## 2 Related Works  
The existing sensitivity criteria of equipment is usually classified into two categories: objective and subjective methods [15]. [PERSON] et al. [16] believed that an interference margin could be used as the sensitivity criterion for analog communication systems, while BER is always used as the sensitivity criterion for digital communication systems. [PERSON] et al. [17] specifically studied the sensitivity criterion of a communication station under single-frequency continuous wave interference. The sensitivity criteria of voice communication and digital communication are defined. In voice communication, the work damage level of communication interruption can be used as the sensitivity criterion, while the error is smaller when adopting 10% BER in digital communication. [PERSON] et al. [18] studied the influence of electromagnetic pulse sequence on digital communication station. In their study, it confirms that it is effective to take the BER as a sensitivity criterion for the digital communication system once again. However, a fixed BER value cannot be taken as the sensitivity criterion in electromagnetic pulse interference. The relationship between BER and the pulse repetition rate could be used as the criterion, which is more suitable for the sensitivity measurement of digital communications. It also demonstrates that the sensitivity criterion should be related to the interference signal type. [PERSON] et al. [19] carried out a relevant piece of research on an unmanned aerial vehicle data link system. It finally shows that the automatic gain control (AGC) voltage and BER could be used as the sensitivity criteria of the system. [PERSON] et al. [20] adopted the field intensity amplitude compression value (1.5 dB, 6 dB, and 12 dB) of the echo signal on the tested radar as the sensitivity criterion. In the relevant research on navigation receivers, [PERSON] et al. [21] defined the sensitivity criterion of a certain type of BeiDou navigation receiver as the C/N0 of 30 dB-Hz on a single-satellite experimental study. [PERSON] et al. [22] studied the influence of different interference signals on the handheld global positioning system (GPS) receiver. By observing the responsiveness of the receiver in the experiment, it adopts five disparate effect phenomena, i.e., no observed effect, interference while working, loss of positioning then self-recovery, loss of positioning requires human intervention, physical damage as the criterion to show the sensitivity effect of the receiver under various jamming signals' interference. To sum up, a researcher could use a distinct electromagnetic sensitivity criterion for a different equipment. Sometimes, the sensitivity criterion is not exactly identical even though the tested equipment is the same one. From the analysis, we can see that the definition of sensitivity criteria on a certain tested equipment is related to the type of interference signal and the research purpose. Navigation receivers are more susceptible to continuous wave electromagnetic signal [23]. In additional, continuous wave interference is the most often used one in these interference signals [24]. The C/N0 is primarily used as an objective criterion in studies. However, the critical interference C/N0 of the navigation receiver is unstable. The critical value is tied to the working signal intensity and experiment configuration. There is a challenge to test the critical interference level with a fixed C/N0. If the sensitive phenomenon is taken as a subjective criterion, a further piece of experimental research on how to classify sensitive phenomenon is indispensable. Furthermore, one thing we can determine is that the sensitive phenomenon is varied with the variation of C/N0. From the unresponsiveness of the receiver to total blocking, there may be a zone where part of the signals is blocked.