Directional Modulation in Time-Modulated Array With a Novel Pseudorandom Ascending Phase Time Sequence

Directional modulation (DM) is an attractive technique for securing wireless communication at the physical layer. DM systems usually require additional phase shifters or radio frequency vector modulators for beamforming. It thus inevitably introduces losses to the system. Due to the “time” degree of freedom, time-modulated array (TMA) has exhibited its unique features in DM system developments. Traditionally, periodic time sequence is always adopted in TMAs, which does not provide sufficient randomness for DM systems. In this work, a novel pseudorandom ascending phase (PS-AP) time sequence is proposed to enhance DM capability. The proposed PS-AP time sequence ensures maximum signal radiation power in desired directions and increases channel randomness in other undesired directions. Thus, the resultant DM system transmits nondistorted signals in desired directions, while it simultaneously distorts the signal constellation points by introducing randomly demodulated waveforms and minimizing radiation power along other undesired directions. Experimental results are presented along with theoretical and numerical analysis to validate the effectiveness of the PS-AP time sequence in TMA for DM systems.