| Summary: | 碩士 === 國立臺灣科技大學 === 電子工程系 === 103 === As GPS technology becomes more popular, its application becomes widely adapted in products across the market. GPS technology can be found in products such as automobile navigation systems, smart phones, wearable devices, and geographical surveying equipment. Among these, automobile navigation systems are the most widely known, with widespread commercial successes. As automobile navigation systems are primarily used in highly urbanized areas, high-rises will inevitably disrupt GPS signal acquisitions due to obstruction of satellites or will cause multipath effect phenomenon when signals are reflected from the surfaces of surrounding buildings. Hence, inaccurate positioning will be generated by GPS receivers. We suppose GPS receiver get satellites information(Elevation、Azimuth、C/No) and a coordinate of latitude & longitude to indicate user’s current position, along with current level of multipath effect, therefore we can make an inference the multipath pseudorange error from positioning calculation.
This study used a fisheye camera mounted atop a vehicle to capture 360° aerial views of the sky via the binary image thresholding technique to identify boundaries of the sky with direct line-of-sight coverage. By incorporating NMEA data, the GPS receiver acquired the satellite aerial position, identified those that were obscured, and evaluated how surrounding buildings were contributing to the multipath effect. Because current position errors in GPS receiver could be preliminarily determined,multipath pseudorange error caused by surrounding interference effect was estimated. REVERSE DGPS algorithm was then applied to correct errors in pseudorange differences. Next, position deviations in direction and distance were calculated to obtain a more accurate position.
This study aims to provide a method to help a vehicle adhere to its proper course when navigating through areas with obstructed satellite signals and multipath effect that may potentially deviate the vehicle from its desired route. The experimental results show that GPS positioning errors can indeed be reduced using this technique.
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