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Development of An Integrated GPS/Loran Prototype Navigation System for Business and General Aviation Applications. by James Davis, Ph.D. and Steve Williams FreeFlight Systems (Waco, TX) Richard Ferrier and Linn Roth, Ph.D. Locus, Inc. (Madison, WI). GPS/WAAS Benefits vs. ILS.

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Development of An Integrated GPS/Loran Prototype Navigation System for Business and General Aviation Applications

by

James Davis, Ph.D. and Steve Williams

FreeFlight Systems (Waco, TX)

Richard Ferrier and Linn Roth, Ph.D.

Locus, Inc. (Madison, WI)

ILA 32 (Boulder, CO) - Page 2

gps waas benefits vs ils
GPS/WAAS Benefits vs. ILS
  • GPS/WAAS offers:
    • Primary means of navigation
    • More direct routes & lower MEAs
    • Some precision approach capability (with WAAS Classes 2 & 3)
    • Decommission of high cost, ground-based navigation equipment
    • Less onboard avionics
    • Increased airspace capacity

ILA 32 (Boulder, CO) - Page 3

additional benefits
Additional Benefits
  • Efficiency
    • Precision approach
      • Back-up for all current ILS approaches (250/¾)
      • Usable with advanced procedures

LNAV/VNAV

350’

  • WAAS RNP can provide lower minima at airport

LPV 250’

ILS 200’

3o

ILA 32 (Boulder, CO) - Page 4

gps vulnerability
GPS Vulnerability
  • Concern with GPS as sole means of navigation
  • “Like any radionavigation system, GPS is vulnerable to interference that can be reduced but not eliminated.” [Volpe Report (2001)]
  • Susceptible to unintentional disruption
    • Ionospheric effects, blockage from buildings, interference from narrow & wideband sources, etc.
  • Susceptible to intentional disruption
    • Jamming & spoofing of GPS signals
    • Disruption of GPS ground stations & satellites

ILA 32 (Boulder, CO) - Page 5

mitigating gps vulnerability
Mitigating GPS Vulnerability
  • “Utilization of backup systems and procedures to GPS in applications where the consequences of losing GPS are unacceptable will ensure optimum safety.” [Volpe Report (2001)]
  • Recommendations in Volpe Report:
    • Encourage development of aviation certifiable Loran-C receivers in the event Loran-C becomes a viable backup
    • Continue the FAA’s and USCG’s Loran-C modernization program until it is determined whether Loran-C has a role as a GPS backup system.
  • (Note: Much Loran infrastructure already in place)

ILA 32 (Boulder, CO) - Page 6

faa response
FAA Response
  • Team of academic, government, and industry personnel assembled to assess Loran
    • FAA Program Manager: Mitchell Narins
    • Determine if Loran can meet non-precision approach standards @ RNP 0.3 as well as stringent requirements for availability, integrity, and continuity
  • Fabrication of integrated GPS/Loran prototype navigation systems for FAA flight tests
    • Rockwell Collins and Locus, Inc.
    • FreeFlight Systems and Locus, Inc.

ILA 32 (Boulder, CO) - Page 7

why locus inc
Why Locus, Inc.?
  • Designs, supplies, and supports radionavigation products
  • SatMate is a digital, all-in-view Loran receiver
    • Adaptive filtering
    • Digital noise blanking
    • Realtime ASF corrections
    • Proprietary DSP techniques
  • Locus provides both E-field and H-field antennas
    • Combination GPS/H-field antenna for this program

ILA 32 (Boulder, CO) - Page 8

why freeflight systems
Why FreeFlight Systems?
  • Avionics products aimed primarily at aircraft other than air transport class (vs. Rockwell Collins)
    • FFS created in 2001 with the acquisition of the Business and Commuter Aircraft segment of Trimble Navigation
    • Choice supports goal of a GPS/Loran product aimed at GA aircraft, business aircraft, regional aircraft, etc.
  • Product range includes FAA-certified GPS/WAAS
    • WAAS Class 1: Non-precision approach (LNAV)
    • WAAS Class 2: LNAV/VNAV (VPL = 50 m)
    • WAAS Class 3: GLS (VPL = 12 m)

ILA 32 (Boulder, CO) - Page 9

freeflight systems locus effort
FreeFlight Systems & Locus Effort
  • Development of a two-unit, prototype integrated GPS/Loran system using 3 principal components:
    • FreeFlight Model 2101 Approach Plus GPS/WAAS Navigation System
    • Locus Beta-2 prototype SatMate 1030 Loran Receiver System
    • AeroAntenna GPS patch antenna and a SatMate H-Field Loran antenna contained in an Bendix-King ADF radome for flight test
  • Also, software, integration, and test effort.

ILA 32 (Boulder, CO) - Page 10

model 2101 satmate prototype
Model 2101/SatMate Prototype

ILA 32 (Boulder, CO) - Page 11

gps loran features
SatMate modified to incorporate:

Real-time ASF corrections for improved accuracy, availability, and continuity

Automated GRI and navigation station selection

Digital front-end to enable adaptation to changes in RF environment

Model 2101 modified to:

Provide front-panel GPS/SatMate control

Accommodate SatMate output at 115 KBaud

Provide WAAS-Class 1 accuracy

Vert/Horiz CDI added for realtime, simultaneous monitoring & comparison of GPS and Loran cross-track course deviations

H-field and GPS antennas in radome housing

H- vs E-field: P-static immunity, higher SNR, lower ECD, no GND

GPS/Loran Features

ILA 32 (Boulder, CO) - Page 12

scatter plot for antenna rotation
Scatter Plot for Antenna Rotation
  • Loran scatter plot for antenna rotated 360o (vertical centerline)
    • Data relevant to aircraft turns
  • Black - Early antenna
    • Excursion~165 ft (max 240 ft)
  • Green-New GPS/H-field antenna
    • Loran preamp update, better H-field antenna tuning, and better QA of ferrite rod & cables
    • Excursion ~ 65 ft
    • If Loran chains better controlled, excursion < 12 ft

ILA 32 (Boulder, CO) - Page 13

two pass cw auto driving test
Two-pass CW Auto Driving Test
  • Using GPS/H-field antenna
    • Yellow trace: GPS baseline
  • Black trace offset towards bottom of the plot:
    • Loran data w/o ASF corrections
  • Black trace more closely aligned with the GPS track:
    • Loran data corrected on-the-fly with ASF corrections stored on a flashcard inside the SatMate
    • ASF values previously gathered at Locus facility in Madison

ILA 32 (Boulder, CO) - Page 14

future effort phase ii
Future Effort (Phase II)
  • Proposal submitted to FAA on 22 August 2003
    • GPS/WAAS and Loran combined in a single Dzus-mount enclosure (cf. Model 2101, but 1-7/8” higher)
    • Capability to simulate loss of WAAS coverage, loss of GPS integrity, and total loss of GPS enables assessment of Loran as a back-up to GPS
  • Multiple navigation solutions with goal of RNP 0.3 accuracy & integrity
    • GPS only
    • Loran only
    • Integration of GPS and Loran position & integrity data

ILA 32 (Boulder, CO) - Page 15

acknowledgement
Acknowledgement
  • Contract DTFA01-98-C-00061
    • Task Order #048 (currently at MOD 011)
    • “Development of Prototype H-Field Electronics and Software for Initial FAA Flight Tests”
  • Sponsorship
    • FAA Navigation & Landing IPT, AND-700
    • FAA Navigation & Landing Team, AND-740

ILA 32 (Boulder, CO) - Page 16

references
References
  • Enge and van Graas, “Chapter 6 - Integration of GPS and Loran-C”, Global Positioning System: Theory and Applications Vol. II (ed. by Parkinson, et.al.), AIAA (1996) pp. 169-186.
  • Roth, Doty, & Hwang, “GPS Safety Net”, GPS World, 14:5 (May 2003) pp. 36-40.
  • Roth et.al., “Performance of DSP-Loran/H-Field Antenna System And Implications For Complementing GPS”, Navigation, 49:2 (Summer 2002) pp. 81-90.

ILA 32 (Boulder, CO) - Page 17

faa references
FAA References
  • John A. Volpe National Transportation Systems Center, “Final Report - Vulnerability Assessment Of The Transportation Infrastructure Relying On The Global Positioning System” (August 29, 2001) 113 pages. (http://www.navcen.uscg.gov/archive/2001/Oct/FinalReport-v4.6.pdf)
  • FAA, “Executive Summary IRB on FAA’s WAAS” (January 18, 2001) 3 pages.

ILA 32 (Boulder, CO) - Page 18