Under Whose Umbrella: The Collaborative Benefits of RS and RIS in Covert Communications

In future sixth-generation (6G) wireless applications, high levels of security and privacy are expected due to the soaring volume of confidential and sensitive data. To achieve this objective, covert communication can be employed as it can hide any activity of a specific legitimate user against a warden. In this study, we investigate the potential of reconfigurable intelligent surfaces (RIS) and rate splitting (RS) as enabling techniques for improving the covert communication performance. To this end, we jointly optimize RIS phase shifts and transmit beamforming to maximize covert transmission rate while maintaining desired levels of covertness for the covert user and quality-of-service (QoS) for the ordinary user. Numerical results reveal a mutually beneficial interaction between the two techniques in the context of covert communication, achieved through their collaborative creation of an undercover communication pathway. This undercover pathway is not a separate entity, but rather a result of suppressing the adversary’s channel, and concealing the covert user’s transmissions within the common, private, or both messages of the ordinary user. By providing the transmitter with the freedom to choose the best cover option, RS significantly improves covert communication performance, resulting in a substantial gain of 651% over NOMA.