Precoder design for MIMO broadcast channels

This paper considers precoder designs in downlink MIMO broadcast channels (BC). A preceding scheme that is analog to the MMSE decision feedback equalizer in the uplink MIMO multiple access channels is first introduced. The proposed scheme can asymptotically achieve the sum-capacity of MIMO-BC at high SNRs. At medium SNRs, its achievable sum capacity is very close to that of MIMO-BC and larger than that of ZF-DR. The new scheme can also offer a significant gain over linear pre-equalization techniques in terms of average error probability. Furthermore, by linking the proposed precoder with the sphere encoder, a modified sphere encoder is devised. The modified sphere encoder is shown to be able to achieve the same diversity order as the maximum likelihood (ML) receiver in dual uplink. Its performance is also approaching the corresponding ML receiver.