1. System Approach to RFI Mitigation for the SKA Rob Millenaar – SKA Program Development Office (SPDO), Manchester, UK http://www.skatelescope.org millenaar@skatelescope.org 4 June, 2010 1 SS2010

2. SPDO Overview Introduction –Concepts of the SKA –Receptor technology types –Array layout System wide approach to RFI mitigation –the RFI/EMI Environment –EMC –Reduction of susceptibility to RFI –Mitigation in hardware and software 2 4 June, 2010 SS2010

3. SPDO Introduction Setting the scene 3 4 June, 2010SS2010

4. SPDO The Square Kilometre Array In a nutshell: The next generation radio telescope with ~50 times sensitivity and ~10,000 times the survey speed of the best current day radio telescopes. It will operate from 70 MHz to 10 GHz Baselines of 3000+ km Candidate sites: –Southern Africa, Karoo –Australasia, Boolardy 4 4 June, 2010 SS2010

5. SPDO The Square Kilometre Array The SKA will have: –up to 3000 dishes, with: –wide band single pixel feeds –phased array feeds –~1 GHz (300 MHz) to >10 GHz –up to 250 dense Aperture Array stations (56m dia), with: –~70,000 dual pol elements, so ~150,000 receiver chains for a total of ~4 10 7 –~400-~1400 MHz –up to 250 sparse Aperture Array stations (180m dia), with: –~10,000 dual pol elements, so ~20,000 receiver chains, for a total of ~5 10 6 –~70-~450 MHz 5 4 June, 2010 SS2010

6. SPDO Configuration 6 4 June, 2010 SS2010

7. SPDO Configuration 7 4 June, 2010 SS2010

8. SPDO The challenge The conclusion should be that: –There will be various types of technology, much of which is concentrated in high densities  risk of strong electromagnetic coupling –With differing frequency ranges  what is (self-generated) out-of-band RFI for one is in-band for the other technology type, so all designs must be done considering the entire SKA frequency range! –With extreme required operational sensitivity  need for a RQZ in the center and handpicked remote sites, plus further regulation –Systems and parts should be cheap to produce and maintain  challenges to high quality, yet affordable shielding and proper engineering methods –Requires manageable data rates  so must limit number of bits to be transported and processed This results in a nightmare for EMI and RFI control, the scale of which was never seen before. Requires a rigorous system-wide mitigation approach. 8 4 June, 2010 SS2010

9. SPDO System Wide Mitigation of RFI 9 4 June, 2010SS2010

10. SPDO System Wide Approach What should be done: fight on all fronts… Provide best RFI/EMI environment EMC policy Reduction of susceptibility to RFI Mitigation in hardware and software 10 4 June, 2010 SS2010

11. SPDO System Wide Approach What should be done Provide best RFI/EMI environment EMC policy Reduction of susceptibility to RFI Mitigation in hardware and software 11 4 June, 2010 SS2010

12. SPDO EMI/RFI Environment Provide best RFI/EMI environment Investigate and select sites Establish RQZ Spectrum regulation/law making on local + national levels + active support of local community Once the perfect site is found, place antennas sensibly (Configuration design) 12 4 June, 2010 SS2010

13. SPDO Site Selection The two shortlisted sites are the best in the preferred region on the globe. Further site characterisation is underway. RFI has been measured and will be done again with higher sensitivity. 13 4 June, 2010 SS2010

14. SPDO RFI environment at the core Site characterisation results of the campaign of 2005 are available. Next slide shows ‘mode 1’ results: inventory of strong RFI, potentially detrimental because of receiver linearity. Includes high speed sampling results (2μs) from 960 to 1400 MHz. Was done for 4 to 6 antenna pointings, two polarisations. Next slide shows results of two sites combined: 1.Take maximum level of pointings/polarisations per site; 2.Plot minima and maxima of the two datasets. 14 4 June, 2010 SS2010

15. SPDO RFI environment at the core Mode 1 overall spectrum, 70MHz to 22 GHz 15 4 June, 2010 SS2010

16. SPDO Unavoidable RFI It is evident that, regardless of all measures that we take, receiver systems will have to deal with unavoidable types of RFI: Airborne –Comms –Narrow pulse & high power: nav/ATC (DME, SSR, …) Satellites –NOAA series –Iridium, GPS, Galileo –Geostationary (broadcasting, FLTSATCOM) –… 16 4 June, 2010 SS2010

17. SPDO New RFI Campaign Purpose: High sensitivity measurements (close to RA769 levels) at the core, and some remote sites at slightly less sensitivity. In addition high time resolution measurements to capture strong short events. The campaign: Deployment at AUS and SA core sites, start measurements for ~2 months –Target start June 2010 –To coordinate with precursor site activities –Measure with identical equipment (tested and verified at same facility), during the same period. Measure selection (~4 per country) of remote sites Write site reports, by April 2011. 17 4 June, 2010SS2010

18. SPDO New RFI Campaign Partners: ASTRON data processing software, binary data format, reporting software SKA SA RF, trailer infrastructure, integration CSIRO Digital spectrometer, data acquisition 18 4 June, 2010 SS2010

19. SPDO New RFI Campaign 19 4 June, 2010 SS2010

20. SPDO Campaign Sensitivity 20 4 June, 2010SS2010

21. SPDO New RFI Campaign Progress Integration of system Testing combined system, first phase done Every trick in the EMC book is required to minimise the amount of self generated RFI, which is difficult because: –Sensitivity required –Low gain antenna used –Compactness of system 21 4 June, 2010SS2010

22. SPDO Radio Quiet Zones Both sites are establishing Radio Quiet Zones at the location of the core. ~150 km radius Specific attention by ITU WP-7D and Correspondence Group Activities are being monitored by a dedicated Task Force under the SCWG. (Ref. Carol Wilson: Radio Quiet Zones and the SKA) 22 4 June, 2010 SS2010

23. SPDO Radio Quiet Zone Targets 23 4 June, 2010 SS2010

24. SPDO Further spectrum regulation Spectrum regulation/law making on local + national levels. Enforcement required. Support of local community –Alternative means of communication –Fibre to the farm –Fix noisy cars –Fix noisy electronics Work with industry on low noise power distribution, etc. 24 4 June, 2010 SS2010

25. SPDO Array Planning and Design Place antennas sensibly: Zones of avoidance defined in ‘masks’ –buffer zones around EMI sources  Roads, rail, farms, towns –buffer zones around RFI sources  Mobile comms, broadcasting Methodology: 1. Define tolerable levels of RFI (based on RA769) 2. Examine various aggregations of sources of RFI and EMI 3. Apply appropriate propagation models to arrive at required buffer zones. 25 4 June, 2010 SS2010

26. SPDO System Wide Approach What should be done Provide best RFI/EMI environment EMC policy Reduction of susceptibility to RFI Mitigation in hardware and software 26 4 June, 2010 SS2010

27. SPDO EMC Policy Appoint EMC Manager, responsible for: Definition of standards, best practice descriptions from industry and radio astronomy community EMC requirements for all parts of project Application of these to all designs and equipment Assessment of COTS hardware risks and modification Development of test systems, methods Development of EMC plan including specifications Ongoing RFI monitoring ‘EMC police’ 27 4 June, 2010 SS2010

28. SPDO EMC Policy EMC rules apply in all directions: 28 4 June, 2010 SS2010

29. SPDO EMC Policy What are items to worry about? Radiating receivers or parts Digitisation at the receiver Telescope drive systems … But also: Wireless XX, remote YY, mobile ZZ in use by staff, contractors, visitors, tourists… This is a worry at any radio telescope, but for the SKA the scale is humongous. 29 4 June, 2010 SS2010

30. SPDO System Wide Approach What should be done Provide best RFI/EMI environment EMC policy Reduction of susceptibility to RFI Mitigation in hardware and software 30 4 June, 2010 SS2010

31. SPDO Susceptibility Receiver robustness: a balancing act 31 4 June, 2010 SS2010 Design for Wide band High gain Low noise Low cost Manufacturability in large quantities Design for Sufficient Rx headroom Linear operation, IP Keep power requirements low

32. SPDO Susceptibility Digitisation: a balancing act 32 4 June, 2010 SS2010 Design for High performance High SFDR Required dynamic range: sky noise vs interference level that one aims to mitigate down the line  many bits Design for Low cost Low power Few bits, because of Cost for hardware Signal transport Signal processing in station and correlator

33. SPDO System Wide Approach What should be done Provide best RFI/EMI environment EMC policy Reduction of susceptibility to RFI Mitigation in hardware and software 33 4 June, 2010 SS2010

34. SPDO Mitigation On-line RFI mitigation is possible and required, but must be robust (!) Hardware architecture/techniques: –Narrow channelisation in frequency and time allows old fashioned RFI excision to be efficient –Cancellation trough:  ANC  Parametric Estimation  Spatial Filtering  Subspace Filtering …… Automated flagging/excision as part of the processing pipeline Mitigation techniques must be planned from the start and not be attempted as an afterthought. (Ref. Willem Baan: The Layers of RFI Mitigation) 34 4 June, 2010 SS2010

35. SPDO Summary 35 4 June, 2010SS2010

36. SPDO Elements of a systems approach Elements of RFI/EMI management discussed: Involvement in spectrum management Spectrum protection/regulation/RQZ Spectrum monitoring Array planning Receiver and backend design for RFI robustness Mitigate risks and effects where RFI does get into the system Investigate and work on a succession of ‘weakest links’ in the system in the broadest sense 36 4 June, 2010SS2010

37. SPDO Conclusions We have a serious problem on our hands… But we can succeed if… A system-wide approach is followed, to –Select the best possible environment –Protect that pristine environment  By preventing self-generated RFI  By setting and enforcing appropriate design practices  By actively participating in all aspects, and on all levels of spectrum protection and regulation –Prevent unavoidable levels of RFI from hurting us  Robust receiver systems  Robust digitisation and processing –RFI hazards that still remain, dealt with by  Effective automatic detection and mitigation in hardware, pre- and postcorrelation, and in (pipeline) software 37 4 June, 2010 SS2010