This paper presents further insights into a recently developed round-trip communication scheme called ``Secret-message Transmission by Echoing Encrypted Probes (STEEP)''. A legitimate wireless channel between a multi-antenna user (Alice) and a single-antenna user (Bob) in the presence of a multi-antenna eavesdropper (Eve) is focused on. STEEP does not require full-duplex, channel reciprocity or Eve's channel state information, but is able to yield a positive secrecy rate in bits per channel use between Alice and Bob in every channel coherence period as long as Eve's receive channel is not noiseless. This secrecy rate does not diminish as coherence time increases. Various statistical behaviors of STEEP's secrecy capacity due to random channel fading are also illustrated.

翻译：本文深入探讨了最近提出的一种名为“回声加密探测的秘密消息传输”（STEEP）的往返通信方案。重点关注一个合法无线信道，其中多天线用户（Alice）与单天线用户（Bob）在存在多天线窃听者（Eve）的情况下进行通信。STEEP不需要全双工通信、信道互易性或Eve的信道状态信息，但能在每个信道相干周期内，只要Eve的接收信道并非无噪声，即可在Alice与Bob之间实现每信道使用比特的正保密率。该保密率不会随着相干时间的增加而降低。此外，本文还展示了由于随机信道衰落导致的STEEP保密容量的各种统计特性。