Iterative MMSE multiuser interference suppression for coded dispersive CDMA wireless channels with multisensor receivers

Abstract

A soft iterative multisensor array receiver for coded dispersive multiuser code division multiple access (CDMA) wireless uplink channels is proposed. The proposed scheme suppresses multiuser interference over a wide range of user signal powers, by iteratively exchanging soft information between a minimum mean square error (MMSE) multiuser demodulator and a bank of single-user decoders, feeding back the outputs of the latter to aid in soft multiuser multisensor MMSE-RAKE demodulation and subtractive interference cancellation. It displays remarkable near-far resistance, since it functions like a successive interference subtracter across iterations. The array responses are also obtained using soft-decoded feedback estimates and (temporal) pilot symbols, seeking neither to rely on the array geometry nor to estimate the directions from which users' signals arrive at the receiver. Simulation studies indicate that this scheme performs remarkably close to the single-user case with a two-sensor receiver array, and perfect channel state information, after four iterations; alternatively, it allows significant overload capability compared with conventional receivers, and suffers only a modest loss with estimated array responses.