AA signal processing

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


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


“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

............


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-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


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


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-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!


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-mid Array


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-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


Possible AA-mid construction

Beamformer

......

......

......

......

Beamformer

The join!

Membrane

Ground plane

Guideframe

Tile support

Ground

Top View

......

......Non-conductingGuideframe


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


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


…..


…..

Optical linksTo Correlator

Each link is 12 fibre lanes@10Gb/s

“All to All”Connections


…..

…..

…..

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


To Element digitisationor Primary

Station Processors

To Secondary Station Processors or long distance fibre drivers


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


Communications


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 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?


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 signal processing

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