Adaptive Pilot Allocation Algorithm for Pilot Contamination Mitigation in TDD Massive MIMO Systems

The pilot contamination problem is one of the major obstacles that limit the performance of time-division duplex (TDD) multicell massive multiple-input multiple-output (MIMO) systems. Pilot contamination results from the re-use of the same set of pilot sequences in the different cells of the system. In this paper, we propose an Adaptive Pilot Allocation (APA) algorithm for pilot contamination mitigation. The proposed algorithm divides the users in the system into two groups according to the inter-cell interference they cause to the other users in the system. To improve the system performance, the algorithm allocates orthogonal pilot sequences to the users that can cause high inter-cell interference. Simulation results show that the proposed algorithm outperforms the conventional (random) allocation method. Also it show that the proposed algorithm improves both the minimum and the mean achievable rates.