Beamspace MIMO systems with reduced beam selection complexity

Beamspace multiple-input multiple-output (B-MIMO) systems with proper beam selection (BS) promise to lower the radio-frequency (RF) chains overhead with no noticeable degradation in performance. Most of the existing BS schemes are not practical due to the computational cost arising from iterative search or alternating optimization. Hence, this letter examines the complexity reduction of the existing BS with incremental QR precoder (I-QR-P) and decremental QR precoder (D-QR-P). The proposed two-stage and three-stage algorithms reduce the complexity of D-QR-P and I-QR-P, respectively. Both aim to lower complexity by decreasing the candidate beam size by eliminating the beams with no contribution to any user and using matrix perturbation theory to update QR decompositions. Numerical results reveal that the proposed algorithms considerably reduce the complexity while maintaining a similar sum-rate with baseline algorithms.