###### Abstract  
The BeiDou Navigation Satellite System (BDS) features a heterogeneous constellation so that it is difficult to mitigate the multipath in the coordinate-domain. Therefore, mitigating the multipath in the observation-domain becomes more important. Sidereal filtering is commonly used for multipath mitigation, which needs to calculate the orbit repeat time of each satellite. However, that poses a computational challenge and damages the integrity at the end of the multipath model. Therefore, this paper proposes a single-difference model based on the multipath hemispherical map (SD-MHM) to mitigate the BDS-2/BDS-3 multipath in a short baseline. The proposed method is converted from double-difference residuals to single-difference residuals, which is not restricted by the pivot satellite transformation. Moreover, it takes the elevation and the azimuth angles of the satellite as the independent variables of the multipath model. The SD-MHM overcomes the unequal observation time of some satellites and does not require specific hardware. The experimental results show that the SD-MHM reduces the root mean square of the positioning errors by 56.4%, 63.9%, and 67.4% in the east, north, and vertical directions; moreover, it contributes to an increase in the baseline accuracy from 1.97 to 0.84 mm. The proposed SD-MHM has significant advantages in multipath mitigation compared with the advanced sidereal filtering method. Besides, the SD-MHM also features an excellent multipath correction capability for observation data with a period of more than seven days. Therefore, the SD-MHM provides a universal strategy for BDS multipath mitigation. BDS; multipath mitigation; single-difference residuals; multipath hemispherical map; advanced sidereal filtering Article  
A Single-Difference Multipath Hemispherical Map for Multipath Mitigation in BDS-2/BDS-3 Short Baseline Positioning  
13204132020304132020304132020304132020304132020304132020304132020304132020203041320202030413202 Navigation Satellite System (GNSS) of the same orbit type, such as GPS and Galileo (except GLONASS, which is the frequency division multiple access). The existing work for BDS multipath mitigation is mainly based on the time-domain correlation and few studies have focused on the BDS multipath spatial-domain correlation, especially the related studies on BDS-2/BDS-3 multipath mitigation. The multipath processing methods can be divided into hardware- and software-based methods. The hardware-based methods mainly improve the receiver antenna [7; 8; 9], which partially mitigate the multipath. However, the cost is high if these devices are widely used. The software-based approaches consist of four categories. The first category is the improved stochastic model [10; 11; 12]; these methods reduce the influence of multipath based on the statistical significance of the observations. However, the multipath still exists in the positioning results. The second category is the time-frequency analysis, such as wavelet analysis [13], Vondrak filtering [14], and empirical mode decomposition with component analysis [15]. However, these methods are only suitable for post-processing. The third category is based on the multi-antenna solution, such as array antennas [16] and dual-polarized antennas [17]. The hardware equipment is complicated, and it is difficult to fit a complex environment with multipath effects. The last category is based on multipath spatiotemporal correlation, which is also a current hot research topic. The modeling based on multipath spatiotemporal correlation requires the environment and the position of the receiver to be in a relatively stable situation. Therefore, these methods can be used for mitigating the multipath in real-time. Sidereal filtering (SF) is a widely-used method to model the historical multipath [18; 19; 20; 21]. The SF applies the multipath time-domain correlation to mitigate the multipath. The GPS constellation in space repeats nearly a sidereal day (23 h 56 min 4 s), and the satellite orbit types are the same.