Opportunism, Cooperation and Feedback for Wireless Secrecy

高效无线网络的设计提出了激动人心的挑战，这与有线网络中的相应挑战截然不同。特别令人感兴趣的是感知到的无线网络对安全攻击的脆弱性。因此，确保网络对各种安全威胁的健壮性是重要的设计目标之一。该项目采用了一种新的乐观视角，将无线媒体视为一种资源，而不是一种负担。特别是，我们确定了三个原则，即机会主义、合作和反馈，通过这些原则可以有效地利用无线信道来对抗被动窃听攻击。第一个研究重点致力于开发一种机会主义保密框架，在该框架中，利用多径衰落波动为合法目的地(S)创造相对于窃听者(S)的优势。我们的研究试图描述机会主义保密的基本限制，并开发能够利用相应性能收益的低复杂性协议。第二个研究重点是：1)在保密约束的启发下，提出新的协作策略；2)推导出某些情况下中继-窃听信道下的精确保密容量结果；3)识别大规模分层和ad-hocWireless网络中协作保密协议的伸缩行为。最后，第三个重点涉及在无记忆、衰落和多用户信道的背景下，刻画在闭环信道上的安全通信的基本限制和相应的反馈策略的结构。

The design of efficient wireless networks presents exciting challenges which are markedly different from their counterparts in wire-line networks. Of particular interest is the perceived vulnerability of wireless networks to security attacks. Ensuring network robustness against various types of security threats is, therefore, one of the important design objectives.This project adopts a new optimistic perspective in which the wireless medium is viewed as a resource instead of a liability. In particular, we identify three principles, namely opportunism, cooperation and feedback by which the wireless channel can be efficiently exploited to counter passive eavesdropping attacks. The first research thrust is dedicated to developing an opportunistic secrecy framework in which the multi-path fading fluctuations are used to create an advantage for the legitimate destination(s) overthe eavesdropper(s). Our investigations seek to characterize the fundamental limits of opportunistic secrecy and develop low complexity protocols capable of leveraging the corresponding performance gain. The second research thrust aims to: 1) develop novel cooperation strategies inspired by the secrecy constraint, 2)derive sharp secrecy capacity results for certain instances of the relay-eavesdropper channel and 3) identify the scaling behavior of cooperative secrecy protocols in large scale hierarchical and ad-hocwireless networks. Finally, the third thrust involves characterizing the fundamental limits of secure communication over closed loop channels and the structure of the corresponding feedback policies inthe context of memoryless, fading and multi-user channels.