This paper considers secure communication in buffer-aided cooperative wireless networks in the presence of one eavesdropper, which can intercept the data transmission from both the source and relay nodes. It is assumed that the relays employ the randomize-and-forward (RF) strategy such that the eavesdropper can only decode the signals received in the two hops independently. Two cooperative secure transmission schemes, i.e., hybrid imitating full-duplex max-max-ratio relay selection (HyIFD) scheme and threshold-based link selection (TBLS) scheme are proposed for adaptive- and fixed-rate transmissions aiming at improving the secrecy throughput and secrecy outage probability, respectively. For adaptive-rate transmissions (ART), the proposed scheme switches among three sub-strategies according to different conditions such as the number of relays and transmit power. Different relays are chosen for reception and transmission according to the ratio of the legitimate channels to the eavesdropper channels to imitate the full-duplex transmission mode. For fixed-rate transmissions (FRT), a hybrid HD/FD transmission mode is designed to increase the transmission probabilities of two hops under the transmission quality constraint. Two parameters are introduced and optimized to minimize the secrecy outage probability. A sub-optimal TBLS (SO-TBLS) scheme is also given. Theoretical analysis of the secrecy throughput and the secrecy outage probability are provided and the closed-form expressions are derived, and verified by numerical results. It is shown that the proposed schemes outperform benchmark schemes in terms of secrecy throughput and secrecy outage probability.

本文考虑了在存在一个窃听者的情况下缓冲辅助协作无线网络中的安全通信，该窃听者可以拦截来自源节点和中继节点的数据传输。假设中继采用随机转发 (RF) 策略，使得窃听者只能独立解码在两跳中接收到的信号。针对自适应和固定速率传输，提出了两种协同安全传输方案，即混合模拟全双工最大最大比中继选择（HyIFD）方案和基于阈值的链路选择（TBLS）方案，旨在提高保密吞吐量。和保密中断概率，分别。对于自适应速率传输 (ART)，所提出的方案根据中继数量和发射功率等不同条件在三个子策略之间切换。根据合法信道与窃听信道的比例选择不同的中继进行接收和传输，模拟全双工传输方式。对于固定速率传输(FRT)，设计了HD/FD混合传输模式，在传输质量约束下增加两跳的传输概率。引入并优化了两个参数以最小化保密中断概率。还给出了一种次优的 TBLS (SO-TBLS) 方案。对保密吞吐量和保密中断概率进行了理论分析，推导了闭式表达式，并通过数值结果进行了验证。