Increased uplink capacity for TDMA systems through joint detection with diversity arrays

Joint detection of Rayleigh faded cochannel signals has previously been shown to produce a new mode of reception behaviour, in which each additional signal costs only a small dB penalty with no loss of diversity order at the base station. Many simultaneous users can be supported in the same time-frequency slot, which results in a large increase in capacity. In this paper, we quantify the capacity increase on a system-wide basis while accounting for the increase in interference from cochannel cells due to the increased number of users. We demonstrate a soft capacity limit, similar to CDMA, and show that with several users per cell, the relative capacity improvement over a single-user TDMA system approaches M (the number of users) as the number of antennas is increased. We also analyze a system that uses conventional MMSE combining of base station antennas, and show that system capacity increases by only a small factor and actually declines as more users are added