The Global System for Mobile is a 2G cellular system standard developed in Europe for overcoming the diversity present in 1G cellular system standards. Although initially adopted by European nations, GSM has become a highly popular technology with a very high user base all over the world. The first GSM system was designed to operate in the 900 MHz band, but owing to increasing demand, it was extended to 850 MHz, 1800 MHz and 1900 MHz bands. Different countries use different GSM variants for operation. Europe, Australia, Middle East, Asia and Africa mostly use GSM 900 and GSM 1800, whereas United States, Mexico, Canada and most countries in South America use GSM 850 and GSM 1900. This 2G cellular system provides voice service and circuit switched data service up to 9.6 kbps.

GSM system uses the Gaussian Minimum Shift Keying modulation technique. The access technique used is a combination of TDMA and FDMA. These techniques have already been described in Chapters 2 and 3. This chapter will discuss in depth the architecture, spectrum allocation, interfaces, radio frequency channels, signalling models and basic processes involved in GSM.

GSM Architecture

Any mobile network can be logically divided into three parts namely the access part, the core part and the maintenance part. The access part of the GSM network is also known as the Base Station Sub-system. It comprises the Base Transceiver Station (BTS) and the Base Station Controller (BSC).