Iterative MIMO Detection for Rank-Deficient Systems

In this letter, a novel iterative multiple-input multiple-output (MIM)O detector reminiscent of sphere decoding (SD) is presented. Its main benefit is that in contrast to other soft-input soft-output (SISO) SD algorithms presented in the literature, the proposed iterative detector is capable of performing well in so-called overloaded systems, where the number of transmit antennas is significantly higher than the number of receive antennas, and hence, the channel's covariance matrix is rank-deficient. Furthermore, the proposed detector is guaranteed to achieve the performance of the max-log detector without the necessity of choosing a specific SD radius or an SD candidate list for generating soft-outputs. For example, when receiving signals from four transmit antennas with the aid of only two receive antennas, the proposed detector is capable of approaching the channel capacity limit within about 2 dBs