Joint Pilot Assignment and Uplink Power Allocation Scheme for Massive MIMO Systems

In order to mitigate pilot contamination in massive multiple-input multiple-output (MIMO) systems and ensure that each user is uniformly provided with good communication quality, an optimization problem with max-min spectral efficiency as the objective function is constructed in this paper, which consists of pilot assignment and uplink power allocation. Unlike previous works, a scenario is considered here, where more resources occupied by pilot sequence but are not sufficient to allow all users in the system to use orthogonal pilots. So virtual users are needed to be introduced when solving pilot assignment. Based on the mutual interference ratio among users, the Hungarian algorithm can be adopted to solve pilot assignment. After the pilot assignment is completed, uplink power allocation is then performed. On the basis of keeping the result of the pilot assignment fixed, the geometric program (GP) method can be used to solve uplink power allocation. Our proposed scheme can be applied to fractional pilot reuse scenario, and also to integer pilot reuse scenario. The simulation results indicate that the proposed optimization scheme not only improves the minimum spectral efficiency, but also significantly outperforms some other existing schemes.