User Selection Method Adopting Cross-Entropy Method for a Downlink Multiuser MIMO System

This letter presents a novel method of user selection in a downlink multi-user multiple input multiple output (MU-MIMO) system employing the precoding procedures of zero forcing or block diagonalization (BD). The proposed technique utilizes the cross-entropy method (CEM) in order to maintain a performance level comparable to that of the full search (FS) method with reasonable complexity. With the CEM, the proposed system can select multiple users at once instead of selecting a single user at each step. From various computer simulations, it has been verified that the proposed method exhibits nearly 98 % of the sum-rate compared to the FS method, which implies that the proposed method far outperforms conventional methods such as semi-orthogonal user selection (SUS) or the capacity-based suboptimal user selection (CBSUS) algorithm. Compared to CBSUS, the proposed technique enhances the sum-rate by approximately 1.1 bps/Hz with about half the complexity when each user is equipped with two receiving antennas. In the case where each user is equipped with a single antenna, the proposed method outperforms the method of SUS by about 0.3 bps/Hz, at the expense of a complexity increase of \(O(2M)\) times.