r traffic den- ultimate capacity of CDMA. One of the key benefits of CDMA is sities to be achieved, and also enable smaller, lower power mobiles the potential to share spectrum with other users, for example fixed to be used. The use of microcells requires improved handover links, and for this reason it is particularly attractive where additional techniques, which allow for fast and reliable handoff, for example spectrum for mobile systems cannot be made available. when turning a street corner. One way of easing handover problems is to employ an 'umbrella cell' arrangement using conventional cells overlaying the microcells such that handover can be made into the 47.8 Conclusion umbrella cell where no suitable adjacent microcell can be identified. This also avoids the need to plan a contiguous coverage of micro- Cellular radio is a comparatively young technology. Networks em- cells in an urban area. ploying analogue systems have developed rapidly and now provide New technology is now enabling the use of more compact and high quality service and excellent coverage in many of the de- cheaper base stations. Conventional base sites have generally re- veloped countries. Technology developments are now increasing quired a purpose built building, or rented space within an existing the potential network capacity, reducing the size of mobiles, and building for installation of base station racks of equipment. Now, bringing advanced features and services to the mobile user. The base stations can be housed in small roadside or roof top mounted decade ahead with the opportunity to introduce new digital systems cabinets, and further reductions in size can be expected. Small base and create a world-wide land mobile standard looks particularly station equipment, and antennas, are essential to enable microcells exciting. to be built cost effectively. 47.7.2 Intelligent networks 47.9 References Intelligent Network techniques (IN), are not, of course unique to Bell (1979) Special issue on Advanced Mobile Phone Service, Bell cellular 