Modified Mutual Superposition Transmission with Complexity-Reduced Detection for Spatial Multiplexing OFDM Systems

In our previous paper, we have proposed mutual superposition transmission (MST) for spatial multiplexing (SM) orthogonal frequency division multiplexing (OFDM) systems. In MST, two data symbols of two different subcarriers are mutually superposed on respective subcarriers after being weighted. As a result, a diversity gain is obtained without degrading the transmission speed. However, one drawback of MST is huge computational complexity of detection of the received signals. In this paper, we propose modified mutual superposition transmission (MMST) together with a two-step maximum likelihood detection (MLD) algorithm to reduce the computational complexity of the signal detection. In the proposed MMST, the superposition operation is modified so that the receiver can detect the superposed pair of symbols separately. In the proposed two-step MLD algorithm, we first detect symbols called the base layer (BL) symbols, then detect symbols called the extended layer (EL) symbols based on the detection results of the BL symbols. By dividing the MLD algorithm into two steps, the number of symbol candidates for searching can be reduced. From simulation results, we can show that the SM-MMST-OFDM system achieves almost the same packet error rate performance as the SM- MST-OFDM system while the computational complexity is reduced.