Combined asterism and sphere decoder for large asymmetric MIMO systems

Multiple input multiple output (MIMO) communications systems have 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 which has an exponential complexity when the constellation size of the number of transmit antennas increases. Sphere and asterism decoders are schemes that achieved ML performance for MIMO systems, but both have shortcomings in computational complexity, sphere decoding when nt>nr and asterism when nt r. The paper combines asterism and sphere decoding for asymmetric MIMO systems to reduce the overall computational complexity for any number of antennas.