An Effective Method for Multipath Mitigation under Severe Multipath Environments

Nobuaki Kubo, Takashi Suzuki, Akio Yasuda and Ryosuke Shibazaki

Abstract:	The support systems to supply highly accurate positioning, such as DGPS or RTK-GPS, must be effective even in the case of severe multipath environments. Therefore, some researches related to the code multipath mitigation under relatively severe multipath environments have been presented in recent years. Generally speaking, multipath phenomenon is caused not only by reflection but also by diffraction and obstruction. Sometimes we happen to receive only signals reflected by tall buildings. Although some correlator equipped with multipath mitigation techniques can reduce the multipath error considerably in the case of direct and multipath signals only, these techniques can’t cope with the cases that the multipath signal is dominant, diffraction loss is large and the delay of multipath signal is shorter than about 20 m. In fact, these types of signal can be received frequently when we drive in dense urban environments with slow speed of several km/hour. We propose two techniques in this paper to reduce the multipath error in the above cases. Signal strength is used as a criterion to remove the multipath dominant signals. Furthermore, in order to reduce the effect of the short delay multipath, the technique aided by maximum likelihood criteria, which has already been proposed by some researchers, is applied to estimate the multipath signal. The feature of our multipath estimation technique is to infer multipath parameters rapidly by making use of multi-correlator outputs. Reducing search space by deducing accurate initial multipath parameters enables us to reduce computational time. The analyses of many field data, obtained by ourselves, have indicated that our two techniques were effective to reduce errors by the multipath dominant signal and the short delay multipath signal. Simulation was also conducted to evaluate our multipath estimation technique, which was tested in the both static and semi-static cases. The method to remove multipath dominant signals was tried in all conditions.
Published in:	Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005) September 13 - 16, 2005 Long Beach Convention Center Long Beach, CA
Pages:	2187 - 2194
Cite this article:	Kubo, Nobuaki, Suzuki, Takashi, Yasuda, Akio, Shibazaki, Ryosuke, "An Effective Method for Multipath Mitigation under Severe Multipath Environments," Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005), Long Beach, CA, September 2005, pp. 2187-2194.
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