Research On The Multiuser Detection Algorithm Of Low-Density Spreading Non-Orthogonal Multiple Access

Compared with orthogonal multiple access,the non-orthogonal multiple access technology has advantages in improving system throughput,accommodating the number of users,and responding to sudden connections,and is one of the candidate multiple access technologies of the fifth generation mobile communication(5G)system.Non-orthogonal multiple access technology actively introduces inter-user interference,and its user information is non-orthogonal.Therefore,multiuser detection at the receiver is the key link in non-orthogonal multiple access.The multiuser detection algorithm is studied from the aspects of improving detection performance and reducing detection complexity for low-density spreading non-orthogonal multiple access.The main contents are as follows:1.The message passing algorithm of Low Density Extended(LDS)system and the soft information transfer of Low Density Parity Check(LDPC)code decoding algorithm is studied,and an iterative algorithm for joint multiuser detection and LDPC code decoding is proposed.The results of the LDS multiuser detector is used as the input for LDPC code decoding,and the LDPC code decoding output is fed back to the LDS multiuser detector.Joint detection and decoding algorithms for different iteration times under different system loads are simulated.The simulation results show that the algorithm significantly reduces the bit error rate without increasing the system overhead and the complexity of the algorithm,and at the same time reduces the difference in user performance is reduced.2.Aiming at the difference of user channel quality in the uplink LDS multiple access system,a multiuser detection algorithm is proposed to reduce the computational complexity based on the user's instantaneous channel quality group detection.The user grouping scheme and the design criteria of the indicator matrix are given.Then a low-complexity group multi-user detection algorithm is introduced and the computational complexity of the algorithm is analyzed.The algorithm is simulated under different channel conditions.The simulation results show that under the condition of effectively reducing the computational complexity of the algorithm,the loss of user performance small.