Transcript Slide 1

System Approach to RFI Mitigation for the SKA
Rob Millenaar – SKA Program Development Office (SPDO), Manchester, UK
http://www.skatelescope.org
[email protected]
4 June, 2010
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Overview
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SPDO
Introduction
– Concepts of the SKA
– Receptor technology types
– Array layout
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System wide approach to RFI mitigation
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the RFI/EMI Environment
EMC
Reduction of susceptibility to RFI
Mitigation in hardware and software
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SPDO
Introduction
Setting the scene
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The Square Kilometre Array
SPDO
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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The Square Kilometre Array
SPDO
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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Configuration
SPDO
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Configuration
SPDO
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The challenge
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The conclusion should be that:
SPDO
– 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 (self-generated) out-of-band
RFI for one is in-band for the other technology type, so all designs must be
done considering the entire SKA frequency range!
– With extreme required operational sensitivity  need for a RQZ in the
center and handpicked remote sites, plus further regulation
– Systems and parts should be cheap to produce and maintain  challenges
to high quality, yet affordable shielding and proper engineering methods
– Requires manageable data rates  so must limit number of bits to be
transported and processed
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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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SPDO
System Wide Mitigation of RFI
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System Wide Approach
SPDO
What should be done: fight on all fronts…
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Provide best RFI/EMI environment
EMC policy
Reduction of susceptibility to RFI
Mitigation in hardware and software
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System Wide Approach
SPDO
What should be done
•
•
•
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Provide best RFI/EMI environment
EMC policy
Reduction of susceptibility to RFI
Mitigation in hardware and software
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EMI/RFI Environment
SPDO
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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Site Selection
SPDO
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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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RFI environment at the core
SPDO
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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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RFI environment at the core
SPDO
Mode 1 overall spectrum, 70MHz to 22 GHz
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Unavoidable RFI
SPDO
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
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NOAA series
Iridium, GPS, Galileo
Geostationary (broadcasting, FLTSATCOM)
…
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New RFI Campaign
SPDO
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),
during the same period.
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Measure selection (~4 per country) of remote sites
Write site reports, by April 2011.
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New RFI Campaign
SPDO
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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New RFI Campaign
SPDO
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Campaign Sensitivity
SPDO
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New RFI Campaign
SPDO
Progress
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Integration of system
Testing combined system, first phase done
Every trick in the EMC book is required to minimise the
amount of self generated RFI, which is difficult because:
– Sensitivity required
– Low gain antenna used
– Compactness of system
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Radio Quiet Zones
SPDO
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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.
(Ref. Carol Wilson: Radio Quiet Zones and the SKA)
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Further spectrum regulation
SPDO
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Spectrum regulation/law making on local +
national levels. Enforcement required.
Support of local community
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Alternative means of communication
Fibre to the farm
Fix noisy cars
Fix noisy electronics
Work with industry on low noise power
distribution, etc.
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Array Planning and Design
SPDO
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
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Methodology:
1.
Define tolerable levels of RFI (based on RA769)
Examine various aggregations of sources of RFI and EMI
Apply appropriate propagation models to arrive at required
buffer zones.
2.
3.
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System Wide Approach
SPDO
What should be done
•
•
•
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Provide best RFI/EMI environment
EMC policy
Reduction of susceptibility to RFI
Mitigation in hardware and software
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EMC Policy
SPDO
Appoint EMC Manager, responsible for:
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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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EMC Policy
SPDO
EMC rules apply in all directions:
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EMC Policy
SPDO
What are items to worry about?
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Radiating receivers or parts
Digitisation at the receiver
Telescope drive systems
…
But also:
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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.
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System Wide Approach
SPDO
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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Susceptibility
SPDO
Receiver robustness: a balancing act
Design for
Design for
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• Sufficient Rx headroom
• Linear operation, IP
• Keep power
requirements low
Wide band
High gain
Low noise
Low cost
Manufacturability
in large quantities
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Susceptibility
SPDO
Digitisation: a balancing act
Design for
Design for
• High performance
• Low cost
• Low power
• Few bits, because of
• High SFDR
• Required dynamic range:
sky noise vs interference
level that one aims to
mitigate down the line
•  many bits
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• Cost for hardware
• Signal transport
• Signal processing in
station and correlator
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System Wide Approach
SPDO
What should be done
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•
•
•
Provide best RFI/EMI environment
EMC policy
Reduction of susceptibility to RFI
Mitigation in hardware and software
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Mitigation
SPDO
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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:
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ANC
Parametric Estimation
Spatial Filtering
Subspace Filtering
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Automated flagging/excision as part of the processing pipeline
Mitigation techniques must be planned from the start and not be
attempted as an afterthought.
(Ref. Willem Baan: The Layers of RFI Mitigation)
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SPDO
Summary
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Elements of a systems approach
SPDO
Elements of RFI/EMI management discussed:
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Involvement in spectrum management
Spectrum protection/regulation/RQZ
Spectrum monitoring
Array planning
Receiver and backend design for RFI robustness
Mitigate risks and effects where RFI does get into the
system
Investigate and work on a succession of ‘weakest links’
in the system in the broadest sense
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Conclusions
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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
SPDO
 By preventing self-generated RFI
 By setting and enforcing appropriate design practices
 By actively participating in all aspects, and on all levels of spectrum
protection and regulation
– Prevent unavoidable levels of RFI from hurting us
 Robust receiver systems
 Robust digitisation and processing
– RFI hazards that still remain, dealt with by
 Effective automatic detection and mitigation in hardware, pre- and
postcorrelation, and in (pipeline)
software
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