SCMA Codebook Design And Research On Multiuser Detection Algorithm

With the rapid development of social economy and the continuous innovation of science and technology,mobile communication systems have experienced exploration and renewal from the first generation(1G)to the fourth generation(4G),and have gradually played a vital role in living,finance,transportation,etc in the modern society.4G has been widely used in today's information age,and the spectrum resources become more and more short,because the huge traffic and rate demand of various services,as well as the massive access of users and devices.The 4G mobile communication system can't meet the development needs undoubtedly,so the research of the fifth generation mobile communication system(5G)has arisen around the world.Therefore,the research wave of 5G is emerging in the world,and the new Sparse Code Multiple Access(SCMA)technology including Sparse Code Multiple Access(SCMA)has become a research hotspot.This paper first introduced the classical constellation design methods,analyzed and summarized the key operation steps of several methods and the degree of ease of implementation.Then proposed a multi-dimensional rotating constellation based on the mixed arrangement of the real part imaginary parts,and introduced the mapping matrix,which is easy to realize because of its similarity with Low Density Parity Check Code(LDPC).This paper presented a SCMA system based on chaotic sequence.According to the understanding of chaotic system,it introduced a classical Logistic chaotic sequence firstly,and it gave the overall design scheme of the system.It used the TCM(Trellis Coded Modulation)-based subset segmentation method to generate the user's constellation graph,then it combined with the mapping matrix generated user code,each user's signal mapped to code of its code word directly,and each code word can be superimposed and transmited on the common resource block,thus it realized the multi-user reusing,further improved the spectrum utilization.The simulate results show that the SCMA system based on chaotic sequence designed in this paper has lower bit error rate than the traditional SCMA system without increasing the decoding complexity.Because of the sparse nature of the SCMA sender's codebook,the simulations use the Message Passing Algorithm(MPA).The decoding complexity of multi-user detection is not high,but the hardware design of this algorithm is not easy to implement.Aiming at this defect,this paper studies several improved algorithms based on MPA algorithm,then simulates all algorithms.After comparing its overall performance,it proposed a new multiuser detection algorithm combining MPA decoding and Turbo decoding.The results show that the system performance has a certain improvement.Finally,it summarizes the general strategy of MPA algorithm optimization.