###### Abstract  
Positioning accuracy is affected by the combined effect of user range errors and the geometric distribution of satellites. Dilution of precision (DOP) is defined as the geometric strength of visible satellites. DOP is calculated based on the satellite broadcast or precise ephemerides. However, because the modernization program of next-generation navigation satellite systems is still under construction, there is a lack of real ephemerides to assess the performance of next-generation constellations. Without requiring real ephemerides, we describe a method to estimate satellite visibility and DOP. The improvement of four next-generation Global Navigation Satellite Systems (four-GNSS-NG), compared to the navigation constellations that are currently in operation (four-GNSS), is statistically analyzed. The augmentation of the full constellation the Quasi-Zenith Satellite System (7-QZSS) and the Navigation with Indian Constellation (11-NavIC) for regional users and the low Earth orbit (LEO) constellation enhancing four-GNSS performance are also analyzed based on this method. The results indicate that the average number visible satellites of the four-GNSS-NG will reach 44.86, and the average geometry DOP (GDOP) will be 1.19, which is an improvement of 17.3% and 7.8%, respectively. With the augmentation of the 120-satellite mixed-orbit LEO constellation, the multi-GNSS visible satellites will increase by 5 to 8 at all latitudes, while the GDOP will be reduced by 6.2% on average. Adding 7-QZSS and 11-NavIC to the four-GNSS-NG, 37.51 to 71.58 satellites are available on global scales. The average position DOP (PDOP), horizontal DOP (HDOP), vertical DOP (VDOP), and time DOP (TDOP) are reduced to 0.82, 0.46, 0.67 and 0.44, respectively. d 6 August 2021 13 September 2021 16 September 2021 1  
the satellites [15], especially in complex urban environments and the Arctic region [16]. Moreover, the reliability of GNSS positioning can be enhanced for the higher measurement redundancy [17]. The performance of positioning and navigation depends on the user range error (URE) and the geometric distribution of satellites [18]. The standard positioning accuracy is given based on a certain percentage of time [19]. However, the actual positioning accuracy varies at different observation points or times. This variability is mainly affected by the geometric distribution of the satellites [19; 20]. Dilution of precision (DOP), a geometric factor, is used to signify the geometric strength of observations and evaluates the effectiveness of potential measurements [16; 21]. Multiplying the range errors with DOP provides positioning and time accuracy [20]. Many efforts have been made with DOP, including preciseness analysis [20], GNSS DOP evaluation [16; 17; 22], the change of DOP [23; 24; 25], and satellite selection [26; 27; 28]. The works cited above are based on the satellite broadcast or precise ephemerides, which are used to calculate the satellite position. However, because the modernization program of each system is still under construction, using the observation-based method is difficult when trying to assess the performance of the next-generation GNSS, as it lacks real ephemerides. [PERSON] et al. [29] presented a method that does not require real ephemerides to analyze the dependency of GPS DOPs on station location. Then, [PERSON] et al. [30] modified this method to assess the DOPs of BDS-3. Moreover, [PERSON] et al. [31] used this method to estimate BDS DOPs with different constellation configurations. However, none of them analyzed the performance of four-GNSS constellations. In this work, we use a well-known method by [PERSON] et al. [29], and we modify it in such a way to calculate the satellite visibility and DOPs of next-generation four-GNSS (four-GNSS-NG) in the absence of data on the real ephemeris of future satellites. By making these estimations, we show the contribution of the next-generation constellations to navigation and positioning services.