Composition Index Modulation for Physical Layer Security in NOMA Networks

In this paper, we propose employing the index modulation to improve the overall system performance and physical layer security in non-orthogonal multiple access (NOMA) networks with an near untrusted user. In the proposed scheme, by virtue of dynamically shifting the antenna activation patterns and energy allocation patterns, an untrusted user located near the base station (BS) can only successfully decode its own information generated by modulated symbols, while the information encoded by antenna and energy combination indices intended for other trusted users located far away from the BS cannot be decoded. Additionally, the secrecy rate is derived to evaluate the performance of the proposed NOMA networks. Simulation results validate the proposed scheme and provide insights into the design for far trusted users to prevent eavesdropping launched by near untrusted users in NOMA networks.