# Radio Frequency Compatibility Evaluation of S Band Navigation Signals for Future BeiDou  
[PERSON]  
1 College of Information & Communication Engineering, Harbin Engineering University, Harbin 150001, China; [EMAIL_ADDRESS] (Y.S.); [EMAIL_ADDRESS] (D.Z.)  
[PERSON]  
1 College of Information & Communication Engineering, Harbin Engineering University, Harbin 150001, China; [EMAIL_ADDRESS] (Y.S.); [EMAIL_ADDRESS] (D.Z.)  
[PERSON]  
1 College of Information & Communication Engineering, Harbin Engineering University, Harbin 150001, China; [EMAIL_ADDRESS] (Y.S.); [EMAIL_ADDRESS] (D.Z.)  
[PERSON]  
2 State Key Laboratory of Space-Ground Integrated Information Technology, Beijing 100086, China  
BPSK(1), BPSK(4) and BPSK(8). For BeiDou system (BDS), a few candidate signals based on BOCs(4,4), BPSK(8), continuous phase modulation (CPM(8)) and minimum shift keying-BOC (MSK-BOC(4,4)) are suggested by some researchers to provide an authorized service in S band [12; 13; 14]. However, in the quite finite S band of 16.5 MHz, mutual interference among different systems is inevitable. Thus, compatibility is a matter of great concern for system providers and has higher priority than other performance before the final confirmation of the new S band signals. To allow peaceful coexistence with minimal mutual interference among systems, radio frequency compatibility evaluation is particularly essential to design S band signals for future BDS.  
A quantity called the effective carrier-to-noise ratio degradation \(\Delta(C/N_{0})_{\text{eff}}\) formulated by ITU-R can reflect the effects of interference among navigation systems at the receiver well [15]. The spectral separation coefficient (SSC) is an essential part of the \(\Delta(C/N_{0})_{\text{eff}}\) and is accepted widely by the global navigation satellite system (GNSS) communities as an effective index to characterize compatibility. Nevertheless, the SSC is just appropriate to describe interference effects on signal acquisition rather than code tracking. To fill the gap, a code tracking spectral separation coefficient (CTSSC) is introduced for the evaluation of the interference level on code tracking loop [16]. To obtain more accurate compatibility assessments for the exploration of desired BDS signals allowing peaceful coexistence with other systems in S band, comprehensive compatibility evaluation methods based on the \(\Delta(C/N_{0})_{\text{eff}}\) using SSC and CTSSC are firstly described and derived from the perspective of output SNIR and code tracking error variance for both scenarios of acquisition and code tracking respectively. A real simulation is established using completed space constellation models of navigation and Globalstar systems, modulation schemes and received power, though it is tough work to calculate each interfering case for different static users on the earth's surface at every moment. The worst results of compatibility between BDS candidate S band signals and other systems are calculated in simulation using the \(10^{\circ}\times 10^{\circ}\) grid for longitude and latitude and sampling time step of 1 minute during a time period of 10 days.  
The rest of this paper is organized as follows. Section 2 presents complete compatibility evaluation methods based on the \(\Delta(C/N_{0})_{\text{eff}}\) for both scenarios of the acquisition and code tracking. Signal parameters and space constellation models of BDS, IRNSS, Galileo and Globalstar are established in Section 3. The real simulation considering the worst situation on compatibility of BDS candidate signals with other system signals in S band is carried out in Section 4. Finally, we conclude the paper in Section 5.