Research On The Suppression Of Pilot Comtamination In Massive MIMO Muti-cell TDD Systems

With the characteristics of high efficiency of spectrum and low transmission power, massive MIMO system obtains extensive attention and research. However, pilot contamination has become the limitation of the development in it, because of the reuse of non-orthogonal pilot sequences in adjacent cells. Pilot scheduling is one of the main methods to suppress the pilot pollution of massive MIMO system. How to design the pilot scheduling criteria and solving method has become one of the promising fields in the massive MIMO system, which is also the the main contents of this thesis.This thesis aims to study the ways to suppress the pilot contamination in the massive MIMO system. An analytical model of this problem is established by proposing the concept of VIP users in the model. This thesis designs a pilot scheduling scheme based on the VIP users for maximuming their downlink rate and taking the experience of ordinary users into account at the same time.According to the pilot scheduling scheme based on the VIP users, this thesis proposes a pilot scheduling method based on genetic algorithm. The proposed scheduling method adopts the traditional genetic algorithm to obtain optimal pilot scheme with the model of combinatorial optimization, then it replaces the model with the multi-objective optimization and the algorithm with the multi-objective genetic algorithm. The simulation results show that the proposed method obtains the approximate optimal solution. It significantly reduces the execution time and improves the efficiency of pilot scheduling algorithm.Inspired by the concept of partial frequency reuse, this thesis studies the concept of partial pilot reuse and a pilot scheduling scheme based on it. The pilot sequences of adjacent cell edges and of adjacent position maintain orthogonality, while the users in the central of the cell use the same set of pilot sequences within this method. Simulation results show that the proposed method can further depress the pilot contamination inter cell. At last the thesis gives some suggestions on the value of partial reuse factor after the analysis of simulation results.