Transcript SKADS-LOGO - Cavendish Astrophysics

December 2010
SKA1 AA-low design
AAVP Workshop
SKA1 AA-low is a major System:
>10x LOFAR sensitivity
>1 km2 collecting area
>6:1 frequency range 70 – 450MHz
~50 deg2 Field of View
Very quiet site
Required in SKA Memo 125
December 2010
SKA1 AA-low design
AAVP Workshop
But........
It is also part of a bigger vision:
SKA2
Some implications....
December 2010
SKA1 AA-low design
AAVP Workshop
SKA1 AA-low System requirements
Priority
• Stand alone instrument meeting SKA1 science goals
• Deployable 2016 onwards
• Specification will mesh with SKA2 system design e.g.
– Frequency range
̶ Data rates
– Calibration capability
̶ Correlation requirements
etc...
• Scaleable architecture for 2018+ commonality with AA-mid
• Architecture will support upgraded processing devices
– Phase 2 expansion
̶ Retro-fit Phase 1 (if good pay-back)
SKA1 performance must not be compromised?
December 2010
SKA1 AA-low design
AAVP Workshop
Element requirements
Feature
Requirements
Comments
Electromagnetics
Frequency range, beampattern,
part of an array
It must work properly!
Quickly deployable
Simple
10,000 per array.....
Manufacturable
Easy, repeatable, cheap
Essential for cost and reliability
Transportable
Ideally “flat pack”
The volume (m3) is huge
Reliable
Failure rate must be very low
MTBF of 100,000 hrs →
~1 element/array/day
“Low” cost
From above
Of course...
Low RFI
Negligible radiation
Low Power
~100-200mW
Essential for solar
Upgrading
Deployed elements cannot be
upgraded
Additions functionally equivalent
Ideally avoid any modifications
December 2010
SKA1 AA-low design
AAVP Workshop
One or two elements?
One element
Two elements
Cost
Minimised
Higher
Doubles # RF chains,
ground planes and
interconnects
Element performance
Some compromise
across band
Less compromise
across band
Station design
Forces highly sparse
design at top-end of
band
Reduces sparcity
while maintaining
sensitivity
Power
Minimises power
Increases power
Filling factor
Good filling factor at
low f
Poor filling factor
unless multiple cores
Matching
Challenging
Easier
December 2010
SKA1 AA-low design
AAVP Workshop
LWA element: mechanical example
Electronics at top – well
away from floods etc.
Simple “skeleton”
elements (delivered flat)
Clamp type rotational
adjustment
Single pole fixing –
just sunk into ground
Buried cables
Cheap mesh
groundplane
Easy and quick deployment
December 2010
SKA1 AA-low design
AAVP Workshop
Integrated AA-low element possibility
Stand-alone power
Optical links only
Elements:
70-450MHz
Solar panel
ADC: 1GS/s
Processing
Power
conditioning
50-100m all
optical
e/o
Data
e/o
Control
e/o
Sync.
Analogue
Energy
storage
Benefits:
Challenges:
Integrated single unit
Low total power
Integration
Manufacturability
Packaging
No copper connection
Easy to deploy
Minimum RFI
Lightning “immunity”
Elements only connected by glass....
December 2010
SKA1 AA-low design
AAVP Workshop
Where to digitise?
At element
At processor
RFI
Maximised
Minimised
Phase stability
LNA & Filters +
Clock distribution
LNA + Filters +
Second stage Gain +
Cables
be done
– safe
option
More Data
advanced
– moreCan
stable
transport
Digital
possibly
over
Likely to fibre
require distributed
Requires: low power, quiet
station.
digitisers.
Low cost shortdigitisation
range At around
Power
element
or over
(Cable cost
and range)
optical drivers.
copper
RF over copper
RequiresCan
good,
protection
bestable
goodanalogue
if link is
Likely,Lightning
requires custom
chips
design fibre
No option to upgrade digitisers.
Bandpass
Very good
Can be challenging if
link is copper
Cross talk
December 2010
Minimised between
elements and
polarizations
SKA1 AA-low design
Over RF cable or at
element
Equalization after
transport
Dependent on
screening and design
of RF boards
AAVP Workshop
Potential AA-low station: Safe solution:
Single element
Cooling
2-Pol
Elements
Analog to clustered digitisation
Centrally powered elements
...
Element Digitisation
Copper
Fibre
...
Element
Station Processing
C&M
...
......
......
Digitisation
Tile
Tile
Digitisation
RFIDigitisation
Shielded
......
Clock
2x 500MHz
Analogue
+ power
Element Digitisation
Front-end
...
Power Distribution
December 2010
Station
Beams
Element Data
SKA1 AA-low design
RFI shielded
Control &
Monitoring
System
clock
To
Correlator
&
Services
Power
Grid
AAVP Workshop
Station processor
Station Processor
…..
0
1
2
…..
Long distance drivers
Optical links
To Correlator
…..
…..
0
1
2
3
4
5
…..
Long distance drivers
…..
Secondary
Station
Processor
Board
(max 35)
…..
“All to All”
Connections
…..
…..
Each link is 12 fibre
lanes@10Gb/s
Primary
Station
Processor
Board
(max 35)
…..
…..
Secondary
Station
Processor
Board
1
…..
Secondary
Station
Processor
Board
0
…..
…..
…..
To
Element
Digitisation
Primary
Station
Processor
Board
1
…..
…..
35
Primary
Station
Processor
Board
0
Long distance drivers
0
1
2
Requirements:
• High bandwidth in
• High bandwidth out
• Largely cross connected
• Scaleable at various levels
• Programmable beamforming
Each link is 12 fibre
lanes@10Gb/s
12-channel Rx
module. e.g Avago
AFBR-820BXXZ
PChip
e/o
e/o
e/o
e/o
e/o
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PChip
PChip
e/o
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PChip
e/o
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PChip
e/o
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PChip
e/o
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PChip
e/o
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o/e
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o/e
o/e
Each link is 12 fibre
lanes@10Gb/s
Total Raw input
data rate: 4.32Tb/s
PChip
o/e
o/e
o/e
o/e
o/e
o/e
To Element
digitisation
or Primary
Station
Processors
30
31
32
33
34
35
Each link is 12 diff.
copper lanes@10Gb/s
o/e
o/e
o/e
o/e
o/e
o/e
PChip
PChip
o/e
o/e
o/e
o/e
o/e
o/e
PChip
o/e
o/e
o/e
o/e
o/e
o/e
PChip
“All to All”
Connections
December 2010
SKA1 AA-low design
To Secondary
Station
Processors or
long distance
fibre drivers
Each link is 12 fibre
lanes@10Gb/s
Total Raw output data
rate: 4.32Tb/s max
Line
Tx/Rx
Control
Processor
12-channel Tx
module. e.g Avago
AFBR-810BXXZ
Station
Control
AAVP Workshop
Station size
• For a given total Aeff the collector cost is roughly constant
– Increasing overhead with many smaller stations
– Possibly increasing station processor complexity with large arrays
• Total data rate to correlator for a fixed survey speed remains
constant whatever number of stations
BUT
• Correlator and central processor demands become more
challenging
Station size largely determined by
central processing costs
December 2010
SKA1 AA-low design
AAVP Workshop
Core Design
Core “stations” are not
separated – there is a “sea”
of elements
Core for SKA1 AA-low
becomes virtually fully filled.
More so for SKA2.
Design options/considerations to be made:
Implies interconnected “station
processing”,
especially
for SKA2
• Non-circular “stations” easier?
e.g. Square
or hexagonal?
• Maximising the sensitivity from each element:
• overlapping “stations”?
• smaller “stations” (how small) with more correlation?
• Apodising element density within areas of the core:
2, but
Correlation
goes
up
as
n
• Benefit? Save money?
incoming data rate is constant
December 2010
SKA1 AA-low design
AAVP Workshop
AA-low: SKA1 to SKA2
Fixed Aspects
Possible Variables
• Frequency range
• Station size & configuration
– Intrinsic to the design
• Core layout (getting bigger)
• Element & array
electromagnetic design
– Move element positions.....?
– Trenching etc.
• Processing technology level
• Front end functionality
– Essential for economical
deployment
• Analogue implementation
– Unlikely to change
• Interfaces
• Upgraded calibration methods
– Needs flexible processing system
– Could bypass a level of
interconnect
December 2010
SKA1 AA-low design
AAVP Workshop
SKA2 System
Aperture Array
Station
0.4-1.4 GHz
Wide FoV
Central Processing Facility - CPF
To 250 AA Stations
Dense AA
Tile &
Station
Processing
Correlator
...
...
Processor
Buffer
Processor
Buffer
Processor
Buffer
Processor
Buffer
Processor
Buffer
Processor
Buffer
Processor
Buffer
Processor
Buffer
Processor
Buffer
Processor
Buffer
Processor
Buffer
Processor
Buffer
Processor
Buffer
Processor
Buffer
Processor
Buffer
Processor
Buffer
Processor
...
...
DSP
1.2-10 GHz
WB-Single
Pixel feeds
Pb/s
Tb/s
......
A tremendous step
forward in SKA2
Buffer
Processor
Buffer
Processor
Buffer
Processor
Buffer
Processor
Buffer
Processor
Data
Archive
Gb/s
Science
Processors
Dish & AA+Dish Correlation
Optical
Data
links
AA slice
Data switch
...
Control
Sparse AA
AA slice
Buffer
Imaging Processors
...
..
70-450 MHz
Wide FoV
AA slice
AA-mid!
...
...
Data
Time
Archive
A reminder for
16 Tb/s
..
UV Processors Image formation
Gb/s
There must be ongoing development:
Control Processors & User interface
DSP
10 Gb/s
Time
Standard
which will also... benefit AA-low
15m Dishes
To 1200 Dishes
December 2010
SKA1 AA-low design
User interface
via Internet
AAVP Workshop
Top design decisions......
Urgent (by CoDR April 2011)
• Confirm specification in Memo 125:
– Frequency range, sensitivity ....
Immediate (by CDR, end 2011):
• Single or dual element?
• Demonstrable element in small array
Medium Term (by AAVS1, end 2013)
• Station size and configuration
• Core configuration
• Station system design
– digitisation, processing location, data flow
December 2010
SKA1 AA-low design
AAVP Workshop