This work considers a time-varying Rayleigh block fading broadcast channel formed by two users and an eavesdropper, external to the legitimate network. One of the users is the legitimate/trusted user and the other an untrusted user. The transmitter uses superposition coding to broadcast information to both users. The aim is to ensure the confidentiality of the legitimate user information against the untrusted user and eavesdropper. To satisfy these secrecy constraints, this work proposes an innovative secure channel-training method applied to a cooperative jamming scenario. The jammer uses interference alignment to achieve secrecy against the untrusted user; meanwhile, the developed channel-training method is designed exploiting the time-varying nature of the channel to extend the system secrecy also to the external eavesdropper. An information theoretical evaluation of the proposed scheme demonstrates that (1/4, 1/4) positive secure degrees of freedom are achievable in the presence of both untrusted users and external eavesdroppers.

中文翻译：

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一种利用信道训练阶段实现衰落广播信道保密的方法

这项工作考虑了一个由两个用户和一个窃听者形成的时变瑞利块衰落广播信道，该信道位于合法网络之外。其中一个用户是合法/受信任的用户，另一个是不受信任的用户。发射机使用叠加编码向两个用户广播信息。目的是确保合法用户信息对不受信任的用户和窃听者的保密性。为了满足这些保密约束，这项工作提出了一种应用于协作干扰场景的创新安全信道训练方法。干扰器使用干扰对齐来实现对不受信任用户的保密；同时，开发的信道训练方法旨在利用信道的时变特性，将系统保密性也扩展到外部窃听者。