Covert wireless communication ensures information security by hiding the existence of the information transmission itself. Available works mainly focused on the covert throughput study of one-hop wireless communications, while the performance limit of covert throughput in important two-way two-hop scenarios remains largely unknown. As the most significant contribution, this paper, for the first time, investigates such performance limit in a system where two sources wish to covertly exchange information through a relay against the detection of a warden, i.e., a malicious node that attempts to detect the existence of communication between the two sources. As the second contribution, this paper considers various scenarios regarding the warden’s prior knowledge about the relay, the sources/relay’s prior knowledge about the warden, as well as different relaying patterns, and then proposes a covertness strategy to resist the warden’s detection for each scenario. As the last contribution, we derive the scaling law result for the covert throughput of the system for each scenario, i.e., the maximum number of bits that the two sources can exchange subject to a constraint on the detection probability of the warden. The results in this paper indicate that the covert throughput of the concerned system follows the well-known square root scaling law, which is independent of the relaying patterns, detection schemes, covertness strategies, and prior knowledges of the sources/relay and warden.

隐蔽的无线通信通过隐藏信息传输本身的存在来确保信息安全。可用的工作主要集中在单跳无线通信的隐式吞吐量研究上，而在重要的双向两跳场景中，隐式吞吐量的性能极限仍然未知。作为最重要的贡献，本文首次研究了系统中的这种性能限制，在该系统中，两个来源希望通过中继秘密地交换信息，而不是检测看守，即试图检测存在的恶意节点两种来源之间的交流。作为第二点贡献，本文考虑了有关看守关于继电器的先验知识，信源/继电器关于看守的先验知识的各种场景，以及不同的中继模式，然后提出一种隐蔽策略，以抵御每个场景的看守的发现。作为最后的贡献，我们针对每种情况得出系统隐蔽吞吐量的缩放定律结果，即，两个源可以交换的最大位数受守望者检测概率的约束。本文的结果表明，相关系统的隐蔽吞吐量遵循众所周知的平方根缩放定律，而独立于中继模式，检测方案，隐蔽策略以及源/中继和管理员的先验知识。我们针对每种情况得出系统隐蔽吞吐量的缩放定律结果，即，两个源可以交换的最大位数受守望者检测概率的约束。本文的结果表明，相关系统的隐蔽吞吐量遵循众所周知的平方根缩放定律，而独立于中继模式，检测方案，隐蔽策略以及源/中继和管理员的先验知识。我们针对每种情况得出系统隐蔽吞吐量的缩放定律结果，即，两个源可以交换的最大位数受守望者检测概率的约束。本文的结果表明，相关系统的隐蔽吞吐量遵循众所周知的平方根缩放定律，而独立于中继模式，检测方案，隐蔽策略以及源/中继和管理员的先验知识。