kristian zarb adami pathfinders for the ska: nlog(n) vs. n 2 imaging instruments:
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Kristian Zarb Adami
Pathfinders for the SKA:Nlog(N) vs. N2 Imaging
Instruments:
N log N Astronomy
In fact... Japan designed the SKA in 1994
8x8 Images in 1994 with Waseda telescope
Extrapolating with Moore’s Law (doubling every 18 months)
2016 is 1x106 antennas
Which is equivalent to SKA-phase-1
Remit of the talk Science Justification for SKA1-Low
Science and Technical simulations towards implementation of the SKA
Physical Implementation on Medicina as a flexible DSP test-bed and a comparison between spatial-FFT and N2 imaging
Industrial Engagement
SKA Phase-1 Specifications
Memo 125
Sensitive (-ity) Issues..
[SKA Memo 100]
Roadmap to the SKA-loN
BW
(16,32)
(16,60)
(1,768)
(25,192)
(400,50x2xNbeams)Super Terp
LOFAR UK
GMRT
Medicina
SKA-1
(32, 64)
MWA-32
LOFAR
(8,50x2xNbeams)
LWA
(78,100)
(32, 1024)
MWA-512
PAPER
(100,128)
MITEOR
(25,16)
H1-Power Spectrum (z≈8)
Theoretical 21-cm Power Spectrum @ 150 MHz
Power Spectrum from a (100,256) instrument
Foregrounds suppressed by frequency/angledifferencing
NlogN vs. N2
LOFAR2010
Super-Terp2011
SKA-Phase 1SKA-Phase 2
HI Power Spectra (SKA-Phase-II)
Blue: HI > 108
Green: HI > 20’
Linear Bias = 1.0Linear bias = 0.8
Co-moving Volume = (500MPc/h)3
SKA1 Low Layout
100km
200m
Bandwidth 70 – 450 MHz (Instantaneous B/W 380 MHz)
ADC Sampling at 1 GSa/s @ 8-bit
Antenna Spacing ~ 2.6m
Array Configuration:
50 stations
11,200 antennas per station (~10,000)
Output beams of 2-bit real; 2-bit imag
The numbers game (SKA1-low)
Numbers cont... SKA-1 ~ 50 stations of 10,000 antennas each Station diameter ≈ 200m Station beam @ 70 MHz ≈ 1○, @ 450 MHz ≈ 0.2○
Nbaselines = 5,000 (50^2/2 *4)
Input data rate to station 160 Tb/s (total data rate 8 Pb/s for the SKA-1 lo) Output rate?
Assume 10 Tb/s off station = 100 x 100Gb/s fibres
Output beams 2+2 bits, ~100kHz channels (1.6Mbps per beam-channel) 6.25 million beam-channels – by DFT need 0.1 Pop/s (6250 beams @ 1000 channels)
Equalise sky coverage so N(f) ~f2 – 100 beams in lowest (70 – 70.1 MHz) channel 100 sq deg instantaneous coverage.
Correlator has to do 1,000 baselines for each 1 kHz beam-channel (for a total ~ 10 Pop/s)
Station Architecture
Station Layout
Richard Armstrong – richard.armstrong@astro.ox.ac.uk
TileProcessorTile
Processor
TileProcessor Tile
Processor
StationProcessor
Optical Fibre
Optical Fibre
Copper
Hierarchical Architecture
Antennas
Multiply and add by weights
Multiply and add by weights
Cross correlation of sub-arrays (for station calibration and ionospheric calibration)
Hierarchical Beam Forming (tiles then station)
Tile Level Weights
Station Level Weights
Direct Station Beam Forming
Station Weights
Sub-Station Cross-correlation (calibration)?
Sub-Station Weights
Tile level
Electronic Calibration
Field or Strong Source Calibration
~CAS-A
Source & Polarisation Calibration
Polarisation Calibration
Tile processor box
RF in (coax) 16 x dual pol
Multi-chip module
Fibre:Data outClock and control in
RegDC in
Tile Processor
ADC
ADCADC
ADC
Coarse freqsplitting
1st LevelBeamforming
RFIMitigation
&4-bit
Quantisation
Tile Processor
Inputs: 16 dual-pol antennasADC @ 1GSA/s @ 8-bit
Coarse frequency splittingInto 4 channels
Outputs: dual-pol beams@ 1GSA/s @ 4-bit re/4-bit imag
Output is optical
Control and Calibration Interface
Space-Frequency Beamforming
Time-delay beamforming is now an option…
Dense mid-freq array: Antenna sep ~ 20cmTime step ~ 1ns ~ 30 cmAngle step > 45 deg
Sparse low-freq array: Antenna sep ~2 mTime step ~ 1ns ~ 30 cmAngle step ~10 deg – less if interpolate
Front end unit can combine space-freq beamforming in a single FIR-like structure
Golden Rule: throw away redundant data before spending energy processing/transporting it
Station processor
Optical-electro
Heirarchicalprocessor
Electro-optical
Multi-chip module
M&C
Optical-electro
Heirarchicalprocessor
Electro-optical
Multi-chip module
M&C
Optical-electro
Heirarchicalprocessor
Electro-optical
Multi-chip module
M&C
Optical-electro
Heirarchicalprocessor
Electro-optical
Multi-chip module
M&C
Optical-electro
Heirarchicalprocessor
Electro-optical
Multi-chip module
M&C
Clock & control
Station Processor
2nd LevelBeamforming
2nd LevelChannelisation
CornerTurner
Station Calibration and Correlator
Inputs: 64-dual pol 1st stage beams
Outputs: selectable dual-pol beams@ 1GSA/s @ 2-bit re/2-bit imag
Channelisation to 4096 channelsWith a 1024 channeliser
Station Calibration and station correlator
Output is optical and correlator ready
Simulations
Multi-Level Beamforming
Split the problem to be hierarchical and parallel.
Station divided into tiles (can be logical).
Dump as much unwanted data as we can early on.
Tile beam
Station beams
Simple Beam Patterns
80 x 80 degrees:
Station beam at (45, 87) degrees.Tile beam at zenith.
Visualisation of beams
Elevation 85 - 90 degrees
1000 MHz65536 antennas, 256 tiles
Station beams 0.05 degrees apartTile beams 2 degrees apart27 tile beams, 31707 station beams
Run time: 5.67 seconds
Station beams 0.20 degrees apartTile beams 2 degrees apart27 tile beams, 8005 station beams Run time: 2.18 seconds
Dynamic Range SimulationCourtesy: S. Schediwy & Danny Price
This is the reason a correlator is required for a beamformer
Auto-power beam Peak power 0 dBArray station sparsed x3
Cross-power beam 3deg rotationPeak power -20dB
Cross-power beam 30 deg rotation Peak power -50dB
Examples of Implementation
Introduction564m24 segments
640m64 cylinders
32m dish
Medicina Radio Telescopes
BEST-2
BEST-3Lo
BEST-2 specs
N cylinders 8
N receivers 32Total collecting area
1357.98 m2
Total effective area 964.17 m2
Central Freq. 408 MHzFrequency BW 16 MHz
IF 30MHzLongest baseline N/S E/W
70m 17.04m
Primary FOV37.65 deg2
Sensitivity / Antenna Gain 0.363 K/Jy
Aeff / Tsys11.651 m2/K
Transit time at delta = 45 deg
2353.3 sec.Marco Bartolini, IRA - INAF
64- C
hann
el A
DC
F - R
OAC
H
X -
ROAC
HS
- RO
ACH
B -
ROAC
H
HOST - PC GPU Imaging & Calibration
GPU Transient
1Gb-E
10 Gb-e
Richard
Griffin
Jack
PCI-XJack
Alessio
Dickie
OeRC
Medicina Radio Telescopes
Medicina Backend: Spatial FFT
Danny Price – Jack Hickish
Medicina Fringes…
Medicina Fringes (Cas. A.)
Cas. A. Image
Industrial Engagement It is NOT the intention of the SKA community to deliver 'finished' chip
designs yet. Aiming for detailed device specifications ready to start prototype
manufacture when NRE money available There are basic engineering processes that have to be done to enable
meaningful sizing, cost & power estimation IP identification and development – potential industrial involvement Development of strategic technology partnerships
ADC design IP macros for eg FFT, switch fabric Embedded controllers Non-packaged device mounting
Identification of key architectural features Identify appropriate optimisation opportunities and trade-offs. Development of accurate models for cost and power analysis at the
wider system level. Identify key interface 'Hot Spots' and apply effort accordingly
Industrial Engagement Multi-Chip Module (One Chip to Rule them all!)
4 x 4 antenna array (currently) – easily extended to 8x8
Can also be used for Phased Array feeds for dishes
Current Chip RFI protection shows -57dB/m (in air)
ADC FIR-FFT
ProcessorBeam Combiner
&Calibrator
Optical I/ORF IN
OpticalOUT
16-8 bit1GS/s
1024 channelsplitter
16 elementBeam combiner
OpticalChip
UWBRX
10mW/FFT10mW/channel 4mW/Beam ??
Requirement Specifications
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