Soft iterative multisensor multiuser detection in coded dispersiveCDMA wireless channels

摘要

A soft iterative multisensor array receiver for coded multiusernwideband code-division multiple-access wireless uplink channels isnproposed, such channels are typically both frequency- andntime-selective. A new equivalent discrete-time synchronousnrepresentation is used to model asynchronous multiuser dispersivenchannels that employ, in general, random spreading. The proposed schemensuppresses multiuser interference over a wide range of user signalnpowers, by iteratively exchanging soft information between a minimumnmean-square-error (MMSE) multiuser demodulator and a bank of single-userndecoders, feeding back the outputs of the latter to aid in softnmultiuser multisensor MMSE-RAKE demodulation and subtractiveninterference cancellation, in the second and subsequent iterations. Itndisplays near-far resistance since it behaves like a successiveninterference subtracter across iterations. The array responses arenobtained via a multipass estimation scheme that uses both (temporal)npilot symbols and soft estimates fed back from the decoders toneffectively provide multisymbol pilot signals and thence successivelynrefined estimates with increasing iterations, while seeking neither tonrely on the array geometry nor to estimate the directions from whichnusers' signals arrive at the receiver. Simulation studies indicate thatnthis scheme performs close to the single-user case with a two-sensornreceiver array, and perfect channel state information, after fourniterations; alternatively, it allows significantly increased userncapacity compared with conventional receivers, and suffers only a modestnloss with estimated array responses