Research And Implementation Of Signal Detection Technology For Non-Orthogonal Multiple Access System

With the arrival of the era of the Internet of things,the fifth-generation mobile communication technology will be faced with the massive connection scenario.Communication systems that have more efficient spectrum,faster transmission rates and larger systems are needed by users.The forth generation mobile communication technology using orthogonal multiple access technology can not meet these needs.To solve this problem,a non-orthogonal multiple access(NOMA)technology is proposed by researchers.This thesis focuses on the NOMA system downlink signal detection technology.The main work is as follows:(1)On the basis of the sorting QR decomposition detection(SQRD)algorithm based on modified Gram-Schmidt,a low-complexity SQRD signal detection algorithm is proposed.In this algorithm,the matrix H is changed to a real-valued matrix.The odd columns and adjacent columns behind them are orthogonal to each other after some arrangement of columns in the real-valued matrix.By normalizing each odd column vector with all column vectors on the right side of it,an upper triangular matrix R is constructed.Then the signal is detected.The complexity analysis and simulation results show that the improved SQRD algorithm reduces the computational complexity by nearly 50% on the premise that the system performance is not significantly reduced.(2)Aiming at the problem that the error of detected signals in the traditional SQRD algorithm will cause interference to the detected signals,an SQRD algorithm based on Givens transformation is proposed.In this algorithm,the quasi-upper triangular matrix for detection is obtained by performing the row transformation on the matrix R.Then the matrix is converted into an upper triangular matrix by using Givens transformation,so as to eliminate the interference caused by the error of detected signals.Simulation results show that the detection performance of the new algorithm is better than that of the improved algorithm.(3)On the basis of SQRD algorithm,a signal detection algorithm based on soft decision is proposed.In this algorithm,the soft decision is used to replace the hard decision in the original SQRD algorithm.The maximum posterior probability is firstly used to calculate the logarithmic likelihood ratio of the signal before the decision,and then each bit is obtained through decoding.The soft decision of the signal is realized,and the loss of information is reduced.Simulation shows that the detection performance of the new algorithm is better than that of the unimproved algorithm.