Max–min fair wireless energy transfer for multiple‐input multiple‐output wiretap channels

In this study, the authors study the max–min fairness for wireless energy transfer in a multiuser multiple‐input multiple‐output communication system with simultaneous wireless information and power transfer. In particular, they aim to maximise the minimum harvested energy among the multiple multi‐antenna energy receivers while guaranteeing secure communication for multi‐antenna information receiver. The dual use of artificial noise to facilitate both wireless energy transfer and secure communication is exploited in the authors’ proposed problem. Both scenarios of perfect and imperfect channel state information (CSI) known at the transmitter are considered. For the perfect CSI case, the formulated max–min energy harvesting (MM‐EH) problem is non‐convex and intractable. To circumvent it, an iterative optimisation algorithm based on Taylor series expansion is proposed. Then, they turn their attention to the imperfect CSI case, where a max–min robust energy harvesting (MMR‐EH) problem is considered. Though the MMR‐EH problem is more complicated than the MM‐EH problem, they reveal that the iterative optimisation method can be extended to the solution of the former, wherein the S‐procedure is introduced. Simulation results show the efficiency of their proposed solutions in terms of energy harvesting.