llocated to each sector. There are two commonly used methods of sectorisation, using Transmitter power (EIRP) 50dBm 39dBm three 120 degree sectors or six 60 degree sectors as shown in Figure Receiver sensitivity 106dBm 113dBm 47.8, both of which reduce the number of prime interference sources (including antenna gain) to one. This is because, of the six surrounding co-channel cells, only one will be directed at the wanted cell. Fade margin (90% of area) Required receiver level1 102dBm 109dBm Maximum path loss 152dBm 148dBm (allowing for fading) Interference budget C/I threshold Target C/I for planning (90% of area) simple and cost effective option is to allocate further radio channels to existing cells. However, this can only be done by an extension band, for example the ETACS allocation in the UK. Other alterna- tives involve rearranging the cellular plan, either by cell splitting or by sectorisation. Cell splitting is achieved by dividing an existing cell up into a number of smaller cells, by adding additional base stations as shown in Figure 47.7; it is then necessary to reallocate the radio channels. By repeatedly splitting cells; the cell size, and hence the system capacity, can be tailored to meet the traffic capacity requirements demanded by customer behaviour in all areas. Figure 47.8 Sectorisation Urban Suburban A disadvantage of sectorisation is that the channel sets are divided between the sectors such that there are fewer channels per sector, Rural and thus a reduction in trunking efficiency. This means that the total traffic which can be carried for a given level of blocking is reduced. However, this effect is offset by the ability to use smaller cells, such that the end result is a significant increase in total capacity. Overview of systems Cellular networks have been developed and deployed at various times and places in many countries across the world. In several Figure 47.7 Cell splitting cases, the local telecommunications authority or company was central to the specification and development of th