This study proposes a scheme to realise secure orthogonal frequency-division multiplexing (OFDM) wireless communication between two full duplex nodes—node A and node B. If node A wants to send secret messages to node B, node A and node B transmit the training signal to each other to acquire channel state information (CSI) in the first time frame. Node A acquires the phases of the received signal from node B (no need to decode). In the second time frame, node A then sends secret messages to node B with the phases of the modulated signal being added to the random phases of the signal from node B in the previous time frame, i.e node A relaying the phases of the signal from node B. Node B can recover the secret messages from node A, but eavesdroppers cannot because they do not know the CSI of the main channel. The secrecy capacity is irrelevant to the CSI of the eavesdropper channel, which is a big advantage over other schemes. The scheme can guarantee secrecy capacity to be positive in all circumstances and work well for single-input single-output systems. A computation efficient algorithm is presented to optimally allocate power over sub-carriers for secrecy capacity maximisation.

中文翻译：

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基于合法节点之间的相位中继的安全全双工OFDM无线通信

本研究提出了一种在两个全双工节点（节点A和节点B）之间实现安全的正交频分复用（OFDM）无线通信的方案。如果节点A要向节点B发送秘密消息，则节点A和节点B会发送训练信息在第一时间帧中相互发送信号以获取信道状态信息（CSI）。节点A从节点B获取接收信号的相位（无需解码）。然后在第二个时间帧中，节点A向节点B发送秘密消息，并将调制信号的相位添加到前一个时间帧中来自节点B的信号的随机相位中，即，节点A中继来自以下节点的信号相位节点B可以从节点A恢复秘密消息，但是窃听者无法进行，因为他们不知道主信道的CSI。保密能力与窃听通道的CSI无关，这是相对于其他方案的一大优势。该方案可以确保保密能力在所有情况下都为正，并且对于单输入单输出系统很好地起作用。提出了一种计算有效的算法，可在子载波上最优分配功率，以实现保密容量的最大化。