CAPACITY OF DIGITAL CELLULAR TDMA SYSTEMS

The market for cellular radio telephony is expected to increase dramatically during the 1990's. Service may be needed for 50% of the population. This is beyond what can be achieved with the present generation analog cellular systems. The evolving digital time division multiple access (TDMA) cellular standards in Europe, North America, and Japan will give important capacity improvements and may satisfy much of the improvements needed for personal communication. The capacity of digital TDMA systems is addressed in this paper. Capacity improvement will be of the order 5-10 times that of analog FM without adding any cell sites. For example, the North American TIA standard offers around 50 Erlang/km2 with a 3-km site-to-site distance. However, in addition, the TDMA principle allows a faster handoff mechanism (mobile assisted handoff, MAHO), which makes it easier to introduce microcells with cell radius of, say, 200 m. This gives substantial additional capacity gain beyond the 5-10 factor given above. Furthermore, TDMA makes it possible to introduce adaptive channel allocation (ACA) methods. ACA is a vital mechanism to provide efficient microcellular capacity. ACA also eliminates the need to plan frequencies for cells. A conclusion is that the air-interface of digital TDMA cellular may be used to build personal communication networks. The TDMA technology is the key to providing efficient hand-over and channel allocation methods.