aircraft positional data utilization transmitted by mode-s...

AARMS TECHNOLOGY Vol. 6, No. 2 (2007) 187–194

Received: February 14, 2007

Address for correspondence:ŠTEFAN LUŽICA

Air Force Research Institute, Prague, Czech RepublicE-mail: [email protected]

Aircraft positional data utilization transmitted by Mode-Sat the automated air traffic control systems

ŠTEFAN LUŽICA, PETR SVOBODA, PAVEL GRECMAN

Air Force Research Institute, Prague, Czech RepublicUniversity of Defence, Brno, Czech Republic

European Air Traffic Control Harmonisation and Integration Programme (EATCHIP)all the time search new manners of air traffic control (ATC) and present-day means forimprovement of the air traffic safeness under all weather conditions. Concern it as AirTraffic Flow Management (ATFM) so development of new electronic systems based onextensive utilization of the satellites for communication and determination of theaircraft positioning in the airspace by the help of Global Positioning Systems (GPS).GPS and air board transponder system so called Mode-S will state obliged air boardequipment for civilian and military aircrafts. Purposes of the paper is present theresults of experimental verification of the positional data transmission in the squatterMode-S and determination of the aircraft position accuracy. Experimental verificationthe Mode-S system usability for positional data transmission in dynamic regime wererealized on the Prague-Kbely military airport runway under close cooperation of theAir Force Research Institute in Prague and University of Defence in Brno.

Introduction

The concept of the communication, navigation and surveillance systems for civilian andmilitary air traffic management (CNS/ATM) builds on the existing systems andtechnology accentuating, however also the development of new systems within FutureAir Navigation Systems (FANS) concept. It is necessary to emphasize, that the ATCsystems may be viewed as a menu of service items to install when a specificrequirement in a CNS area appears. The PSR and SSR/MSSR are presently used forairspace situation surveillance. The radars are the sources of airspace information andoffer the flow of positional data from PSR as PPSR{nA/C(R,β+IFF)} and from SSR asPSSR{nA/C(R,β+Flight-number,Hbar)} for automated air traffic control systems. The SSRfunction uses mode A and C or mode S to transmit the information of flight-number(mode A) and the aircraft barometric altitudes Hbar (mode C) from the aircraft to theground secondary radar system. Mode S is a system with selective addressing thatsupports a ground station network with data communication ability.3

Š. LUŽICA et al.: Aircraft positional data utilization

188 AARMS 6(2) (2007)

Mode S, besides the flight-number and aircraft barometric altitude data, allowstransmission of additional information, among which belongs also the transmission ofinformation about instantaneous aircraft position obtained by airborne GPS receiver in“Squitter Mode S” (Figure 1).

Figure 1. Message in Mode S

The mode S system together with the Automatic Dependent System (ADS) belongamong the perspective surveillance systems for aircraft position tracking in airspace innear future.2

Experimental measurement of positional information transmission in Mode S

For the experimental measurement of aircraft positioning data received by airborne GPSreceiver and transmitted in Mode S a special workplace has been established in cooperationof the University of Defence and Air Force Research Institute Prague (Figure 2).

This workplace enables:1) Verification of the accuracy of positional data transmission from Squitter

Beacon Transmitter (SQB) to receiver in static mode.2) Verification of the accuracy of positional data transmission from Squitter

Beacon Transmitter (SQB) to receiver in dynamic mode, i.e. from the movingtransmitter part at the AF Base Prague-Kbely, Czech Republic.


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3) Verification of the application of error ellipse (ellipsoid) utilisation for theevaluation of transmitter (aircraft) position determination accuracy.

A SQB mobile transmitter of GPS positional data with a unique identifier is designedfor ATC surveillance systems support. It consists of a Mode-S transmitter and an imple-mented 12-channel GPS receiver, type Jupiter 11, made by NAVMAN Co. (Figure 3).

The receiving and evaluating part of the workplace comprises a Mode-S receiver, adecoder and a PC for positional data processing and evaluation. The function verificationand measuring of the positional data flow from the SQB transmitter was carried out forgeodetic fixed-points in ETRS89 geodetic system and transformed into rectangular planecoordinate system UTM (Universal Transverse Mercator) and altitude (ALT).

SQB was placed into a point of exactly known position and a set of measurements wascarried out for all visible NAVSTAR system satellites. From measured data, themeasurement errors were calculated both for GPS and for DGPS. The GPS measurementerror in 2D horizontal plane is CEP(95%)=6.46 m and for DGPS CEP(95%)=7 cm.1,2

The measured three-dimensional (3D) data rate is presented in Figure 4. Theaccuracy of transmitter position determination in 3D system on error ellipsoid basis isshown in Figure 5.

Figure 2. Workplace for experimental GPS/Mode S positional data measurement


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The obtained data of measurement accuracy in static mode confirmed theapplicability of Mode S system also for positional data transmission in dynamic mode,it means from the aircraft to the ground receiver.

Figure 3. Mode S trasmitter

Figure 4. Dispersion of measured positioning data


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Figure 5. Error ellipsoid

Determination of the SQB transmitter positional error in dynamic regime

The experimental verification of GPS positional data transmission system in Mode Swas carried out in the AF Base Prague-Kbely, Czech Republic. The reason was thefollowing: the runway lengthwise axis is accurately geodetically fixed in geodeticcoordinates. The geodetic coordinates’ data then served for moving car positional datameasurement accuracy evaluation.2

Figure 6. The SQB transmitter on vehicle roof


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Figure 7. Receiving antenna of the Mode S system

In this experiment, the SQB transmitter was placed on top of a driving vehicle(Figure 6) and the car position is evaluated in relation to the runway lengthwise axis.The receiving part of the experimental workplace was placed on a flat-roof building(Figure 7).

The received positioning data evaluation and transformation into geodetic coordinateswere done with a special programme in MATLAB programming environment.

Once the received positional data were evaluated, the maximum found averagedeviation from the runway lengthwise axis was 2.25 m. The evaluated passages throughthe runway are graphically displayed in Figures 8 and 9.


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Figure 8. Routes of the vehicle on the runway centre line evaluated from the DGPS positioning datatransmitted by SQB system in Mode S

Figure 9. Detail of the trajectory part evaluated from the DGPS positioning data transmitted by SQB system inMode S.


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Conclusion

The performed position measurements of moving SQB/Mode S transmitter showed,numerically and graphically, deviations in merely metres that were determined throughDGPS, from the referential runway lengthwise axis defined by accurate geodeticbearing. It should be noted here that measuring was performed under good conditions, itmeans without jamming. The attained accuracy of position determination in motion isalmost ten times better than are the ICAO standard specifications for GPS-SPSminimum performance. Such accuracy is certainly sufficient for automated air trafficcontrol systems (for civilian aviation and Air Forces).

References

1. ANDRLE M., GRECMAN P.: Possibilities of measuring variance of GPS position data from Mode Ssquitter. 3rd International PhD Conference on Mechanical Engineering. Czech Republic, 2005.

2. GRECMAN P.: Mode-S utilisation criteria analysis for radar positioning data reliability verification.Doctoral Dissertation Thesis. University of Defence, Czech Republic, 2005.

3. LUŽICA Š.: Flight inspection and calibration simulation on GPS-based precision approach system. XXXSesiune de comunicari stiintifice cu participare internationale. Academia Tehnica Militara. Bucuresti, 2000.

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