Less is More: The Dilution Effect in Multi-Link Wireless Sensing

TL;DR

This study reveals that in wireless sensing, fewer strategically placed links outperform dense sensor networks due to a dilution effect where unnecessary links add noise, emphasizing the importance of link placement over quantity.

Contribution

The paper demonstrates that a single well-placed link can outperform dense sensor deployments in wireless sensing, highlighting the significance of strategic placement over quantity.

Findings

Single well-placed link outperforms dense mesh

Random link selection matches optimized selection

Link placement is 2.7 times more impactful than classifier choice

Abstract

Wireless sensing approaches promise to transform smart infrastructures into privacy-preserving motion detectors, yet commercial adoption remains limited. A common assumption may explain this gap: that denser sensor deployments yield better accuracy. We tested this assumption with a 12-day naturalistic study using a 9-node ESP32-C3 mesh (72 sensing links) in a residential environment. Our results show that a single well-placed link outperformed the full 72-link mesh (AUC 0.541 vs. 0.489, Cohen's $d$=0.86). Even a random link selection matched optimized selection ($p$=0.35). The benefit comes from avoiding multi-link fusion, not from choosing the right link. We attribute this to a "dilution effect": links whose Fresnel zones miss activity regions contribute noise that overwhelms signal from informative links. In our deployment, strategic link placement mattered 2.7$\times$ more than classifier choice. We release 312 hours of labeled CSI data, firmware, and analysis code to enable validation across diverse environments.