Joint Pilot Allocation and Pilot Sequence Optimization in Massive MIMO Systems

Pilot contamination (PC) is recognized as a bottleneck for the achievable throughput of multi-cell massive multiple-input multiple-output (MIMO) systems. In this paper, we propose a joint pilot allocation and pilot sequences optimization (JPA-PSO) scheme to mitigate the effects of PC and maximize the system spectral efficiency (SE). Specifically, we first construct a range of pilot sequence in line with the coherent interval. Then, we establish an allocation basis by defining a similarity to distinguish PC among users. An angle of arrival (AOA) positioning method is designed to obtain the user's location information. Under the location information, we can monitor and estimate the distance between users in different cells to denote the potential interference of transmit power among users. Then, we execute pilot allocation strategy in line with the similarity and distance between users in different cells, that is, assign orthogonal pilots to the users with greater similarity and shorter distance. Finally, we provide a pilot sequence optimization algorithm to maximize the system SE. Simulation results verify that combining pilot allocation and pilot sequence optimization can significantly improve the system SE.