Performance of combined low complexity QRD-M and DFE detection in MIMO-OFDM systems

Multiple-input multiple-output (MIMO) technology applied with orthogonal frequency division multiplexing (OFDM) is considered as the ultimate solution to improve channel capacity without any additional spectral resources. At the receiver side, the challenge resides in designing low complexity detection algorithms capable of separating independent streams sent simultaneously from different antennas. In this paper, we propose a novel combined low complexity QRD-M (LQRD-M) and decision feedback equalization (DFE) MIMO detector that combines the feature of QRD-M detector and DFE detector. The original QRDM algorithm decomposes the MIMO channel matrix into upper triangular matrix and applies a limited tree search. To accomplish near-MLD(Maximum Likelihood Detection) performance for QRD-M algorithm, number of search points at each layer must be the modulation size. In the proposed scheme, each of survival branches are extended only to the corresponding QR decomposition (QRD)-based detection symbol in the next layer and its neighboring symbols in the constellation. In our detection technique with L transmit antennas, after LQRD-M detection is executed for first T detection steps, DFE detection is executed for last M - T detection steps. This approach is simple and has low complexity, because the computations for LQRD-M is limited by the newly adopted parameter T. From simulation results, the complexity of the proposed technique with 8 × 8 and T = 2 is reduced by 36% compared with that of QRDM-DFE algorithm at the expense of about 0.8dB in degradation of BER performance at BER = 10^-4.