Improved Decoding Algorithms for Quasi-Orthogonal Space-Time Block Codes

Recently, a variety of full-rate, full-diversity quasi-orthogonal space-time block codes (QO-STBCs) have been designed. Though the quasi-orthogonality does reduce the decoding complexity from order of MQ^N to MQ^N/2 for Q-ary QAM modulation with N transmit and M receive antennas, there is still need for improvement. Several simple suboptimum decoding algorithms were proposed but suffer quite severe performance losses over maximum likelihood (ML) decoding. Here, we propose a class of decoding algorithms for QO-STBCs based on interference cancellation with complexity on the order of MQ ^{N/2 -1} and performance virtually identical to that of ML decoding. A modification to the base algorithm is also developed with complexity approximately 1/radic(Q) times that of the base algorithm.