Research On Physical Layer Security In Novel Multiple Access Systems

Sparse Code Multiple Access(SCMA)technology is a novel multi-dimensional non-orthogonal multiple access technology based on code domain multiplexing in 5G.It can not only provide a large amount of connection and unauthorized access for uplink,but also can design low-complexity receiving technology by using the sparsity of code word.However,the air interface of the wireless communication system based on SCMA technology is open,the channel instability is aggravated,the data of multiple users are superimposed on the same time frequency resource block,and the other users' decoding information is allowed,leading to the communication security of the system will be more challenging.Hence,there are lots of physical layer security problems to be improved and solved in SCMA systems.This paper mainly focuses on the research of the security capacity problem under the multiuser eavesdropping scenarios in the SCMA system,and provides the theoretical basis for improving the security performance of the 5G system.The main contents are as follows:Firstly,in view of the multiuser eavesdropping scenarios in single cell SCMA downlink,the problem of user subcarrier allocation based on secret capacity is studied.A novel many-to-many matching algorithm is proposed.The initial matching is established by the improved delay acceptance algorithm,and the user sets and subcarrier sets are regarded as the two parties of the cooperative game.The optimal stable matching is achieved by swap matching.Simulation results show that the proposed algorithm outperforms the random matching scheme and the orthogonal multiple access scheme.Secondly,in view of the multi-relay multiuser eavesdropping scenarios in single cell SCMA downlink,the expression of system ergodicity and secrecy capacity in two scenarios which is without direct link and direct link between the base station and the user is derived,and the optimal relay one-dimension search algorithm is designed to solve the optimization of security capacity in the two scenarios.Simulation results show that the proposed algorithm is superior to the random selection scheme and the orthogonal multiple access scheme.