THE GSM COMMUNICATION IS A DIGITAL CELLULAR COMMUNICATION , HOWEVER THE FREQUENCIES CAN NOT BE REUSED FOR HUNDRED OF KILOMETRES AS LIMITED TO THE COVERING AREA OF THE TRANSMITTERS.

The Global system for mobile communications is a digital cellular communication system .It was developed in order to exchange the information needed to maintain the communication links with in the cellular net work.several radio channels are reserved for the signaling information s. In order to work properly, a cellular system must verify the following two main conditions : (1) The power level of a transmitter with in a single cell must be limited in order to reduce the interference with the transmitters of neighbouring cells.The interference will not produce any damage to the system if a distance of about 2.5 to 3 times the diameter of a cell is reserved between transmitters .The receivers filters must also be very performant .(2) Neighbouring cells can't share the same channels .In order to reduce the interference, the frequencies must be reused only with in a certain pattern .