Two physical-layer mechanisms for achieving user-side differential privacy in communication systems are proposed. Focusing on binary phase-shift keying (BPSK) modulation, differential privacy (DP) is first studied under a deterministic phase rotation applied on the BPSK modulation at the transmitter, while the receiver is assumed to be unaware of the rotation angle. In this setting, privacy is achieved through an effective reduction in the decision distance, resulting in a controlled increase in the bit error rate (BER) without explicit noise injection. Next, a BPSK transmission scheme with intentionally induced inter-symbol interference (ISI) is studied, where the receiver is likewise unaware of the deterministic timing offset that generates the ISI. Unlike the rotated BPSK scheme, the DP obtained via ISI is shown to depend explicitly on the input data distribution. In particular, numerical results demonstrate that, for a fixed ISI parameter, the privacy loss is maximized when the binary input symbols are equiprobable. While conventional DP mechanisms rely on artificially added noise, often incurring additional energy or communication costs, it is shown that structured modifications, such as modulation rotation or induced ISI inherent to realistic communication channels can itself provide DP guarantees. While the analysis focuses on deterministic transmitter modifications unknown to the receiver, it is noted that real-world devices naturally introduce unintentional rotations or ISI due to hardware nonidealities and implementation errors. These effects can therefore provide a level of privacy without requiring explicit noise injection. Hence, it is possible to avoid deliberately perturbing the data, instead leveraging inherent device imperfections to achieve privacy guarantees with no additional privacy cost.

翻译：本文提出了两种在通信系统中实现用户侧差分隐私的物理层机制。首先针对二进制相移键控调制，研究了在发射端对BPSK调制施加确定性相位旋转、而接收端未知旋转角度的场景下的差分隐私特性。在此设置中，隐私保护通过有效缩短判决距离实现，可在不显式注入噪声的情况下，以可控方式提升误码率。其次，研究了通过人为引入符号间干扰的BPSK传输方案，其中接收端同样未知产生ISI的确定性定时偏移。与旋转BPSK方案不同，通过ISI获得的DP被证明显式依赖于输入数据分布。数值结果表明，在固定ISI参数下，当二进制输入符号等概率出现时隐私损失达到最大。传统DP机制依赖于人为添加噪声，通常会产生额外的能量或通信开销，而本研究表明：诸如调制旋转或实际通信信道固有的符号间干扰等结构化修改，其本身即可提供DP保障。虽然分析聚焦于接收端未知的确定性发射端修改，但需注意现实设备因硬件非理想性和实现误差会自然引入非故意的旋转或ISI。因此，这些效应可在无需显式噪声注入的情况下提供一定程度的隐私保护。这意味着有可能避免刻意扰动数据，转而利用设备固有的非理想特性来实现隐私保障，且不产生额外的隐私成本。