Low complexity metric for joint MLD in overloaded MIMO system

This paper presents a low complexity metric for joint maximum-likelihood detection (MLD) in overloaded multipleinput multiple-output (MIMO)-orthogonal frequency division multiplexing (OFDM) systems. In overloaded MIMO systems, a nonlinear detection scheme such as MLD combined with error correction coding achieves better performance than is possible with a single signal stream with higher order modulation. However, MLD incurs high computation complexity because of the multiplications in the selection of candidate signal points. Thus, a Manhattan metric has been used to reduce the complexity. Nevertheless, it is not accurate and causes performance degradation in overloaded MIMO systems. Thus, this paper proposes a new metric whose calculations involve only summations and bit shifts. New numerical results obtained through computer simulation show that the proposed metric improves bit error rate (BER) performance by more than 0.2 dB at the BER of 104 in comparison with a Manhattan metric.