Three Artificial-Noise-Aided Secure Transmission Schemes in Wiretap Channels

We examine the secrecy performance of three artificial-noise-aided secure transmission schemes, namely, the partially-adaptive, fully-adaptive, and on-off schemes. To this end, we provide new analysis to facilitate the optimization of the fraction ϕ of the transmit power allocated to the useful signal and redundancy rate RE. Surprisingly, our examination indicates that the partially-adaptive scheme, in which only the codeword rate RB varies with the instantaneous channel gains, significantly outperforms the on-off scheme, in which both RB and RE vary. This performance gain can be characterized in terms of a higher average secrecy rate, subject to an upper bound on the secrecy outage probability. Furthermore, our results also demonstrate that the partially-adaptive scheme can achieve almost the same secrecy performance as the fully-adaptive scheme, which is of a much higher complexity, where ϕ, RB, and RE all vary with the instantaneous channel gains