## 4 EMC Evaluation Method for Communication Receiver
The formula for the BER of the BDS receiver subjected to pulsed interference can be derived as:  
\[P_{e}=Q(\sqrt{\frac{\frac{2}{SNR}+\frac{2d\cdot SIR}{N}}{N}})\frac{T_{chip}+W}{ T_{PRP}} \tag{28}\]  
\[d=\frac{1}{B_{j}}\int\limits_{f_{j}-B_{j}/2}^{f_{j}+B_{j}/2}\sin c^{2}[(f_{0}- f)\frac{2}{B}]df \tag{29}\]  
Considering that the main energy of pulse signals in the same frequency band falls on the passband of the receiver, the above BER can be approximated as:  
\[P_{e}=Q(\sqrt{4\frac{R_{p}}{R\cdot SIR}})\frac{T_{chip}+W}{T_{PRP}} \tag{30}\]  
The block diagram of the experimental design of the BDS subject to pulsed signal interference is shown in Figure 13. It mainly includes satellite navigation signal repeater, satellite navigation signal receiving/transmitting antenna, interference signal generator, interference signal transmitting antenna, interference signal receiving antenna, spectrum analyzer, oscilloscope, BDS receiving antenna and upper computer. We mainly judge whether the BDS receiver is disturbed by observing the change of the number of satellites in the upper computer. The flow chart of receiver EMC evaluation method is shown in Figure 14. The experiment operation details are as follows:  
Figure 13: Experimental design block diagram. (1) Establish stable functional link of BDS. To prevent the external electromagnetic environment from affecting the experimental results, the experiment was carried out in the microwave anechoic chamber. Considering that the BDS in the microwave anechoic chamber cannot receive the satellite navigation signal, the satellite navigation signal repeater can be used to forward the satellite navigation signal to the microwave anechoic chamber. The number of satellites displayed on the upper computer can be used to judge whether the BDS has established a stable functional link. The upper computer is connected with the BDS receiving antenna through the data line. By post-processing the received signal, it can display the working status information of the BDS receiving satellite, including the number of satellites, the longitude, latitude and altitude of the receiver position, time, working mode, etc. During the experiment, when the number of satellites displayed by the upper computer is stable at 10, we believe that BDS establishes a stable functional link. (2) Measure the SIR. With the BDS in stable operation, the environmental receiving antenna is connected to the spectrum analyzer. The signal power received by the BDS receive antenna is measured in the experimental environment. Turn on the interference signal generator, adjust the external output signal power, and radiate the pulsed interference signal in the microwave anechoic chamber through the interference signal transmitting antenna. The power value of interference signal received by BDS can be read through the upper computer. During the experiment, the external output power of the interference signal generator remains unchanged, and the SIR of BDS can be calculated according to Equation (14), which is 46.5 dB. (3) Measure the pulse width and repetition period. With the BDS in stable operation, turn on the interference signal generator, measure the pulse width and repetition period through spectrum analyzer. By adjusting the pulse width and repetition period of the external output pulse signal, the number of satellites that can be stably tracked by the BDS is recorded and displayed on the upper computer. (4) Calculate the value of BER. Changing the pulse width and repetition period of the pulse interference signal can affect the BER of BDS. Using the method proposed in this paper, the BER of BDS is calculated according to Equations (11)-(18), (25)-(30). Figure 14: Flow chart of receiver EMC evaluation method. (5) Evaluate the EMC of the BDS. The BER of BDS is calculated through step (4). According to [43], the interference degree of BDS by pulse signal can be predicted through the BER. The accuracy and reliability of the method proposed in this paper are verified by comparing with the display results of upper computer.