Directional Modulation for Multi-Node Interaction from an Artificially Intelligent Power Amplifier Array: Simultaneous Radar and Communication while Optimizing Circuit Performance

Abstract

Spectral efficiency and security in wireless applications can be enhanced through directional transmission of multiple signals from a single array aperture. Directional modulation allows the array to transmit multiple, directionally distinct signals out of the same aperture at the same time and frequency. This is accomplished through calculated antenna current excitations to ensure desired directional transmissions. A critical issue in this process involves the power amplifiers in each array element. Due to mutual coupling differences between array elements and the variations in power amplifier nonlinearities, signals leaving the power amplifiers may be distorted and no longer contain the desired information. This can result in bit errors in communication. To correct this issue, real-time impedance tuning and signal equalization are applied to reduce the distortion of the directionally transmitted messages. Signal equalization is corrective feedback technique similar to digital predistortion (DPD). Experimental simulation results are presented using directional modulation in an array of power amplifiers with reconfigurable load impedance tuners. The signal equalization technique applies corrective feedback to adjust the amplifier input signals, compensating for the undesired distortion such that the desired currents will be input to the antennas. Because the impedance tuning and signal equalization techniques may have conflicting effects on the overall distortion, impedance tuning is applied initially, and signal equalization is applied after the impedance tuning operation is complete.