# Radio Frequency Compatibility Evaluation of S Band Navigation Signals for Future BeiDou
## 4 Radio Frequency Compatibility Evaluation
Since IRNSS is designed to provide positioning for India as well as the region extending up to 1500 km from its boundary, the compatibility analysis mainly focuses on the extended service area enclosed by the rectangle with latitude 30\({}^{\circ}\) S to 50\({}^{\circ}\) N and longitude 30\({}^{\circ}\) E to 130\({}^{\circ}\) E. As shown, the CPM(8) has the minimal \(\Delta(C/N_{0})_{\text{eff,SSC}}^{\text{inter,worst}}\) on IRNSS BOCs(5,2) with its mean 0.03539 dB, followed by BPSK(8), BOCs(4,4)and MSK-BOCs(4,4), at the same time, in code tracking the CPM(8) also behaves the smallest \(\Delta(C/N_{0})_{\text{eff,CTSSC}}^{\text{inter,worst}}\) on IRNSS BOCs(5,2) with its mean 0.03981 dB, followed by MSK-BOCs(4,4), BPSK(8), and BOCs(4,4). Figure 12: _Cont._  
Figure 11: The \(\Delta(C/N_{0})_{\text{eff,CTSSC}}^{\text{inter,worst}}\) of Galileo candidate BPSK(8) in dB level interfered by BDS: (a) CPM(8); (b) BOCs(4,4); (c) BPSK(8); (d) MSK-BOCs(4,4). Case 6: Single FDMA Globalstar signal is interfered by BDS candidate signals, i.e. \[\left\{ \begin{array}{c}I_{\text{intra}}=I_{\text{SRRC,others}}^{\text{Globalstar}}\\ I_{\text{inter}}=I_{\text{candidate}}^{\text{BDS}}\end{array} \right.. \tag{35}\]  
The Figures 14 and 15 show compatibility evaluation results between BDS and Globalstar. In real simulation, CPM(8) naturally entails less received power than other BDS candidates, together with comparable SSC and CTSSC, thus CPM(8) tends to introduce less interference on Globalstar for acquisition and code tracking shown clearly in Figures 14 and 15. The figures indicate that CPM(8) has less \(\Delta(C/N_{0})_{\text{eff,SSC}}^{\text{inter,worst}}\) on single FDMA Globalstar signal than BOCs(4,4), BPSK(8) and MSK-BOCs(4,4) at 0.0421 dB, 0.0867 dB and 0.0263 dB in average, whereas the mean \(\Delta(C/N_{0})_{\text{eff,CTSSC}}^{\text{inter,worst}}\) of single FDMA Globalstar signal subjected by CPM(8) for code tracking is around 0.042 dB, 0.087 dB and 0.026 dB smaller than that induced by BOCs(4,4), BPSK(8) and MSK-BOCs(4,4). Figure 12: The \(\Delta(C/N_{0})_{\text{eff,SSC}}^{\text{inter,worst}}\) of IRNSS BOCs(5,2) in dB level interfered by BDS: **(a)** CPM(8); **(b)** BOCs(4,4); **(c)** BPSK(8); **(d)** MSK-BOCs(4,4). Figure 13: The \(\Delta(C/N_{0})_{\text{eff,CTSSC}}^{\text{inter,worst}}\) of IRNSS BOCs(5,2) in dB level interfered by BDS: **(a)** CPM(8); **(b)** BOCs(4,4); **(c)** BPSK(8); **(d)** MSK-BOCs(4,4). Case 7: BDS candidate signals are interfered by IRNSS, Galileo candidate, and Globalstar, i.e.,  
\[\left\{ \begin{array}{l}I_{\text{Intra}}=I_{\text{candidate,others}}^{\text{BDS}} \\ I_{\text{Inter}}=I_{\text{SRRC}}^{\text{Globalstar}}+I_{\text{BOCs(5,2)}}^{\text{ IRNSS}}+I_{\text{BPSK(1)}}^{\text{JGalileo}}+I_{\text{candidate}}^{\text{Galileo}}\end{array} \right. \tag{36}\]  
where \(I_{\text{candidate}}^{\text{Galileo}}\) denotes the equivalent PSD of Galileo candidate interfering signals, and in this case the Galileo candidate is assumed as CBOC(6,1,1/11). Figure 14: The \(\Delta(C/N_{0})_{\text{eff,SSC}}^{\text{inter,worst}}\) of single FDMA Globalstar signal in dB level interfered by BDS: (a) CPM(8); (b) BOCs(4,4); (c) BPSK(8); (d) MSK-BOCs(4,4). Figure 15: The \(\Delta(C/N_{0})_{\text{eff,CTSC}}^{\text{inter,worst}}\) of single FDMA Globalstar signal in dB level interfered by BDS: (a) CPM(8); (b) BOCs(4,4); (c) BPSK(8); (d) MSK-BOCs(4,4). The compatibility evaluation of BDS candidates interfered by IRNSS, Galileo candidate, and Globalstar in terms of \(\Delta(C/N_{0})^{\mathrm{inter,worst}}_{\mathrm{eff,SSC}}\) and \(\Delta(C/N_{0})^{\mathrm{inter,worst}}_{\mathrm{eff,CTSSC}}\) are respectively depicted in Figures 16 and 17. In signal acquisition, the MSK-BOCs(4,4) has minimal \(\Delta(C/N_{0})^{\mathrm{inter,worst}}_{\mathrm{eff,SSC}}\) induced by IRNSS, Galileo candidate and Globalstar, and its mean is 0.065 dB, 0.009 dB and 0.264 dB smaller than that of CPM(8), BOCs(4,4) and BPSK(8), which is mainly attributed to the best SSC of MSK-BOCs(4,4) with BPSK(1).