Roshene McCool1 Phase Transfer & WANs 4 th SKADS Workshop, Lisbon, 2-3 October 2008 Local Oscillator distribution over fibre Roshene McCool SPDO – Signal Transport & Networks

Roshene McCool2 Phase Transfer & WANs 4 th SKADS Workshop, Lisbon, 2-3 October 2008 Contents 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

Roshene McCool3 Phase Transfer & WANs 4 th SKADS Workshop, Lisbon, 2-3 October 2008 Transfer of Local Oscillator Signals 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

Roshene McCool4 Phase Transfer & WANs 4 th SKADS Workshop, Lisbon, 2-3 October 2008 Merlin L-Band Link (LBL) MHz signal arrives at the antenna with delay Φ one way Good quartz oscillator locks a 10 MHz local oscillator signal using the incoming MHz The LBL equipment switches to transmit At Jodrell the phase Φ round trip of the incoming MHz signal is measured. Φ round trip /2 = Φ one way

Roshene McCool5 Phase Transfer & WANs 4 th SKADS Workshop, Lisbon, 2-3 October 2008 L Band link over fibre

Roshene McCool6 Phase Transfer & WANs 4 th SKADS Workshop, Lisbon, 2-3 October 2008 Back to Back nm nm 110 km no thermal control 110 km thermal control Phase stability of an LBL over fibre link round trip /2 - one way

Roshene McCool7 Phase Transfer & WANs 4 th SKADS Workshop, Lisbon, 2-3 October 2008 Back to Back nm nm 110 km no thermal control 110 km thermal control Phase stability of an LBL over fibre link

Roshene McCool8 Phase Transfer & WANs 4 th SKADS Workshop, Lisbon, 2-3 October 2008 Back to Back nm nm 110 km no thermal control 110 km thermal control Phase stability of an LBL over fibre link

Roshene McCool9 Phase Transfer & WANs 4 th SKADS Workshop, Lisbon, 2-3 October 2008 Back to Back nm nm 110 km no thermal control 110 km thermal control Phase stability of an LBL over fibre link 1 ps r.m.s stability in 1 second, 2 ps r.m.s stability in 10 minutes 5 ps r.m.s stability in 3 hours.

Roshene McCool10 Phase Transfer & WANs 4 th SKADS Workshop, Lisbon, 2-3 October 2008 Do we need round trip correction? Why not use a directly transmitted frequency standard?

Roshene McCool11 Phase Transfer & WANs 4 th SKADS Workshop, Lisbon, 2-3 October 2008 Do we need round trip correction?

Roshene McCool12 Phase Transfer & WANs 4 th SKADS Workshop, Lisbon, 2-3 October 2008 Interferometry 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

Roshene McCool13 Phase Transfer & WANs 4 th SKADS Workshop, Lisbon, 2-3 October 2008 Link Phase stability, microwave and fibre

Roshene McCool14 Phase Transfer & WANs 4 th SKADS Workshop, Lisbon, 2-3 October 2008 Astronomy Phase at 5 GHz (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.

Roshene McCool15 Phase Transfer & WANs 4 th SKADS Workshop, Lisbon, 2-3 October 2008 Conclusions 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

Roshene McCool16 Phase Transfer & WANs 4 th SKADS Workshop, Lisbon, 2-3 October 2008 Questions

Roshene McCool17 Phase Transfer & WANs 4 th SKADS Workshop, Lisbon, 2-3 October 2008 Wide area data networks Roshene McCool SPDO – Signal Transport and Networks

Roshene McCool18 Phase Transfer & WANs 4 th SKADS Workshop, Lisbon, 2-3 October 2008 Contents Defining the problem Identifying the risks How to approach it Questions

Roshene McCool19 Phase Transfer & WANs 4 th SKADS Workshop, Lisbon, 2-3 October 2008 Introduction 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 Stankey x3 !

Roshene McCool20 Phase Transfer & WANs 4 th SKADS Workshop, Lisbon, 2-3 October 2008 Technology 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)

Roshene McCool21 Phase Transfer & WANs 4 th SKADS Workshop, Lisbon, 2-3 October 2008 Risks

Roshene McCool22 Phase Transfer & WANs 4 th SKADS Workshop, Lisbon, 2-3 October 2008 Risks related to scale Cost !!

Roshene McCool23 Phase Transfer & WANs 4 th SKADS Workshop, Lisbon, 2-3 October 2008 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 

Roshene McCool24 Phase Transfer & WANs 4 th SKADS Workshop, Lisbon, 2-3 October 2008 How do we approach this problem ? 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

Roshene McCool25 Phase Transfer & WANs 4 th SKADS Workshop, Lisbon, 2-3 October 2008 How do we approach this problem ? 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

Roshene McCool26 Phase Transfer & WANs 4 th SKADS Workshop, Lisbon, 2-3 October 2008 Questions