Simplified Parallel Interference Cancelation for Underdetermined MIMO Systems

In this paper, a low-complexity detection scheme is proposed for an underdetermined multiple-input-multiple-output (UD-MIMO) wireless communication system that employs N transmit antennas and M <; N receive antennas. The proposed scheme combines a simplified parallel interference cancelation (S-PIC) with the block decision feedback equalization (BDFE) algorithm. To account for the extra (N - M)-dimension in the transmitted signal, the UD-MIMO system is partitioned into two subsystems: one with (N - M) transmit antennas and the other one with M transmit antennas. The interference from the first subsystem to the second one is canceled in parallel, and BDFE is performed over the second subsystem. Unlike conventional PIC methods that exhaustively search all the Q(N-M) sequences in the first subsystem, with Q being the constellation size, the proposed scheme explores only a small number of candidate sequences in the first subsystem; thus, it achieves significant complexity reduction. Two new candidate sequence selection methods are proposed. In the first iteration, the candidate sequences used for PIC are selected by exploring the statistical properties of the received signals. In the second iteration and beyond, the set containing the candidate sequences is constructed by utilizing the soft information generated from the previous iteration. The proposed scheme provides a balanced tradeoff between computational complexity and bit error rate (BER) performance.