Max-Min Fair Precoder Design for Non-Orthogonal Multiple Access
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In this paper, a downlink multiple input multiple output (MIMO) non-orthogonal multiple access (NOMA) wireless communication system is considered. In NOMA systems, the base station has unicast data for all users, and multiple users share the same resources. Maximizing the minimum cluster rate amongst multiple NOMA clusters through transmit precoding under quality-of-service (QoS) and total transmit power constraints is investigated. It is first shown that maximizing the minimum cluster rate and minimizing the maximum weighted cluster mean square error problems lead to the same optimal point. For the latter problem, Karush-Kuhn-Tucker (KKT) optimality conditions are derived and the expressions satisfied by the optimal receivers, minimum mean square error (MMSE) weights and the optimal precoders are obtained. Then, an iterative and low complexity transmit precoder design algorithm is proposed. Simulation results show that the proposed algorithm significantly outperfoms orthogonal multiple access (OMA) and multi-user linear precoding (MULP) schemes.
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