Capacity of an adaptive TDMA cellular system: comparison with conventional access schemes

This paper reports work carried out, largely within the COST 231 programme, on the uplink capacity of cellular multiple access schemes, and in particular CDMA and TDMA. It determines the probability density function of the interference in the various types of system, and hence estimates the capacities attainable with “industry standard” FEC codes of various rates. This shows that under the assumptions made, conventional CDMA can give a capacity about 65% greater than TDMA. The paper then introduces a new multiple access scheme called adaptive TDMA (A-TDMA) which adapts the code rate to the interference conditions encountered. A proposed A-TDMA system is outlined, using a packet reservation multiple access (PRMA) protocol, and an initial capacity estimate is given, and compared with the conventional schemes. The estimated spectral efficiency obtained is more than twice that of conventional CDMA