# Considering Inter-Frequency Clock Bias for BDS Triple-Frequency Precise Point Positioning
## 3 Results
### Space Segment and Navigation Signals
The five GEO satellites are fixed in longitude because of active control, whereas their ground tracks exhibit small variations of up to 2\({}^{\circ}\) in latitude. Similar to the GPS, GLONASS and Galileo satellites, the BDS MEO satellites offer complete global coverage. The ground tracks of the MEO satellites are confined from 56.1\({}^{\circ}\)S to 56.1\({}^{\circ}\)N latitude. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Generation** & **Satellite** & **PRN** & **COSPAR ID** & **NORAD ID** & **Type** & **Orbit** \\ \hline \multirow{9}{*}{BDS-2} & G1 & C01 & 2010-001A & 36287 & GEO & 140.0\({}^{\circ}\)E \\  & G6 & C02 & 2012-059A & 38953 & GEO & 80\({}^{\circ}\)E \\  & G3 & C03 & 2010-024A & 36590 & GEO & 110.5\({}^{\circ}\)E \\  & G4 & C04 & 2010-057A & 37210 & GEO & 160.0\({}^{\circ}\)E \\  & G5 & C05 & 2012-008A & 38091 & GEO & 58.75\({}^{\circ}\)E \\  & I1 & C06 & 2010-036A & 36828 & IGSO & \(\sim\)122\({}^{\circ}\)E \\  & I2 & C07 & 2010-068A & 37256 & IGSO & \(\sim\)119\({}^{\circ}\)E \\  & I3 & C08 & 2011-013A & 37384 & IGSO & \(\sim\)120\({}^{\circ}\)E \\  & I4 & C09 & 2011-038A & 37763 & IGSO & \(\sim\)96.5\({}^{\circ}\)E \\  & I5 & C10 & 2011-073A & 37948 & IGSO & \(\sim\)92.5\({}^{\circ}\)E \\  & M3 & C11 & 2012-018A & 38250 & MEO & \(\sim\)21,528 km \\  & M4 & C12 & 2012-018B & 38251 & MEO & \(\sim\)21,528 km \\  & M6 & C14 & 2012-050B & 38775 & MEO & \(\sim\)21,528 km \\  & I6 & C15/C13 & 2016-021A & 41434 & IGSO & \(\sim\)95\({}^{\circ}\)E \\ \hline \multirow{9}{*}{BDS-3} & I1-S & C31 & 2015-019A & 40549 & IGSO & \(\sim\)93.5\({}^{\circ}\)E \\  & I2-S & C32 & 2015-053A & 40938 & IGSO & \(\sim\)96.5\({}^{\circ}\)E \\ \cline{1-1}  & M1-S & C33 & 2015-037A & 40748 & MEO & \(\sim\)21,528 km \\ \cline{1-1}  & M2-S & C34 & 2015-037B & 40749 & MEO & \(\sim\)21,528 km \\ \hline \hline \end{tabular}
\end{table} 
Table 2: BDS space segment as of October 2016. The BDS-2 satellites transmit navigation signals in QPSK modulation on a total of three frequency bands, namely B1, B2 and B3 [35]. Compared with the BDS-2 satellites, the signals of BDS-3 satellites are modified. In addition to B1 and B3 signals, the BDS-3 satellites are also capable of transmitting several new navigation signals, namely B1C, B2a and B2b. The B1C signal centered at 1,575.42 MHz is transmitted in TMBOC(6,1) modulation, and is compatible with GPS L1 signal and Galileo E1 signal. The B2a signal with a center frequency of 1176.45 MHz is modulated using BPSK(10), AltBOC(15,10) or TD-AltBOC(15,10) modulation, and is compatible with GPS L5 signal and Galileo E5a signal. The AltBOC(15,10) or TD-AltBOC(15,10) modulated B2b signal matches the Galileo E5b signal. It should be noted that the B2 signal of BDS-2 satellites and the B2b signal of BDS-3 satellites share the same frequency, but their modulation types are different. The carrier phase frequencies and chip rates of BDS signals covered by test receivers are provided in Table 3. The B1, B1C, B2a, B2b and B3 signals can be simultaneously tracked for the BDS-3 satellites I2-S, M1-S and M2-S, while the receiver can only track the B1 and B3 signals for the II-S satellite.