Research On Limited Feedback Scheme For Massive MIMO Systems

Massive MIMO technology is considered to be one of the key technologies in the fifth generation(5G)wireless communication system.By configuring a large number of antennas at the base station,the power efficiency,spectrum efficiency and link reliability are greatly improved.However,when the number of antennas is increased in a large amount,the feedback overhead in the system will increase significantly.In massive MIMO systems,the accuracy of channel state information acquisition affects the performance of the overall system.In the large-scale MIMO system in the frequency division duplex mode,the UE transmits the quantized channel state information to the base station through a limited feedback technique,but the number of antennas of the base station(BS)is hundreds of thousands.With the increase,the complexity of the acquisition of channel state information increases exponentially,and the number of feedback bits of the system also increases.Therefore,the system feedback overhead is too large to become an urgent problem to be solved.To this end,the thesis studies the problem of excessive feedback overhead in large-scale MIMO systems under FDD,and proposes a new limited feedback scheme.Firstly,the thesis analyzes the problem of excessive overhead caused by the increase of the number of antennas in large-scale MIMO systems from the aspects of computational complexity and feedback bit number.Secondly,based on the high computational complexity problem in finite feedback,a finite feedback quantization method based on direction markers is proposed.By uniformly grouping the codebooks in the quantization process,each group selects a direction marker vector representing the group,and when the channel state information is quantized,first compares with the direction markers of each group to obtain a direction marker closest to the channel vector.The group in which it is located is the candidate codebook group,and is subjected to secondary quantization in the codebook group to be selected to obtain the best codeword.The complexity analysis shows that the method can effectively reduce the quantization computational complexity in the limited feedback process.Finally,for the problem of high feedback bit number,a limited feedback quantization method based on codebook rotation is proposed.Taking the best codeword of the user at the moment as the reference,the codewords in the left and right rotation regions are rotated,and are rotated to the initial position of the current user codebook,which is the virtual codebook of the current time user,and quantized in the virtual codebook.Get the best codeword.Theoretical analysis and simulation results show that for users close to static or low mobility,this method can effectively reduce the number of feedback bits from the UE to the base station,thus reducing the system feedback overhead.