The relationship between user bandwidth and re-use efficiency for CDMA cellular radio

Conventional CDMA (as may be envisaged, for example, for use in future local loop applications) can support a variety of different bit rates within a given bandwidth depending on the spreading factor and therefore processing gain chosen. For a small number of high bit rate users, the mechanism of interferer diversity is less effective and re-use efficiency is compromised. The work reported in this paper evaluates this effect in terms of the minimum processing gain required to support a given number of users. Two affiliation strategies are evaluated and the one based on selecting the base station which can support communications with the minimum terminal transmit power is found to be the better. For this strategy it was found that the loss of re-use efficiency at low numbers of users could be modelled simply in terms of a small number of “lost terminals” which becomes a significant proportion of the total when the total is small