AA-CoDRApril 2011 High Level System DescriptionAndrew Faulkner
AA signal processing
AA-CoDRApril 2011 High Level System Description
Discussion
Signal processing is at the heart of SKA Aperture Arrays• Ingredients:
– Distribution– The core– Digitisation– Communications– Data rates– Beam precision
• Noise insertion?
• UNIBOARDx• CASPER • AAVSx processing• Scaleability• RF over fibre
• Algorithm development• Programming tools
AA-CoDRApril 2011 High Level System Description
Tile Digitisation
Tile Digitisation
Element
Digitisation
RFI Shielded......
......
......
...
Power Distribution
Element Digitisation
...
Cooling
Element Digitisation
......
Station Processing
RFI shielded
System clock
Control &Monitoring
StationBeams
PowerGrid
Element Data
C & M
Clock
To Correlator
& Services
2x 500MHzAnalogue+ power
FibreCopper
2-PolElements
Front-end
An AA-low station layout
AA-CoDRApril 2011 High Level System Description
“Advanced”AA-low Station
......
…....
Cooling
Station Processing
RFI shielded
System clock
Control &Monitoring
StationBeams
PowerGrid
Element DataC & MClock
To Correlator
& Services
Single or multiple fibres
Fibre
Stand-aloneElements
Self powered element
............
AA-CoDRApril 2011 High Level System Description
Core Design
Core for SKA1 AA-low becomes virtually fully filled.
More so for SKA2.
Core “stations” are not separated – there is a “sea” of elements
Design options/considerations to be made:
• 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:
• Benefit? Save money?
Implies interconnected “station processing”, especially for SKA2
Correlation goes up as n2, post processing nx …Incoming data rate is constant
AA-CoDRApril 2011 High Level System Description
AA-low signal path
LNA
Antenna
GainBlock
Analogconditioning
SignalTransport
ADC
ADC – Processor comms
Digitisation P
rocessingTile – station processor
optical comms
Prim
ary Station P
rocessing
Secondary S
tation Processing
Wide areaoptical comms
To Correlator
Digitisation box Station ProcessingElement assembly
optical interconnect
Clock Distribution
ControlProcessor
AA-CoDRApril 2011 High Level System Description
Where to digitise?At element At processor
RFI Maximised MinimisedPhase stability LNA & Filters +
Clock distributionLNA + Filters + Second stage Gain + Cables
Data transport Digital possibly over fibre
RF over fibre or copper
Power At element or over copper
Over RF cable or at element
Lightning protection Can be good if link is fibre
Can be challenging if link is copper
Bandpass Very good Equalization after transport
Cross talk Minimised between elements and polarizations
Dependent on screening and design of RF boards
AA-CoDRApril 2011 High Level System Description
Standalone SKA-low element(option)
Processing
e/o
e/o
e/oPower
conditioning
Solar panel
Energy storage
Elements:70-450MHz
Analogue
ADC: 1GS/s
Data
Control
Sync.
50-100m all optical
Benefits:Integrated single unitNo copper connectionEasy to deployMinimum RFILightning “immunity”
Challenges:Low total powerIntegration ManufacturabilityPackaging
No need for digitisation boxes
AA-CoDRApril 2011 High Level System Description
AA-low element: RF on Fibre
Data Pol1e/o
Powerconditioning
Elements:70-450MHz
Analogue
Data Pol 2e/o
Power over copper
Still no need for digitisation boxes!
AA-CoDRApril 2011 High Level System Description
Beamforming Processing
1st stage beamformer size: No. of elements to combine
1st stage o/p data rate: precision of station beams
Digitisation resolution: From RFI environment
Technology: AAVSx →SKA1→SKA2
Level of programmability: How much is “fixed”
RFI excision: Algorithms and where
Flexibility: Bandwidth/beams/bits etc.
Inter-station comms: Variable station “sizes”, core
Is Analogue beamforming
a sensible consideration?
AA-CoDRApril 2011 High Level System Description
AA-mid Array
AA-CoDRApril 2011 High Level System Description
1st stage Beamforming: AA-midTech. Technique Benefits Disadvantages Comments
Analogue Cheap – at present
Each beam has own hardwareLimited calibration abilityStability over time & temp
Analogue systems require more hardware for more performance
Phase shift Integrated on chip Limited bandwidth Useful technology today and in AAVS1
True time delay Full bandwidth
Large, hard to integrate. Harder for low freq.
There are early trials of integrated TTD
Digital Very flexibleCan create many beams
Power and cost high? Digital better and cheaper over time.
Frequency Domain
Excise some RFI immediatelyGood calibration and flatten bandpassCan extract just the desired bands
Requires digitisation and processing resources.
Very flexible, requires Poly Phase filter per channel which is expensive. More FoV is cheap
Time domain
Time resolutionReduced processing load
No RFI excisionHarder to calibrateInterpolation precision
No PFF per channel, but keeps full bandwidth for B/F
AA-CoDRApril 2011 High Level System Description
AA-mid signal path
LNA
Antenna
GainBlock
AnalogCond.
SignalTransport
ADC
ADC – Processor comms
Tile Digital P
rocessing
Tile – station processoroptical comms
Prim
ary Station P
rocessing
Secondary S
tation Processing
Wide areaoptical comms
To Correlator
Tile Processing Station ProcessingFront-end
optical interconnect
Clock Distribution
RF B
eamform
ing
AA-CoDRApril 2011 High Level System Description
Possible AA-mid construction
Beamformer
......
......
......
......
Beamformer
The join!
Membrane
Ground plane
Guideframe
Tile support
Ground
Top View
......
......Non-conductingGuideframe
AA-CoDRApril 2011 High Level System Description
Station processing
Similar for AA-low and AA-mid:
• Station level beamforming on all the tiles
• Distributes the clock information for all the tiles
• Station calibration calculations and corrections (using
the tile processors)
• Transmits observation beams to the correlator
• Station monitoring and control functions
AA-CoDRApril 2011 High Level System Description
Station processor
PrimaryStation
ProcessorBoard
0
…..
PrimaryStation
ProcessorBoard
1
…..
PrimaryStation
ProcessorBoard
(max 35)
…..
…..
SecondaryStation
ProcessorBoard
0
SecondaryStation
ProcessorBoard
1
SecondaryStation
ProcessorBoard
(max 35)
…..
…..
…..
…..
…..
…..
…..
012
35
ToElement
Digitisation
Long distance drivers
…..
012
Long distance drivers
…..
Long distance drivers
…..
Optical linksTo Correlator
Each link is 12 fibre lanes@10Gb/s
“All to All”Connections
Each link is 12 fibre lanes@10Gb/s
…..
…..
…..
Station Processor
o/eo/eo/eo/eo/eo/e
o/eo/eo/eo/eo/eo/e
o/eo/eo/eo/eo/eo/e
o/eo/eo/eo/eo/eo/e
o/eo/eo/eo/eo/eo/e
o/eo/eo/eo/eo/eo/e
e/oe/oe/oe/oe/oe/o
e/oe/oe/oe/oe/oe/o
e/oe/oe/oe/oe/oe/o
e/oe/oe/oe/oe/oe/o
e/oe/oe/oe/oe/oe/o
e/oe/oe/oe/oe/oe/o
PChip
PChip
PChip
PChip
PChip
PChip
PChip
PChip
PChip
PChip
PChip
PChip
012345
303132333435
Each link is 12 fibre lanes@10Gb/s
To Element digitisationor Primary
Station Processors
To Secondary Station Processors or long distance fibre drivers
Each link is 12 fibre lanes@10Gb/s
Each link is 12 diff. copper lanes@10Gb/s
12-channel Rx module. e.g Avago
AFBR-820BXXZ
12-channel Tx module. e.g Avago AFBR-810BXXZ
Total Raw input data rate: 4.32Tb/s
Total Raw output data rate: 4.32Tb/s max
“All to All”Connections
ControlProcessor
LineTx/R
x
Station Control
Requirements:• High bandwidth in • High bandwidth out• Largely cross connected• Scaleable at various levels• Programmable beamforming
AA-CoDRApril 2011 High Level System Description
Communications
AA-CoDRApril 2011 High Level System Description
Two stage beamforming
Tile beam
Station beams
Central ‘perfect’ beam
Incoming signal
Electronic Delay
+ + + + + + + + + + + + + + + + + + + + + + +
Beam
Elements
+ + + + +
TilesStation processor
t
Del
ay
Element #
Tile Beam
0
Filling “Tile beams” with station beams leads to discontinuities in the beamforming for off-centre beams
Can be resolved with
higher data rate Tile
to station processor
AA-CoDRApril 2011 High Level System Description
AA DemonstratorsArray Scale Site Purpose & Comments
AAVS02011/2
AA-low 10-16 elements Local to developers
Prove electromagnetic performance on full-size elements in small array. Multiple arrays to be built.
AA-mid ~1m2 tile Test chambersFor ORA: prove concept and LNA interfaceFor Vivaldi: refine array and manufacturing techniques
AAVS12013/4
AA-low 256-512 elements Selected SKA
site strongly preferred.
Single station to prove complete front-end including the LNA and analogue chain. Show actual Tsys, beam performance and time stability. Single station showing beam performance and the limits of analogue power requirementsAA-mid 256-512 clusters
of ≥4 elements
AAVS22015/6
AA-low
,000’s of elements in a single and/or multiple arrays Selected SKA
site.
Pre-production system for SKA1 AA-low system, testing the actual SKA1 components. This provides essential input to the PRR. May be configured in one or multiple arrays as required.
AA-midArray of stations of 256-512 tiles of ≥4 elements
Multiple stations, similar to AAVS1, to show imaging performance. Final proving for SKA2. Small numbers of beams for processing reasons.
Simple processing
UNIBOARD?
UNIBOARD2?
AA-CoDRApril 2011 High Level System Description
Discussion
Signal processing is at the heart of SKA Aperture Arrays• Ingredients:
– Distribution– The core– Digitisation– Communications– Data rates– Beam precision
• Noise insertion?
• UNIBOARDx• CASPER • AAVSx processing• Scaleability• RF over fibre
• Algorithm development• Programming tools
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