Research On Channel Estimation Using Superimposed Pilot In Large-scale MIMO Systems

Large-scale multiple-input multiple-output(MIMO)technology is a candidate technology for the fifth generation mobile communication systems,which can multiply the system spectrum efficiency without increasing the transmission power by arranging a large antenna array at the base station side.Large-scale MIMO technology usually employs in multi-cell multi-user system,and the available pilot resources are limited because of the constrained channel coherence time under the time division multiplexing(TDM)pilot configuration mode.In TDM model,the same set of orthogonal pilot sequences are reused among the different cells,hence the inaccurate channel estimation results achieve due to the pilot contamination.On the other hand,in order to ensure that the user sends the orthogonal pilot in the cell,the length of the pilot sequences must increases linearly with the number of users,which makes the bandwidth resources not be fully utilized.The existence of these two factors seriously hampers the effective improvement of the system spectral efficiency.Therefore,it is necessary to study the channel estimation algorithm of large-scale MIMO system based on superposition pilot.The superimposed pilot configuration mode can achieve channel estimation in the case of shared transmit data bandwidth,which effectively improves the bandwidth utilization of the system.The superimposed pilot can be divided into periodic pilot and orthogonal pilot.Therefore,the thesis focuses on the research on channel estimation algorithms of large-scale MIMO systems for these two kinds of specific superimposed pilot configuration modes,and the main contents are outlined as follows.1.Combining with user scheduling,a channel estimation method based on superimposed periodic pilot sequence is proposed in large-scale MIMO systems.Firstly,the first-order statistical characteristics of the transmitted signal and the additional noise are used to eliminate the interference between the two signals.Then,the optimal power distribution factor is obtained by analyzing the Signal to Interference plus Noise Ratio(SINR),and finally,based on the fairness of the user from the perspective of signal leakage,select the appropriate user in each cell and assign the same pilot.The numerical simulation results show that the proposed method of convergent user scheduling can reduce the pilot pollution and improves the channel estimation accuracy.2.Using the alternative iteration criterion,a pilot superimposed channel estimation method with the perturbation theory is proposed in large-scale MIMO systems.The scheme first reconstructs the system model from the perspective of the disturbance by analyzing the factors that affect the accuracy of the channel estimation under the superimposed pilot model,and then the initial channel estimation is carried out under the condition of reducing the system perturbation.Finally,the more accurate channel estimation is realized based on the idea of alternating iterations by minimizing the cost function.The numerical simulation results show that the method can realize the accurate estimation of the channel in the case of making full use of the bandwidth resources.