RFI Detection and Identification at OVRO Using Pseudonymetry

TL;DR

This paper demonstrates a novel passive watermarking technique called Pseudonymetry for radio-frequency interference detection at OVRO, enabling transmitter attribution at low SNR without requiring direct demodulation.

Contribution

It introduces a new spectrogram-only watermark decoding method for passive RFI attribution, validated through real-world field tests at OVRO.

Findings

Watermarks recovered at SNR as low as -20 dB.

Passive backend measurements suffice for transmitter attribution.

Supports accountable coexistence in radio astronomy environments.

Abstract

Protecting passive radio astronomy observatories from unintended radio-frequency interference (RFI) is increasingly challenging as wireless activity expands near protected bands. While radio quiet zones, database-driven coordination, and post-processing mitigation can reduce interference risk, they often lack the ability to attribute detected RFI to a specific transmitter, particularly in low signal-to-noise ratio (SNR) regimes where conventional demodulation is infeasible. This paper presents the first over-the-air field demonstration of Pseudonymetry at the Owens Valley Radio Observatory (OVRO), evaluating an accountable coexistence approach between heterogeneous systems: an SDR-based narrowband OFDM transmitter and a wideband radio telescope backend. The transmitter embeds a pseudonym watermark on a dedicated OFDM subcarrier using coded power modulation, while OVRO passively extracts the watermark from standard backend spectrogram (power) products without IQ access. We develop a spectrogram-only receiver that performs correlation-based packet alignment, compensates timing resolution mismatch via resampling, and decodes pseudonym bits using energy-domain template matching. Field results across -20 to -5 dB SNR show that pseudonym watermarks can be recovered at low SNR, enabling practical transmitter attribution using only passive backend measurements. These findings suggest that observatories can support lightweight accountability mechanisms that complement dynamic protection and enforcement-oriented spectrum sharing frameworks.