ples of cellular systems were used by the network. The radio channels are grouped together into established by Bell Laboratories in 1949, but it was not until the a number of channel sets, and these sets are then allocated to the early 1980s that technology allowed real commercial networks to cells, one set per cell, on a regular basis across the whole coverage be built and service offered to the public. area. Each channel will therefore be re-used many times by the network. The method of radio planning and allocation of channels Systems were developed at different times in different countries to the cells is described later in this chapter. and subject to a variety of different constraints such as frequency band, channel spacing etc. As a result, a number of different and incompatible cellular standards are in use throughout the world, and 47.2.2 Signalling the more important standards are summarised later in this chapter. Work is already well in hand to specify and develop second Generally, one radio channel is set aside in each cell to carry generation cellular systems, for which the opportunity is being signalling information between the network and mobile stations. In taken to develop common standards and systems across several the land to mobile (L-M) direction, overhead information about the countries. One such notable system, GSM, has been developed in operating parameters of the network, including an area identifier Europe, and is described in some detail later in this chapter. code, is broadcast to all mobiles located in the cell's coverage area. In addition specific commands are transmitted to individual mobiles in order to control call setup and mobiles' location updating. In the mobile to land (M-L) direction, the signalling channel is Principles of operation used by the mobiles to carry location updating information, mobile originated call setup requests, and responses to land originated call 47.2.1 Network configuration setup requests. In a cellular radio system, the area to be covered is divided u