## 6 Dual-Mode WAAS (GPS + GALILEO)  
Galileo is the Europe's contribution to a global navigation satellite infrastructure. Galileo is expected to reach the Full Operational Capability (FOC) in 2013. In June 2004, the European Union and the United States signed an agreement to envisage the compatibility and interoperability of GPS  
Figure 8: The 99.9% VPL contour of the dual-frequency GPS/WAAS user with an improved signal model. The VPL values could not meet the CAT I requirement. and Galileo. In other words, one will be able to calculate a position with the same receiver from any of the satellites in both systems. It will make the user more robust to the loss of the satellites. Figure 10: The 99.9% VDOP contour for WAAS with GPS and Galileo. The VDOP values are from 1-2 in all of CONUS, and in all of Alaska. Figure 9: The 99.9% VDOP contour for WAAS with GPS alone. The VDOP values are from 1-4 in CONUS, and the VDOP values are from 1-2 in Alaska. WAAS should also take advantage of the new satellite constellation. Therefore, WAAS should provide corrections to Galileo as well as GPS. In the service volume analysis, this paper treats Galileo satellites the same as GPS satellites but in different orbits. With a combined GPS and Galileo constellation, the MAAST simulation shows that the number of satellites in view over a twenty four hour period is more than twenty for each simulation time step (five minutes). This is about twice the number with GPS only. One could expect significant improvement in the geometry for the position estimation. Figure 9 and Figure 10 show the VDOP (Vertical Dilution of Precision) [1,2] for WAAS with GPS alone and for WAAS with GPS and Galileo, respectively. In comparison with Figure 9, Figure 10 shows a significant improvement in VDOP. As can be seen in Equation (4), generally good geometries (small VDOP) as well as good confidence bounds (small \(\sigma_{i}\)) are required to obtain high availability [1]. Figure 11 shows the VPL contour for the dual-mode (GPS + Galileo) and dual-frequency (L1 + L5 and/or E1 + E5) WAAS user avionics sensor. As shown in Figure 11, the VPL values are less than 12 m (CAT I VAL) in most of CONUS, Alaska, and Canada. Furthermore, as can be seen in Figure 11, the VPL values are less than 10 m in most of CONUS, in most of Canada, and in some of Alaska. In other words, it is possible for WAAS to achieve 10 m VAL (a more stringent landing requirement) with new additional civil signals and additional satellites from Galileo. The VPL is a very important criterion to evaluate the performance of WAAS, and many resources have been focused on reducing this term. The goal is not only to meet the current LPV requirement but also be capable to meet the  
Figure 11: The 99.9% VPL contour of the dual-mode (GPS + Galileo) and L1-L5 dual-frequency WAAS user avionics sensor. The VPL values in most of CONUS, Alaska, and Canada are less than 12 m (CAT I VAL). Importantly, The VPL values are less than 10 m in most of CONUS and Canada. more stringent required navigation performance (RNP), such as LPV 200 (VAL = 35 m) and CAT I (VAL = 12 to 10 m) requirements. For instance, the FAA's performance goals of WAAS are first to provide full LPV service by September 2008, then provide LPV 200 service in 2009-2013, and finally provide dual-frequency WAAS service (possible Category I) in 2014-2028. This paper discusses the modernized aviation L1-L5 dual-frequency GNSS/WAAS user, thus, it is necessary to explore all possible techniques to gain better VPL performance (_i.e._, reduction in VPL). As a result, it is important to find the future architectures which allow aviation users to enhance the performance of a GPS/WAAS approach and landing system. This paper extends the same analysis to investigate the aviation navigation performance of Japanese MSAS and European's EGNOS. Figure 12 presents the VPL contours for Japanese MSAS.