Trident: Interference Avoidance in Multi-reader Backscatter Network via Frequency-space Division

TL;DR

Trident presents a novel backscatter interference-avoidance approach that leverages frequency-space division to enable concurrent operation of multiple readers with minimal cross-talk. The tag side combines a frequency-band detector, a frequency-selective reflector, and a reflection power adjuster to select a single active band and control reflection strength, while a reader-frequency assignment algorithm minimizes co-channel interference. Experimental results on a PCB/USRP prototype demonstrate up to 3.18× throughput improvement over TDMA, with robust performance under dense reader deployments and non-uniform tag distributions. The work shows practical viability via careful bandpass design, low-power detection, and adaptive load switching, offering a scalable path for large-scale battery-free IoT deployments.

Abstract

Backscatter is a key technology for battery-free sensing in industrial IoT applications. To fully cover numerous tags in the deployment area, one often needs to deploy multiple readers, each of which communicates with tags within its communication range. However, the actual backscattered signals from a tag are likely to reach a reader outside its communication range and cause interference. Conventional TDMA or CSMA based approaches for interference avoidance separate readers' media access in time, leading to limited network throughput. In this paper, we propose TRIDENT, a novel backscatter design that enables interference avoidance via frequency-space division. By incorporating a tunable bandpass filter and multiple terminal loads, a TRIDENT tag can detect its channel condition and adaptively adjust the frequency and the power of its backscattered signals. We further propose a frequency assignment algorithm for the readers. With these designs, all the readers in the network can operate concurrently without being interfered. We implement TRIDENT and evaluate its performance under various settings. The results demonstrate that TRIDENT enhances the network throughput by 3.18x, compared to the TDMA-based scheme.

Figures (18)

• Figure 1: Illustration of interference in the multi-reader backscatter network.
• Figure 2: The three key components of Trident tag.
• Figure 3: The structure of the frequency-tunable bandpass filter.
• Figure 4: Trident tag adjusts the $V_{bias}$ of the varactor diode to change its capacitance, thus tuning the resonator.
• Figure 5: The frequency band detector completes the comparison of signal strengths at two frequency bands through two steps.