Research Of Channel Estimation Technology In The Uplink Massive MIMO System

Massive MIMO(Multiple-Input Multiple-Output) technology by configuring the root of hundreds antenna array at the base station side, the communication system’s capacity and spectral efficiency can be dozens or even hundreds of times to improve, it has become one of the key technologies of the fifth generation of mobile communication( 5G). However, large-scale MIMO system for the protection of high reliability and high speed communications system must obtain accurate channel state information(CSI). Consider a time division duplex(TDD) mode of communication, using its channel reciprocity characteristics, then only the uplink channel need to be estimated. But the limited coherence length of time, the use of inter-cell non-orthogonal pilot sequence set for channel estimation, so that system performance severely affected by the pilot pollution. Considering these problems, mainly as follows:First we introduce the multi-cell system model and channel characteristics at the scene of large-scale MIMO technology, and then use least squares(LS) method and linear minimum mean square error(LMMSE) channel estimation method to analyze the cause of pilot pollution problems. Then use the maximum combined ratio(MR) algorithm for the uplink signal to interference ratio(SINR) analysis, through theoretical explanation for pilot pollution problem is mainly reason inhibiting system performance.Next, the pilot pollution problems, we are based on research from a full pilot system and pilot location information based on user collaboration scheduling of two perspective, to study and solve the problem of the feasibility of the algorithm.Referring to the full pilot system, we consider the pilot reuse factor parameters’ influence, which takes advantage of all the estimated channel direction. Firstly we consider pilot reuse factor and power control parameters to establish the communication system model, and using a minimum mean square error algorithm for channel estimation. Then a detailed study of the uplink and downlink spectrum efficiency and overall system spectral efficiency of the system. Finally, given in detail in the spectral efficiency based minimum mean square error(PM) detection algorithm during the full pilot, the simulation shows that the algorithm can get higher spectral efficiency compared to the traditional detection algorithm, and it can effective mitigate pilot pollution problems.Put forward a cooperation dispatching through base station side to take advantage of location information and to allocate the users for pilot sequences. Firstly, multi-cell system scenarios is modeled, and use the traditional multiple signal classification algorithm to estimate the user reaches the corner, and then based on the estimated angle parameters, according to known slow fading channel information, and then through different users use overlap angle of arrival angle criterion within a cell cluster to pilot assign, and then use the last minimum mean square error algorithm for channel estimation. The simulation results show that the scheduling scheme can greatly eliminate pilot pollution problems.