Secure Line-of-Sight Communications: Optimal Antenna Selection and Beamforming Design

The joint antenna selection and secure beamforming optimization problem is considered for a multi-antenna line-of-sight (LOS) wiretap channel. By utilizing the mathematical property of the optimal secure beamformer and physical property of the LOS channel, a branch-and-bound (BAB)-based method is proposed to achieve the optimal secrecy performance with a reduced time complexity than the brute-force search. To further improve the security-complexity trade-off, a greedy-based method is developed to achieve a close to optimal secrecy performance while involving much lower complexity than the BAB-based method. Numerical results confirm the effectiveness of the proposed methods compared to baseline schemes.