GPS World, August 2015

Signal Quality and Authentication RECEIVER TECHNOLOGY FIGURE 11 Multipath error envelope for coherent rising edge double delta code discriminator with inner spacing of 0017 C A chips FIGURE 11 illustrates the multipath error envelope for the coherent rising edge double delta discriminator Performance is consistent with a traditional secondderivative discriminator FIGURE 12 illustrates the performance of the various risingedge tracking discriminators for a live sky GPS SPS signal de trended code minus carrier measurement This figure clearly demonstrates robust code tracking and the multipath and noise mitigating benefit of ultra narrow rising edge discriminators Conclusions An empirical chip rising edge based tracking technique was used to observe the underlying chip shapes of live sky GPSSPS signals at high fidelity These results reveal positive versus negative chip asymmetries that are characteristic to each satellite The novel concept and technique of directly monitoring chip asymmetry has potential to extend the state of the art in the areas of GNSS signal quality monitoring and authentication Disclaimers The views expressed in this paper are those of the authors and do not reflect the official policy or position of the United States Air Force Department of Defense or the United States Government Acknowledgments This research was supported by the Air Force Research Laboratory Sensors Directorate The authors thank Ohio University Avionics Engineering Center for making available a cluster of high performance computers to process the 20 TB dataset for this research and Kadi Merbouh of Ohio University for maintaining and overseeing operation of this equipment Our ChipShape processing is an extension of the signal compression technique first published by Larry Weill and licensed by NovAtel for use in its Vision Correlator technology This article is based on a paper presented at ION Pacific PNT 2015 in Honolulu FIGURE 12 Code tracking performance for live sky data of various rising edge based coherent early late code discriminator functions SANJEEV GUNAWARDENA is a research assistant professor with the Autonomy Navigation Technology ANT Center at the Air Force Institute of Technology AFIT He earned a Ph D in electrical engineering from Ohio University JOHN RAQUET is a professor of electrical engineering and the Director of the ANT Center at AFIT He has been involved in navigation related research for more than 25 years FRANK VAN GRAAS is the Fritz J and Dolores H Russ professor of electrical engineering and principal investigator with the Avionics Engineering Center at Ohio University He received the ION Johannes Kepler Thurlow and Burka awards and is a Fellow and past president of the ION www gpsworld com August 2015 GPS World 43