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RFI Detection and Identification at OVRO Using Pseudonymetry

Meles Weldegebriel, Zihan Li, Greg Hellbourg, Ning Zhang, Neal Patwari

TL;DR

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, suggesting that observatories can support lightweight accountability mechanisms that complement dynamic protection and enforcement-oriented spectrum sharing frameworks.

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.

RFI Detection and Identification at OVRO Using Pseudonymetry

TL;DR

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, suggesting that observatories can support lightweight accountability mechanisms that complement dynamic protection and enforcement-oriented spectrum sharing frameworks.

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.

Paper Structure

This paper contains 29 sections, 3 equations, 5 figures, 1 table, 1 algorithm.

Table of Contents

  1. Introduction
  2. Background and Related Work
  3. RFI mitigation in radio astronomy
  4. Protection criteria and low-SNR interference
  5. Coexistence and dynamic protection
  6. Machine learning for RFI detection
  7. Pseudonymetry for cooperative accountability
  8. Positioning of this work
  9. OVRO Field Trial: System Overview and Design Goals
  10. Experiment motivation
  11. System overview
  12. Design goals
  13. Design rationale for OVRO backend
  14. Pseudonym Watermark Design for Spectrogram-Based Identification
  15. PN-based coded modulation
  16. ...and 14 more sections

Figures (5)

  • Figure 1: Field trial setup at OVRO. (1) USRP B210 with laptop control, (2) Bicolog 20300 transmit antenna, (3) DSA-110 receiving antenna.
  • Figure 2: Example watermark code $Q_p(t)$ over one pseudonym-bit duration using CPAM, where a length-15 maximum-length PN chip pattern is mapped to two power levels (e.g., $1+\alpha$ and $1-\alpha$). Adapted from Meles2025StopSec.
  • Figure 3: Transmitted pseudonym power pattern (red dashed) and measured received power pattern (blue solid) at OVRO/DSA.
  • Figure 4: Spectrogram examples at two SNR levels.
  • Figure 5: Probability of pseudonym bit error versus SNR for OVRO field trial.