# A Fast Acquisition Algorithm for Hybrid Signals of 5G and BeiDou B1
## 2 Proposed Method  
### Compatibility Analysis of 5G and BeiDou B1 Signal  
#### 2.1.1 BeiDou B1 Signal System  
The BeiDou system provides various services, including RNSS services provided by L-band signals, satellite-based augmentation, ground-based augmentation, global short message communication, and regional short message communication provided by S-band. The frequency distribution of BeiDou signals is the same as that of other satellite navigation systems such as global positioning system (GPS) and Galileo. The signals in the L-band of BeiDou include three frequency points B1, B2, and B3. Officials have further developed the classification into B1I, B1C, B2a, B2b, and B3I based on specific types of services. A summary of the primary modulation mode, pseudorandom noise (PRN) code, channel coding, messages, and other parameters of the BeiDou satellite L-band signals is shown in Table 1.  
Figure 1: Organization of this paper. The BeiDou signal is broadcast from the satellite, and the power is only about \(-160\) dBw when it reaches the ground after a long distance of space propagation and attenuation. Since satellite communication belongs to the category of spread-spectrum communication, the navigation signal is submerged under the noise after being decorated, which can lead to spread-spectrum gain. According to the official BeiDou interface control document (ICD) [27; 28; 29; 30], multiple signals are broadcast on the same BeiDou satellite, and the same signal is broadcast on multiple satellites. The way the signals are broadcast is shown in Table 2.  
The specific frequency ranges and approximate power spectra of the BeiDou B1, B2, and B3 signals are shown in Figure 2. There are signals from other navigation systems at the three signal frequencies of BeiDou. The BeiDou system has been designed to be compatible with other navigation systems by optimizing the signal design method. However, only the signal design is optimized. There are no other measures to resist other radio systems (e.g., 5G systems) in the adjacent frequency bands except for spread-spectrum gain and the pilot frequency component. The B1I signal is generated by modulating the carrier wave with the \"range code + navigation message\", as the official BeiDou ICD document shows. The expression is as follows:  
\[S_{B1I}^{j}(t)=A_{B1I}C_{B1I}^{j}(t)D_{B1I}^{j}(t)\cos(2\pi f_{1}t+q_{B1I}^{j}) \tag{1}\]  
where \(j\) is the satellite number of BeiDou; \(A_{B1I}\) is the amplitude of the B1I signal; \(C_{B1I}^{j}\) denotes the PRN code of the B1I signal; \(D_{B1I}^{j}\) is the navigation message data; \(f_{1}\) denotes the carrier frequency of the B1I signal; and \(q_{B1I}^{j}\) denotes the initial carrier phase of B1I signal. The B1I signal of BeiDou is modulated by binary phase shift keying (BPSK). BPSK-R is a modulation method that adds spread-spectrum modulation to BPSK, the most basic and common spread-spectrum modulation method in satellite navigation systems. In the navigation field, 1.023 MHz is a reference value, and the parameter \(n\) in BPSK-R(\(n\)) means the spreading code rate \(f_{c}=n\times 1.023\) MHz. The spreading code rate of the BeiDou B1I signal is 2.046 MHz, which can be recorded as BPSK-R(2). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Signal Name** & **B1I** & **B1C** & **B2a** & **B2b** & **B3I** \\ \hline Message Type & D1/D2 & B-CNAV1 & B-CNAV2 & B-CNAV3 & D1/D2 \\ \hline \multirow{2}{*}{Broadcast Method} & D1:MEO/IGSO & \multirow{2}{*}{MEO/IGSO} & \multirow{2}{*}{MEO/IGSO} & \multirow{2}{*}{MEO/IGSO} & D1:MEO/IGSO \\  & D2:GEO & & & & D2:GEO \\ \hline \hline \end{tabular}
\end{table} 
Table 2: BeiDou signal message types and broadcasting methods. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
\begin{tabular}{c} D1:50 \\ D2:500 \\ \end{tabular} & 40.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: BeiDou signal basic parameters. Compared with other signals, the BeiDou B1C signal consists of the data component and the pilot frequency component.