This letter proposes a secure orthogonal frequency division multiplexing (OFDM) waveform based on two physical-layer secrecy enhancing methods. The first method is time-domain pre-coding that involves interleaving and scaling based on a key shared between two legitimate parties adopting the OFDM waveform. The second method is a random change of the cyclic prefix (CP) size resulting in the randomization of the OFDM symbol time. The CP size is also changed based on a key agreed upon between the legitimate parties. The proposed methods not only increase the detection complexity at the eavesdropping node, but also suppress any cyclic features that distinguish OFDM waveforms. The evaluation of the proposed methods is carried out by deriving a closed-form expression for the ergodic secrecy rate of the system. Then, the effect of pre-coding on the quality-of-service performance is analyzed. The proposed methods achieve a considerable secrecy performance gain when proper equalization is implemented at the legitimate receiver.

中文翻译：

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具有增强的物理层安全性的新型OFDM波形

这封信提出了一种基于两种物理层保密增强方法的安全正交频分复用（OFDM）波形。第一种方法是时域预编码，涉及基于采用OFDM波形的两个合法方之间共享的密钥进行交织和缩放。第二种方法是循环前缀（CP）大小的随机变化，从而导致OFDM符号时间的随机化。CP的大小也会根据合法方之间商定的密钥进行更改。所提出的方法不仅增加了在窃听节点处的检测复杂度，而且还抑制了区分OFDM波形的任何循环特征。通过推导系统遍历保密率的闭式表达式，可以对所提出的方法进行评估。然后，分析了预编码对服务质量性能的影响。当在合法接收器处实现适当的均衡时，所提出的方法可实现相当可观的保密性能增益。