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SKA – The Reference Design
Peter HallSKA International Project Engineer, ISPO
www.skatelescope.org
Next-Generation Correlators WorkshopGroningen, June 28, 2006
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PJ Hall, June 2006
ISPO
Outline
SKA SKA Reference Design
– Selected antenna technology – Correlator matters (brief)
Project news
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PJ Hall, June 2006
ISPO
SKA At A Glance Aperture synthesis radio telescope
with 1 km2 of effective collecting area by 2020
1 km2 ~ 100 x VLA area – Limited gains by reducing receiver noise– Just need more microwave photons!
Frequency range 0.1 - 25 GHz– Large bandwidths (4 GHz), large fields-of-view (50
deg2) New capabilities: area re-use (“multi-
fielding”), RFI mitigation, high dynamic range
imaging, ….
Innovative design to reduce cost– € 1000 per m2 target is about 0.1 current practice
International funding: ~ € 1 billion 17-country international consortium 4 potential sites; ranking in progress
Hugedata rates& volumes
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2000
Site short-listing
‘1% SKA’Science
ISSCMoAs
ScienceCase
published
Inter-governmental discussions
including site selection
First SKA WorkingGroup
Initial concept
2000
‘10% SKA’Science
92 96 04 05 06 07 08 09 10 14 18 22
Feasibility study
Full arrayBuild
100% SKA
SKAComplete
Phase 1Build
10% SKA
Conceptexposition
Define SKA
System
SKA Timeline
Optimise Design
Reference design selected
Construct 1% SKA Pathfinders
Radio interferometers can be built in stages(Inbuilt risk mitigation)
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PJ Hall, June 2006
ISPO
SKA: Radio Meets IT (Again)
Is SKA a software telescope? Almost!
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PJ Hall, June 2006
ISPO
Reference Design - Background
Reference Design (RD)– Provides recognizable SKA image– Focuses science and engineering– Forms basis of SKA costing– Is a strong candidate for actual implementation
Result of wide exploration of design space– Original SKA concepts pushed boundaries in key areas: often
simultaneously!» Brightness sensitivity, field-of-view, no. FOVs, frequency coverage,
…» RD retains major precepts in each frequency range» All SKA concepts had/have much common system design
RD balances innovation and risk– Recognizes need to optimize within selected technology mix – Maps out technology contingencies
» Fall-back positions at every decision point
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PJ Hall, June 2006
ISPO
SKA Reference Design
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PJ Hall, June 2006
ISPO
SKA Reference Design A sparse aperture array for 0.1 - 0.3 GHz (Low-Band)
– “Era of Recombination” array» Super LOFAR, MWA etc
– Multiple independent FOVs, wide FOVs– Low risk
A small dish + “smart feed” for 0.3 - 25 GHz– Radio camera– Dish ~ 10 m diameter– Smart feed wide response in angle OR frequency
» Mid-Band 0.3 – 3 GHz: wide FOV» High-Band 3+ GHz: wide bandwidth
– Both low risk + high risk components– Driven in part by need for sensitive, wide FOV telescope a.s.a.p (SKA Phase
1)
An innovation path– Radio “fish eye” lens– Dense aperture array for 0.3 – 1 GHz– Independent FOV capability to 1 GHz– All-sky monitoring capability– High risk (but potentially high return)
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PJ Hall, June 2006
ISPO
radio “fish-eye lens”
Inner core
Station
Digital radio camera+ stations to3000 km
Radio fish-eye lens
Reference Design
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PJ Hall, June 2006
ISPO
SKA – Schematically
(About 150 stations)
(About 2000 antennas – all correlated)
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PJ Hall, June 2006
ISPO
Reference Design: Some Technology
> 3 GHz: wide-band feed
< 0.3 GHz: sparse aperture array
0.3 – 3 GHz:phased arrayfeed
Innovation path: dense aperture array
Mid-Band
High-Band
Swinburne/CVA visualization
Low-Band
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PJ Hall, June 2006
ISPO
Small Dish + Phased Array Feed
Digital beamformer
Phased array feed
Correlator & further processing
Multiple fields
10 m dish cost target:~ €30k exc. feed
FOV expansion factors ~30 maybe practical
~ D radian
D
Terminology: PAF is one type of Focal Plane Array
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PJ Hall, June 2006
ISPO
PAF Operation
Key question:
How calibratable arePAFs?
D. Hayman, T. Bird,P. Hall
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PJ Hall, June 2006
ISPO
Reference Design Practicalities Full frequency range unlikely to be affordable
– Possible outcome: (EoR array) + (0.3 – 10 GHz) Dense AA is least mature technology in cost terms
– Balance between AA and SD collecting area will depend on cost and performance demonstration
– AA probably has most scientific value as a central collecting area But SD+PAFs also need rapid demonstration
– Cheap dishes and astronomically-capable PAFs are not trivial– Low frequency efficiency is a potential issue
Ultimate contingency if AA, SD+PAF fail:– Super-LOFAR, 0.1 - 0.3 GHz, plus– “small” dishes (~10 m) + single pixel feed, > 0.3 GHz
» 7 deg2 FOV at 0.7 GHz; “small” FOV partially compensated by better Aeff/Tsys
Large-scale cost – performance estimation begins Q4 ’06– Closely allied with variational analysis wrt science goals– Strawman design for forthcoming Paris meeting
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PJ Hall, June 2006
ISPO
Wide Fields Same FOV same no. of receiver chains
– Concept independent (almost) Many small antennas correlator intensive
– Small dishes or AA patches Fewer, larger antennas with FOV expansion
reduced correlator load– Use focal plane beamforming to reduce order of correlation challenge
» Bigger dishes + PAF (or larger AA patches)» Big question: does extra PAF calibration cost negate correlator saving?
– Bigger antennas» Better low freq performance» More sensitive, easier to calibrate» Better RFI discrimination
– Smaller antennas» Probably more attractive production costing» Easier to calibrate?
Low & mid-band wide-FOV operation fits within processing envelope defined by high band SKA spec.
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PJ Hall, June 2006
ISPOSKA Correlator – Output Data Rate
4000 stations4 polarization products2x16-bit fixed point numbers/complex value 128 MB per visibility set
Integration time 0.1 sec 1000 spectral channels10 station beams 9 TB/sec output data rate
Need special purpose hardware for initial stages of post-correlation processing
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PJ Hall, June 2006
ISPO
SKA Correlator Attributes Extreme flexibility
– Simultaneous low, medium, high band operation– Complete trade-off of parameters (no. inputs, bandwidths, no. FOVs,
processing accuracy, ….)– Support for “new” science:
» High time resolution imaging, real-time VLBI, ….
Highly scaleable, reliable, maintainable, upgradeable– “Open telescope” ? ; standard data formats/interfaces (accept overheads)
; graceful degradation + hot spares operating model– Minimize NRE over life of telescope maximum re-useability
Station correlators can be modest– E.g. calibration to optimize station beamforming may not require full or
continuous bandwidth coverage Signal connection and routing will be a major issue Power is a major issue (remote sites, minimize op cost)
Line between correlator and other DSP will be blurred Line between DSP engines and computers will be
blurred SKA DSP will likely be a mix of ASIC, FPGA and
computers
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PJ Hall, June 2006
ISPO
SKA – Many Other Challenges
Low-noise, integrated, receivers– E.g. millions-off for mid-band
High speed data transport– Looking for 100 Gb/s trans-continental and trans-oceanic
Signal processing– beyond just correlation (IM, tied array modes, …)
Post-processing– 2015-2020 computing capacity will limit initial science but
cannot dominate system design– Archive and sharing of data will be a major challenge
Pathfinders and demonstrators are pivotal– Allen Telescope Array, LOFAR, xNTD, Karoo Array
Telescope, DSNA, APERTIF, EMBRACE, 2-PAD ….– €200M committed so far; €80M explicitly for SKA;
additional €40M expected in China shortly
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PJ Hall, June 2006
ISPO
SKA Engineering Philosophy Strong emphasis on
technology demonstration – Retire risk as early as
possible
Focus on:– Aggressive cost reduction
strategies (e.g. SKADS)– International collaboration
& deliverables– Industry engagement
» Pre-competitive R&D» Paradigm shift to deliver
SKA on required timescales
e.g. SD+PAF Demonstrator - NTD
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PJ Hall, June 2006
ISPO
Current SKA Happenings Site assessment
– RFI and other studies complete; list of “acceptable” or “qualified” sites soon
Funding agencies and SKA– Formed Inter-agency Working Group; continuing engagement
Funding opportunities (e.g. ESFRI) Forthcoming Engineering – Science meeting
– Paris, 4-8 Sept– Emphasis on Reference Design, project costing
International engineering review Q4/07 – Q1/08– Reference Design, specifications, …
Continued science and engineering exposition More outreach
– New animations, telescope model, …. More industry engagement
– Major structural, governance implications More inter-region collaboration
– Easier as technology concepts coalesce
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PJ Hall, June 2006
ISPO
Summary
Site selection in progress Reference Design identified RD technologies being developed via
regional pathfinders– Rapidly increasing inter-region collaboration
Initial SKA system design in progress– Incl. cost and performance modelling– Preliminary engineering reviews 2007-08
Industry interaction increasing SKA Phase 1 - start 2011