Extending Asterism decoding to QAM and its complexity in Rician fading MIMO systems

The area of Multiple Input Multiple Output (MIMO) communications systems has received enormous attention recently as they can provide a roughly linear increase in data rate by using Multiple Transmit and Receive antennas. The optimal detection strategy for a MIMO receiver is to perform a Maximum-Likelihood (ML) search over all possible transmitted symbol combinations has an exponential complexity when the constellation size of number of transmit antennas increase. A number of sub-optimal decoders, such as VBLAST, provide linear decoding only where the number of receive antennas is at least equal to the number of transmit antennas . Asterism decoding proposed in [7] [8], described a scheme that achieved ML performance for PSK MIMO systems. By considering the larger complex constellation created by a multiple transmit antennas and a single receive antenna. The decoder was then extended to achieve ML like performance for any number of receive antennas. This paper investigates the extension of Asterism decoding for QAM modulation schemes. It further shows that Asterism decoding has an approximate order of magnitude reduction in computational complexity when compared to ML decoding, and shows that this reduction is possible not only for Rayleigh fading channels, but also most Rician flat fading channels.