# A Comprehensive Signal Quality Assessment for BDS/Galileo/GPS Satellites and Signals
## 3 Experiment Results  
### Experimental Analysis of Signal Power  
Using the model given above, the _C/N0_ values of BDS-3 satellites at different signals are analyzed. For ease of presentation, BDS-2 is represented as capital II, the BDS-3 experimental system is represented as capital IIIs, and BDS-3 is represented as III in the following diagrams.  
The average _C/N0_ values of all satellites for BDS-2, BDS-3s, and BDS-3 at different signals as a function of elevation are depicted in Figure 1, derived from the first model of C/N0. The _C/N0_ values of the same types of satellites are represented by lines of the same color, indicating that the difference in signal power between satellites of the same type is very small. In terms of B1I and B3I, the average _C/N0_ values of BDS-3 MEO satellites are all about 1-2 dB higher than that of BDS-2 MEO satellites and 3-4 dB higher than that of BDS-2 GEO and IGSO satellites. The lower signal strength of GEO and IGSO satellites is due to their high satellite orbit altitude, resulting in greater signal attenuation.  
Due to the small differences between satellites of the same type, the _C/N0_ values of satellites of the same type are calculated together according to the second _C/N0_ model to further analyze and compare the signal performances of different GNSS systems, which are shown in Figure 2. In the experiment, it was found that the experimental results obtained by different types of receivers were basically consistent; therefore, only performances of the receiver type JAVAD TRE_3 3.7.6 are described in the contribution.  
The left panel of Figure 2 first shows the comparison of signal powers at various frequency points of BDS-2 and BDS-3. Consistent with the above analysis results, the signal  
Figure 1: Average _C/N0_ values against the elevations of all the satellites for BDS B1I/B2I/B3I/B2a based on observations collected from MGEX stations during DOY 134–140 in 2019. Only the results of the representative receiver type JAVAD are plotted. (II: BDS-2; IIIs: BDS-3 experimental system; III: BDS-3).  
powers of BDS-3 satellites at B1I and B3I show a higher level than BDS-2 satellites. Among all the signals of BDS, B2a performs the best, varying from 46 to 60 dB-Hz.  
The right panel of Figure 2 shows the C/N0s comparison of various types of signals for BDS-2, BDS-3, GPS, and Galileo. Among all the signals, the GPS L5, BDS-3 B2a, and Galileo E5b perform slightly better than the other signals, and L2 of GPS always has the lowest signal power.  
The average _C/N0_ values of BDS-2, BDS-3, GPS, and Galileo on different types of receivers at each signal are shown in Figure 3. There is little difference in signal power on different types of receivers. Comparing the _C/N0_ averages on the first seven stations of JAVAD, which can receive B2a signals, the B2a signal has significantly higher power than the other signals, regardless of station. Among all the BDS-2 signals, the signal power of B1I is always smaller than that of B2I and B3I on the same station, while the order of signal power for GPS is L5 > L1 > L2. For Galileo, the signal power of E5 is the strongest, although on some stations equipped with LEICA-type receivers, the E5 signal is not the best.