The capability of exploiting Orthogonal Space-Time Block Codes (OSTBC) for increasing physical layer security of wireless systems is studied. A technique named “hidden OSTBC” is introduced, in which, a pseudorandom sequence is utilized by both transmitter and legitimate receiver to provide required security. Traditionally, employing pseudorandom sequences with methods such as spread spectrum or cooperative jamming involves huge amount of bandwidth or transmission power constraints, which are major challenges for wireless systems. Without requiring additional power or bandwidth, this study is designed to address exploitation of a pseudorandom antipodal sequence as a precoder. Elements of this sequence are multiplied to each antenna’s transmitting symbol, and legitimate receiver employs the same sequence upon its combining rule. Mathematical analysis and simulations prove that an eavesdropper who does not know the pseudorandom sequence suffers from a degraded equivalent channel. Security enhancement is studied by investigating eavesdropper’s higher error rate compared with that of legitimate receiver. Also, by employing lattice-based codebooks, a lower-bound is drawn for secrecy capacity, implying the achievability of nearly perfect secrecy regarding information theoretic analysis.

中文翻译：

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通过使用伪随机预编码器增强物理层安全性的隐藏 OSTBC 方案

研究了利用正交空时分组码（OSTBC）提高无线系统物理层安全性的能力。引入了一种名为“隐藏 OSTBC”的技术，其中，发射器和合法接收器都使用伪随机序列来提供所需的安全性。传统上，通过扩频或协作干扰等方法使用伪随机序列涉及大量带宽或传输功率限制，这是无线系统面临的主要挑战。无需额外的功率或带宽，本研究旨在解决利用伪随机对映序列作为预编码器的问题。该序列的元素与每个天线的发射符号相乘，合法接收器根据其组合规则使用相同的序列。数学分析和仿真证明，不知道伪随机序列的窃听者会遭受等效信道退化。通过调查窃听者与合法接收者相比更高的错误率来研究安全性增强。此外，通过采用基于格的码本，为保密能力绘制了一个下限，这意味着关于信息理论分析的近乎完美的保密是可实现的。