Joint Queue-Aware and Channel-Aware Scheduling for Non-Orthogonal Multiple Access

Abstract

Non-orthogonal multiple access (NOMA) has received considerable attention as a promising candidate for future mobile networks. How to reduce traffic delay through cross-layer scheduling in NOMA systems is a challenging issue. In this paper, a cross-layer approach for NOMA systems is designed to fulfill the delay requirements. In particular, scheduling decisions should adapt to the system dynamics. With the distribution information of the system dynamics, the constrained Markov decision process (CMDP) is employed to characterize the scheduling decision. The optimal scheduling policy can be obtained by converting the scheduling problem to linear programming. A computational approach based on the Kronecker product is conceived to formulate the linear programming when the dimension of the CMDP is high. Then the optimal delay-power tradeoff can be achieved. Moreover, the optimal decoding order is demonstrated that it can be obtained directly based on the channel states. The threshold-based structure of the optimal scheduling decisions is revealed. Without the distribution information, the Lyapunov approach is exploited to propose an online scheduling policy, where the virtual power queue is used to tackle the power constraint. In NOMA systems, our CMDP-based approach achieves a better performance over the Lyapunov approach by taking advantage of the distribution information.