Improving Secrecy Outage Probability with Symbol Extension

This paper reveals symbol extension is capable of improving secrecy performance in the multiple-input single-output (MISO) wiretap channel. We propose a symbol extension scheme jointly with the existing beamforming and artificial noise generation strategy to exploit the time variation of fading channel. After multiplying the data symbol vector by a proper designed square matrix, the data symbol can be extended to multiple time-slots. As a result, without any symbol rate loss, the proposed scheme enhances the secrecy performance in terms of secrecy outage probability. Furthermore, we also analyze the asymptotic secrecy outage probability and derive the achievable diversity order. Both analytical and numerical results show that the proposed scheme can bring more diversity gains into secrecy communication.