Simple ARQ mapping diversity and sphere decoding in MIMO wireless communications

Summary form only given, as follows. We describe a new ARQ mechanism for effective packet retransmissions. We begin with a low-complexity method for enhancing and exploiting retransmission diversity by varying the symbol mapping for each retransmission of a packet, and combining retransmissions at the receiver with a joint ML demapper. A methodology is constructed to select mappings that minimize a bound of the demapper bit error rate (BER). The minimizing mappings produce very substantial BER gains when applied to AWGN and flat-fading channels. We also generalize mapping diversity to allow for greater flexibility in retranstmission formatting and the presence of error control coding. This generalization uses a sequence of log-likelihood ratios (LLR), formulated from previous transmissions, of the bits that constitute the current retransmission. For the recently popular MIMO wireless systems, we generalize the mapping diversity -design. A sphere decoder is proposed for efficient joint detection of retransmitted symbols under mapping diversity.