GSM Principles

GSM Principles
Global System for Mobile Communications (GSM)

GSM is a digital, mobile; radio standard developed for mobile, wireless, voice communications. GSM uses a combination of both the time division multiple access (TDMA) and frequency division multiple access (FDMA). With this combination, more channels of communications are available, and all channels are digital.

The GSM service is available in following frequency bands:
• 900-MHz & 900 E
• 1800-MHz
• 1900-MHz

GSM Network Elements

A GSM network consists of the following network components:
• Mobile station (MS)
• Base transceiver station (BTS)
• Base station controller (BSC)
• Mobile switching center (MSC)
• Authentication center (AuC)
• Home location registers (HLR)
• Visitor location registers (VLR)

Mobile Station;

The mobile station (MS) is the starting point of a mobile wireless network. The MS can contain the following components:
• Mobile terminal (MT)—GSM cellular handset
• Terminal equipment (TE)—PC or personal digital assistant (PDA)
The MS can be two interconnected physical devices (MT and TE) with a point-to-point interface or a single device with both functions integrated

Base Transceiver Station;

When a subscriber uses the MS to make a call in the network, the MS transmits the call request to the base transceiver station (BTS). The BTS includes all the radio necessary for radio transmission within a geographical area called a cell. The BTS is responsible for establishing the link to the MS and for modulating and demodulating radio signals between the MS and the BTS.

Base Station Controller;

The base station controller (BSC) is the controlling component of the radio network, and it manages the BTSs. The BSC reserves radio frequencies for communications and handles the handoff between BTSs when an MS roams from one cell to another. The BSC is responsible for paging the MS for incoming calls.

Mobile Switching Center;

The mobile switching center (MSC) is a digital ISDN switch that sets up connections to other MSCs and to the BSCs. The MSCs form the wired (fixed) backbone of a GSM network and can switch calls to the public switched telecommunications network (PSTN). An MSC can connect to a large number of BSCs.