Robust secure transmission for cooperative ARQ based on secrecy rate and outage optimization

Physical layer security is an emerging technique to improve the wireless communication security and the corresponding techniques under practical scenarios especially with imperfect channel state information (CSI) need to be taken into consideration. In this paper, we investigate the robust secure transmission for cooperative decode-and-forward (DF) automatic-repeat-request (ARQ) in multiple-input-single-output (MISO) relaying wiretap channels with channel estimation errors. Firstly, the robust transmit covariance matrices and the optimal beamforming weights are obtained using the semi-definite relaxation (SDR) approach to maximize the secrecy rate under power constraint and channel uncertainties. Besides, we further propose a robust design scheme from the secrecy outage-based characterizations for minimizing the secrecy outage probability of legitimate destination. Moreover, a non-robust scheme, in which the designed beamformer refers to the generalized eigenvectors of the channels´ matrix pencil, is also considered as a benchmark. Simulation results verify the robustness of the proposed schemes against the estimation errors and shows that the robust design schemes can significantly improve the security performance of the network.