Alternate Position, Navigation & Time APNT for Civil Aviation For Working Group B of the International GNSS Committee Shanghai, May 2011 by Per Enge & Leo Eldredge Work supported by the Federal Aviation Administration under CRDA 08-G-007. This briefing is NOT intended to convey a US Government position; rather, it is provided to facilitate a working-level discussion and exchange of ideas.
Danger of Radio Frequency Interference
Danger of Radio Frequency Interference
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Why APNT? GPS radio frequency interference (RFI) requires mitigation Waiting the interference source to be turned off is unacceptable Continuity of operations must be assured at high density airports NextGen capabilities establish greater demand for precise PNT services, provided by GPS 2X traffic is more than a controller can handle using radar vectors Trajectory-based operations (TBO) will be used to improve capacity Automation will sequence aircraft performing TBOs 3 nm separation will be based on precise RNAV/RNP paths Surveillance used for conformance monitoring Controllers intercede to provide control by exception DME/DME/IRU is not accurate enough to enable 3 nm separation FAA would like to avoid $1B cost to replace aging VORs VORs are not compatible with RNAV and RNP
RFI Challenges without APNT Transitioning from 3-mile to 5-mile separation en route and on arrivals outside of 40 nm when a GPS RFI event occurs Shifting some aircraft to radar vectors significant implications Rerouting aircraft around interference area to reduce demand Throttle back demand to compensate for loss of capabilities like parallel runway approaches Limit RNAV/RNP arrivals and departures and reduce options to handling arrivals
APNT Performance Zones FL-600 Zone- 1 Enroute High CONUS FL-180 Zone- 2 Enroute Low CONUS Zone-3 Terminal OEPs + Next 100 Busiest Airports 5000 AGL 2 Slope from 500 AGL 5 SM of Airport 27 SM 89 SM
Combined Network of DMEs and GBTs 1090 DMEs 646 GBTs 8
Bay Area Coverage from Terrestrial Radio 9
Ground-to-Ground Synchronization GEO: WAAS L5 MEO: GPS LEO: Iridium DMEs + New Terminal Area DMEs + GBTs 10
Ground-to-Air Synchronization one-way ranging (aka pseudo-range) request/reply (aka two-way ranging or true range) DMEs + Planned DMEs + GBTs 11
Coverage at 500 AGL True Ranging to DMEs + GBTs 38.1 from R. Niles at Mitre & S. Lo 38 37.9 37.8 ε FTE =.0625 NM ε R = 328 m Latitude (deg) 37.7 37.6 37.5 SFO OAK 37.4 37.3 SJC 37.2-123 -122.8-122.6-122.4-122.2-122 -121.8 Longitude (deg) RNP 0.3 0.5 1 2 5 10 12
Coverage at 500 AGL True Ranging to DMEs + GBTs 38.1 from R. Niles at Mitre & S. Lo 38 37.9 37.8 ε FTE =.0625 NM ε R = 160 m Latitude (deg) 37.7 37.6 37.5 SFO OAK 37.4 37.3 SJC 37.2-123 -122.8-122.6-122.4-122.2-122 -121.8 Longitude (deg) RNP 0.3 0.5 1 2 5 10 13
Coverage at 500 AGL True Ranging to DMEs + GBTs + New DMEs 38.1 from R. Niles at Mitre & S. Lo 38 37.9 37.8 ε FTE =.0625 NM ε R = 160 m Latitude (deg) 37.7 37.6 37.5 SFO OAK 37.4 37.3 SJC 37.2-123 -122.8-122.6-122.4-122.2-122 -121.8 Longitude (deg) RNP 0.3 0.5 1 2 5 10 14
Signal Design Objectives Ranging accuracy! Present DME is not precise enough for approach operations Wider bandwidth than DME? Better coverage? New avionics would require new benefits Data capacity to support new benefits Authentication, time, identification & location + Wide area GBAS (ΔΦ) for Category II & III AGPS for GPS anti-jam WAAS & ISM for LPV Transportability to VHF? 15
APNT Signals in the DME Band 45 40 35 30 DME all histogram (X & Y) 1522 sta DME JTIDS Transponder 25 Count 20 15 978 1030 1090 GPS L5 10 5 0 950 1000 1050 1100 1150 1200 1250 Freq (MHz) Any new signal in the DME band should be pulsed to minimize impact on legacy users. Bench tests needed to verify non-interference with 4 ms pulses. 16
Aviation Signals of Opportunity INS FMS Guidance T DME R L band VHF band R T R R T GNSS UAT VOR VHF Comm ADS-B Position out 17
Aviation Signals of Opportunity INS FMS Guidance T DME R L band VHF band R T R R T GNSS UAT VOR VHF Comm APNT ADS-B Position out 18
Pulse Position Modulation (PPM) or Pulse Pair Position Modulation (PPPM) 15-10 -5 0 5 10 15 time (µsec) 15-10 -5 0 5 10 15 time (µsec) 15-10 -5 0 5 10 15 time (µsec) 15-10 -5 0 5 10 15 time (µsec) PPPM data capacity of 300 to 1200 bps 19
Universal Access Transceiver (UAT) 20
Summary 200,000 civil aircraft rely on GPS With NextGen, our reliance is increasing Consolidate & re-purpose ground navigation aids Backup GPS RNAV & RNP to ensure NextGen success 21