AD-AI38 569 PERFORMANCE EVALUA1N ON f A MAGNAVOX GPS (GLOBAL I/POSITONING SYSTEM IZ- S ET U IDE FENCE RESEARCHESTABLISHMENOAWA(ONTARIO) M FVINNINSAPR 83

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MICROCOPY RESOLUTION TEST CHARTNATIONAL BUREAU OF STANDARDS-1963-A

UNCLASSIFIED

RESEARCH AND DEVELOPMENT BRANCH

DEPARTMENT OF NATIONAL DEFENCE

CANADA

DEFENCE RESEARCH ESTABLISHMENT OTTAWA

TECHNICAL NOTE NO. 83-3

PERFORMANCE EVALUATION OF A MAGNAVOX GPS Z-SET

by

M. Vinnins

Electromagnetics Section

Electronics Division

PROJECT NO. p T-1 .Cr.. Sala; its APRIL 198332GI0 , , -. OTTAWA

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ABSTRACT

A Magnavox Global Positioning System (GPS) Z-Set Receiver was obtainedon loan from the United States NAVSTAR/GPS Joint Program Office for evaluat-ion. Tests were carried out in an electronically-equipped trailer, on-boarda naval research yessel and in a Twin Otter flying laboratory. Data wasmanually recorded during static positioning tests and waypoint navigationtests. Results indicated a static positioning accuracy consistantly betterthan 100 feet in both latitude and longitude under 4-satellite availability.

, Accession ForNTIS GRAIDTIC TAB

Unannounced ElJustification

Distribution/Availability Codes-

Avail and/or

RESUME

Le Joint Program Office du syst~me de localisation par satelliteNAVSTAR nous a pr~t6 un r~cepteur Z-set du systtme de localisation parsatellite Magnavox pour en faire l'Ovaluation. Nous avons effectuf des testsdans une remorque munie d'fquipmements 6lectroniaues etinstall ea bordde recherche, et dans un laboratoire am~nagd a bord d'un Twin Otter. On aenregistr@ a la main les donndes lors de tests de positionnement au point fixeet de tests de navigation par point de cheminement. Dans tous les cas, laposition au point fixe pouvait toujours @tre d~termin~e avec une marned'erreur de moins de 100 pieds en latitude et en lonaitude, A partir de quatresatellites.

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TABLE OF CONTENTS

Page

ABSTRACT/RESUME.................................................. iii

TABLE OF CONTENTS ................................................ v

1. BACKGROUND ................................................... 1

1.1 TEST PHILOSOPHY.......................................... 1

1.2 THE MAGNAVOX Z-SET....................................... 1

2. TEST PROCEDURES .............................................. 6

2.1 VAN TESTS ............................................... 6

2.2 SHIP TESTS .............................................. 10

2.3 AIRCRAFT TESTS........................................... 10

3. TEST RESULTS ................................................. 12

3.1 VAN TEST RESULTS......................................... 12

3.2 SHIP TEST RESULTS........................................ 15

3.3 AIRCRAFT TEST RESULTS ..................................... 15

4. CONCLUSIONS ................................................ 20

ACKNOWLEDGEMENTS............................................ 20

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1.0 BACKGROUND

The Navigation Sub-program at the Defence Research Establishment Ottawais involved in many aspects of navigation technology. Over the past fiveyears, direct support has been provided to the Canadian Marconi Company (CMC)who are under contract to develop a Class 'V' (2-channel, high accuracy,medium dynamics) GPS receiver scheduled for delivery in early 1984. Inaddition a newly-developed Marine Integrated Navigation System (MINS) designedand built at DREO began sea trials in mid-1982.

In order to satisfy the requirement for a reference system againstwhich to evaluate the MINS and as preparation for delivery of the Canadian -built GPS receiver, a request was submitted to the GPS Project Office for theloan of a GPS receiver. A Magnavox GPS Z-Set was loaned to DREO for the monthsof October, November and part of December 1982. This report summarizes someof the tests performed on this receiver and the results obtained.

1.1 TEST PHILOSOPHY

Detailed performance evaluation of the Magnavox GPS Z-Set has beenperformed by the GPS Joint Program Office and it was not our intent to repeatany of that work. Instead, our evaluation was aimed at acquiring some 'hands-on' experience with the GPS System in as many environments as possiblewithin the time span of the receiver loan. The principal purposes of thetests were to establish GPS as a credible primary location sensor at sea fortesting and evaluating MINS-derived location accuracies and to demonstrateGPS to the Canadian Forces in various environments.

In preparation for the delivery of the CMC GPS receiver, test plansare in the process of being written for tests within land vehicles, shipsand various aircraft. The Magnavox GPS Z-Set was employed (in a limited way)in each of these environments during our tests.

Since no interfacing capabilities were provided with the receiver,data collection was limited to that available through switch selection onthe Control Display Unit (CDU). The results of these tests are presentedI. here.

1.2 THE MAGNOVOX Z-SET

The Magnavox GPS Z-Set is a single-channel, low dynamics, C/A code-only receiver. Performance specifications for this receiver are taken fromthe Magnavox Z-Set User Manual (April 1982) and are shown in Table 1-1.

Photographs of the receiver as installed onboard a Twin Otter testaircraft are shown in Figures 1-1, 1-2 and 1-3. Figure 1-1 shows the ControlDisplay Unit (CDU), on the right Figure 1-2 the Receiver Processor Unit (RPU)

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PARAMETERS CHARACTERISTICS

OPERATIONAL

RF Signal input level -163 to -150 dBW, L1 1575.42 MHz

Maximum dynamics

Velocity 0-400 meters per second

Acceleration 0-5 meters per second2(between 5 m/sand 10 m/s2 set will enter HOBYT)

Antenna coverage Reception of satellite signals morethan 5 degrees above horizon

Equipment stabilization period Less than 15 minutes from turn-on to thestart of data acquisition between 0 to+ 490C

Static propagation delay error Error in displayed navigation solution(GDOP less than 5) less than 180 meters

Fix accuracy 500 meters

Pseudorange measurement accuracy 15 meters (C/A-signal)

Jamming-to-signal power ratio Up to 25 dB

Data recovery Undetected bit error rate less than0.00001 with jamming-to-signal ratioof 25 dB

Time-to-first-fix

Normal (wide) acquisition mode Less than 300 seconds

Narrow acquisition mode Less than 215 seconds

Digital output signal 2.4 kilobits per second

PHYSICAL

Volume 0.016 cubic meter

Weight 15 Kilograms

Power 53 Watts

* Position uncertainty <13 Km

Initial velocity uncertainty <17 m/s

TABLE 1-1

Performance Details

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and RF preamp and Figure 1-3 the Chu antenna that was employed during allof the tests.

Satellite coverage during the entire test period was quite limited.Four-satellite coverage was available for only 2 hours a day but fortunatelyoccurred during the late morning and early afternoon facilitating demonstra-tions to future operational users as an additional benefit to the tests.A computer plot of Geometric Dilution of Precision (GDOP) vs time of day isshown in Figure 1-4 and elevation angle vs time of day in Figure 1-5. Notethat the best coverage in the Ottawa area occurred between 1745 and 1915 hrs(GMT) or 1245 and 1415 hrs local time with a GDOP between 2 and 7. (GDOPis an indicator of satellite geometry with respect to the user).

2.0 TEST PROCEDURES

Tests were carried out on three different platforms; a fully instrum-ented van, a naval research ship and a Twin Otter 'flying-laboratory' aircraft.

2.1 VAN TESTS

Tests on an instrumented van were carried out between 5 November and1 December 1982. Prior to installation, the receiver was checked for properoperation. A problem was discovered with the Magnavox antenna so a Chuantenna (as shown in Figure 1-3) was substituted and receiver operationverified.

For the purposes of determining receiver static positioning accuracy,verifying proper operation and performing speed calibration and low-dynamicsway point navigation, a survey crew was hired to locate and mark a series ofexisting first-order survey points which could be accessed by truck in thelocal Ottawa area. A list of the waypoints and their positions is given inTable 2-1.

Some of the selected survey points were in fact, some distance fromthe road so stakes were driven into the ground at the shoulder of the roadand then the distance and bearing to the survey marker were taken if possible.The latitude and longitude of each stake was then calculated with referenceto its nearby survey marker. By this method, the exact position of the stakesis known to within several feet and the van can be brought to a stop withintwenty feet (or less) of most stakes.

Table 2-1 also contains the corrected latitude and longitude for eachstake used in the tests. Unfortunately, some stake positions could not beaccurately determined because the corresponding survey markers were severalhundred feet away from the road in heavy underbrush; these were left uncorr-ected in the data.

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The test procedure consisted of initializing the receiver at the startpoint, the DREO Tower, where all four satellites were acquired before eachtest was begun. The time, actual position, receiver latitude, longitudeand altitude, Estimated Position Error (EPE) and number of satellites beingtracked were recorded. An example of a test data sheet is shown in Table2-2.

The position of each subsequent survey point along the route was thenloaded into the receiver as a waypoint and the distance and bearing from thepresent (start) position to the first waypoint was also recorded. The vanwas then driven and parked at each waypoint where all receiver data weretaken and the distance and bearing to the next waypoint were recorded.

This entire procedure was carried out six times between 5 Nov. and1 Dec 1982. In actual fact, as many as 12 waypoints were used in some testsbut limited satellite coverage often resulted in 2 and 3-satellite fixes withpoor GDOP since the tests often over-ran the coverage times. Most datapresented here are from a so-called 'short' route during which 4-satellitecoverage was always available.

In addition a fifth-wheel system was used as a velocity referenceduring several tests. GPS velocity was recorded and later plotted forcomparison.

2.2 SHIP TESTS

During the week of 15-20 Nov. 1982, the DREO - developed Marine Integ-rated Navigation System (MINS) was taken to Victoria, B.C. for demonstrationsand sea trials onboard the research vessel CFAV Endeavour.

The GPS Z-Set was installed on the ship as a reference system againstwhich MINS could be compared.

Unfortunately, due to the early hours of satellite visibility and thefact that the ship had not left dockside during the visibility period, due tobad weather no useful navigation data were acquired during this period. Plansare in progress to secure the loan of another GPS receiver during 1983 suchthat another series of sea trials can be carried out using GPS as a referencesystem.

2.3 AIRCRAFT TESTS

After completion of the van tests, the GPS Z-Set was installed in aTwin Otter research aircraft owned by the National Aeronautical Establishment.The photos previously shown as Figures 1-1, 1-2 and 1-3 are actually those ofthe installation on the Twin Otter.

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It was decided that in order to get useful results, it would be bestto attempt a series of single point positioning tests over a precisely knownand closely accessible survey point. Such a point was that of the intersec-tion of two runways at the Ottawa International Airport. The aircraft couldcarry out touch-and-go passes from either runway, and it was estimated thatan 'on-top' could be called with an error of less than twenty feet. In act-ual fact, the aircraft did not touch down on the runway, but rather 'glided'approximately six feet above the ground.

Two flights employing this 'touch-and-go' method were flown totallingover 25 data points. Data were recorded by voice onto tape and later trans-cribed to data sheets. Data recorded included EPE, latitude, longitude,altitude, speed, True Ground Track and time.

A series of waypoint navigation tests was also carried out. Three eas-ily accessible landmarks in the Ottawa area (DREO Tower, Ottawa VOR and theairport runway intersection) were chosen as waypoints and the triangularroute was flown several times. This test was used mainly to acquire a feelfor receiver performance as a baseline for later comparison with other rec-eivers and systems to be tested.

The tests were completed and the receiver was returned to the JPO on10 Dec. 1982.

3.0 TEST RESULTS

Since all data were recorded manually, the data were limited to thatwhich were available via the CDU only and by the one-second rate at which thedisplays are updated.

3.1 VAN TEST RESULTS

Table 3-1 shows a comparison between the survey marker positions andthe GPS Z-Set positions for each of the six test runs as well as the averagedGPS Z-Set position. The most notable characteristic of the data is its repeat-ability; although each run was done on a different day and at a different time,rarely is the difference in position greater than one second of arc (approx-imately 100 feet) and is, in fact, usually identical.

It is interesting to note that for three of the waypoints (DREO Tower,Dirleton and Panmure) the marker at the roadside is actually several hundredfeet from the survey point. Using the waypoint navigation function, it waspossible to get a bearing and distance to the waypoint while parked at theroadside marker. The most notable example of this occurs using the datagathered at the DREO Tower. It can be seen from the averaged GPS positions

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that, in fact, GPS and the survey coordinates disagree by approximately 580feet in latitude and 85 feet in longitude. While parked at the tower, thereceiver consistantly gave a bearing to the waypoint of 1700 True. If onecalculates the bearing from the latitude and longitude difference, the resultis 1680 True! Evidently, the survey location seems incorrect. In fact, afterdiscussions with the survey crew, it was learned that the coordinates givento us had been taken from an old map and that the tower had since been moved.A comparison of the old map and the tower position led us to conclude thatthe tower had, indeed, been moved approximately 600 feet on a bearing of 3500 T.

Table 3-2 shows the deviation between survey marker position and GPSposition. Note that for the three corrected markers (Woodlawn, Arnprior andMarathon) the average GPS position is within 100 feet of the stated surveyposition. For the three uncorrected markers, the bearing and distance to thewaypoint as given by the receiver agree closely with the calculations (asdone for the DREO Tower). The consistancy and repeatability demonstratedduring these tests was most impressive.

In addition to static positioning and waypoint navigation, we weremost interested in the velocity (Gnd-Speed) indication provided by the receiver.It is, in fact, this feature which has most impressed people to whom the systemhas been demonstrated. A 'fifth wheel' system connected to the test van allowedaccurate velocity comparisons to be made during the tests. A velocity profiletaken during one of the tests is shown in Figure 3-1. It can be seen that thevelocity derived from the GPS receiver agrees very closely with that of thefifth wheel although a slight offset of approximately 1 to 1 miles per houris noticeable on several sections of the plot. This could be due to a mis-calibration of the fifth wheel which was not checked before beginning thetests due to lack of time but has since been corrected.

3.2 SHIP TEST RESULTS

No useful data were acquired during the MINS sea trials since only aone-day trial was carried out and, unfortunately, satellite coverage was notavailable during the necessary time. An attempt will be made to repeat thesetests in the spring and summer of 1983 during continuing MINS sea trials.

3.3 AIRCRAFT TEST RESULTS

Table 3-3 shows the data taken during a 11 hour, point-positioning touch-and-go flight test using a runway intersection as a traget point. Again, itcan be seen that the data are very consistant; in fact, the limitation here isthe 1-second updata rate of the CDU displays which limits the resolution ofthe position data. When averaged, the GPS position is within 50 feet inlatitude and 100 feet in longitude of the survey position. This data ispresented in another fashion in Figure 3-2. Note the quantization error dueto the arc second resolution of the CDU display. To eliminate possible

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PASS # LATITUDE LONGITUDE GND SPD Gnd Tk EPE

450 18 57" 750 39 54 73 knots 237.8 .OINM

2 450 18 58 750 39 54 74 237.4 .023 450 18 57" 750 39 55" 67 238.2 .04

4 450 18 58" 750 39 55" 74 238.1 .02

5 450 18' 57" 750 39 54" 76 237.8 .026 450 18' 58" 750 39 55" 75 238.0 .02

7 450 18 57" 750 39 55" 74 237.7 .028 45 18 58" 750 39' 55" 77 237.5 .029 450 18' 58" 750 39 55" 80 237.1 .02

10 45o0 18' 58" 750 39' 54" 81 237.6 .0211 450 18 58 750 39 55" 80 237.3 .02

12 450 18 58" 750 39' 55" 78 237.4 .0213 450 18' 58 750 39 54 84 237.7 .02

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20 450 18 58 750 39 54 78 237.6 .04

21 450 18 58" 750 39 54" 81 237.0 .04

GPS Avg. Lat = 450 18' 57.86

GPS Avg. Long = 750 397 54.715

~Runway Intersection:

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A Lat = .42 A Long = .96

TABLE 3-3

Twin Otter/GPS Data 7 Dec. 82

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measurement biases, the same survey point was approached from a differentdirection along the second runway. The results indicated no significantbias:

GTK = 2370 Avg. Lat. = 450 18' 57.85"(Runway 07)

Avg. Long = 750 39' 56"

GTK = 3060 Avg. Lat = 450 18' 58"(Runway 24)

Avg. Long = 750 39' 56"

It is interesting to note at this point that during the circuits beingrun between the Airport runway intersection, DREO Tower and Ottawa VOR, theresults were, again, much the same except for the DREO Tower. Using the(incorrect) coordinates for the tower, each time the waypoint was passed,displays frozen and the data recorded, the results indicated that the actualwaypoint location was 5 arcseconds in latitude and slightly less than 2 arc-seconds in longitude away on a bearing of approximately 1660 True. As discussedin section 3.1, the reason for this was later discovered yet the consistancyand accuracy of the data in its agreement with the earlier van tests was mostimpressive.

4.0 CONCLUSIONS

Evidently, these tests were not by any means extensive nor did they proveanything new or remarkable about the Magnavox GPS Z-Set or the GPS System ingeneral. On the other hand, the remarkable repeatability and consistantsystem performarhce did a great deal to improve our confidence and expectationsof GPS performance. This will be invaluable in the upcoming extensive testsof the Canadian-built receivers. The opportunity to demonstrate the systemto potential military users and employ it in various operational environmentshelps lend credibility to the high expectations one has of GPS when readingthe literature.

ACKNOWLEDGEMENTS

We would like to extend our sincere appreciation to the GPS Joint ProgramOffice and to the NATO GPS Steering Cbmmittee for making the loan of thisreceiver possible.

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DOCUMENT CONTROL DATA - R & 0ISecuwtIy cldssa-catlon ol title. body oF abstract aoid ioidexing annotation nut tv enlete whei i the overall o)-i iw I (Id'sledi

I ORIGINATING ACTIVITY 2d DO(UMENI SECURIIY CIASSIFFIATION

DEFENCE RESEARCH ESTABLISHMENT OTTAWANATIONAL DEFENCE HEADQUARTERS 2b GROUPQTTAWA C.ANAD)A I IA 074

3 DOCUMENT TITLE

PERFORMANCE EVALUATION OF A MAGNAVOX GPS Z-SET

4 DESCRIPTIVE NOTES (Type of report and inclusive dales)

TECH NOTE5 AUTHOR(SI ILa$t name. first name. middle initial)

VINNINS, MICHAEL F.

6. DOCUMENT DATE 23 Feb. 83 ?a TOTAL NO OF PAGES I 7b NO OF REFS

8a. PROJECT OR GRANT NO 9a ORIGINATOR'S DOCUMENT NUMBER(S)

32G01

Bb CONTRACT NO 9b. OTHER DOCUMENT NOISl 1An V othe, nrumteis that nay I,assigned ths document)

10. DISTRIBUTION STATEMENT

UNLIMITED DISTRIBUTION

11 SUPPLEMENTARY NOTES 12. SPONSORING ACTIVITY

13 ABSTRACT

A Magnavox Global Positioning System (GPS) Z-Set Receiver was obtainedon loan from the United States NAVSTAR/GPS Joint Program Office for evalua-tion. Tests were carried out in an electronically-equipped trailer, onboard a naval research vessel and in a Twin Otter flying laboratory.Data was manually recorded during static positioning tests and waypointnavigation tests. Results indicated a static positioning accuracy consis-tantly better than 100 feet in both latitude and longitude under 4-satelliteavailability.

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