Covert Transmission With a Self-Sustained Relay

• Published in: IEEE transactions on wireless communications Vol. 18; no. 8; pp. 4089 - 4102
• Main Authors: Hu, Jinsong, Yan, Shihao, Shu, Feng, Wang, Jiangzhou
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.08.2019; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Communication system security; Covert communications; Energy conversion efficiency; Energy harvesting; Energy transmission; Error detection; Error probability; power splitting; Receivers; Relay; relay networks; Relays; Security; time switching; Upper bounds; Wireless communication
• ISSN: 1536-1276; 1558-2248
• DOI: 10.1109/TWC.2019.2920961

This paper examines the possibility, performance limits, and associated costs for a self-sustained relay to transmit its own covert information to a destination on top of forwarding the source's information. Since the source provides energy to the relay for forwarding its information, the source does not allow the relay's covert transmission and to detect it. Considering the time switching (TS) and power splitting (PS) schemes for energy harvesting, where all the harvested energy is used for transmission at the self-sustained relay, we derive the minimum detection error probability <inline-formula> <tex-math notation="LaTeX">\xi ^{\ast } </tex-math></inline-formula> at the source based on which we determine the maximum effective covert rate <inline-formula> <tex-math notation="LaTeX">\Psi ^{\ast } </tex-math></inline-formula> subject to a given covertness constraint on <inline-formula> <tex-math notation="LaTeX">\xi ^{\ast } </tex-math></inline-formula>. Our analysis shows that <inline-formula> <tex-math notation="LaTeX">\xi ^{\ast } </tex-math></inline-formula> is the same for the TS and PS schemes, which leads to the fact that the cost of achieving <inline-formula> <tex-math notation="LaTeX">\Psi ^{\ast } </tex-math></inline-formula> in both the two schemes in terms of the required increase in the energy conversion efficiency at the relay is the same, although the values of <inline-formula> <tex-math notation="LaTeX">\Psi ^{\ast } </tex-math></inline-formula> in these two schemes can be different in specific scenarios. For example, the TS scheme outperforms the PS scheme in terms of achieving a higher <inline-formula> <tex-math notation="LaTeX">\Psi ^{\ast } </tex-math></inline-formula> when the transmit power at the source is relatively low. If the covertness constraint is tighter than a specific value, it is the covertness constraint that limits <inline-formula> <tex-math notation="LaTeX">\Psi ^{\ast } </tex-math></inline-formula>, and otherwise, it is upper bound on the energy conversion efficiency that limits <inline-formula> <tex-math notation="LaTeX">\Psi ^{\ast } </tex-math></inline-formula>.