Beamforming for Simultaneous Energy and Information Transfer and Physical-Layer Secrecy

With increased crowding of the electromagnetic spectrum, interference must be leveraged as an available resource. To address this problem, we develop an array processing technique that provides wireless communications devices with enhanced physical layer secrecy using interference within the same space–time–frequency subspace and the ability to harvest energy by exploiting co-channel interference. This is in contrast to current techniques that attempt to minimize the array response to interference. The proposed directional modulation technique optimizes a set of array steering vectors to enable direction-dependent modulation, thus adding a degree of freedom to the space–time–frequency paradigm. Steering vector selection is formulated as a convex optimization problem for rapid computation given arbitrarily positioned elements. We show that our technique allows us, prior to digitization, to spectrally separate co-channel interference from a desired signal. This technique enables the energy from the interference to be diverted for harvesting during the digitization and decoding of the desired signal. We also show that it is able to transmit to selectively self-interfere in predetermined directions. Finally, we prove that the self-interference can be generated with enough specificity to generate a spoofed signal, providing added security against eavesdroppers.