An alternative method for detection and mitigation of static multipath in L1 carrier phase measurements

Julio C. Farret and Marcelo C. Santos

Abstract:	Multipath affects the Global Positioning System measurements in different ways. For example, in the receiver, multipath distorts the correlation function hampering its peak detection in the delay lock loop, with a consequent error in the pseudorange and its derived products. It also takes a toll in the carrier phase, causing the receiver to measure a distorted phase, with deleterious consequences in differential applications. Maybe for these reasons, multipath remains a major source of error in both static and kinematic high accuracy positioning, and a limiting factor in various applications, such as the Wide Area Augmentation System. Improvements in receiver and antenna technologies, in addition to models based on daily repeatability, have resulted in a better handling of this problem. Some authors have shown that multipath is highly correlated for an array of closely spaced antennas. This paper presents a methodology aimed at evaluating multipath by introducing a temporal factor in the measurements. The methodology makes use of the assumption that multipath parameters and satellite geometry have a slow variation in time and space. The method uses L1 single difference carrier phase measurements that have been collected by two closely spaced antennas. These observables feed a filter that estimates multipath parameters. We believe that he same procedure may be adopted for the L2 carrier phase. Multipath was analysed for various satellites at different azimuth and elevation angles over consecutive days using the same scenario. The high daily repeatability was used to ascertain the presence of multipath. The results show a short variation in the efficiency of the method, i.e., the percentage between the estimated multipath vis-à-vis the measured one. Generally, the efficiency reached 65%. It is concluded that the assumption of the low variation of the multipath parameters over a short period of time can be used to explore the proposed objectives. We believe that very good carrier phase multipath estimates were obtained. This means the method can be an interesting alternative for reference stations, users and also for /research, analysis, and modelling of multipath using different scenarios, especially of low cost.
Published in:	Proceedings of the 2001 National Technical Meeting of The Institute of Navigation January 22 - 24, 2001 Westin Long Beach Hotel Long Beach, CA
Pages:	261 - 270
Cite this article:	Farret, Julio C., Santos, Marcelo C., "An alternative method for detection and mitigation of static multipath in L1 carrier phase measurements," Proceedings of the 2001 National Technical Meeting of The Institute of Navigation, Long Beach, CA, January 2001, pp. 261-270.
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