Physical-layer secret key generation (PSKG) stands as a promising privacy protection technique, establishing shared encryption keys through the analysis of highly correlated wireless channel measurements. This approach relies on exploiting reciprocal channel characteristics between uplink and downlink transmissions. Nonetheless, the distinct carrier frequencies employed for uplink and downlink in frequency-division duplexing (FDD) systems pose a challenge in identifying common features. This paper presents a novel approach that exploits the inherent reciprocity between scattering parameters of passive two-port networks within same frequency ranges to overcome this obstacle. By capitalizing this reciprocity and considering closely situated FDD bands, a seamless continuity is anticipated in phase differences extracted form the corresponding S-parameters, between neighboring antennas of an antenna array from both uplink and downlink directions. This continuity, thereby ensures consistency in the generated keys from both transmission ends. Furthermore, a two-stage pre-processing method is proposed to enhance performance effectively. Additionally, the paper suggests the utilization of polynomial curve-fitting through measurement data to improve reciprocity and proposes a non-linear framework for quantizing the merging points of the two FDD bands. A statistical analysis employing multiple linear regression is provided to determine the error probability associated with the generated keys. Empirical results validate the feasibility and effectiveness of the proposed key generation scheme, affirming its attributes in terms of randomness, efficiency, key distribution uniformity, and key disagreement ratio (KDR).

中文翻译：

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FDD 系统的成对物理层密钥生成


物理层密钥生成 （PSKG） 是一种很有前途的隐私保护技术，它通过分析高度相关的无线信道测量来建立共享加密密钥。这种方法依赖于利用上行链路和下行链路传输之间的互易信道特性。尽管如此，在频分双工 （FDD） 系统中，上行链路和下行链路采用的不同载波频率对识别共同特征构成了挑战。本文提出了一种新方法，利用相同频率范围内无源双端口网络散射参数之间的固有互易性来克服这一障碍。通过利用这种互易性并考虑紧密定位的 FDD 频段，预计从天线阵列的相邻天线之间从上行链路和下行链路方向提取的相应 S 参数中提取的相位差将无缝连续。这种连续性，从而确保了从两个传输端生成的密钥的一致性。此外，提出了一种两阶段预处理方法以有效提高性能。此外，本文还建议通过测量数据利用多项式曲线拟合来提高互易性，并提出了一个非线性框架来量化两个 FDD 波段的合并点。提供了采用多元线性回归的统计分析，以确定与生成的键相关的错误概率。实证结果验证了所提出的密钥生成方案的可行性和有效性，肯定了其在随机性、效率、密钥分发均匀性和密钥不一致率 （KDR） 方面的属性。