Tag-to-Tag Range Estimation for Passive Backscattering Tags

Passive tag-to-tag backscatter networks consist of battery-free RF tags that communicate directly with one another by reflecting an external RF signal. This architecture differs from traditional systems, such as RFID, by eliminating the need for expensive active readers and enabling direct tag-to-tag links. However, the passive nature of these tags makes measuring the distance between them (ranging) a non-trivial challenge. Accurate ranging is critical for leveraging the dense web of tag connections in downstream applications, most notably localization. This poster paper proposes a technique for passive tag-to-tag ranging using the Frequency Domain Phase Difference of Arrival (FD-PDoA) method. In multipath-rich indoor environments, the proposed method achieves a median ranging error of ≈7cm for inter-tag distances up to 2 meters.