GPS World - May 2008 - (Page 35)

Vehicle Integration | AVIONICS & TRANSPORTATION the P-unit completing the trip just before the car arrived and not starting until the car was passing. The calculated differential positions and velocities were used as inputs to the collision-prediction algorithms. An adjacent photo shows the test setup. To achieve accurate predictions, we must quantify three thresholds: ped movement car turning ped safety margin. The last is the base DGPS accuracy times HDOP. The first is based on the DGPS velocity error, as is the second, but the latter has an added factor involving consecutive velocity changes that indicate there is a turn radius and angular velocity to calculate for the prediction. With only one second of movement before the crash, this is the most difficult crash discrimination challenge for the algorithms; no alert can be given before movement is detected so only one Danger alert should show on the warning state plots. FIGURE 9 shows one of the plots with the ped movement threshold set to 0.1 meters/second. The ped position is green, the Danger alert positions are red, and the no-alert positions are empty diamonds. Clearly car movement (counter-clockwise) is confounding detecting ped movement. FIGURE 10 shows the warning state plot with ped movement threshold set to 0.4 meters/second, showing correct response on three of the five approach loops. With more work, these thresholds could be tuned to achieve accurate warnings. Map-matching would greatly help predicting turns on a roadway. with more testing and analysis. A future system can be improved further by utilizing carrier-cycle resolution, new civil signals, inertial aiding, ad hoc network ranging, map-matching, custom communication protocols, and custom radio boards. Disclaimer Charles Rodgers led this research while employed by OPTIMUS Corporation as chief technology ofﬁcer. The views expressed in this paper are the authors' and not the views of OPTIMUS Corporation or the FHWA. Acknowledgments The authors wish to thank Pete Mills and the FHWA for their support of this research. We also would like to thank Hiroshi Tsuda and Nissan for their interest in this program and for providing the test vehicle. The authors also thank the other engineers on the team that designed and developed the PAS for their outstanding efforts: Darrell Greenlee, senior hardware engineer; Robert Nelsen, senior software engineer; and George Likakis, software engineer. Manufacturers Both V and P units tested here carry the u-blox (www.u-blox.com) TIM-LP GPS receiver and a Sarantel (www.sarantel. com) GeoHelix antenna. The radio transceivers are a 9XCite FHSS radio and 9XStream transceiver with output power of 100 mW. PAS uses the QNX real-time operating system, RTD rugged PC/104/ + SBC module containing a NS Geode MMX 300 MHz, 2.0VDC processor. CHARLES RODGERS, president of NavSpace Engineering, received BSEE and MSEE degrees from the Georgia Institute of Technology. He has been working with both military and civil GPS for 20 years, and has five patents for GPS applications including the PAS. Field Test Conclusions The performance demonstrated provides proof of our concept to solve the complex problem of reliably warning drivers of pedestrians when there is a high probability of a crash, even if they are hidden by visual/radar screens. This system is applicable to all pedestrian crash types and can be extended to bicycles. A U.S. patent has been granted for the device. The current system could be improved www.gpsworld.com RICHARD BLOMBERG, president of Dunlap and Associates, Inc., received his MS and BS degrees from Columbia University. His extensive experience has included the application of human engineering, safety, and systems analytic principles in a variety of environments. Much of his work has been directed toward pedestrian and bicycle safety. May 2008 | GPS World 35 http://www.u-blox.com http://www.sarantel.com http://www.sarantel.com http://www.oxts.com http://www.gpsworld.com

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GPS World - May 2008

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