Soft iterative multisensor multiuser detection in coded dispersive CDMA wireless channels

A soft iterative multisensor array receiver for coded multiuser wideband co de-division multiple-access wireless uplink channels is proposed. Such chan nels are typically both frequeney and time-selective, A new equivalent disc rete-time synchronous representation is used to model asynchronous multiuse r dispersive channels that employ, in general, random spreading. The propos ed scheme suppresses multiuser interference over a wide range of user signa l powers, by iteratively exchanging soft information between a minimum mean -square-error (MMSE) multiuser demodulator and a bank of single-user decode rs, feeding back the outputs of the latter to aid in soft multiuser multise nsor MMSE-Rake demodulation and subtractive interference cancellation, in t he second and subsequent iterations, It displays near-far resistance since it behaves like a successive interference subtracter across iterations. The array responses are obtained via a multipass estimation scheme that uses b oth (temporal) pilot symbols and soft estimates fed back from the decoders to effectively provide multisymbol pilot signals and thence successively re fined estimates with increasing iterations, while seeking neither to rely o n the array geometry nor to estimate the directions from which users' signa ls arrive at the receiver. Simulation studies indicate that this scheme per forms close to the single-user case with a two-sensor receiver array, and p erfect channel state information, after four iterations; alternatively, it allows significantly increased user capacity compared with conventional rec eivers, and suffers only a modest loss with estimated array responses.