Passive Self-Interference Suppression for Full-Duplex Infrastructure Nodes

TL;DR

This paper investigates the effectiveness and limitations of passive self-interference suppression techniques in full-duplex wireless nodes through measurement-based analysis, highlighting environmental impacts and design implications.

Contribution

It provides a comprehensive measurement-based analysis of passive suppression methods and their limitations, informing better design of full-duplex wireless infrastructure.

Findings

Passive suppression can achieve over 70 dB in certain environments.

Environmental reflections significantly limit passive suppression.

Passive suppression increases the frequency selectivity of residual interference.

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.