Secure and Energy-Efficient Beamforming for Simultaneous Information and\n Energy Transfer

Next-generation communication networks will likely involve the\nenergy-efficient transfer of information and energy over the same wireless\nchannel, for which the physical layer will become more vulnerable to cyber\nattacks by potential multi-antenna eavesdroppers. To address this issue, this\npaper considers transmit time-switching (TS) mode, in which energy and\ninformation signals are transmitted separately in time by the BS. This protocol\nis not only easy to implement but also delivers the opportunity of\nmulti-purpose beamforming, in which energy beamformers during wireless power\ntransfer are useful in jamming the eavesdropper. In the presence of imperfect\nchannel estimation and multi-antenna eavesdroppers, the energy and information\nbeamformers and the transmit TS ratio are jointly optimized to maximize the\nworst-case user secrecy rate subject to UEs' harvested energy thresholds and a\nBS transmit power budget. New robust path-following algorithms, which involve\none simple convex quadratic program at each iteration are proposed for\ncomputational solutions of this difficult optimization problem and also the\nproblem of secure energy efficiency maximization. The latter is further complex\ndue to additional optimization variables appearing in the denominator of the\nsecrecy rate function. Numerical results confirm that the performance of the\nproposed computational solutions is robust against the channel uncertainties.\n