Transponder Based Ranging

Transcription

1 Transponder Based Ranging Transponderbasierte Abstandsmessung Gerrit Kalverkamp, Bernhard Schaffer Technische Universität München

2 Outline Secondary radar principle Looking around corners: Diffraction of radio waves Roundtrip time of flight: Measurement principle and signals Comparison of modulations and estimation methods SafeTAG prototype hardware System performance Comparing SafeTAG to other technologies Conclusion Transponder Based Ranging 2

3 Secondary Radar Principle Higher received signal power Detection and ranging in non-line of sight situations Unambiguous target classification No phantom targets by passive reflections Multi-user capability Data link from transponders allows additional information (e.g. inertial sensor data) Transponder Based Ranging 3

4 Electric field strength (db) Looking around corners: Diffraction of radio waves Reception even in optically occluded regions Example: Diffraction at a corner: Incident plane wave 1 I II III α -1 Solid Metal III Angle α (Degrees) Transponder Based Ranging Source: McNamara, D. A.; Pistorius, C. W. I.; Malherbe, J. A. G.: Introduction to the Uniform Geometrical theory of diffraction, Artech House 199

5 Roundtrip Time of Flight: Measurement Principle Onboard unit sends out ranging signal Road users with transponders receive the signal Transponders send code back after a defined waiting time Onboard unit calculates roundtrip time of flight and distance In risk situations: Warning or autonomous maneuvers Transponder Based Ranging 5

6 Roundtrip Time of Flight: Measurement Principle Measuring the distance by correlation: Transmitted ranging signal: Received response from tag: Correlation result: Roundtrip time of flight t time Distance to transponder: Distance 1 2 (Roundtrip time of flight Waiting time) speed of light Transponder Based Ranging 6

7 Roundtrip Time of Flight: Signals Ranging signal:.5 1 x 14 Inphase Quadrature Amplitude Sample Preamble PN-Code (2-way) OFDM sequence TAG PN-Code Pulse compression: Carrier frequency: Transmit power: Receiver bandwidth: 255 bit m-sequence; 4.8 μs 5.8 GHz ~18 dbm 54 MHz (IF SAW Filter) Transponder Based Ranging 7

8 Comparison of Modulations and Estimation Methods Research topics: Application of parametric algorithms for increased resolution Multicarrier waveforms for spectral flexibility and agility Methods for simultaneous communication and ranging Transponder Based Ranging 8

9 SafeTAG 2. Prototype Platform Transponder INERTIAL SENSORS DAC FPGA CONTROL MAC FPGA RTOF APHY CLOCK 125 MHz RF FRONTEND ADC Modular, flexible prototype Identical hardware for transponder and OBU Size and power consumption can be drastically reduced in future implementations Transponder Based Ranging 9

10 SafeTAG 2. Prototype Platform Onboard Unit ANGLE OF ARRIVAL MODULE Antenna array mounting position DAC FPGA CONTROL MAC FPGA RTOF APHY CLOCK 125 MHz ADC RF FRONTEND Antenna Module Onboard Unit Transponder Based Ranging 1

11 Performance: Laboratory Measurements Distance standard deviation: σ = ~7 mm at 6 db, 1 cm at 1 db Distance packet error rate: < 1 % up to 15 db Data packet error rate: < 1 % up to 14 db ( Sensitivity: -86 dbm) OBU Coax- cable Variable Attenuator db Transponder Distance / m Occurence Channel Attenuation / db PER / % Channel Attenuation / db Channel Attenuation / db Transponder Based Ranging 11 Std. Deviation / cm RTOF packets DATA packets

12 Performance: Outdoors, Line of Sight Distance / m Range > 2 m Std. deviation of error: 23 cm unfiltered, untracked raw data! RTOF Value Reference: DGPS Car with OBU Multipath distortions can occur (here: between 1 and 14 m) Multipath resolution: theoretical: c/b = 5.5 m, measured: > 6.8 m Distance Error / m m: σ = 23 cm 1-1 Color: Correlation Result Amplitude -2 m: σ = 43 cm Transponder in line of sight Time / s Reference Distance / m Transponder Based Ranging

13 Performance: Outdoors, Non-Line of sight Distance / m Range > 1 m Distortions due to diffraction, reflection and multipath Car with OBU Typical distance error 1-2 m (depends on environment) Unfiltered, untracked raw data! RTOF Value Reference: Const. Velocity Line Time / s Distance Error / m Transponder behind parked car Reference Distance / m Transponder Based Ranging Color: Correlation Result Amplitude -1 m: σ = 1.38 m -6 m: σ = 8 cm

14 Comparing SafeTAG to Other Sensors SafeTAG Camera Radar Lidar Target response active passive Target resolution very good computationally expensive ~ bandwidth good Accuracy high low high Field of view even in NLOS similar to driver Phantom Targets none some many Influence of weather low strong strong strong Range > 2m < 5 m < 2 m < 2 m Transponder Based Ranging 14

15 Conclusion Cooperative transponder system for traffic safety applications High precision detection and ranging Even in non-line of sight situations Distance accuracy considerably higher than camera and GPS Very low false alarm rate Unambiguous classification (car / pedestrian / roadside unit) Design and implementation of prototype hardware Evaluation of performance in laboratory and field tests Further applications: Self-localization High precision reference positioning Transponder Based Ranging 15

16 Thank you for your attention!