Simplified Antenna Selection and User Scheduling for Orthogonal Space-Division Multiplexing

In this paper, we study simplified algorithms for user scheduling in conjunction with receive antenna selection (RAS) for two downlink multiuser orthogonal space-division multiplexing techniques: block diagonalization (BD) and successive optimization (SO). Proposed algorithms select user and antenna subsets that maximize total power gain of the equivalent channel through mutual null-space projections of the active user channels. With this approach, algorithms add the best user at a time from the set of users not selected yet to the set of selected users until the desired number of users have been selected. To reduce the complexity further, users whose channel correlation to the signal subspace of the previously selected users is under some specified threshold are grouped at each step of the algorithm such that next user is selected from that group. This avoids the search through all K - i remaining users at the ith step of the algorithm. Two RAS algorithms are proposed, which further enhance the power gain of the equivalent channel by selecting a subset that contributes most towards the sum rate. For SO, user selection accounts for the interference of the previously selected users and maximizes the ratio of the total power of the equivalent channel to the approximate interference power on the desired signal subspace. Proposed algorithms perform close to the previously proposed algorithms with much less complexity.