MIMO Broadcast Communications Using Block-Diagonal Uniform Channel Decomposition (BD-UCD)

Variable-rate coding for a multiple input multiple output (MIMO) channel increases transceiver complexity. In single user case, the uniform channel decomposition (UCD) scheme overcomes this problem by generating decoupled subchannels with identical SNRs so that equal-rate (ER) coding can be applied. In this paper, the solution is extended to the multi-user broadcast case. The block-diagonal geometric mean decomposition (BD-GMD) is used to design a capacity-achieving scheme, called the block-diagonal UCD (BD-UCD). It allows each user to apply ER coding on its own subchannels. An efficient near-optimal algorithm for multiuser uplink beamforming with SINR constraints is also proposed. Using this and duality, a scheme that allows ER coding to be applied to every subchannel of every user is designed. Simulations have shown that both schemes have superior BER performance and higher achievable sum-rates than conventional schemes.