Enhancing physical layer security through beamforming and noise injection

In this paper, we evaluate how much beamforming and noise injection can improve physical layer security by deriving the probability of non-zero secrecy capacity and the secrecy outage probability. Our model is a typical wiretap channel model, composed of three participants - the transmitter Alice, the legitimate receiver Bob and the eavesdropper Eve. A typical cellular scenario is considered where Alice has multiple antennas while Bob and Eve each have only one antenna (MISOSE). Beamforming and noise injection at Alice are applied to achieve a higher instantaneous signal-to-noise ratio (SNR) at Bob and a lower SNR at Eve. The probability density functions (pdf) of Bob and Eve's SNR are figured out in both noise-injection condition and injection-free condition, and we derive the closed-form expressions for the probability of non-zero secrecy capacity and the secrecy outage probability. Numerical analysis is also addressed using the two probabilities introduced above.