Theoretical Research On Random Multiple Access Technology Based On Non-binary LDPC Code

Massive Machine Type Communication(mMTC)is one of the three application scenarios of the fifth-generation mobile communications(5G).The mMTC scenario is characterized by massive connections,infrequent access,and short data packets.In view of these characteristics,considering issues such as delay,complexity,and energy consumption,mMTC uses an authorization-free access method,also known as random multiple access.For random multiple access,because there are a large number of user equipments randomly sending information,the interference between different users is very large.In this case,how to ensure the reliability of multi-user communication is an important issue in the design of random multiple access system.Channel coding technology is usually used to improve communication reliability.Low-density parity-check(LDPC)code is a type of channel codes that can approach Shannon's limit.Compared with the binary LDPC code,Non-binary LDPC code has better performance when the code length is short,so it is more suitable for short data packet communication.This article will study the random multiple access technology based on non-binary LDPC codes.First of all,this article introduces the basic principles of non-binary LDPC codes.In the construction part of LDPC codes,the classic superposition(SP)coding method is introduced.In the coding part,a non-binary Gaussian elimination method is proposed.In the decoding part,the classic Fast Fourier Transform(FFT)-based-ary Sum-Product Algorithm(QSPA)is introduced.Finally several short code-length non-binary LDPC codes are constructed.And the performance simulation results and analysis are presented.Then,this paper presents the design scheme of multi-user access codebook,which is based on the maximization of channel capacity and the unique decodability of the receiver.Under the condition of maximization of channel capacity,the design scheme of multi-user access codebook is obtained by optimizing the channel capacity expression.Under the condition unique decodability of the receiver,a non-binary unique decodable codebook is proposed.Finally,the system model of multi-user access in random multiple access scenario is given,and several multi-user access design schemes are given.The spectral efficiency,minimum Euclidean distance and the average signal to noise ratio of these schemes are compared.In active users detection at the receiver,two detection algorithms are proposed based on maximum a posteriori probability and serial interference cancellation,respectively.In multiuser decoding part,two kinds of decoding algorithms are given according to two codebook schemes.Finally,the simulation results of system error performance and spectral efficiency are given.Compared with the classical Sparse Code Multiple Access(SCMA)scheme and the non-orthogonal Multiple Access scheme,it is found that the proposed schemes can achieve a bit error rate of 10^-4when the bit-signal-to-noise ratio is about 6 dB and 7 dB,and the corresponding spectral efficiencies are 2 bit/channel use and 2.68 bit/channel use,respectively.Compared with SCMA and NOMA systems,the spectral efficiency and bit error rate have been greatly improved.