Tags Helping Tags: Coordination-Free Power Boosting for Battery-less Backscatter Networks

Abstract

Battery-less backscatter sensor nodes powered by radio-frequency wireless power transfer are attractive for large or hard-to-reach deployments, but their range is typically limited by the forward power-transfer link rather than by communication sensitivity. We present a method for improving power delivery, and thus range, in dense tag deployments by having nearby tags act as helpers: each helper terminates its antenna in purely reactive impedances, reflecting the power beacon's signal toward a target tag so that it combines constructively with the direct line-of-sight path and increases the power the target harvests. On a hardware testbed, helpers using discrete impedance control are shown to increase the target tag's harvested power by over 50% above an all-absorbing baseline, while randomly set helper impedances give no reliable benefit, and are sometimes even detrimental. We further propose and implement a local algorithm that lets each helper tune its own impedance using only measurements of the target's packet rate, without channel estimation or coordination between helpers, and we show that it brings the target's packet rate close to that of an independently tuned configuration. These results suggest that independent, passive sensor nodes can cooperatively extend each other's power-transfer range with minimal added infrastructure.