Exact Secrecy Rate Analysis of Randomized Radiation Technique With Frequency Diverse Subarrays

Frequency diverse subarrays (FDSA) can provide angle-range-dependent beam steering by introducing different frequency offset increments to subarrays. Such selectivity in the angle-range dimension can be exploited for physical layer security by suppressing the information leakage to an eavesdropper existing along the mainlobe, which is highly vulnerable in directional beamforming. In addition, randomized radiation can be combined with FDSA for creating artificial noise to sidelobes for the eavesdropper. In the existing work, the secrecy rate of this combined technique is analyzed by approximating its subarray subset sampling into a sequence of independent and identically distributed Bernoulli random variables, which can cause considerable errors in the performance evaluation. Motivated by this limitation, we provide an exact secrecy rate analysis without any approximation, also considering path attenuation. The closed-form expression of the secrecy rate is validated by comparing it with simulation results. Furthermore, we show that our analysis can be used to maximize the secrecy rate by pertinently adjusting subset size and frequency offsets, while the conventional analysis cannot be employed for its inaccuracy.