## 2 Materials and Methods
### Multichannel Orthogonal Correlation Detection Method
#### 2.2.3 Signal Detection and Station Identification  
Station identification detects the expected stations based on the different transmission sequences of \(f_{1}\), \(f_{2}\), and \(f_{3}\), which are the frequency signals of the five stations of the Alpha navigation system. The specific goal was to detect the correlation peak by comparing the correlation results, namely \(R_{1}(t),\ R_{2}(t)\), and \(R_{3}(t)\), of the three frequency signals with their corresponding thresholds. Figure 4 illustrates the station identification process. The conditions for the successful detection of the five stations in the Alpha navigation system are described below. The condition for the master station signal to be detected successfully. When the correlation results of the \(f_{1}\) frequency signal are all greater than the threshold \(T_{1}\) in the time period \(t+10\ \text{ ms}\) to \(t+480\ \text{ms}\), all of the correlation results of the \(f_{2}\) frequency signal are greater than the threshold \(f_{3}\) in the time period \(t+610\ \text{ms}\) to \(t+1080\ \text{ms}\), and all of the correlation results of the \(f_{3}\) frequency signal are greater than the threshold \(T_{3}\) in the time period \(t+1210\ \text{ms}\) to \(t+1680\ \text{ms}\); therefore, we confirm that the main station detection is successful. The threshold calculations for the three frequency signals of the main station are as follows:  
\[T_{1}=\frac{R_{1}(t)+R_{1}(t+490\ \text{ms})}{2}, \tag{12}\]  
\[T_{2}=\frac{R_{2}(t+600\ \text{ms})+R_{2}(t+1090\ \text{ms})}{2}, \tag{13}\]  
\[T_{3}=\frac{R_{3}(t+1200\ \text{ms})+R_{3}(t+1690\ \text{ms})}{2}. \tag{14}\]  
The condition for the western secondary station signal to be detected successfully. When the correlation results of the \(f_{1}\) frequency signal are all greater than the threshold \(T_{1}\) in the time period \(t+10\ \text{ms}\) to \(t+480\ \text{ms}\), all of the correlation results of the \(f_{2}\) frequency signal are greater than the threshold \(T_{2}\) in the time period \(t+610\ \text{ms}\) to \(t+1080\ \text{ms}\), and all of the correlation results of the \(f_{3}\) frequency signal are greater than the threshold \(T_{3}\) in the time period \(t+2410\ \text{ms}\) to \(t+2880\ \text{ms}\); therefore, we confirm that the western secondary station detection is successful. The threshold calculations for the three frequency signals of the western secondary station are as follows:  
\[T_{1}=\frac{R_{1}(t)+R_{1}(t+490\ \text{ms})}{2}, \tag{15}\]  
\[T_{2}=\frac{R_{2}(t+600\ \text{ms})+R_{2}(t+1090\ \text{ms})}{2}, \tag{16}\]  
\[T_{3}=\frac{R_{3}(t+2400\ \text{ms})+R_{3}(t+2890\ \text{ms})}{2}. \tag{17}\]  
The condition for the eastern secondary station signal to be detected successfully. When the correlation results of the \(f_{1}\) frequency signal are all greater than the threshold \(T_{1}\) in the time period \(t+10\ \text{ms}\) to \(t+480\ \text{ms}\), all of the correlation results of the \(f_{2}\) frequency signal are greater than the threshold \(T_{2}\) in the time period \(t+3010\ \text{ms}\) to \(t+3480\ \text{ms}\), and all of the correlation results of the \(f_{3}\) frequency signal are greater than the threshold \(T_{3}\) in the time period \(t+2410\ \text{ms}\) to \(t+2880\ \text{ms}\); therefore, we confirm that the eastern  
Figure 4: Flow chart of Alpha navigation station identification. secondary station detection is successful. The threshold calculations for the three frequency signals of the eastern secondary station are as follows:  
\[T_{1}=\frac{R_{1}(t)+R_{1}(t+490\text{ ms})}{2}, \tag{18}\]  
\[T_{2}=\frac{R_{2}(t+3000\text{ ms})+R_{2}(t+3490\text{ ms})}{2}, \tag{19}\]  
\[T_{3}=\frac{R_{3}(t+2400\text{ ms})+R_{3}(t+2890\text{ ms})}{2}. \tag{20}\]  
The condition for the northern secondary station signal to be detected successfully.