System Approach to RFI Mitigation for the SKA

Rob Millenaar – SKA Program Development Office Albert-Jan Boonstra – ASTRON

Rodolphe Weber – University of Orleans

30 March, 2010 1RFI2010

SPDOOverview

• Introduction– Concepts of the SKA– Receptor technology types– Array layout

• System wide approach to RFI mitigation– the RFI/EMI Environment– EMC– Reduction of susceptibility to RFI– Mitigation in hardware and software

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Introduction

Setting the scene

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SPDOThe Square Kilometre Array

In a nutshell:• The next generation radio telescope with ~50

times sensitivity and ~10,000 times the survey speed of the best current day radio telescopes.

• It will operate from 70 MHz to 10 GHz• Baselines of 3000+ km • Candidate sites:

– Southern Africa, Karoo– Australasia, Boolardy

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SPDOThe Square Kilometre Array

The SKA will have: – up to 3000 dishes, with:

– wide band single pixel feeds– phased array feeds– ~1 GHz (300 MHz) to >10 GHz

– up to 250 dense Aperture Array stations (56m dia), with:– ~70,000 dual pol elements, so ~150,000

receiver chains for a total of ~4 107

– ~400-~1400 MHz

– up to 250 sparse Aperture Array stations (180m dia), with:– ~10,000 dual pol elements, so ~20,000

receiver chains, for a total of ~5 106 – ~70-~450 MHz

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SPDOConfiguration

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SPDOConfiguration

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SPDOThe challenge

• The conclusion should be that:– There will be various types of technology, much of which is concentrated in

high densities risk of strong electromagnetic coupling– With differing frequency ranges what is out-of-band RFI for one is in-band

for the other technology type, so all designs must be done for entire SKA frequency range!

– With extreme required operational sensitivity RQZ and handpicked remote sites, plus further regulation

– Systems and parts should be cheap to produce, to maintain challenges expensive shielding methods

– Requires manageable data rates must limit number of bits to be transported and processed

• This results in a nightmare for EMI and RFI control, the scale of which was never seen before.

• Requires a rigorous system-wide mitigation approach.

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System Wide Mitigation of RFI

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SPDOSystem Wide Approach

What should be done

• Provide best RFI/EMI environment• EMC policy• Reduction of susceptibility to RFI• Mitigation in hardware and software

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SPDOSystem Wide Approach

What should be done

• Provide best RFI/EMI environment• EMC policy• Reduction of susceptibility to RFI• Mitigation in hardware and software

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SPDOEMI/RFI Environment

Provide best RFI/EMI environment• Investigate and select sites• Establish RQZ• Spectrum regulation/law making on local +

national levels + active support of local community

• Once the perfect site is found, place antennas sensibly (Configuration design)

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SPDOSite Selection

• The two shortlisted sites are the best in the preferred region on the globe.

• Further site characterisation is underway• RFI has been measured and will be done again

with higher sensitivity.

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SPDORFI environment at the core

• Site characterisation results of the campaign of 2005 are available.

• Next slide shows ‘mode 1’ results: inventory of strong RFI, potentially detrimental because of receiver linearity.

• Includes high speed sampling results (2μs) from 960 to 1400 MHz.

• Was done for 4 to 6 antenna pointings, two polarisations.• Next slide shows results of two sites combined:

1. Take maximum level of pointings/polarisations per site;2. Plot minima and maxima of the two datasets.

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SPDORFI environment at the core

Mode 1 overall spectrum, 70MHz to 22 GHz

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SPDOUnavoidable RFI

It is evident that, regardless of all measures that we take, receiver systems will have to deal with unavoidable types of RFI:•Airborne

– Comms– Narrow pulse & high power: nav/ATC (DME, SSR, …)

•Satellites– NOAA series– Iridium, GPS, Galileo– Geostationary (broadcasting, FLTSATCOM)– …

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SPDONew RFI Campaign

Purpose: High sensitivity measurements (close to RA769 levels) at the core, and some remote sites at slightly less sensitivity. In addition high time resolution measurements to capture strong short events.The campaign:•Deployment at AUS and SA core sites, start measurements for ~2 months

– Target start June 2010– To coordinate with precursor site activities– Measure with identical equipment (tested and verified at same facility),

same period. •Measure selection (~4 per country) of remote sites•Write site reports, by April 2011.

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SPDONew RFI Campaign

Partners:•ASTRONdata processing software, binary data format, reporting software

•SKA SARF, trailer infrastructure, integration

•CSIRODigital spectrometer, data acquisition

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SPDONew RFI Campaign

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SPDOCampaign Sensitivity

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SPDORadio Quiet Zones

• Both sites are establishing Radio Quiet Zones at the location of the core.

• ~150 km radius• Specific attention by ITU WP-7D and

Correspondence Group • Activities are being monitored by a dedicated

Task Force under the SCWG.

Note: Presentations on RQZ’s yesterday2130 March, 2010 RFI2010

SPDORadio Quiet Zone Targets

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SPDOFurther spectrum regulation

• Spectrum regulation/law making on local + national levels. Enforcement required.

• Support of local community– Alternative means of communication (cf. Adrian

Tiplady’s talk)

– Fibre to the farm– Fix noisy cars– Fix noisy electronics (cf. Pravin Raybole’s talk)

• Work with industry on low noise power distribution, etc.

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SPDOArray Planning and Design

Place antennas sensibly:• Zones of avoidance defined in ‘masks’

– buffer zones around EMI sources Roads, rail, farms, towns

– buffer zones around RFI sources Mobile comms, broadcasting

See presentation by Carol Wilson

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SPDOSystem Wide Approach

What should be done

• Provide best RFI/EMI environment• EMC policy• Reduction of susceptibility to RFI• Mitigation in hardware and software

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SPDOEMC Policy

Appoint EMC Manager, responsible for:• Definition of standards, best practice descriptions from

industry and radio astronomy community• EMC requirements for all parts of project• Application of these to all designs and equipment• Assessment of COTS hardware risks and modification• Development of test systems, methods• Development of EMC plan including specifications• Ongoing RFI monitoring• ‘EMC police’

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SPDOEMC Policy

EMC rules apply in all directions:

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SPDOEMC Policy

What are items to worry about?• Radiating receivers or parts• Digitisation at the receiver• Telescope drive systems• …

But also:• Wireless XX, remote YY, mobile ZZ in use by staff,

contractors, visitors, tourists…• This is a worry at any radio telescope, but for the SKA

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SPDOSystem Wide Approach

What should be done

• Provide best RFI/EMI environment• EMC policy• Reduction of susceptibility to RFI• Mitigation in hardware and software

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SPDOSusceptibility

Receiver robustness: a balancing act

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Design for• Wide band• High gain• Low noise• Low cost• Manufacturability

in large quantities

Design for• Sufficient Rx

headroom• Linear operation, IP• Keep power

requirements low

SPDOSusceptibility

Digitisation: a balancing act

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Design for• High performance

• SFDR• Required dynamic range:

sky noise vs interference level that one aims to mitigate down the line

• many bits

Design for• Low cost• Low power• Few bits, because of

• Cost for hardware• Signal transport• Signal processing in

station and correlator

SPDOSystem Wide Approach

What should be done

• Provide best RFI/EMI environment• EMC policy• Reduction of susceptibility to RFI• Mitigation in hardware and software

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SPDOMitigation

• Mike K: on-line RFI mitigation is possible and required, but must be robust

• Hardware architecture/techniques:– Narrow channelisation in frequency and time allows old fashioned

RFI excision to be efficient– Cancellation trough:

ANC Parametric Estimation Spatial Filtering Subspace Filtering …

• Automated flagging/excision as part of the processing pipeline

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Conclusions

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SPDOConclusions

• We have a serious problem on our hands…But we can succeed if

• A system wide approach is followed, to– Select the best possible environment– Protect that pristine environment

By preventing self-generated RFI By setting and enforcing appropriate design practices

– Prevent unavoidable levels of RFI from hurting us Robust receivers Robust digitisation and processing

– RFI consequences that still remain, dealt with by Effective automatic detection and mitigation in hardware, pre- and

postcorrelation, and in (pipeline) software

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