Deploying multi-antenna energy-harvesting cooperative jammers in the MIMO wiretap channel

We consider the deployment of an energy harvesting (EH) cooperative jammer (CJ) to increase the security of a three-terminal wiretap channel with a passive eavesdropper, all users being equipped with multiple antennas. We first investigate the optimal offline EH CJ policy with complete non-causal information of energy arrivals and changes in channel state and show that it has an efficiently-computable global optimum. Subsequently, an online CJ policy with causal side information and probabilistic energy constraints is presented and transformed into a conservative convex program with deterministic constraints. The impact of CJ on the secrecy rate of the MIMO wiretap channel is also quantified. Numerical examples for a range of energy arrival and array parameters show that EH cooperative jammers are generally effective in augmenting the security of the wiretap channel.