Research On Sparse Code Multiple Access Detection Technique And Secure Transmission

Since the commercialization of 4th generation(4G)mobile networks,researchers have focused on the new air-interface technology,to meet the demands of high reliability,high transmission efficiency and low latency in the forthcoming 5th generation(5G)mobile networks.Multiple access is an important component of air-interface technology.To further improve the frequency spectrum and tackle the severe degradation of conventional orthogonal multiple access(OMA)under massive access and overloading condition,nonorthogonal multiple access(NOMA)is proposed.In this thesis,we mainly focus on a code-domain NOMA scheme,i.e.,sparse code multiple access(SCMA),which is proposed by Huawei and considered to be a promising 5G candidate in massive Machine Type of Communication(mMTC)scenario.The SCMA receiver and secure transmission is studied in this paper,the main contributions and novelties are listed as follows:(1)As the detection algorithm for SCMA is message passing algorithm(MPA),which is with high computational complexity in practical implementation,we propose a simplified detector based on truncated messages.The basic idea of the algorithm is to decrease the number of messages that involving in the message passing,so that the complexity can be reduced.According to the simulation results,the proposed algorithm can significantly simplify MPA with negligible performance loss.Furthermore,the convergence performance,robustness against channel estimation error and the computational complexity are also investigated in this paper.(2)We consider a binary low-density parity-check(B-LDPC)and non-binary lowdensity parity-check(NB-LDPC)coded SCMA system.Since both the LDPC code and SCMA can be represented by sparse graph,we link these two sparse graphs together,and design a joint detection and decoding algorithm.Significant gain can be achieved compare to conventional receiver.Furthermore,the simplified joint detection algorithm for a NBLDPC coded SCMA system is also proposed to decrease the computational complexity.(3)Due to the latency and power consumption demand in 5G,conventional cryptology is too expensive costly to apply to practical scenario.Therefore,we firstly introduce the idea of physical layer security(PLS)into the study of SCMA,and two secure transmission schemes are proposed.Furthermore,to illustrate the feasibility and reliability of the schemes,theoretically analysis is also made in this thesis.Not only our studies are with values in the practical implementation of SCMA,but also providing a new direction for the research of SCMA system,which can be referenced for the standardization of SCMA in forthcoming 5G.