Stackelberg Game for User Clustering and Power Allocation in mmWave-NOMA Systems

In this paper, the joint design of user clustering and power allocation is investigated in a downlink non-orthogonal multiple access based millimeter wave (mmWave-NOMA) system. To reduce the system overhead, hybrid precoding techniques are adopted at the base station (BS) by using the channel state information (CSI) of cluster heads (CHs) only. In order to maximize the sum rate of the system, Stackelberg game based optimization problems are formulated for two cases with different quality of some targets: Case 1 focuses on improving the data rates of CHs; and Case 2 aims to increase the rates of cluster members (CMs) when the CHs’ data rates are caped. With the aid of coalitional game theory, a low complexity algorithm is proposed to dynamically allocate users into different clusters. Then, the optimal power allocation coefficients of the users in each cluster are obtained by the derived closed-form expressions. The properties of the proposed joint algorithms are analyzed in terms of Stackelberg equilibrium, the complexity, the convergence and the stability. Simulation results demonstrate that: i) the proposed algorithms can significantly improve the sum rate and reduce the outage probability of the mmWave-NOMA system; ii) the application of NOMA in mmWave systems is capable of achieving promising gains over conventional orthogonal multiple access (OMA) based frameworks in both cases.