Adaptive Pilot Design for Massive MIMO HetNets with Wireless Backhaul

In this paper, we investigate the problem of pilot optimization, resource allocation, and user association in a massive MIMO heterogeneous network (HetNet) with wireless backhaul (WB) and linear processing. The objective is to maximize the sum downlink rate of all users, subject to constraints on data rate of WB and fairness-aware constraints. Such a problem is formulated as an integer programming problem with both coupled variables and coupled constraints. We first develop a centralized scheme in which we decompose the original problem into two subproblems and iteratively solve them until convergence to achieve a near-optimal solution. We then propose a distributed scheme by formulating a repeated game among all users and prove that the game converges to a Nash Equilibrium (NE). Simulation studies show that the proposed schemes are adaptive to different network scenarios and traffic patterns, and achieve considerable gains over several benchmark schemes.