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© Laboratory of Specialized Embedded System, Navigation and Avionics (LASSENA), 2013
Department of Electrical Engineering
LASSENA (Laboratory of Specialized Embedded System, Navigation and Avionics)
Design and test of robustness of a DME avionic system integrated with a mode S transponder component
Samuel Elbaz
Omar Yeste
René Jr. Landry
DME Overview:Knowledge of the aircraft’s position is a basic requirement for airnavigation and one means of satisfying this requirement is to supportthe pilot with bearing and distance information [1].
The DME (Distance Measuring Equipment) provides information on thedistance (slant range) from the aircraft (interrogator) to the groundstation (transponder). It’s used to establish the position along anairway and also to establish hold points. Therefore, shaped RF doublepulses are transmitted by the aircraft to the ground station and, after adefined delay (reply delay), the ground station sends the pulses backagain. The receiver in the aircraft uses the round trip time of thedouble pulses to determine the distance to the ground station.
DME Characteristics: Frequency Band:
Airborne:
• 1025 MHz – 1150 MHz
Ground:
• 63 MHz below Tx frequency 1025 – 1087 MHz
• 63 MHz above Tx frequency 1088 – 1150 MHz
It has 126 channels with two codings, X and Y, which doubles thecapacity. Figure 2 shows the time characteristic of the envelope ofthe DME interrogation pulses from the interrogator and the replypulses from the transponder.
What is DME ?
RESEARCH METHODOLOGY : FROM
SIMULINK TO SDR IMPLEMENTATION
RESULTS & CONCLUSION
REFERENCES
Interrogation signal X channel
Interrogation signal Y channel
Transponder (reply) signal X channel
Transponder (reply) signal Y channel
Pulse pair spacing 12µs
Pulse pair spacing 36µs
Pulse pair spacing
12µs
Pulse pair spacing 36µs
Delay 50µs
Delay 55µs
Figure 2 : Time characteristic of DME signal envelope for X and Y channel.[2]
General Principle:•Airborne transceiver transmits a pair of pulses (spaced at 12μs formode X and 36μs for mode Y)•Ground transmitter receives the pulses, waits 50μs and then transmitsanother pair of pulses back to the aircraft•Airborne transceiver measures the time between transmission andreception. The slant range is computed by subtracting 50μs to themeasured delay, multiplying by the speed of light and dividing by 2.•This is very simple but gets more complicated when we want toservice more than one aircraft. We need a method for distinguishingamong the signals from up to 100 aircraft. This is done essentially bygenerating a random set of pulses and correlating with the replies todetermine the correct ones.
Detection Threshold
Figure 3: DME pulses.
Ground Range
Altitu
de Ground Range
Alt
itu
de
Figure 4 : DME slant range.
Standards applied:DO-189: Minimum Operational Performance Standards forAirborne Distance Measuring Equipment (DME) Operating withinthe Radio Frequency Range of 960 - 1215 MHz.
Simulink:Figure 6 presents the three stages used to simulate the DME system.The first block (interrogator) simulates the plane which send pulses,measures the delay and computes the distance. After modulation, theblock “I Pulse Generator” sends the signal to the communicationchannel which transmits it to the block “T Receiver” of thetransponder. This last block demodulates the signal and send a reply tothe plane.
Figure 5 : Simulink simulation model.
FUTURE WORK
Software Defined Radio:The Matlab conception and model is followed by the development ofthe system with a Software Define Radio (SDR). This system allows tosolve problems related to design and repair of avionics systems bysoftware signal processing. This method permits to add new modes byonly doing software updates without the user has to change thephysical layer. The SDR’s used in our case are USRP (Universal SoftwareRadio Peripheral) N210 Network version and E110 Embedded version.Also we use the toolkit GNU Radio which provides signal processingblocks to implement software radios.
Figure 8 : Simulation and prototype testing architecture.
• Extensive performance characterization (& certification?).• Full integration with the Universal Glass Cockpit (UGC).[3]
• Limited by computational capabilities: Simultaneous operation On-the-fly reconfiguration Migration to Nutaq SDR platforms.[4]
• Multi-DME capabilities: Automatic location of ground stations. DME/DME Alternate Positioning, Navigation and Timing (APNT).
• Integration with other SDA systems: GNSS. ILS. …
1. Civil Aviation Authority Australia, (2008), Operational Notes on Distance Measuring Equipment, Australia.
2. Rohde & Schwarz (2009). Test of DME/TACAN Transponders, Germany.
3. Landry, R., Trocmé, B. and Blais, S. Universal Glass Cockpit for in-Flight and in-Simulation Performance Analysis. Sytacom Symposium 2012.
4. Nutaq SDR product line. http://nutaq.com/en/products/applications/+sdr (accessed on Sept. 13, 2013)
• A fully DME transponder is implemented on SDR.• Fully compliant with DO-189 standard as shown by tests with
certification equipment (IFR-6000).• Accuracy is approximately 15m (