roshene mccool1 phase transfer & wans 4 th skads workshop, lisbon, 2-3 october 2008 local...

Roshene McCool 1Phase Transfer & WANs4th SKADS Workshop, Lisbon, 2-3 October 2008

Local Oscillator distribution over Local Oscillator distribution over fibre fibre

Roshene McCool

SPDO – Signal Transport & Networks


ContentsContents

• Distribution of LO signals over fibre

• Merlin L-Band Link (LBL)

• L-Band Link over fibre

• Results of experiments

• Is round trip correction required?

• Interferometry using a fibre LBL

• Results

• Conclusions


Transfer of Local Oscillator Transfer of Local Oscillator Signals Over FibreSignals Over Fibre

• Motivation– Accurate timing signals to all antenna & data processing stations

– Like to have transmission over fibre to avoid RFI

• Specifications– Not specified directly, yet…

– Working to ±1 ps in 1 second (driven by astronomy at high frequencies) and ±10 ps over 10 minutes

• Other LO over fibre systems– EVLA, 22 km

– ATCA, 4.5 km

• LO over fibre for the SKA & e-MERLIN– Same specifications, similar distances

– e-MERLIN, 400km (120km longest unrepeatered hop)

– Adapted MERLIN LO distribution equipment for optical transmission


Merlin L-Band Link (LBL)Merlin L-Band Link (LBL)1486.3 MHz signal arrives at the antenna with delay Φone way

Good quartz oscillator locks a 10 MHz local oscillator signal using the incoming 1486.3 MHz

The LBL equipment switches to transmit

At Jodrell the phase Φround trip

of the incoming 1486.3 MHz signal is measured.

Φround trip /2 = Φone way


L Band link over fibreL Band link over fibre

Master L-Band Link

HP 8508A Vector Voltmeter

Aerial switch

Slave L-band Link

120 MHz over 30m of RG214

120MHz over 10m of RG59

SMF28 Fibre Link (variable length)

1486.3 MHz signal

1486.3 MHz signal

Master Laser

Master Receiver

Slave Receiver

Slave Laser

-23dB

-40dB

Line stretcher


Back to Back

28.6 km @ 1550 nm

28.6 km @ 1310 nm

110 km no thermal control

110 km thermal control

Phase stability of an LBL over fibre linkPhase stability of an LBL over fibre link

ᶲround trip /2 - ᶲone way


Back to Back

28.6 km @ 1550 nm

28.6 km @ 1310 nm





Back to Back

28.6 km @ 1550 nm

28.6 km @ 1310 nm




1 ps r.m.s stability in 1 second,2 ps r.m.s stability in 10 minutes5 ps r.m.s stability in 3 hours.


Do we need round trip correction? Do we need round trip correction? Why not use a directly transmitted Why not use a directly transmitted frequency standard? frequency standard?


Do we need round trip Do we need round trip correction? correction?


Interferometry with a fibre LBLInterferometry with a fibre LBL

• Observations of calibrator sources at 5 GHz

• Used a fibre LBL, distributing LO signals from Jodrell Bank to Pickmere (28.6 km)

• Other telescopes remained on a microwave LBL

• Direct comparison of competing architectures impossible – only 1 LO connections per antenna!!

•Observations were successful.

•Fibre LBL results impressive


Link Phase stability, microwave Link Phase stability, microwave and fibreand fibre


Astronomy Phase at 5 GHz Astronomy Phase at 5 GHz (correlated and round trip correction added)(correlated and round trip correction added)

Using a microwave LBL Using a fibre LBL

** These plots are not direct comparisons and are made, using the same baseline (Knockin – Pickmere) over 5 hrs at different dates. Changes in Atmosphere will effect phase stability. However, we can certainly conclude the fibre LBL system is no worse than the microwave system.


ConclusionsConclusions• LO distribution over fibre is possible

• Over short links it may be possible to distribute phase with no round trip correction.‼ Hostage to external temperature changes

• Distribution over long links is possible using thermally controlled lasers

• Interferometry, performed at 5 GHz, using a fibre distributed LO was successful

• Further work will address fibre distributed LOs over longer distances, using repeatered and optically amplified links


QuestionsQuestions


Wide area data networksWide area data networks

Roshene McCool

SPDO – Signal Transport and Networks


ContentsContents

• Defining the problem

• Identifying the risks

• How to approach it

• Questions


IntroductionIntroduction• Defining the problem

– 6.5 Peta bits per second total data transport requirements

– In one day SKA will transport 35,000x total internet traffic of the USA* !!

– Network along arms of 3,000 km length

– To a network of ~ 300 AA stations & 600 dishes

* AT&T Analyst Conference 2007 - Stankey

x3 !x3 !


Technology risksTechnology risks• Technology risk in wide area networks – relatively low

– 40 Gbps DPQSK systems

– 10 GE SFP+ and XFP transponders commodity & address even long links

– optical transmission mature technology - EDFAs, DCMs, DWDM, CWDM

– Many possible suppliers

• Long distance fibre networks (> 500 km)– Cost of high bit rates over long distance

– Use commercial systems to avoid re-gen at lengths > 480 km

– Availability of commercial dark fibre over long distances

• Interfaces (may be none standard)


RisksRisks


Risks related to scaleRisks related to scale

Cost !!


How do we approach this problem ?How do we approach this problem ?

• Use industry & obtain a turn key solution– Transfer risk from the project to the supplier

– Now we can all go home!

• This option doesn’t let us off the hook! – Have to produce a contract that will deliver for the SKA

– Don’t know what it will cost

– Evaluate ability of suppliers to deliver

– Need a Plan B



• Target development of subsystems to directly address SKA digital signal processing design block– Efficient use of development resource

– address interface issues

– power

– Identify cost effective solutions



• Critical Analysis of solutions– Technical risk is low, telecoms industry & pathfinders can provide

solutions – but this can encourage complacency

– Implementation is on a scale not yet conceived in industry

– Hand-crafted designs in pathfinders do not necessarily scale either

– Ask questions, build systems that lead to objective metrics upon which to base costed designs for implementation.

– Optimisation is required to reduce costs


QuestionsQuestions

roshene mccool1 phase transfer & wans 4 th skads workshop, lisbon, 2-3 october 2008 local...

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