# Analysis of the Impact of Multipath on Galileo System Measurements
## 2 Multipath for Galileo  
The Galileo system is currently in its final construction stage and is close to achieving full operational capability with a target number of 30 satellites in the constellation. The current constellation comprises 22 fully operational satellites [28]. This ensures the visibility of at least five satellites at every point on the globe [29]. The constant development of the system makes its use increasingly widespread. Observations obtained using this system are used not only by advanced geodetic receivers but also increasingly often by mobile receivers. The growing popularity of the system can also be explained by a variety of civil signals that it uses. Galileo satellites transmit signals on four frequency bands intended for civilian users. Each signal has two additional channels: one for navigation data and a pilot channel without this data. The addition of a pilot channel is to increase the sensitivity of code tracking under increased signal interference conditions [30]. The civilian signal on the E1 frequency is transmitted using the Composite Binary Offset Carrier modulation technique: CBOC(6,1,1/11) [31]. The use of Binary Offset Carrier (BOC) modulation derivatives guarantees a higher quality of observation under the conditions of increased signal interference in relation to the legacy code C/A of the GPS system as well as ensures interoperability between different GNSS systems using the same radio frequency bands [27]. Research on the selection of the appropriate signal type for the Galileo satellites was carried out as part of the GIOVE test missions. The CBOC technique used for the Galileo E1 signal allow us to increase the accuracy of code observations by 20-25% relative to BOC(1,1), which has similar characteristics to the Binary Phase Shift Keying (BPSK(1)) signal of the GPS C/A code [25]. For a 5\({}^{\circ}\) satellite elevation, the code multipath error for a CBOC signal was approximately 0.6 m, while for BOC(1,1), it was 0.9 m.  
Signals at E5a and E5b frequencies can be recorded as independent observations using BPSK(10) modulation techniques. However, these signals modulate the carrier wave at E5 frequency using the Alternative BOC (AltBOC) method, thereby creating a signal with a very wide frequency bandwidth [32]. In theory, this signal is supposed to offer the greatest resistance to the multipath effect and measurement noise. Analyses for all Galileo signals, transmitted by GIOVE-A satellite, indicate smaller values of the multipath error compared to the C/A GPS code [26]. The STD of the multipath error for the C/A GPS signal was determined at the level of 1.2 m for a satellite elevation less than 10\({}^{\circ}\) and of 0.6 m for an elevation above 10\({}^{\circ}\). For the Galileo signals, the STD values were 0.5 m and 0.3 m for E5a, 0.5 m and 0.3 m for E5b, 0.2 m and 0.2 m for E5, and 0.5 m and 0.3 m for E6, which is used in the High Accuracy Service (results for elevations lower and higher than 10\({}^{\circ}\), respectively). Multipath error analyses for code observations at International GNSS Service (IGS) stations, based on CMC analysis as well as the wavelet analysis, also prove the superiority of Galileo observations over GPS C/A code [24]. The smallest value of error was obtained for the E5 AltBOC signal. [PERSON] [2] presented a theoretical compilation of multipath errors for both code and phase observations of the GPS and Galileo systems using a GNSS signal generator. For the most unfavorable simulation conditions, the E5 AltBOC signal turned out to be even several times more resistant to the impact of multipath than the other tested signals: 0.2 m relative to 1.0 m for E5a/E5b, 0.6 m for E6, and over 1 m for E1 for the Double-Delta correlation technique [33]. In the case of phase multipath, the differences between the signals are solely due to the different carrier wavelengths, and the modulation technique used does not affect the quality of the phase observations.