Low-complexity Detection Algotithms In Massive MIMO System

Massive Multiple-Input Multiple-Output(M-MIMO)technology as an extension of MIMO,with tens to hundreds of antennas at the base-station(BS),can improve the system spectrum efficiency,reliability,throughput,energy efficiency,is recognized as one of the core technologies of 5G standards.However,in M-MIMO system,the high computational complexity of the signal detection algorithm becomes the bottleneck of its hardware implementation.Based on this background,this paper studies low complexity signal detection algorithms for M-MIMO systems in order to achieve a good tradeoff between complexity and performance.The main research contents are as follows:In the case that the antenna scale is not very large and the symbol modulation order is high,the Breath First Tree Search(BFTS)algorithm can achieve near Maximum Likelihood(quasi-ML)solution with lower complexity if the received sequence is detected in the right sequence order.However,finding the right detection sequence has exponential complexity overhead.In view of this,we proposed that BFTS be applied repeatedly to all possible sequences.Obviously,the redundant iteration will increase the complexity,and a stopping criterion is also proposed.When an iteration has already found the quasi ML solution,the iteration is terminated in advance so as to reduce the number of iterations and reduce the complexity.In the case of large number of antennas,message passing algorithm(MPA)can achieve near optimal detection.Channel hardening is defined as the size of the channel matrix H grows,the non-diagonal elements of HTH become smaller than the diagonal elements.Applying this phenomenon to the MPA can reduce the number of nodes on the factor graph corresponding to the MIMO model,simplify the calculation of the message in message passing,and greatly reduce the complexity.Simulation results show that the proposed iterative tree search algorithm based on stopping criterion reduces the complexity significantly with small loss of performance.In the case of large antenna size,the MPA using channel hardening can achieve better performance than linear detection with the complexity of near linear detection.