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John Pahl and Steve Munday Transfinite Systems Ltd

Re-examination of the protection requirements for the Radio Astronomy Service in light of the Broadband Fixed Wireless Access Multimedia Wireless Systems proposed for the 42.5 - 43.5 GHz frequency band. John Pahl and Steve Munday Transfinite Systems Ltd. Presentation Structure.

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John Pahl and Steve Munday Transfinite Systems Ltd

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  1. Re-examination of the protection requirements for the Radio Astronomy Service in light of the Broadband Fixed Wireless Access Multimedia Wireless Systems proposed for the 42.5 - 43.5 GHz frequency band John Pahl and Steve Munday Transfinite Systems Ltd BFWAtg - BFWA sharing with RAS at 43 GHz

  2. Presentation Structure • Project objectives and approach • System parameters used • Approach to analysis • Results of runs • Conclusions BFWAtg - BFWA sharing with RAS at 43 GHz

  3. Project objectives • To analyse the feasibility of BFWA operating in the 42.5 - 43.5 GHz band, taking into account the need to protect the RAS • Determine the conditions that would facilitate sharing, such as operating restrictions • Evaluate existing work and approaches to sharing such as in ERC Report 36 • Derive, where necessary, methodologies to model interference and assist in sharing BFWAtg - BFWA sharing with RAS at 43 GHz

  4. System Parameters • Obtained from review of previous studies, current literature and discussion with operators • Data sets developed for different types of BFWA systems: • 3 types of Mesh system - low, medium and high density • 6 types of Point-to-Multipoint system • Urban Symmetric and Asymmetric models • Sub-urban Symmetric and Asymmetric models • Rural Symmetric and Asymmetric models • 2 types of Feeder link • Variations to analyse impact of modeling assumptions and mitigation BFWAtg - BFWA sharing with RAS at 43 GHz

  5. BFWA Baseline Models • From the data sets, the following were selected as baseline reference models for use in the analysis: • P-MP Urban, Commercial, Symmetric Model (UCS) • P-MP Rural, Residential, Asymmetric Model (RRA) • Low Density Mesh Model • High Density Mesh Model • Feeder Link Model • P-MP models included both BS and UT transmit, giving a total of 7 BFWA models BFWAtg - BFWA sharing with RAS at 43 GHz

  6. BFWA Mitigation • Study alternative modeling assumptions and to facilitate sharing • BFWA mitigation models included: • Realistic model • Baseline model with antenna modeled as Bessel function • Pointing model • Realistic model with restriction to avoid pointing at RAS site • Full Mitigation • Pointing model with antenna height restriction, shielding and spreading loss BFWAtg - BFWA sharing with RAS at 43 GHz

  7. RAS Reference Models-1 8 potential sites that could operate RAS at 43 GHz BFWAtg - BFWA sharing with RAS at 43 GHz

  8. RAS Reference Models-2 • Three RAS sites considered - Jodrell Bank, Defford and Cambridge • Protection criteria obtained from ITU-R Rec. RA.769 for three types of observation: RAS protection criteria / 1 MHz BFWAtg - BFWA sharing with RAS at 43 GHz

  9. RAS Reference Models-3 • Baseline model: • Gain pattern Rec. SA 509-2, ie 32-25log() • Minimum elevation 5° • Realistic model: • Baseline model with antenna modeled as Bessel function • Pointing model: • Realistic model with minimum elevation of 19° In all cases observation time 2000 seconds BFWAtg - BFWA sharing with RAS at 43 GHz

  10. RAS gain patterns Up to 35 dB difference ! BFWAtg - BFWA sharing with RAS at 43 GHz

  11. Summary Summary of Baseline and Mitigation Models BFWAtg - BFWA sharing with RAS at 43 GHz

  12. Approach to Analysis • Start from ERC Report 36 • Analyse its assumptions and models • Develop new modelling methodology to calculate interference • Develop methods to facilitate sharing • Study impact of implementation details such as: • RAS operational methods • potential distribution of BFWA systems BFWAtg - BFWA sharing with RAS at 43 GHz

  13. ERC Report 36 • Proposes co-ordination distance of 50 km • Based upon: • single FS transmitter • smooth earth ITU-R Rec. P.452 propagation • antenna heights of 5-10m • None of these realistic, eg: using RAS & BFWA heights of 30m  36 dB worse BFWAtg - BFWA sharing with RAS at 43 GHz

  14. Single vs Aggregate Interference • ERC Report based upon single transmitter • Analysed impact of large numbers of transmitters • Simulated impact of adding rings of transmitters every 4 km from 50 - 110 km • Interference increased: • ~12 dB single station to all stations in 50 km ring • ~17.5 dB single station to all rings 50 - 110 km BFWAtg - BFWA sharing with RAS at 43 GHz

  15. Single Entry vs Aggregate Interference by distance BFWAtg - BFWA sharing with RAS at 43 GHz

  16. Modelling Conclusions 1. Analysis of BFWA sharing with RAS using ITU-R Rec. P.452 propagation should be based upon realistic antenna heights. 2. Analysis of BFWA sharing with RAS should be based upon aggregate interference from all potential transmitters. 3. The calculation of aggregate interference need not include transmitters at a distance of more than 110 km from the RAS site. 4. Accurate modelling of interference from BFWA into RAS should include the impact of terrain on propagation loss. BFWAtg - BFWA sharing with RAS at 43 GHz

  17. Methodology • Needed to develop methodology to analyse interference from large numbers of BFWA transmitters • Methodology included impact of: • terrain • mitigation • variation in BFWA cell configurations • type of RAS observation • Approach based on cells as Building Blocks, using Monte Carlo techniques to aggregate interference BFWAtg - BFWA sharing with RAS at 43 GHz

  18. Example Building Block BFWAtg - BFWA sharing with RAS at 43 GHz

  19. Example EIRP Distribution BFWAtg - BFWA sharing with RAS at 43 GHz

  20. Example distribution of test stations BFWAtg - BFWA sharing with RAS at 43 GHz

  21. Monte Carlo Approach BFWAtg - BFWA sharing with RAS at 43 GHz

  22. Analysis and Results-1 • Based upon ERC Report exclusion distance of 50 km • Study impact of input parameters: • Compare modelling assumptions • Compare impact mitigation methods • Compare BFWA architectures • Compare RAS sites BFWAtg - BFWA sharing with RAS at 43 GHz

  23. Baseline results: EZ=50km no mitigation Runs exceeding limit: all BFWAtg - BFWA sharing with RAS at 43 GHz

  24. Baseline results: EZ=50km with mitigation Runs exceeding limit: Mesh LD, Mesh HD, RRA BS BFWAtg - BFWA sharing with RAS at 43 GHz

  25. Results of initial runs • 50 km exclusion distance in ERC Report is not sufficient to protect RAS site • Modeling gain patterns using Bessel functions significantly reduces interference (25 - 30 dB) • Imposing pointing restrictions on BFWA reduced interference by further 12 - 30 dB • Results between RAS sites similar - variation 0 - 10 dB. Jodrell Bank and Defford most alike as similar terrain profile. BFWAtg - BFWA sharing with RAS at 43 GHz

  26. Implications • No one BFWA architecture was worse under all situations, e.g.: • Mesh worst without mitigation, but has more ability to decrease interference • P-MT RRA best without mitigation, but limited ability to decrease interference • Most important factors are: • use of pointing mitigation • gain pattern assumed - in particular for RAS BFWAtg - BFWA sharing with RAS at 43 GHz

  27. Methods to facilitate sharing • BFWA operating restrictions • Combining mitigation with Exclusion Zones (EZs) • BFWA cell distribution and architectures based upon UK census data • RAS operational considerations • observation types BFWAtg - BFWA sharing with RAS at 43 GHz

  28. Exclusion Zone Methods • Traditionally based upon distance, D • Not appropriate when including terrain: • azimuth dependent • does not linearly increase along azimuth • Propose use of new EZ method: • Exclude all locations where L452(10%) < X • Compare these two EZ methods • Change size of EZ (D or X) using iteration until just meet RAS criteria BFWAtg - BFWA sharing with RAS at 43 GHz

  29. EZ based upon distance EZ for RRA BS smooth earth analysis D=66km BFWAtg - BFWA sharing with RAS at 43 GHz

  30. EZ based upon L452(10%) < X EZ for RRA BS with terrain L452(10%) < -176 dB BFWAtg - BFWA sharing with RAS at 43 GHz

  31. Impact of L452(10%) method • Easy to define and implement • Reduces area excluded • e.g. from 13,872 km2 to 2,816 km2 • Excludes points such as tops of mountains unlikely to be used anyhow Note: L452(10%) is height dependent, so must specify maximum tx/rx antenna heights BFWAtg - BFWA sharing with RAS at 43 GHz

  32. Multi-Zone approach BFWAtg - BFWA sharing with RAS at 43 GHz

  33. Analysis and Results-3 • Following Multi-Zone approach: • EZ: no BFWA operation • RZ: BFWA operating with pointing mitigation • UZ: BFWA operating unrestricted • Boundaries EZ/RZ and RZ/UZ based upon where L452(10%) = X1, X2 (derived in analysis) • Distribution of BFWA cells based upon UK Census data • Multiple runs for alternative RAS assumptions BFWAtg - BFWA sharing with RAS at 43 GHz

  34. Production of realistic BFWA distribution • Mapped 1991 UK Census data to BFWA types based on populated weighted density (persons / km2) : • Mesh LD rather than P-MP RRA used for low population areas as needed ability to mitigate BFWAtg - BFWA sharing with RAS at 43 GHz

  35. Realistic BFWA distribution Key: circles = P-MP in urban areas, crosses = mesh LD in rural areas BFWAtg - BFWA sharing with RAS at 43 GHz

  36. Worst case: RAS mask gain pattern + no BFWA mitigation Single EZ - RAS Baseline and BFWA Realistic BFWAtg - BFWA sharing with RAS at 43 GHz

  37. Improvement due to use of MZ and Bessel gain pattern Key: circles = BFWA cells in UZ, crosses = BFWA cells in RZ Multi-Zone - RAS Realistic BFWAtg - BFWA sharing with RAS at 43 GHz

  38. RAS observing method • Analysis above based upon RAS most stringent criteria -220.6 dBW/MHz • This is to protect a single RAS site making Continuum observations • Criteria to protect VLBI and Spectral line observations are higher • Analysis was also done against these thresholds BFWAtg - BFWA sharing with RAS at 43 GHz

  39. Results: VLBI • Based upon: • BFWA using MZ (EZ/RZ/UZ) • RAS modelled using higher elevations and Bessel gain patterns • Comparing against VLBI threshold • Conclusion: • BFWA can operate close (~10 km) of RAS site BFWAtg - BFWA sharing with RAS at 43 GHz

  40. Locations of EZ/RZ/UZ for VLBI Key: circles = BFWA cells in UZ, crosses = BFWA cells in RZ BFWAtg - BFWA sharing with RAS at 43 GHz

  41. Best case sharing scenario RAS: • operates only as VLBI and SL (single site) • antenna gain pattern similar to Bessel function • generally operates at elevations  19° BFWA: • uses multiple zones EZ/RZ/UZ • zones based upon L452(10%) • at least pointing mitigation used within RZ • frequency plan takes account of SL frequencies BFWAtg - BFWA sharing with RAS at 43 GHz

  42. Impact of RAS assumptions • Worst case - sharing very difficult with large areas excluded: • RAS single site Continuum observations, gain pattern 32-25log() • Intermediate case - sharing possible but significant areas excluded: • RAS single site Continuum observations, gain similar to Bessel • Best case - sharing possible almost everywhere except very close to RAS site: • RAS VLBI & Spectral line observations, gain pattern similar to Bessel, elevation angles  19° BFWAtg - BFWA sharing with RAS at 43 GHz

  43. Conclusions • On its own, an exclusion zone of 50 km as in ERC Report 36 is insufficient to protect the RAS • The methodology and assumptions used to derive this figure are inappropriate for BFWA scenarios • New methodology described here can be used to calculate aggregate interference BFWA  RAS • Use of Exclusion Zones based upon L452(10%) are more efficient than using distance • Multiple zones can be used to improve coverage without requiring mitigation everywhere • The characteristics of RAS operating in this band will determine the extent for which BFWA can be deployed BFWAtg - BFWA sharing with RAS at 43 GHz

  44. Areas for Further Study • The following require further study: • whether the RAS will use the 43 GHz band to make Continuum observations from single sites • what is the average gain pattern of RAS antennas towards the horizon over typical observation time From above can determine EZs to protect RAS for specified BFWA systems Further work also needed to define how to model correlation of propagation effects using Rec. 452. • More runs could analyse wider range of scenarios BFWAtg - BFWA sharing with RAS at 43 GHz

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