Poster Abstract: Suppressing CSI Leakage in Multi-user MIMO Networks via Precoding

In multi-user MIMO (MU-MIMO) systems using zero-forcing beamforming (ZFBF), an Access Point (AP) utilizes downlink channel state information (CSI) to transmit data streams to multiple clients simultaneously. Since private information of clients can be extracted from CSI, leaking CSI to attackers is considered as harmful so that some research efforts suggest to encrypt CSI feedback. However, a recent study shows that an attacker can infer CSI by eavesdropping data streams with known symbols, not the feedback. To this end, we propose CSIstray that intentionally increases the proportion of inter-client interference to suppress CSI leakage while maintaining bit error rates (BERs) at the clients. Simulation results with a 2×2 MU-MIMO scenario show that CSIstray effectively degrades the attack performance with little impact on downlink transmission. We further implement CSIstray on our testbed to validate the proposed mechanism works properly in a room-scale environment as well as in simulation results.