A Low-Complexity Iterative Receiver for Multiuser Space-Time Coding Systems

Iterative processing has been shown to be very effective in multiuser space-time block coding (STBC) systems, where each user employs channel coding and iterations are performed between the soft-output multiuser detector and the soft-input soft-output channel decoders. The complexity of an iterative receiver depends heavily on how the log-likelihood ratios (LLRs) are computed for users' coded bits in order to implement the iterations. The use of sigma mapping for M-QAM constellations is proposed in this paper to ease the computation of the LLRs and allow bit-level interference cancellation in the iterative processing. It is demonstrated that the proposed iterative receiver performs very close to the conventional one, but with a much less computational complexity