Abstract
The multipath effect is a crucial error source caused by the environment around the station and cannot be eliminated or mitigated by differential algorithms. Theoretically, the maximum value for the carrier phase is a quarter the wavelength, i.e., about 4.8 cm for the GPS L1 signal. Considering the increasing demands of high-precision applications, the multipath error has become a major factor affecting the accuracy and reliability of GPS millimeter-level data processing. This paper proposes a multi-point hemispherical grid model (MHGM) to mitigate the multipath effect. In this method, the hemisphere centered on each station is divided into a grid, and the multipath error at the station is estimated based on the parameterization of the grid points. The double-differenced (DD) observed-minus-calculated (OMC) values on some previous days are treated as the observation values to model the present multipath error. Contrary to the present methods which rely much on the platform of data collection and processing, MHGM can be potentially applied to GPS data processing with the existing hardware and software. Experiments in high-multipath and low-multipath environments are designed by mounting a baffle or not. The experimental results show that MHGM is effective in mitigating the multipath effect. When using data from the previous day, an average improvement of about 63.3% in the RMS of DD OMC can be made compared with that without correction, and this is basically consistent with the sidereal filtering (SF) method which is 63.0%. Furthermore, the effectiveness of the above two methods is better than that of the empirical site model (ESM). The kinematic positioning results are also basically consistent with the statistical results of the RMS values of DD OMC. Historical data from more than one day can more explicitly and effectively model the MHGM. Furthermore, compared with the SF method, the MHGM can be used not only to mitigate the multipath error, but also to orientate the sources of the multipath error around the station, and give guidance in the physical elimination of these sources.
Highlights
When the direct signals, reflected signals and diffracted signals of global positioning system (GPS) satellites reach the receiver antenna simultaneously, the interference will lead to an important error called the multipath error [1]
This paper proposes a novel method for the mitigation of multipath error at stations based on a multi-point hemispherical grid model
The method divides the hemisphere centered on each station into meshes, and estimates the multipath error at the station based on the parameterization of the grid points
Summary
When the direct signals, reflected signals and diffracted signals of global positioning system (GPS) satellites reach the receiver antenna simultaneously, the interference will lead to an important error called the multipath error [1]. The influence of the reflected signal on the receiver’s antenna can be mitigated through the use of choke rings [8,9], or the reflected signal can be prevented from reaching the lower part of the antenna through the mounting of antenna ground planes [10] All these methods acting on the antenna can be applicable for both pseudorange and carrier multipath mitigation; or (3) designing of algorithms in GPS data processing to mitigate the multipath error when the observation environment and receiver equipment cannot be guaranteed. Dong (2016) proposed a multipath error correction method based on a multipath hemispherical map [39] This method averages the residual of observed values corresponding to the fixed solution of single-difference ambiguity between stations of the satellite when a common-view satellite passes through a grid on the hemisphere between stations. We draw some conclusions and give some suggestions of potential applications of MHGM in the future
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