Iterative MMSE-sphere list detection and graph decoding MIMO OFDM transceiver

An enabling transceiver system which uses a larger digital signal constellation for higher spectral efficiency is proposed in this paper in the context of multi-input and multi-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. We approach this problem by using a low density parity check (LDPC) code combined with a simple constellation mapping scheme at the transmitter, and a turbo-iterative demapping and decoding scheme at the receiver. The receiver utilizes a reduced complexity soft-input and soft-output detection scheme - a regularized minimum mean-square sphere list detection. In simulation we show that the proposed transceiver achieves a near capacity limit while the computational complexity of the receiver is kept at a certain manageable size. Simulation results indicate that the results are less than a few dB away from the outage capacity at the spectral efficiency of 8 bits/sec/Hz using 16-QAM symbols on all four antennas and a rate 1/2 LDPCC of length 16 K.