1. Roshene McCool SKADS Workshop 2007 DS3 – T1 Network Infrastructure and Data Transmission Roshene McCool Simon Garrington University of Manchester

2. Roshene McCool SKADS Workshop 2007 DS3 – T1 Network Infrastructure and Data Transmission U.o.M Objectives 1.Development of a prototype phase transfer system over installed fibre links. 2.Cost model analysis for all aspects of the data network including installation and equipment costs.

3. Roshene McCool SKADS Workshop 2007 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 over 1 minute (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)

4. Roshene McCool SKADS Workshop 2007 Adapting a working design for the SKA MERLIN LBL The MERLIN telescope, based at Jodrell Bank, achieves coherent operation using a frequency standard transmitted at 1486.3MHz. This system is locally known as the ‘L-band Link’ (LBL). The LBL measures the round trip delay to a distant antenna and corrects for half this delay in the correlator. The system assumes reciprocity between the go and return path delays. The current MERLIN LBL works to 1 ps over periods of hours

5. Roshene McCool SKADS Workshop 2007 Adapting a working design for the SKA LO Over Fibre Plan to use our existing equipment, simply transmit the signal optically, rather over microwave links. Observe if the fibre link is reciprocal over distances up to 120 km Show the current system is no worse than the existing system Show that the system is accurate to 1 ps over 1 minute and 10 ps over 10 minutes

6. Roshene McCool SKADS Workshop 2007 Experimental set up

7. Roshene McCool SKADS Workshop 2007 Experimental procedure Data sampled at one second intervals. Measure the one way transmission delay & compare this to, half, the round trip delay. –(Link Delay – Lab Delay = Difference) If the fibre is reciprocal the difference value should be zero. Measure the stability of the difference value over 1 min and 10 minutes. –Take samples of the difference values at 1 minute & 10 minute intervals –Draw a straight line through the points –Calculate the excursion of the measured data from the predicted value based on the straight line between the points

8. Roshene McCool SKADS Workshop 2007 Results so far…..

9. Roshene McCool SKADS Workshop 2007 Results so far …..

10. Roshene McCool SKADS Workshop 2007 Phase transfer - conclusions The stability of the link within a 1 minute and 10 minute timescale is within ±5 ps. This means the LO over fibre is in spec on the 10 minute timescale. The experimental error does not allow measurements down to 1 ps over 1 minute and therefore we need further work to obtain measurements at that accuracy. The 110 km fibre link works as well as a link with no fibre at all in both cases.

11. Roshene McCool SKADS Workshop 2007 SKADs Costing Exercise Asked to look at costing for the communications sections of the SKADs design. –Assumed 8.6 Tbits/s per station. –Assumed the use of lasers mounted on custom built DSP boards and transmission over a private fibre network. –Not restricted to the use of commercial protocols and equipment. –Used detailed cable installation & test cost analysis commissioned for the ALMA project (€ 45/km) –Civils costs included separately

12. Roshene McCool SKADS Workshop 2007 SKADs Costing Exercise - Conclusions Costing model shows communication costs are estimated at €155 Million, 8% of the total SKADs design. –(Much greater if links > 480km are included) For the costing model data links were restricted to 480km. –Further work is required to assess the best way to build links at longer distances. –Illustrated the need for compromises on bandwidths at long distances. Next steps –More optimisation of design solution required –Maintain a watching brief on technology solutions.

13. Roshene McCool SKADS Workshop 2007 Questions