Protecting Human Activity Signatures in Compressed IEEE 802.11 CSI Feedback
For wireless network users, this work provides a standards-compatible method to protect location and activity privacy from eavesdroppers exploiting CSI feedback.
The paper addresses the privacy leakage of human activity signatures from compressed IEEE 802.11 CSI feedback and proposes a differentially private quantization mechanism that achieves ε-DP with minimal beamforming performance loss.
Explicit channel state information (CSI) feedback in IEEE~802.11 conveys \emph{transmit beamforming directions} by reporting quantized Givens rotation and phase angles that parametrize the right-singular subspace of the channel matrix. Because these angles encode fine-grained spatial signatures of the propagation environment, recent work have shown that plaintext CSI feedback can inadvertently reveal user activity, identity, and location to passive eavesdroppers. In this work, we introduce a standards-compatible \emph{differentially private (DP) quantization mechanism} that replaces deterministic angular quantization with an $\varepsilon$-DP stochastic quantizer applied directly to the Givens parameters of the transmit beamforming matrix. The mechanism preserves the 802.11 feedback structure, admits closed-form sensitivity bounds for the angular representation, and enables principled privacy calibration. Numerical simulations demonstrate strong privacy guarantees with minimal degradation in beamforming performance.