Analog Cooperative Beamforming With Spherically-Bound Random Arrays for Physical-Layer Secure Communications

In this letter, we propose an analog cooperative beamforming (ACB) technique using random antenna arrays for physical-layer (PHY) secure communications, where the array elements are assumed to be uniformly distributed in a spherical volume. Motivated by the fact that the sidelobe of radiating elements at undesired directions can be used for eavesdropping, the proposed ACB aims at randomizing the radiation pattern at the undesired directions for PHY secure communications. To achieve this aim, it allows the radiating elements to be randomly selected and adapt their phases to a desired direction. To evaluate the PHY security performance, we derive the average secrecy capacity by subtracting the channel capacity for a given undesired direction from that for a desired direction. The analysis and simulation results indicate that the proposed ACB outperforms the existing PHY security technique with a fixed antenna array especially when its array elements are widely dispersed.