Covert Communication in Downlink NOMA Systems With Random Transmit Power

• Published in: IEEE wireless communications letters Vol. 9; no. 11; pp. 2000 - 2004
• Main Authors: Tao, Liwei, Yang, Weiwei, Yan, Shihao, Wu, Dan, Guan, Xinrong, Chen, Dechuan
• Format: Journal Article
• Language: English
• Published: Piscataway IEEE 01.11.2020; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Communication; Covert communication; Downlink; Downlinking; Error detection; Error probability; Gold; NOMA; Optimization; power allocation; random transmit power; Receivers; Resource management; Signal to noise ratio; Systems design
• ISSN: 2162-2337; 2162-2345
• DOI: 10.1109/LWC.2020.3011191

This letter considers covert communication in downlink NOMA systems, where a public action (communication from Alice to the NOMA-weak user U1) is used to provide a cover for a secret action (communication from Alice to the NOMA-strong user U2). To aid system design, we first derive the detection error probability (DEP) at Willie and the connect outage probabilities (COPs) at U1 and U2. Then, considering the covertness and outage constraints, the optimization of power allocation factor ratio between U1 and U2 is tackled in order to maximize the effective covert rate. The results demonstrate that the minimum DEP is the power allocation factor for U1. In addition, for a given covert constraint, relaxing the outage constraint will effectively increase the maximum effective covert rate within a certain range of the maximum transmit power of U1.