Research On Mitigating Pilot Contamination In Massive MIMO System

Massive multiple-input multiple-output(MIMO)technology has many advantages,such as miniaturized antenna equipment and high antenna gain,which can effectively meet the requirement of high transmission rate in the future communication system.Besides,by using a large number of antennas at base station(BS),massive MIMO system can significantly improve the spectrum efficiency and channel capacity.It is worth noting,the wonderful advantages of massive MIMO system could come true when the BS obtains the accurate channel state information(CSI).However,the target BS has difficulty in getting the perfect CSI due to pilot contamination,which makes the system work abnormally.Therefore,how to mitigate pilot contamination in massive MIMO system has become an urgent problem.To solve this problem,this thesis bases on the multi-cell multi-user massive MIMO time division duplexing(TDD)system,aims at better system performance,mainly studies the pilot decontamination methods.The main works in this thesis are following.1.Massive MIMO system and the problem of pilot contamination in this system are analyzed in detail.Besides,the 3D MIMO channel simulation model is built,which is more suitable for massive MIMO system.The works mentioned above provide the basic knowledge for the further research of this thesis.2.Based on the existed pilot decontamination methods,the pilot decontamination methods at the system level and the receiver are studied respectively in this thesis.At the system level,a new pilot allocation strategy is proposed for the cell edge user who suffers serious pilot contamination.The proposed strategy improves the usage of non-orthogonal pilot to some extent,which can prominently mitigate pilot contamination.At the receiver,the interference rejection combining(IRC)algorithm in massive MIMO system is studied and the high dimensional matrix inversion operation in this algorithm is optimized.The optimized IRC algorithm makes full use of the correlation of the interference from the multiple antennas,which can significantly mitigate the inter-cell interference caused by pilot contamination.3.A pilot decontamination approach using the new pilot allocation strategy and the optimization IRC algorithm for massive MIMO system is proposed.The performance of the proposed method is better than the typical decontamination methods.The simulation results demonstrate that the proposed method can dramatically enhance the bit error rate(BER)performance and the uplink throughput in per cell.