Transmitter diversity for DS-CDMA with MMSE decision feedback

We study the forward link of a DS-CDMA system with transmitter diversity, assuming the channel is known at the receiver but not at the transmitter. Space-time coding is compared to orthogonal designs for a block fading channel, including frequency-selective fading. A Minimum Mean Squared Error (MMSE) Decision-Feedback Detector (DFD) suppresses multiple-access interference and cancels self-interference from the multiple transmitter antennas. This receiver can be implemented adaptively in the absence of channel estimates. We consider both hard decision-feedback and iterative soft decision-feedback in combination with MAP decoding. Our results show that for the cases considered, the hard and soft DFDs perform close to the receiver with perfect cancellation, which offers significant gain with respect to the orthogonal designs.