Research And Implementation Of Pilot Pollution Reduction In Massive MIMO System

The rapid growth of wireless communication data volume and the extreme increase in the number of wireless links are driving the rapid development of the fifth generation of mobile communication systems.Large-scale multiple-input multiple-output(MIMO)technology is one of the key technologies for the fifth generation of mobile communication systems.By configuring a base station(BS)with a large number of antennas,it is possible to achieve communication between BS and multiple user equipments on the same time-frequency resource which can significantly improve system spectrum utilization.However,the signal interference,especially the pilot interference among adjacent cells becomes the bottleneck of system performance improvement in massive MIMO multiple cells systems.Consequently,based on the multi-cell multi-user massive MIMO system,and focusing on the pilot design and pilot allocation,two methods that can effectively reduce pilot pollution are proposed.The main research contents of the thesis are as follows:1.The number of orthogonal pilots in a massive MIMO system is limited by the coherence interval,and in different cells orthogonal pilots are totally reused,which leads to pilot pollution.In this thesis,a new pilot scheme based on ZC sequences is proposed,by assigning specific orthogonal codes to each cell to make the ZC sequences orthogonal between different cells,and then zero-autocorrelation properties of ZC sequences are used to generate Intra-cell User Pilots,which inhibits the pilot pollution.Theoretical derivation verifies that the proposed pilot design can eliminate pilot pollution in channel estimation.Simulation results show that the channel estimation mean square error performance of the proposed pilot scheme is close to the system performance without pilot pollution.2.Under Rice's fading channel,the line-of-sight(LOS)interference components in the signal received at the uplink BS were analysed.When the number of base station antennas approaches infinity,the LOS interference metric between two users is related to the user arrival angle.Considering the characteristics related to LOS interference between users and the location information of user,a pilot allocation strategy is proposed in the case where all cells reuse the same pilot.Simulation results show that the inter-user LOS interference can be effectively reduced and the system uplink sum rate can be improved.3.The proposed method of reduce pilot pollution is implemented with DSP,and the above scheme is comprehensively evaluated by the actual system performance,hardware memory resources and operation efficiency.