rfi mitigation and burst detection with a digital receiver
TRANSCRIPT
RFI Mitigation and Burst Detectionwith a Digital Receiver
RFI2004July 16 - 18, 2004
Cedric Dumez-Viou1,4, Andrée Coffre4,Pierre Colom2,Laurent Denis4, Alain Lecacheux2, Jean-Michel Martin3,
Philippe Ravier1, Rodolphe Weber1, Philippe Zarka2
1 LESI, Polytech'Orleans - Université d'Orléans 2 LESIA, Observatoire de Paris/CNRS3 GEPI, Observatoire de Paris/CNRS4 Station de Radioastronomie de Nançay
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RSR: Radio Spectrum Reconquest
● High dynamic receiver ( > 70dB )
● Highly reconfigurable
● for multipurpose use2
RSR: Radio Spectrum Reconquest
● High dynamic receiver ( > 70dB )
● Highly reconfigurable
● for multipurpose use3
Current implementations
● Sigma detectors forTime-Frequency Blanking
● T-FDMA RFI mitigation● Wideband RFI mitigation
● Fine Structures
● Future works...4
Given constraints
● Implementation of basic methods to be used today.
● RFIs detection based on power estimation.
● Real-time algorithms.- Only a small part of the signal is available.- Limited data-flow.
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Blanking of T-FDMA modulation:principle
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Blanking of T-FDMA modulation:principle
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Blanking of T-FDMA modulation:principle
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Blanking of T-FDMA modulation:principle
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Original Data
Frequency
Time
Blanking of T-FDMA modulation:principle
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Original Data
Frequency
Time
Blanking of T-FDMA modulation:principle
Full Spectrum Blanking
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Original Data
Frequency
Time
Blanking of T-FDMA modulation:principle
Time-frequency
Block blanking
Full Spectrum Blanking
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Blanking of T-FDMA modulation:method
● T-FDMA are narrow band signals--> efficient mean and variance estimate
using median filtering or robust mean.
● Full spectrum blanking:- 20% loss of data.- Excellent rejection of RFI.
● Time-frequency Block blanking:- 2.5% loss of data.- Unequal equivalent time of integration.
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Blanking of T-FDMA modulation:IIIZw35 OH megamazer results
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Blanking of Wideband RFIs:principle
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Blanking of Wideband RFIs:principle
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Blanking of Wideband RFIs:principle
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● Lightnings, Radars, ...● Occupy the full band or most of it.– Median filtering not applicable.– Estimation of mean and variance compromised.
Blanking of Wideband RFIsmethod
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● Lightnings, Radars, ...● Occupy the full band or most of it.– Median filtering not applicable.– Estimation of mean and variance compromised.
Blanking of Wideband RFIsmethod
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● Lightnings, Radars, ...● Occupy the full band or most of it.– Median filtering not applicable.– Estimation of mean and variance compromised.
Blanking of Wideband RFIsmethod
● Lightnings, Radars, ...● Occupy the full band or most of it.– Median filtering not applicable.– Estimation of mean and variance compromised
● Wideband BUT not continuous in time.– Some spectrum are free of RFIs– Time averaging to find clean spectrum
Blanking of Wideband RFIsmethod
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Blanking of Wideband RFIsresults
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● Blanking simulation on real data.● Current results allow 10 minutes of
integration without signs of RFIs.● Further testes needed to evaluate RFI
rejection.
Blanking of Wideband RFIsresults
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Fines Structures:principle
● Solar and Jovian radio-emissions● Very brief « Chirps » (~100ms).
● High frequency and time resolutionrequired to understand the underlying physics
● High volume of data (50Go/h)--> Backup of interesting events only.
● Automatic recorder✔ Detection of RFI-like SOIs,✔ Corrupted by RFIs (frequency lines and wide-band signals),✔ With real-time constraints.
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Fines Structures: method
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Fines Structures: results
More advanced methods for the future...
● Encouraging results for real-time RFI mitigation.● Should work shortly for daily-use observation.● Classifier (SVM, neural networks, expert systems,...).
– Automatic determination of RFIs characteristics.– Selection of the appropriate parameters for blanking.
● Implementation of cyclostationary detector.– Highlight hidden periodicities of signals.– Present in telecommunications.– Absent in most natural signals.
www.obs-nancay.fr/rfi27
More advanced methods for the future...
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