A low-complexity antenna subset modulation for secure millimeter-wave communication

In this paper, we present a low-complexity version of the Antenna Subset Modulation (LC-ASM), to enhance the physical layer security. LC-ASM consists of a conventional phased-array transmitter followed by antennas with an on-off switching circuit. The proposed solution maintains the objective of scrambling the constellation points in both amplitude and phase in undesired directions, while preserving a clear constellation in the target direction. LC-ASM is different from the original ASM in the following ways: (1) LC-ASM is not restricted to the use of phase modulation, and can accept any modulation type including QAM, (2) it does not need to modulate the signal in the RF domain, where the conventional phasedarray transmitter circuits remain unchanged, (3) in the far-field, LC-ASM scrambles the signal constellation by randomly driving a subset of the transmitting antennas, (4) LC-ASM can easily integrated with the current infrastructure of phased-array transmitters, and (5) LC-ASM breaks up the correlation between the data rates and the switching speed. We analysed the LC-ASM performance and derived an exact expression of the bit error probability, and we derived the secrecy capacity in a closed form. The results show that LC-ASM is a simple and very efficient solution to improve the physical layer security of mm-wave communication.