Pilot Contamination Precoding In Massive MIMO

Massive MIMO is one of the key 5G technologies.The most important feature of this technology employs multiple antennas in base station.Studies show that with the increase of the number of antennas on the base station,the interference caused by the fast fading and unrelated noise will gradually vanish and the only remaining impairment is the inter-cellular interference caused by re-use of the pilot sequences in other cells(pilot contamination).However,the impairment of pilot contamination cannot vanish with the increase of antennas and it becomes the main factor limiting the performance of Massive MIMO system.Therefore,it is important for us to reduce or eliminate the impact of pilot contamination.In this thesis,multi-cell multi-user TDD system model under the Massive MIMO is established to analyze the causes of pilot contamination,as well as its impact on system performance.Then some schemes are analyzed to solve the problem of pilot contamination.In these schemes,precoding schemes are emphasized.Studies show that a simple linear precoding scheme can achieve great system performance without pilot contamination in a Massive MIMO system.Therefore,some traditional linear precoding algorithms like matching filtering,zero forcing and minimum mean square error are analyzed in multi-cell multi-user Massive MIMO systems.Then several pilot contamination precoding schemes based on multi-cell cooperation are analyzed.If the number of antennas approaches infinity,these schemes can theoretically completely eliminate pilot contamination.However,it requires a lot of backhaul for these precoding schemes to share channel state information and user data between base stations.Finally,aimed at the problems of high complexity and large backhaul of pilot contamination precoding,a pilot contamination precoding scheme with low complexity based on pilot allocation strategy is proposed.On the basis of the proposed scheme,a simplified precoding scheme based on partial collaboration is proposed as well.The simulation results show that the simplified scheme can reduce the backhaul of this algorithm,and the overall achievable rate of the system is not reduced.