Multiple access interference cancellation in fading multipath channels: progress and limitations

Successive interference cancellation is a promising technique for increasing the capacity of uplink CDMA channels. Fundamental research has shown that in an AWGN channel, the technique can approach the Shannon capacity (see Viterbi, A.J., 1990). However, a multipath channel presents a difficult challenge for interference cancellation, as each multipath component separated by more than a chip time appears to the receiver as an independent user. Recent research has addressed this issue for a small number of paths. Here we show an approach using recently derived optimum power control (see Andrews, J. and Meng, T.H., 52nd IEEE Veh. Tech. Conference, vol.3, p.1211-15, 2000) that significantly increases the capacity over the previously published results for interference cancellation in multipath fading channels, while using only a single cancellation stage. However, simulations show that the capacity is inversely proportional to the number of multipath components. Thus, it appears that current work on interference cancellation can be successfully applied only to channels with a very limited number of multipath components