1. 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
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2. System wide approach to RFI mitigation
Overview
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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3. Introduction Setting the scene
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4. The 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 km
Candidate sites:
Southern Africa, Karoo
Australasia, Boolardy
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5. The 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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6. Configuration
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7. Configuration
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8. The challenge Requires a rigorous system-wide mitigation approach.
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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9. System Wide Mitigation of RFI
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10. Provide best RFI/EMI environment EMC policy
System Wide Approach
What should be done
Provide best RFI/EMI environment
EMC policy
Reduction of susceptibility to RFI
Mitigation in hardware and software
30 March, 2010
RFI2010

11. Provide best RFI/EMI environment EMC policy
System Wide Approach
What should be done
Provide best RFI/EMI environment
EMC policy
Reduction of susceptibility to RFI
Mitigation in hardware and software
30 March, 2010
RFI2010

12. Provide best RFI/EMI environment Investigate and select sites
EMI/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)
30 March, 2010
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13. Further site characterisation is underway
Site 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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14. RFI 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:
Take maximum level of pointings/polarisations per site;
Plot minima and maxima of the two datasets.
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15. RFI environment at the core
Mode 1 overall spectrum, 70MHz to 22 GHz
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16. Unavoidable 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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17. New 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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18. SKA SA RF, trailer infrastructure, integration
New RFI Campaign
Partners:
ASTRON data processing software, binary data format, reporting software
SKA SA RF, trailer infrastructure, integration
CSIRO Digital spectrometer, data acquisition
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19. New RFI Campaign
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20. Campaign Sensitivity
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21. Specific attention by ITU WP-7D and Correspondence Group
Radio 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 yesterday
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22. Radio Quiet Zone Targets
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23. Further 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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24. Array 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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25. Provide best RFI/EMI environment EMC policy
System Wide Approach
What should be done
Provide best RFI/EMI environment
EMC policy
Reduction of susceptibility to RFI
Mitigation in hardware and software
30 March, 2010
RFI2010

26. Appoint EMC Manager, responsible for:
EMC 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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27. EMC rules apply in all directions:
EMC Policy
EMC rules apply in all directions:
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28. What are items to worry about?
EMC 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 the scale is humongous.
30 March, 2010
RFI2010

29. Provide best RFI/EMI environment EMC policy
System Wide Approach
What should be done
Provide best RFI/EMI environment
EMC policy
Reduction of susceptibility to RFI
Mitigation in hardware and software
30 March, 2010
RFI2010

30. Receiver robustness: a balancing act
Susceptibility
Receiver robustness: a balancing act
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
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31. Digitisation: a balancing act
Susceptibility
Digitisation: a balancing act
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
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RFI2010

32. Provide best RFI/EMI environment EMC policy
System Wide Approach
What should be done
Provide best RFI/EMI environment
EMC policy
Reduction of susceptibility to RFI
Mitigation in hardware and software
30 March, 2010
RFI2010

33. Mitigation
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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34. Conclusions
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35. Conclusions
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
30 March, 2010
RFI2010