Robust secure switching transmission in multi-antenna relaying systems: cooperative jamming or decode-and-forward beamforming

In this study, the authors investigate the physical layer security for safeguarding secure transmission in multi-antenna relaying networks with imperfect channel state information (CSI). Different from traditional strategies in multi-antenna relaying systems, which would terminate the communication if the relay could not decode the signals successfully, the authors propose robust secure transmission strategy which switches between cooperative jamming (CJ) and decode-and-forward (DF) beamforming. Specifically, if the received signal-to-noise ratio at the relay is lower than a predefined threshold, it will impose CJ signals on potential eavesdropper, otherwise the relay would operate DF beamforming. The authors’ objective is to maximise secrecy rate and minimise secrecy outage probability in different practical communication scenarios with relaxed or strict time-delay constraint. Thus, given the unavailability of the perfect eavesdropping CSI, the authors propose a worst-case robust design and a statistical-approach robust design based on secrecy rate and secrecy outage criterion, respectively. In addition, a traditional DF robust scheme and a non-robust scheme are also considered as benchmarks. Simulation results verify that the proposed scheme significantly outperforms the traditional DF robust scheme and the non-robust scheme.