SKA – The Reference Design

Peter HallSKA International Project Engineer, ISPO

www.skatelescope.org

Next-Generation Correlators WorkshopGroningen, June 28, 2006

PJ Hall, June 2006

ISPO

Outline

SKA SKA Reference Design

– Selected antenna technology – Correlator matters (brief)

Project news

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

}

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)

PJ Hall, June 2006

ISPO

SKA: Radio Meets IT (Again)

Is SKA a software telescope? Almost!

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

PJ Hall, June 2006

ISPO

SKA Reference Design

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

PJ Hall, June 2006

ISPO

SKA – Schematically

(About 150 stations)

(About 2000 antennas – all correlated)

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

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

PJ Hall, June 2006

ISPO

PAF Operation

Key question:

How calibratable arePAFs?

D. Hayman, T. Bird,P. Hall

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

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.

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

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

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

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

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

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