplexer which is used for separating transmitting and receiving signals from the antenna and an Antenna which is an external part of the BTS.

Sector Antenna

Transmitting and reserving signals 

Alarm extension system
Collects working status alarms and external alarm (door,main power ,rectifier alarm )  of various units in the BTS and extends them to operations and maintenance (O&M) monitoring stations.

Base band receiver unit (BBxx)

This functions are frequency hopping, handover and signal DSP.

3) Base Station Controller (BSC) 

BSC manages the radio resources for BTS. BSC handles Radio channel setup, Frequency hopping, and handovers. The BSC is the connection between the BTS and the MSC. BSC transmit the data to the BTS using Abis interface. BSC assigns frequencies and time slots for the Mobile Station (MS). The BSC also handles intercell handover. It controls the power transmission of the BSS and Mobile Station (MS) in its area. The function of the BSC is to allocate the necessary time slots between the BTS and the MSC. It is a switching device that handles the radio resources.

BSC Function 

1. BTS  is connected to BTS and MSC
2. Radio resource management
3. Reallocation of frequencies
4. Control of frequency Hopping   
5. Power control
6. Inter-cell handover
7. Time delay measurement of the received signals from MS with respect to BTS clock
8. Performs traffic concentration to reduce the number of lines from BSC to MSC
9. BSC performs call processing
10. TRAU are generally located at the site of MSC
11. BTS configurations as per requirement
12. Data from OMC and can be down loaded to BSC

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