Research On Technologies Of Multiple Access Based On Non-binary LDPC Codes

With the increasing capacity requirements of communication systems,nonorthogonal multiple access has become a popular research.Non-binary Low Density Parity-Check(NBLDPC)is a non-binary linear code with strong error correction,which can be combined with the modulation to get better error performance.In this paper,we first construct some non-binary LDPC codes that are suitable for Bit Interleaved Coded Modulation(BICM)multiple access system.And ensure that the codebook has a higher code rate and better error correction capability.It's the foundation for non-binary LDPC-based multiple access research.Then,the capacity of the discrete source complex domain multiple access channel in Gaussian channel is analyzed.Consider the capacity of a multiple access system when the user is equal power access,and each user can send signals with two complex domains symmetrical about the origin.By proving and simulation,we get the conclusions that when the number of access users is an odd or or can be divided by odd,the maximum channel capacity is achieved when the phases of different users are almost uniformdistribution,on the premise of that the users' information can be separated.And when the number of access users is an integer power of 2,the uniform distribution of the user constellation points is the optimal constellation point distribution scheme that maximizes system capacity.This conclusion is generalized to the total power of the access user is a fixed value.When the power of each access user is equal and their phases are uniformly distributed or approximately evenly distributed,the system capacity reaches the maximum value or the sub-optimal value.Based on the obtained theory of optimal or suboptimal multiuser constellation point distribution and the constructed non-binary LDPC codes,we proposed a BICM multiple access based on non-binary LDPC codes.According to the number of users in the system,the corresponding code modulation and constellation point mapping is designed.And when the receiver detects the signal,a detection and decoding algorithm based on the superposition constellation point is proposed.Through the emphasis analysis and simulation of the two-user,three-user and four-user access systems,the error performance of the multiple access downlink based on non-binary LDPC codes is better than that of CDMA and SCMA.With the increase of the number of access users and the increase of the coding rate,the resource utilization efficiency of the system also increases,which is higher than CDMA and SCMA too.