# An In-Depth Assessment of the New BDS-3 B1C and B2a Signals
## 5 Quality of Code Observation
### Mp  
CC used in Section 5.1 is usually used for the evaluation of single-frequency receivers, which are susceptible to the ionosphere and multipath noise. The MP can deal with these problems, which are geometry-free and ionosphere-free. The interference delay effect caused by the satellite signal entering the receiver through multiple reflection paths is called the multipath. The expression of dual-frequency MP observation is shown in Equation (2) [22,23]. MP was determined by the pseudo-range multipath and noise, which is defined as Equation (3). \(P\) and \(\varphi\) the code and phase observation, respectively. \(f\) and \(\lambda\) represent the frequency and wavelength of the GNSS signal, respectively. \[MP_{i}=P_{i}-\frac{f_{i}^{2}+f_{j}^{2}}{f_{i}^{2}-f_{j}^{2}}\cdot\lambda_{i} \varphi_{i}+(\frac{f_{i}^{2}+f_{j}^{2}}{f_{i}^{2}-f_{j}^{2}}-1)\cdot\lambda_{ j}\varphi_{j}-B_{ij} \tag{3}\]  
where the subscripts \(i\) and \(j\) (\(i=j\)) indicate the difficult frequencies, \(MP_{i}\) is the multipath combination in meters. In the absence of cycle slips, bij is considered constant because it is composed of ambiguous terms and hardware delay deviation. In order to make the MP values statistically significant, the authors analyzed all GEO/IGSO satellites, with the results are shown in Tables 12 and 13. For the MP13 combination, the average value of BDS-3 GEO satellites is 0.03 m lower than BDS-2, while for the MP31 combination, the average value of BDS-3 is also 0.02 m lower than that of BDS-2. In contrast, for the MP13 combination, the average value of BDS-3 IGSO satellites is 0.07 m lower than of BDS-2, while for the MP31 combination, the average value of BDS-3 is also 0.07 m lower than that of BDS-2. Regardless of the BDS-2 or BDS-3 GEO/IGSO satellites, MP31 is lower than MP13 by more than 0.3 m. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**GNSS** & **Type** & **Sat** &
\begin{tabular}{c} **Elevation** \\ **(Average)** \\ \end{tabular} & **B1C(L1/E1)** & **B2a(L5/E5a)** \\ \hline BDS-3 & MEO & C24 & 39.30 & 0.21 & 0.14 \\ GPS & MEO & G04 & 33.86 & 0.26 & 0.15 \\ Galileo & MEO & E13 & 37.78 & 0.17 & 0.14 \\ QZSS & QZS & J01 & 47.53 & 0.29 & 0.10 \\ \hline \hline \end{tabular}
\end{table} 
Table 11: CC statistics of different GNSS satellites. Figure 12 shows the comparison of the MP values of the C14 satellite of BDS-2 and the C24 satellite of BDS-3. When the elevation of the C14 satellite increases, the MP value decreases, but after the elevation exceeds 50\({}^{\circ}\), the MP values also show an extremely abnormal increase. In contrast, the MP value of C24 of BDS-3 decreases with the increase in elevation, and there is no abnormal phenomenon in C24. It can be seen that BDS-3 improves the systematic deviation of BDS-2 MEO satellites in MP. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**System** & **Satellite** &
\begin{tabular}{c} **Elevation** \\ **(Average)** \\ \end{tabular} & **MP13** & **MP31** \\ \hline \multirow{8}{*}{**BDS-2**} & average & 54.67 & 0.30 & 0.18 \\  & C06 & 55.09 & 0.32 & 0.21 \\  & C07 & 55.41 & 0.33 & 0.20 \\  & C08 & 54.51 & 0.34 & 0.17 \\  & C09 & 54.37 & 0.26 & 0.18 \\  & C10 & 54.54 & 0.27 & 0.18 \\  & C13 & 53.50 & 0.30 & 0.16 \\  & C16 & 55.24 & 0.28 & 0.18 \\  & average & 54.88 & 0.23 & 0.11 \\  & C38 & 55.07 & 0.27 & 0.13 \\  & C39 & 55.17 & 0.21 & 0.11 \\  & C40 & 54.40 & 0.20 & 0.10 \\ \hline \hline \end{tabular}
\end{table} 
Table 13: Statistics of MP values of all IGSO satellites. Figure 12: Comparison of MP values of MEO satellites (C14 vs. C24). Table 14 shows the MP13 and MP31 values of all BDS-2 and BDS-3 satellites. By analyzing the average value, it can be found that the value of MP31 is nearly 0.07 m lower than that of MP13, while the MP noise of the MEO satellite of BDS-3 is better than that of BDS-2 exceed 0.05 m. At the same time, the research results of the MP noise of the new BDS-3 signals B1C and B2a show that it is nearly 0.03 m lower than the traditional frequency combination of B1I and B3I, while MP21 is also nearly 0.03 m lower than MP12.