SCMA Technology Based On Digital Fountain Modulation

The fifth generation(5G)and future communication systems need to support ultra reliable,lower latency and more terminals.However,traditional orthogonal multiple access(OMA)technology is limited by limited spectrum resources,and it can not deal with the scenarios of simultaneous access of massive terminals.Therefore,in order to meet the demand of 5G communication,it is necessary to use reliable short code length channel coding to achieve ultra-high reliability and low latency,and to increase the number of access terminals through non-orthogonal multiple access technology.This paper aims to design a new cascade scheme of physical layer coding modulation and sparse code multiple access(SCMA),which can meet the requirements of ultra reliable and low latency communication(URLLC)scenarios.The research of this paper is divided into two aspects:one is to study the design and optimization of short analog fountain code(S-AFC),and the other is to research how to cascade S-AFC and SCMA to solve the end-to-end communication latency and reduce the access delay of massive devices communicating with the base station.The innovation points and specific work contents of this paper are as follows:(1)In this paper,the degree distribution function of S-AFC is designed based on Sum Or tree.Because of the small average degree of S-AFC,when the decoding overhead is also small,some information symbols will not participate in coding.Therefore,S-AFC will have error code platform.In order to eliminate the error code platform of S-AFC,the generation matrix of S-AFC is optimized to ensure that all information symbols can participate in coding,and simulation results show that the error code platform of S-AFC is eliminated.The block error rate(BLER)and the shortest code length of S-AFC are simulated,and results show that S-AFC can achieve10^-5 BLER,and the code length approaches the performance limit of short code length channel coding.(2)In the URLLC scenario with massive terminal access,in order to avoid the access delay caused by the lack of spectrum resources of scheduling OMA,S-AFC and SCMA are cascaded in this paper.Because S-AFC is a kind of analog coding,its massive generating symbols cannot map to SCMA codebook.Therefore,based on S-AFC,this paper proposes digital fountain modulation(DFM)technology.The generating symbol of DFM can be adapted to the size of SCMA code book.According to the simulation comparison of various cascading schemes of SCMA in URLLC scenario,it can be concluded that LDPC-DFM-SCMA technology can meet the requirements of ultra reliable and low latency of URLLC scenarios due to its two properties of error correction and code rate adaptation.