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DME and GNSS L5/E5 Compatibility

DME and GNSS L5/E5 Compatibility. ICAO EUR FMG / WRC-19 Workshop – Paris, SEP 2017. Gerhard Berz & Valeriu Vitan Navigation and CNS Research Unit. Background. Initial Compatibility Studies and ITU Agreements concluded in 2000

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DME and GNSS L5/E5 Compatibility

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  1. DME and GNSS L5/E5 Compatibility ICAO EUR FMG / WRC-19 Workshop – Paris, SEP 2017 Gerhard Berz & Valeriu Vitan Navigation and CNS Research Unit

  2. Background • Initial Compatibility Studies and ITU Agreements concluded in 2000 • Implementation of new GNSS signals and Dual Frequency Receivers advancing slower than expected (SV exceeding design life) • Normal that assumptions evolve over such a timespan • Both on DME environment and GNSS Receiver technologies • DME has clear priority over GNSS per ITU • GNSS has higher operational performance and utility • Implementation of PBN expected to lead to equalization of DME density • If DME is really required which increases hotspot, it can go there • Only wish to be smart about managing compatibility • Demonstrate proactive frequency management within aviation DME and GNSS L5/E5 Compatibility

  3. Motivation ICAO GNSS Manual (Doc 9849) 5.2.5: • Initial compatibility studies concluded that: • The impact of interference on the processing of the new GNSS signals is tolerable. • A high density of DME/TACAN facilities operating in or near the new GNSS band could result in interference with GNSS signals at high altitudes. • “States should assess whether an increase of the DME/TACAN infrastructure is compatible with expanded use of GNSS and if necessary reallocate DME assignments away from GNSS frequencies” • Objective of this work is to AVOID reallocations • Especially any impact on paired VOR • Long term evolution towards target PBN Infrastructure DME and GNSS L5/E5 Compatibility

  4. Previous Work • Simulations of C/N0 degradation at FL 400 carried out by ENAC and EUROCONTROL in 2015 • The results showed that compatibility is ensured over Europe even in the most pessimistic scenario (EUROCAE Rx antenna Mask, Terrain not considered, JTIDS/MIDS case 8). • Results presented to RAFT & FMG meetings. Actions agreed: • Further update of SAFIRE COM3 mainly in what regards the operational status of DME/TACAN assignments – Frequency Managers • Present a DME interference margin map to assist in assessing the assignment of operating channels for new DME stations – NM (EUROCONTROL) • Collect and post-process flight test data aiming at validating the simulation results – NM (EUROCONTROL) DME and GNSS L5/E5 Compatibility 4

  5. Updated Assessments (1) • Parameters • Updated DME/TACAN database (only operational facilities) • DTED 1 terrain model • 40 000 feet altitude • RTCA/EUROCAE GPS antenna and IF filter masks (2 different scenarios) • JTIDS/MIDS Case 8 scenario (considered also by the previous studies) • ECAC area, 1 arc deg. granularity • Types of plots • C/N0 degradation • C/N0 degradation margin - Max allocation to DME/TACAN/JTIDS: 7.5dB (takes into account the inter-system interference) DME and GNSS L5/E5 Compatibility

  6. Updated Assessments (2) • EUROCAE scenario • Simulated C/N0 degradation exceeds 7dB, in some areas of core ECAC • Practically no margin available (less than 0.5 dB) • RTCA scenario • Maximum C/N0 degradation approx. 6dB, at least 1dB less than in the EUROCAE scenario. • 1 dB margin still available • New DME channels in L5/E5 band in/near the European hotspot to be avoided • Still possible to operate new facilities in this sub-band in areas with lower DME/TACAN network density. DME and GNSS L5/E5 Compatibility

  7. Monitoring Flight 2016 • Several monitoring objectives: VDL2, 1030/1090 MHZ, L5 • Executed by NLR - Cessna Citation II (PH-LAB) • Data recorded and processed by CCRM – Full Report presented to MOST 1 meeting. Executed by NLR DME and GNSS L5/E5 Compatibility

  8. Monitoring Flight – Data Analysis DME and GNSS L5/E5 Compatibility

  9. Monitoring Flight - Main Findings • Navaids database and line-of-sight prediction confirmed in most cases • Location of hotspots confirmed in Frankfurt and Paris areas • Measured DME PRF (in average 1000 ppps) significantly lower than max squitter rate (2700 ppps) • Measured TACAN PRF (in average 3200 ppps) close to the assumed value (3600 ppps) • Recorded signal levels in general lower than predicted • Measured blanking duty cycle lower than predicted even when using the less pessimistic methodology: RTCA/ITU • JTIDS/MIDS signals identified (e.g. over Frankfurt) DME and GNSS L5/E5 Compatibility

  10. Monitoring Flight - Blanking duty cycle Frankfurt Paris DME and GNSS L5/E5 Compatibility

  11. Monitoring Flight - Limitations • Discrepancy observed between the estimated and measured noise floor, potential impact on the level measurements calibration • A number of anomalies observed in the recorded data • Detection algorithm sensitive to noise floor setting, potential impact on measured PRF • The measurements may not be representative for the peak traffic hours • Results should not be taken as a worst case scenario • Additional data to be recorded in the future monitoring flights; • Acquisition setup and data processing to be refined DME and GNSS L5/E5 Compatibility

  12. Monitoring Flight - 2017 • PRF recorded at the transponder for AFI (by courtesy of BELGOCONTROL) • Average PRF level very close to that measured from the data recorded in the previous flight: 824 ppps DME and GNSS L5/E5 Compatibility

  13. New DME channels assignment method • Currently the RFF best practices recommend not to assign channels 77X to 126X (reply frequency above 1164 MHz) • Concern expressed in previous RAFT meeting: Very limited number of channels available for new assignments in the hotspot. If these channels are assigned elsewhere, new incompatibilities might be created. Idea is to balance assignments to ease hotspot. • New assessment methodology proposed • D > 250NM to the hotspot (C/N0 margin less than 2dB) • 1st priority - channels 77X to 101X (reply on1164 – 1188 MHz, i.e. L5/E5 ) • D < 250NM to the hotspot • 1st priority - channels 17 to 69 X&Y (reply on 978 – 1148 MHz) • 2nd priority - channels 102X to 126X (reply on1189 – 1215 MHZ, i.e. E5b / G3 - GLONASS) • Currently discussing application of additional far away limit (no channels in 77X-126X) DME and GNSS L5/E5 Compatibility

  14. New DME channels assignment D > 250NM Priority: 77X to 101X (L5/E5 band) C/N0 margin <2dB D < 250NM Priority: 17 to 69 X&Y 102X to 126X DME and GNSS L5/E5 Compatibility

  15. Maximum number of new stations in radio-LoS DME and GNSS L5/E5 Compatibility

  16. FMG22 Meeting (2016) • Work seen as necessary and appreciated, however some view points and concerns expressed: • MCMF GNSS has clear advantages that would support the provision of operational benefits mainly in the terminal areas and the approach phase of flight. Not critical for en-route operations. • The need for protecting the MCMF receivers at en-route flight levels was questioned. • More exhaustive analyses, in particular regarding operational needs for MCMF GNSS receivers, should be conducted. • FMG agreed to: • Invite PBN experts and airspace designers to attend the next FMG meeting • Addresses the FMG concerns to the EANPG DME and GNSS L5/E5 Compatibility

  17. Reply from Eurocontrol NSG / ICAO PBN TF • Agreed that lack of GNSS L5 reception at ENR altitude will likely not result in critical operational issues • However, continuous DF reception during all phases of flight remains highly desirable • Especially if compatibility can be ensured without undue effort • In line with agreement achieved in ITU compatibility studies • Two Main Supporting Arguments • Current experience with GPS outages is that they occur primarily at En-Route Altitudes • May include aircraft without DME/DME avionics or areas with limited DME/DME coverage • Multi-Constellation GNSS Design Flexibility • Online ARAIM Architecture envisages hourly ISM update rate, assumption is that it can be received while en-route with slow repeat rates • ISM message for all architectures likely to be sent on L5 only • In general, limiting to one frequency limits design options for both core constellation providers and augmentations DME and GNSS L5/E5 Compatibility

  18. Conclusions • In Cooperation with Eurocontrol Network Manager Radio Frequency Function, a “DME Hotspot Management Process” is being agreed and implemented to facilitate GNSS L5 Compatibility • Development of Best Practice to help ease DME channel shortage while ensuring compatibility with GNSS L5 • Supports DME as short term A-PNT solution • Have updated corresponding tools • Compared simulation tools and methods (ENAC) • Taking into account actual operational stations • Validation of models and DME performance parameters through flight tests in DME hotspot areas • Expect to further refine methods when GNSS L5 capable receiver prototypes become available DME and GNSS L5/E5 Compatibility

  19. Thanks for your attention !! DME and GNSS L5/E5 Compatibility

  20. C/N0degradation – EUROCAE scenario Red – 6dB Black – 7.5dB DME and GNSS L5/E5 Compatibility

  21. C/N0degradation – RTCA scenario Red – 6dB Black – 7.5dB DME and GNSS L5/E5 Compatibility

  22. C/N0degradationmargin – EUROCAE scenario Red – 2dB Margin Black – 0.5dB Margin DME and GNSS L5/E5 Compatibility

  23. C/N0degradationmargin – RTCA scenario Red – 2dB Margin Black – 0.5dB Margin DME and GNSS L5/E5 Compatibility

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