Joint Covariance Matrix Estimation and Pilot Allocation in Massive MIMO Systems

Pilot contamination is a throughput limiting factor in cellular massive MIMO systems. Previous work has shown that the impact of pilot-contamination can be reduced by exploiting structural information in form of channel covariance matrices. Additionally, significant gains can be obtained through coordinated user assignment. In this paper, we extend these approaches to a realistic scenario with imperfect knowledge of the channel and its distribution at the base station. We formulate an optimization problem for assigning users to the available pilot sequences, which at the same time takes the estimation of the covariance matrices into account and propose a suboptimal greedy algorithm for efficient implementation. Simulation results with established physical channel models demonstrate the significant performance gains of the proposed method in the case of imperfect knowledge of the covariance matrices at the base station.