Pilot Contamination Mitigation In Multi-Cell Massive MIMO Systems

To utilize multi-cell massive MIMO in real scenario,there should be perfect knowledge of channel state information(CSI)at transmitter and receiver.For this purpose,training sequences(pilot signals)are employed to obtained channel estimation.Because of the limited training resources,some of the users in different cells are subjected to utilize the same set of pilot sequences that results in inter-cell interference(ICI)which causes pilot contamination(PC).Therefore,it is difficult for the base station(BS)to estimate the channel between BS and UEs using same pilot sequences.Pilot contamination is the major problem in uplink time division duplex scheme(TDD).Hence,the dilemma of pilot contamination(PC)in massive multiple-input multiple-out(MIMO)Systems is in question for both academia and industry.In this thesis,pilot contamination mitigation scheme is proposed to reduce the effects pilot contamination in multi-cell massive MIMO systems.Proposed scheme bisects the users into high interference(UH)and low interference(UL)users according to their large scale-fading.After grouping process,the orthogonal pilots are assigned to high interference users to mitigate the severe PC,and same set of pilot sequences are utilized among the low interference users.Now,the high interference users are free from serious PC but there is still slight ICI existed among the users of low interference group which degrades the system performance.Thus,to decontaminate the low interference users,an efficient pilots' assignment strategy which is based upon edge weighted interference graph(EWIG)is proposed.The simulation results illustrate that the proposed scheme improves both signal-to-interference-plus-noise-ratio(SINR)and achievable data rate.The proposed scheme is highly capable to mitigate PC and improve the system performance.