Fair Pilot Assignment Based on AOA and Pathloss with Location Information in Massive MIMO

Massive multiple-input multiple-output (MIMO) is a promising technology for the next generation of wireless communication systems, which improves the spectrum efficiency and reduces the energy consumption. However, because of the shortage of both time and frequency resources, it is inevitable to reuse pilot sequences among users, which leads to a degradation in terms of channel state information (CSI). This degradation is known as pilot contamination. For the purpose of solving this issue, the pilot reuse (PR) scheme was proposed to alleviate the pilot contamination by non-overlapping the angles of arrivals (AOAs) between the signals of the identical pilot sequences. In the conventional AOA-based PR schemes, there is a difference in channel estimation accuracy between users, according to the order of pilot assignment, because these PR schemes assign greedily pilot sequences to user, which provides the most benefit for the first user, and less benefit for later users. In this paper, we propose a location-based PR scheme to alleviate the pilot contamination by assigning pilot sequences based on the path-loss as well as the AOAs. Furthermore, a low-complexity coordinated pilot assignment algorithm that brings benefits across multiple cells is introduced. Simulation results show that the proposed scheme provides a good channel estimation accuracy and fairness among users.