An SDR-Based Monostatic Wi-Fi System with Analog Self-Interference Cancellation for Sensing

TL;DR

This paper introduces a monostatic Wi-Fi sensing system with analog self-interference cancellation that enables contactless vital sign monitoring and detection of small targets at distances up to 10 meters, overcoming phase and interference challenges.

Contribution

The system uses an auxiliary RF chain for effective SI cancellation and reuses cancellation filter weights for sensing, achieving stable performance without frequent fine-tuning.

Findings

Achieves 40 dB SI cancellation comparable to custom hardware

Stable cancellation over 30 minutes in real environments

Detects small, slow-moving targets up to 10 meters away

Abstract

Wireless sensing offers an alternative to wearables for contactless monitoring of human activity and vital signs. However, most existing systems use bistatic setups, which suffer from phase imperfections due to unsynchronized clocks. Monostatic systems overcome this issue, but are hindered by strong self-interference (SI) that require effective cancellation. We present a monostatic Wi-Fi sensing system that uses an auxiliary transmit RF chain to achieve SI cancellation levels of 40 dB, comparable to existing solutions with custom cancellation hardware. We demonstrate that the cancellation filter weights, fine-tuned using least-mean squares, can be directly repurposed for target sensing. Moreover, we achieve stable SI cancellation over 30 minutes in an office environment without fine-tuning, enabling traditional vital sign monitoring using channel estimates derived from baseband samples without the adaptation of the cancellation affecting the sensing channel -- a significant limitation in prior work. Experimental results confirm the detection of small, slow-moving targets, representative for breathing chest movements, at distances up to 10 meters in non-line-of-sight conditions.