# Radio Frequency Compatibility Evaluation of S Band Navigation Signals for Future BeiDou
## 4 Radio Frequency Compatibility Evaluation  
This section provides compatibility evaluation results of BDS candidate signals with interfering signals from other systems in S band. Corresponding simulation parameters are shown in Table 2. Based on the previous analysis, the SSC and CTSSC are the essential quantities for the calculation of \(\Delta(C/N_{0})_{\text{eff}}\) in both scenarios of acquisition and code tracking. The Table 3 and Figure 2 respectively report the SSC and CTSSC of each S band signal as desired signal with other interference signals, where Globalstar\({}^{\text{single}}_{\text{max}}\) means the single FDMA Globalstar signal corresponding to the maximum SSC and CTSSC with interference signal, and the delay between early and late varies from 0.1 to 1 chip of desired signal. Figure 1: S band Signal PSD: (**a**) IRNSS; (**b**) Galileo candidates; (**c**) Globalstar; (**d**) BDS candidates. \begin{table}
\begin{tabular}{c c} \hline \hline
**Simulation Parameter** & **Parameter Setting** \\ \hline Simulation Time & 10 days \\ Time Resolution & 1 min \\ Grid Resolution & Longitude: 10\({}^{\circ}\); Latitude: 10\({}^{\circ}\) \\ Minimum Elevation Angle & 10\({}^{\circ}\) \\ Receiver Bandwidth & Navigation signal: 16.363 MHz; Globalstar signal: 1.23 MHz \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Simulation parameters and corresponding settings. From Table 3 and Figure 2, it clearly appears that each CTSSC is different from corresponding SSC, which implies interfering signals have disparate impacts on same desired signal in terms of acquisition and code tracking. Besides the CTSSC is very sensitive to \(d\) due to the \(\sin^{2}(\pi fd)\) function that would produce large amounts of compatibility evaluation results in code tracking using various \(d\) for each sampling time. Here we analyze the worst situation considering the minimal desired signal power, maximum interfering signal power as well as the maximum equivalent PSD of the intersystem or intrasystem interference. Then the worst \(\Delta(C/N_{0})_{\text{eff}}\) of desired signal induced by the intrasystem interference in acquisition is expressed by  
\[\Delta(C/N_{0})_{\text{eff,SSC}}^{\text{intra,worst}}=\Delta(C/N_{0})_{ \text{eff,SSC}}^{\text{intra}}, \tag{25}\]  
where \(C_{jk}^{\text{intra,max}}\) is the maximum receiver antenna output power of the \(k\)th interfering signal of the \(j\)th intrasystem satellite. The worst \(\Delta(C/N_{0})_{\text{eff}}\) of desired signal induced by the intersystem interference in acquisition is expressed by  
\[\Delta(C/N_{0})_{\text{eff,SSC}}^{\text{inter,worst}}=\Delta(C/N_{0})_{\text{ eff,SSC}}^{\text{inter}}, \tag{26}\]  
where \(C_{i,j,k}^{\text{inter,max}}\) is the maximum receiver antenna output power of the \(k\)th interfering signal from the \(j\)th intrasystem satellite of the \(i\)th intersystem. Likewise, the worst \(\Delta(C/N_{0})_{\text{eff}}\) of desired signal induced by the intrasystem and intersystem interference in code tracking are expressed respectively as follows  
\[\Delta(C/N_{0})_{\text{eff,CTSSC}}^{\text{intra,worst}}=\Delta(C/N_{0})_{ \text{eff,CTSSC}}^{\text{intra}}, \tag{27}\]  
\[\Delta(C/N_{0})_{\text{eff,CTSSC}}^{\text{inter,worst}}=\Delta(C/N_{0})_{ \text{eff,CTSSC}}^{\text{inter}}. \tag{28}\]  
To fairly determine the maximum and minimal power at receiver antenna output for each S band navigation signal, we assume their minimal power required to guarantee the same raw thermal noise pseudorange error of 0.2 m. Figure 3 depicts the code-tracking errors of S band navigation signals using noncoherent discriminator in white noise, where an early-late spacing of 0.1 chip, a receiver bandwidth of 16.363 MHz, and integration time of 4 ms are used to produce the results. The corresponding minimal power can be read back from Figure 3 for a particular code noise of 0.2 m, where the noise density \(N_{0}\) is considered to be \(-204\) dBW/Hz.