Multipath Interference in Orbiting Receivers Due to Earth Surface Reflections

Juan G. Ceva and Bradford W. Parkinson

Abstract:	The results of a computer simulation to study the possibility of the existence of interference multipath signals that could affect a GPS user satellite’s receiver are presented. It is an extended assumption in the GPS community that interfering multipath signals due to GPS direct signals being reflected off the earth’s surface do not exist once the GPS receiver is allocated at an ahitude above one chip length of the coded signal. The present results show that this assumption is erroneous and that the described multipath effect could indeed occur. Simulations of satellites orbiting earth at typical altitudes ranging from 250 km. to 1000 km. demonstrate that whenever a GPS user satellite receives a direct GPS signal from an elevation angle near the GPS user satellite’s depression angle, the delayed (earth surface reflected) version of the direct signal may arrive inside the code chip length window, thus creating an interference multipath signal. However, the results also show that due to the relative motion of the GPS constellation and the user, this type of multipath interference only lasts for short intervals of time, and can be avoided by proper selection of masking angles. In addition, the study shows that any GPS receiver located at a critical altitude of less than three-quarters of the code chip length will experience the described multipath effect independently of the elevation angle of the incoming direct GPS signal, and that above the aforementioned critical altitude the multipath interference will occur below some critical elevation angle.
Published in:	Proceedings of the 6th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1993) September 22 - 24, 1993 Salt Palace Convention Center Salt Lake City, UT
Pages:	1557 - 1563
Cite this article:	Ceva, Juan G., Parkinson, Bradford W., "Multipath Interference in Orbiting Receivers Due to Earth Surface Reflections," Proceedings of the 6th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1993), Salt Lake City, UT, September 1993, pp. 1557-1563.
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