The Joint University Program in Air Transportation Systems provides opportunities for progress by students, staff and faculty at the Avionics Engineering Center, Ohio University. During the 1992-93 year, four conference papers and two M.S. theses were produced; these are summarized in the bibliography. The conference papers are included in their entirety, for reference

Lilley, Robert W.

English

NASA Technical Reports Server

N94- 27288
INVESTIGATION OF AIR TRANSPORTATION TECHNOLOGY
AT OHIO UNIVERSITY
1992-1993
Robert W. Lilley
Avionics Engineering Center
Department of Electrical and Computer Engineering
Ohio University
Athens, Ohio
gS
SUMMARY OF RESEARCH
The Joint University Program in Air Transportation Systems provides opportunities
for progress by students, staff and faculty at the Avionics Engineering Center, Ohio
University. During the 1992-93 year, four conference papers and two M. S. theses were
produced; these are summarized in the bibliography below. The conference papers are
included in their entirety, for reference.
Interest in the satellite-based Global Positioning System (GPS) in the interferometric
mode implies the need for highly accurate position and velocity estimates in real time,
from multiple antennas. Such advanced applications require also an excellent knowledge
of the transmitted signal's characteristics (studies of Selective Availability and methods
for mitigation).
Differential mode operations are also implicit when interferometric GPS is applied to
aircraft approach operations (studies of ground station siting and performance).
GPS hybridization with other systems is a key element in eventual sole-means
navigational use of the system. Studies of combined GPS/Loran-C and GPS/IRS are
supporting this future priority.
GPS system availability is a pervasive concern, and is a complicated quantity related to
required user accuracy, position and time. A comprehensive coverage model is under
development.
Although specific papers were not generated in the weather-uplink research area, this
work did support a spin-off effort. Knowledge gained in the weather-uplink work is now
being applied in differential GPS uplink studies supported by FAA.
Fault detection and isolation (FDI) work continues, in direct support of GPS integrity
assurance standards being developed for FAA by RTCA. Much of the past FDI work
generated in the Joint University Program has been adopted as part of these
national/international standards.
pRIL_CIDtNG PAGE BLANK NOT FILMED
31
https://ntrs.nasa.gov/search.jsp?R=19940022785 2020-06-16T13:31:44+00:00Z
ANNOTATED BIBLIOGRAPHY OF 1992-93 PUBLICATIONS
1. Braasch, M. S.; Fink, A. B.; Duffus, K.: Improved Modeling of GPS Selective Availability.
Proceedings of the ION National Technical Meeting, San Francisco, CA, January 20-22, 1993.
Selective Availability (SA) represents the dominant error source for stand-alone users of
GPS. Even for DGPS, SA mandates the update rate required for a desired level of accuracy in
realtime applications. As has been witnessed in the recentliterature, the ability to model this
error source is crucial to the proper evaluation of GPS-based systems. A variety of SA models
have been proposed to date; however, each has its own shortcomings. Most of these models
have been corrupted by additional error sources. This paper presents a comprehensive treatment
of the problem. The phenomenon of SA is discussed and technique is presented whereby both
clock and orbit components of SA are identifiable. Extensive SA data sets collected from Block
II satellites are presented. System Identification theory then is used to derive a robust model of
SA from the data. This theory also allows for the statistical analysis of SA. The stationarity
of SA over time and across different satellites is analyzed and its impact on the modeling
problem is discussed.
2. Braasch, S.: Realtime Mitigation of GPS SA Errors Using Loran-C. Wild Goose
Association, Annual Convention and Technical Symposium, August 24-27, 1992, Birmingham,
England.
3. Braasch, S.: Realtime Mitigation of GPS Selective Availability Using Loran-C. M.S. Thesis,
Ohio University, Department of Electrical and Computer Engineering, Athens, OH, June 1993.
The hybrid use of Loran-C with the Global Positioning System (GPS) has been shown
capable of providing a sole-means of enroute air radionavigation. By allowing pilots to fly direct
to their destinations, use of this system is resulting in significant time savings and therefore fuel
savings as well. However, a major error source limiting the accuracy of GPS is the intentional
degradation of the GPS signal known as Selective Availability (SA). SA-induced position errors
are highly correlated and far exceed all other error sources (horizontal position error: 100
meters, 95 %). Realtime mitigation of SA errors from the position solution is highly desirable.
This paper discusses how that can be achieved. The stability of Loran-C signals is exploited to
reduce SA errors. The theory behind this technique will be discussed and results using bench
and flight data will be given.
4. Skidmore, T. A.: A GPS Coverage Model. Proceeding of the ION National Technical
Meeting, Washington, DC, June 29 - July 1, 1992.
This paper summarizes the results of several case studies using the Global Positioning
System coverage model developed by Ohio University. Presented are results pertaining to
outage area, outage dynamics, and availability. Input parameters to the model include the
satellite orbit data, service area of interest, geometry requirements, and horizon and antenna
mask angles. It is shown for precision-landing Category I requirements that the planned GPS
32
21Primary SatelliteConstellationproducessignificantoutageareaand unavailability. It is also
shownthata decreasein theuserequivalentrangeerrordramaticallydecreasesoutageareaand
improvesthe serviceavailability.
5. Waid, J. D.: Ground Station Siting Considerationfor DGPS. Proceedingsof the ION
NationalTechnicalMeeting, SanFrancisco,CA, January20-22, 1993.
6. Waid, J. D." Developmentof an Interferometric Differential Global Positioning System
Ground ReferenceStation. M.S. Thesis, Ohio University, Departmentof Electrical and
ComputerEngineering,Athens,OH, March 1992.
Aircraft guidanceand positioning in the final approachand landing phasesof flight
requiresa high degreeof accuracy. The Global PositioningSystemoperatingin differential
mode(DGPS)is beingconsideredfor this application. Prior to implementation,all sourcesof
error must be considered. Multipath hasbeenshownto be the dominantsourceof error for
DGPSand theoreticalstudieshaveverified that multipathis particularly severewithin thefinal
approachand landing regions. Becauseof aircraft dynamics,the ground stationsegmentof
DGPSis thepartof thesystemwheremultipathcanmosteffectivelybereduced. Groundstation
sitingwill bea keyelementin reducingmultipatherrors for aDGPSsystem. This situationcan
also be improved by using P-code or narrow correlator C/A-code receiversalong with a
multipathrejectingantenna.This paperpresentsa studyof GPSmultipatherrors for a stationary
DGPS groundstation. A discussionof GPSmultipatherror characteristicswill be presented
alongwith someactualmultipathdata. Thedatawascollectedfor differentgroundstationsiting
configurations using P-code, standardC/A-code and narrow correlator C/A-code receiver
architecturesandtwo separateantennaconstructions.
33
7i
i


Investigation of air transportation technology at Ohio University, 1992-1993

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server