Enhancing Physical Layer Security of DF Buffer-Aided Relay Networks With Small Buffer Sizes

In this paper, we propose a novel max-weight secure link selection (MWSLS) scheme to enhance physical layer security of decode-and-forward (DF) buffer-aided relay networks. The MWSLS scheme can select the link with the largest weight among all secure and available source-to-relay and relayto-destination links. By modeling the dynamic buffer state transitions as a Markov chain, we derive the closed-form expressions of the secrecy outage probability, the secrecy diversity gain, the average secrecy throughput and the end to end delay, which provide a comprehensive and effective way to evaluate the impacts of different parameters on the secrecy performance. The results of this paper reveal that: 1) For the case with small buffer sizes, a significant enhancement on the secrecy outage performance can be observed compared with the popular max-link secure link selection (MLSLS) scheme. 2) When L ≥ 3, the secrecy diversity gain of the system can achieve 2M, while the MLSLS scheme achieves the same secrecy diversity gain only when L → ∞ (where M denotes the number of relays and L is the buffer size). 3) The MWSLS scheme outperforms the MLSLS scheme in terms of the average secrecy throughput and the end to end delay in the low signal-to-noise ratio (SNR) regime, and obtain the same performance as the latter in the high SNR regime.