Efficient maximum likelihood detector for MIMO systems with small number of streams

The problem of maximum likelihood detection (MLD) of overlayed data symbols, which occurs in MIMO communications and interference mitigation applications, is addressed. A simple algorithm is presented that reduces the complexity of MLD by a factor of the constellation size compared to the complexity assumed in other publications. Although the complexity remains exponential in the number of transmit antennas, this reduction in complexity makes implementation of full-set MLD for MIMO systems with two-three streams feasible. The main difference compared to suboptimal schemes such as QRD-M and sphere decoding is that the result is exactly equivalent to full-set MLD. An efficient implementation is also presented.