LAUSR

Rate splitting (RS) can significantly improve the spectrum efficiency and degrees of freedom of multi-access transmissions. However, due to the characteristics of RS decoding, the secure transmission remains a challenge especially when there is an untrusted near user. Thus, two RS schemes are proposed with different successive interference cancellation (SIC) layers. For both schemes, the users first decode the common stream. In the one-layer-SIC scheme, the users then decode their own private streams without interference via zero-forcing. For the two-layer-SIC scheme, maximum ratio transmission is adopted for the trusted far user. The users decode the private stream of the untrusted user and then decode the other. Outage probability and secrecy outage probability are analyzed based on the channel statistics and the achievable rate. Simulation results verify the theoretical results and demonstrate the advantages of two schemes in terms of the common stream transmission and the security of far user.