Alternative Positioning, Navigation and Timing (APNT) for Performance Based Navigation (PBN)

Transcription

1 DLR.de Chart 1 Alternative Positioning, Navigation and Timing (APNT) for Performance Based Navigation (PBN) Presented by Boubeker Belabbas Prepared by : Nicolas Schneckenburger, Elisabeth Nossek, Dmitriy Shutin, Boubeker Belabbas DLR, Institute of Communications and Navigation For the International Technical Symposium on Navigation and Timing Session 3: Air Navigation Toulouse, 18 November 2014

2 DLR.de Chart 2 Current Situation GNSS in Civil Aviation GNSS as the primary means of navigation by both SESAR and NextGen for all phases of flight. Satellite Weak signals GNSS is a vulnerable to radio frequency interference and GNSS could potentially be unavailable in a very large area APNT (alternative positioning, navigation and timing) system needed as backup for GNSS in civil aviation Interferer ~20 km radius

3 DLR.de Chart 3 Ranging Source Candidates (Existing Infrastructure) Improved distance measuring equipment (DME) Standard DME including increased performance and increase of number of ranging source. Enhanced DME (UTC synchronized beat, DME carrier phase tracking) ADS-B transmitted signals Mode S Extended Squitter (mode ES) using 1090 MHz 978 MHz UAT Secondary surveilliance radar mode N in the band [ MHz]

4 DLR.de Chart 4 LDACS1 Signals for Communication L-band Digital Aeronautical Communication System, Type 1 Cellular deployment concept with frequency division duplexing Ground stations (GS) are separated in frequency Multiple-access : OFDM (forward link) and OFDMA+TDMA(reverse link) LDACS1 channels are allocated between DME channels Net data rates: up to 2.59 Mbit/s GS ff 4 GS ff 5 GS ff 3 GS ff 1 GS ff 6 GS ff 2 GS ff 7 DME L-DACS1

5 DLR.de Chart 5 LDACS Signals for Navigation The LDACS1 communication system is a cellular network Ground stations (GS) are separated in frequency Time-synchronous transmission is assumed Communication signals from multiple ground stations can be used for ranging and navigation

6 DLR.de Chart 6 LDACS-NAV Measurement Campaign (2012) Ground station setup C A B D ( OpenStreetMaps)

7 DLR.de Chart 7 Station Setup For GPS Time Transfer Station configuration within laboratory Dual Frequency GPS Time Transfer Solution Calibrated time transfer equipment Temperature controlled atomic clock setup Robust tracking of station offsets to GPS time Application to synchronize LDACS signals

8 DLR.de Chart 8 Stabilities of Time Transfer Within Specification Stabilities dominated by measurement noise (slope -1) Rubidium clocks proven for campaign

9 DLR.de Chart 9 Flight Scenarios (2013) 10 MHz: En-Route Maximum RX-TX distance: 410 km Openstreetmap/MapQuestOpen

10 DLR.de Chart 10 Flight Scenarios (2013) 10 MHz: Approach & Landing Three missed approaches at low altitude High banking angles (45 ) Openstreetmap/MapQuestOpen

11 DLR.de Chart 11 Flight Scenarios (2013) Calibration Direct connection between TX and RX allows compensation of all internal delays & filter characteristics (except antennas) Atomic clocks are synchronized before start and after landing Clock & TX-RX synchronization error: < 1ns

12 DLR.de Chart 12 Doppler-Delay Plot Video Channel impulse response shows power of different multipath components over delay By combining multiple snapshots ii = 1 II, the Doppler frequency of each component can be resolved Video

13 DLR.de Chart 13 Power Delay Profile (PDP) PDP is a statistical tool to evaluate the channel impulse response h ii ττ over the snapshots ii = 1 II NN YY h ττ = cc kk exp ( jjjjjjj kk kk=1 ) CC kk NN cc Power AA ττ is normalized to the free space loss (FSL) AA ττ = 1 II II ii=1 h ii ττ 2 LL FFFFFF PDP shows probability for a power AA for a certain delay ττ pp( AA, ττ)

14 DLR.de Chart 14 Power Delay Profile (PDP) Approach & Landing Altitude: Range: Data length: m above ground km 12 min Histogram

15 DLR.de Chart 15 Power Delay Profile (PDP) En-Route Altitude: Range: Data length: 11 & 8 km above sea level km 10 min

16 DLR.de Chart 16 Ranging results Multipath Mitigation Super resolution algorithm detects two prominent propagation paths and estimates their parameters (delay, Doppler, Amplitude) Can we use those to estimate the scatterer positions

17 DLR.de Chart 17 Localization of Scatterers Delay Scatterers with constant delay lie on the surface of a rotated ellipsoid with receiver and transmitter as foci RR xx (xx xx 0 ) 2 aa 2 +RR yy (yy y 0 ) 2 bb 2 + RR zz (zz zz 0 ) 2 bb 2 = 1 (RR : Rotation matrix) Cutting the ellipsoid with the ground plane (zz = 0) produces a new ellipse in the xxxx plane (xx xx 0 ) 2 aa 2 + (yy yy 0) 2 bb 2 = 1

18 DLR.de Chart 18 Localization of Scatterers Doppler Scatterers with constant Doppler frequency lie on the surface of a rotated cone with its axis pointing in the same direction as the aircraft flying direction -RR xx (xx xx 0 ) 2 aa 2 +RR yy (yy y 0 ) 2 bb 2 + RR zz (zz zz 0 ) 2 bb 2 = 0 (RR : Rotation matrix) Cutting the cone with the ground plane (zz = 0) produces a hyperbola*, in the xxxx plane (xx xx 0 ) 2 aa 2 - (yy yy 0) 2 bb 2 = 1 (* Under certain circumstances also an ellipse is possible)

19 DLR.de Chart 19 Localization of Scatterers Long Range Range: 232 km Altitude m Excess Delay: 24 m

20 DLR.de Chart 20 Localization of Scatterers Long Range

21 DLR.de Chart 21 Localization of Scatterers Short Range Range: 17 km Altitude 3300 m Excess Delay: 2363 m

22 DLR.de Chart 22 Localization of Scatterers Short Range

23 DLR.de Chart 23 Ranging Performance: Improvements through carrier phase smoothing Ranging errors measured at altitude 8.5km (AMSL)

24 DLR.de Chart 24 Ranging Performance: Nominal Case Standard deviation of Gaussian over bounds for the range error deduced from measurement data of the 2012 flight trial using different smoothing constants for the carrier phase smoothing. Code 3s 12s 60s 3km 370.9m 11.7m 3.6m 1.1m 8.5km 17.4m 4.3m 2.1m 1.1m 11.5km 10.0m 3.1m 2.1m 1.5m

25 DLR.de Chart 25 Horizontal Dilution of Precision Horizontal dilution of precision for one ground station per airport. Horizontal dilution of precision for DME station locations.

26 DLR.de Chart 26 Horizontal Positioning Performance according to Range Accuracy (Results from Simulations) Standard deviation of overbound of the horizontal positioning error with σ rrrrrrrrrr = 17.4m at 8.5km (AMSL). Standard deviation of overbound of the horizontal positioning error with σ rrrrrrrrrr = 2.1m at 8.5km (AMSL).

27 DLR.de Chart 27 Horizontal Positioning with Flight Trial Data Ranging errors measured at altitude 8.5km (AMSL)

28 DLR.de Chart 28 RNP level over Germany using all DME locations

29 DLR.de Chart 29 Conclusion Very detailled channel modelling providing a good characterization of the multipath effect have been presented LDACS1 ranging performance are very promissing although the limited bandwidth, Code smoothing using Doppler frequency provides very good results, RNP0.3 achievable in an LDACS1 covered area

30 DLR.de Chart 30 Future Work Low altitude PBN using sparse LDACS Network Augmention with other signals of opportunity to improve geometry and integrity Augmention with additional airborne sensors to fill in the PBN gaps, Integrity assessment of the fused solution Synergies between Surveillance, Communication and Navigation towards an optimized use of the frequency band.