Can full-duplex jamming reduce the energy-cost of a secure bit?

In this work we study the secrecy energy efficiency (SEE) of a multiple-input-multiple-output multiple-antenna eavesdropper (MIMOME) wiretap channel, in terms of the securely communicated bits-per-Joule, where the legitimate receiver is equipped with full-duplex (FD) capability. In particular, we seek answer to the question: if and how the application of an FD jammer can enhance the system SEE, considering the additional power consumption used for jamming and self-interference cancellation, as well as the degrading effect of residual self-interference. In this regard, an SEE maximization problem is formulated. Due to the intractable problem structure, an iterative solution is provided with a guaranteed convergence to a local optimum. Moreover, the proposed solution is extended for a system with a bidirectional communication, where both legitimate nodes are equipped with FD capability. Numerical simulations indicate a marginal SEE gain, via the utilization of FD jamming, for a wide range of system conditions. However, the observed gain is significant for the scenarios with a small distance between the FD node and the eavesdropper, a high signal-to-noise ratio (SNR) condition or for a bidirectional FD communication setup, under the condition that the self-interference can be effectively and efficiently mitigated.