Receiver Designs For MIMO HSDPA

Optimal linear receivers for MIMO HSDPA (as for SISO/SIMO) are symbol-level (deterministic) multiuser receivers, known unfortunately to be time-varying in nature and thus prohibitively complex. Traditional less complex alternative is dimensionality-reducing linear chip-equalization followed by further non-linear (interference canceling) or joint detection stages to improve symbol estimates. Well-known versions of former include inter-stream Successive Interference Canceling (SIC) involving all codes while the latter leads to per-code joint spatial maximum-likelihood (ML) receiver. We investigate the class of MIMO HSDPA receivers based upon LMMSE chip- level MIMO (equalizer) front end, and introduce two (one static and the other time-varying) models of the resulting spatial channel, a consequence of treating the scrambler as random or deterministic. It is shown that in the random case, statistical properties can be exploited to design MIMO receivers while the deterministic point-of-view leads to another set of reduced- dimensionality linear receivers or interference cancelers.