When wireless communication signals impinge on a moving human they are affected by micro-Doppler. A passive receiver of the resulting signals can calculate the spectrogram that produces different signatures depending on the human activity. This constitutes a significant privacy breach when the human is unaware of it. This paper presents a methodology for preventing this when we want to do so by injecting into the transmitted signal frequency variations that obfuscate the micro-Doppler signature. We assume a system that uses orthogonal frequency division multiplexing (OFDM) and a passive receiver that estimates the spectrogram based on the instantaneous channel state information (CSI). We analyze the impact of our approach on the received signal and we propose two strategies that do not affect the demodulation of the digital communication signal at the intended receiver. To evaluate the performance of our approach we use an IEEE 802.11-based OFDM system and realistic human signal reflection models.

翻译：当无线通信信号照射到运动的人体时，会产生微多普勒效应。无源接收器可通过计算得到的频谱图，根据人体活动模式生成不同的特征。当人体对此毫不知情时，这构成了严重的隐私侵犯。本文提出一种在需要时主动阻止此类隐私泄露的方法：通过向发射信号中注入特定频率变化，从而混淆微多普勒特征。我们假设系统采用正交频分复用（OFDM）技术，无源接收器基于瞬时信道状态信息（CSI）估计频谱图。我们分析了该方法对接收信号的影响，并提出了两种不影响预期接收端数字通信信号解调的策略。为评估方法性能，我们使用基于IEEE 802.11的OFDM系统及真实人体信号反射模型进行实验验证。