CSI Obfuscation: Single-Antenna Transmitters Can Not Hide from Adversarial Multi-Antenna Radio Localization Systems

TL;DR

This paper demonstrates that single-antenna transmitters cannot prevent multi-antenna adversaries from localizing signals, even when using obfuscation techniques, highlighting a significant privacy vulnerability in radio localization systems.

Contribution

It introduces a simple CSI recovery method for multi-antenna receivers that can bypass obfuscation, revealing limitations of current privacy-preserving strategies.

Findings

Obfuscation ineffective against multi-antenna localization

CSI recovery enables reliable user localization despite obfuscation

Multi-antenna systems pose privacy risks for single-antenna transmitters

Abstract

The ability of modern telecommunication systems to locate users and objects in the radio environment raises justified privacy concerns. To prevent unauthorized localization, single-antenna transmitters can obfuscate the signal by convolving it with a randomized sequence prior to transmission, which alters the channel state information (CSI) estimated at the receiver. However, this strategy is only effective against CSI-based localization systems deploying single-antenna receivers. Inspired by the concept of blind multichannel identification, we propose a simple CSI recovery method for multi-antenna receivers to extract channel features that ensure reliable user localization regardless of the transmitted signal. We comparatively evaluate the impact of signal obfuscation and the proposed recovery method on the localization performance of CSI fingerprinting, channel charting, and classical triangulation using real-world channel measurements. This work aims to demonstrate the necessity for further efforts to protect the location privacy of users from adversarial radio-based localization systems.