Recent advances in antenna design and interference cancellation algorithms for in-band full duplex relays

TLDR

In-band full‑duplex relays transmit and receive simultaneously at the same frequency, boosting spectral efficiency, but require effective self‑interference mitigation. The article proposes new antenna designs and digital self‑interference cancellation techniques for compact MIMO full‑duplex relays intended for low‑cost local‑area‑network deployments. The solution employs resonant wavetrap antennas delivering 60–70 dB passive isolation and advanced nonlinear digital cancellation tailored to power‑amplifier distortion near saturation. Experiments on a complete demonstrator show the combined RF and digital cancellation achieves nearly 100 dB total self‑interference suppression, proving the feasibility of compact full‑duplex MIMO relays.

Abstract

In-band full-duplex relays transmit and receive simultaneously at the same center frequency, hence offering enhanced spectral efficiency for relay deployment. In order to deploy such full-duplex relays, it is necessary to efficiently mitigate the inherent self-interference stemming from the strong transmit signal coupling to the sensitive receive chain. In this article, we present novel state-of-the-art antenna solutions as well as digital self-interference cancellation algorithms for compact MIMO fullduplex relays, specifically targeted for reduced-cost deployments in local area networks. The presented antenna design builds on resonant wavetraps and is shown to provide passive isolations on the order of 60–70 dB. We also discuss and present advanced digital cancellation solutions, beyond classical linear processing, specifically tailored against nonlinear distortion of the power amplifier when operating close to saturation. Measured results from a complete demonstrator system, integrating antennas, RF cancellation, and nonlinear digital cancellation, are also presented, evidencing close to 100 dB of overall self-interference suppression. The reported results indicate that building and deploying compact full-duplex MIMO relays is already technologically feasible.