GSM

To accommodate more calls within the limited amount of radio spectrum4 available, the industry developed a digital5 wireless technology called GSM

GSM stands for Global System for Mobile Communications .It represents different systems of sharing of the radio spectrum for communication.

GSM is a form of multiplexing, which divides the available bandwidth among the different channels.

GSM is a combination of Time and Frequency-Division Multiple Access (TDMA/FDMA). The FDMA part involves the division by frequency of the (maximum) 25 MHz bandwidth into 124 carrier frequencies spaced 200 kHz apart. Each of these carrier frequencies is then divided in time, using a TDMA scheme. The fundamental unit of time in this TDMA scheme is called a burst period and it lasts 15/26 ms (or approx. 0.577 ms). Eight burst periods are grouped into a TDMA frame (120/26 ms, or approx. 4.615 ms), which forms the basic unit for the definition of logical channels. One physical channel is one burst period per TDMA frame. Thus GSM allows eight simultaneous calls on the same radio frequency.

The number of GSM subscribers has increased over the years, with around 160 million new customers added in 2002 alone. GSM, which is continuously evolving at a rapid pace, provides several voice and data enabled services.