QRM-MLD combined with MMSE-based multipath interference canceller for MIMO multiplexing in broadband DS-CDMA

This paper proposes maximum likelihood detection with QR decomposition and the M-algorithm (QRM-MLD) sophisticatedly combined with the multipath interference canceller (MPIC) based on multipath interference (MPI) replica generation exploiting two-dimensional minimum mean squared error (MMSE) for multiple-input multiple-output (MIMO) multiplexing in broadband DS-CDMA. Simulation results clarify that the proposed QRM-MLD coupled with MPIC exhibits excellent signal separation capability by sufficient MPI suppression effect through a three-stage MPIC comprising two-dimensional MMSE, followed by QRM-MLD associated with soft-decision Turbo decoding. We also show that the throughput values of 200,250, and 300 Mbps (corresponding frequency efficiency values are 5.0, 6.0, and 7.5 bits/sec/Hz, respectively) are achieved at the average received signal energy per bit-to-noise power spectrum density ratio (E_b/ N₀) of approximately 6.0,9.5, and 13.0 dB by QPSK with the coding rate of R = 8/9, 8PSK with R = 3/4, and 8PSK with R = 8/9, respectively in 4-by-4 MIMO multiplexing, for broadband DS-CDMA assuming a 40-MHz bandwidth in a six-path Rayleigh fading channel with the maximum Doppler frequency of 20 Hz.