Widely linear detector for QAM MIMO system

Detection algorithm based on widely linear filtering is proposed for the QAM modulated MIMO system. Unlike the existing works which focus on non circular signals (e.g. BPSK, PAM), this paper extends the widely linear detection to MIMO system transmitting circular signals (e.g. QAM, QPSK) by eliminating the I (or Q) component of the transmitted signals. The proposed algorithm has a ML-approaching performance with a computational complexity independent of the modulation order, whose upper bounder is O(2^N_T) (for QPSK) or O(3^N_T) (for M-QAM, M >4), lower than the complexity (O(M^√NT)) of FSD (Fixed-complexity Sphere Decoding) for a practical interval of N_T, the number of transmitting antennas. Simulation results show that the proposed algorithm can achieve quasi-ML performance with complexity comparable with FSD(1, ···, M) for QPSK signal, and much lower complexity than FSD(1, ···, M) when the system is 16-QAM (64-QAM) modulated.