Passive Self-Interference Suppression for Full-Duplex Infrastructure Nodes

TLDR

Full‑duplex wireless communication is feasible for short‑range links, yet most self‑interference suppression arises from passive isolation of transmit and receive antennas rather than active cancellation. The study investigates the capabilities and limitations of directional isolation, absorptive shielding, and cross‑polarization for passive self‑interference suppression. The authors conducted measurement‑based experiments evaluating directional isolation, absorptive shielding, and cross‑polarization as passive suppression techniques. More than 70 dB of passive suppression is achievable in some environments, but environmental reflections limit the maximum suppression and increase frequency selectivity, so deployments should minimize near‑antenna reflectors and combine passive suppression with higher‑order or per‑subcarrier active cancellation.

Abstract

Recent research results have demonstrated the feasibility of full-duplex wireless communication for short-range links. Although the focus of the previous works has been active cancellation of the self-interference signal, a majority of the overall self-interference suppression is often due to passive suppression, i.e., isolation of the transmit and receive antennas. We present a measurement-based study of the capabilities and limitations of three key mechanisms for passive self-interference suppression: directional isolation, absorptive shielding, and cross-polarization. The study demonstrates that more than 70 dB of passive suppression can be achieved in certain environments, but also establishes two results on the limitations of passive suppression: (1) environmental reflections limit the amount of passive suppression that can be achieved, and (2) passive suppression, in general, increases the frequency selectivity of the residual self-interference signal. These results suggest two design implications: (1) deployments of full-duplex infrastructure nodes should minimize near-antenna reflectors, and (2) active cancellation in concatenation with passive suppression should employ higher-order filters or per-subcarrier cancellation.