## 5 Simulation Experiment Analysis
### Jamming Performance  
Although the spectrum plot may look more crowded in practice for clarity, the spectrum plot of the proposed joint waveform with relatively few subcarriers (see Figure 12) shows that the jamming spectrum energy distribution is mainly concentrated in the main lobe. The main lobe spectrum of the jamming signal is relatively flat and shows a bump in the frequency domain with an approximate 15 MHz bandwidth. The dense false target jamming is spiky and can achieve the same spectral effect as the conventional comb-spectrum noise suppression type of jamming. Figure 11: Simulation results of the joint system communication. Figure 12: Spectrogram of the joint waveform based on FBMC chirp. Figure 13a shows the results of the time-frequency analysis of the FBMC-chirp-based jamming signal with a Hamming window for the intercepted signal containing 16 radar pulses, which can be seen by taking one of the range lines and analyzing it in the time-frequency domain. Figure 13b,c present the effect of time-frequency analysis of the interfering signal with dense and sparse false target spacings, respectively. The horizontal coordinates refer to the number of time sampling points, while the vertical coordinates represent the number of frequency points. As shown in the figures, the jamming signal designed in this study can be aimed at the frequency, and the frequency of the jamming signal varies linearly with time and lasts for the whole jamming cycle. To verify the jamming performance of the joint system against the radar, a real target and jamming signals were set using the values in Tables 2 and 3. The results of processing echo signals with and without jamming are shown in Figure 14. In addition, we compared the proposed waveform with the state-of-the-art method in [24]. Figure 13: (**a**) Time–frequency analysis result of the FBMC chirp-based jamming signal; (**b**) the result with dense false target spacing; (**c**) the result with sparse false target spacing. As shown in Figure 14, for the target echoes without jamming signals processed by moving target detection (MTD), the radar system was able to accurately detect the real target. When the jamming signal was included in the echo, the real target's echo was covered by the interfering signal. After MTD and CFAR processing, the opponent's radar system was unable to find the real target, with the jamming signal acting as a shield for the real target. Because the FBMC spectrum has good out-of-band suppression, the proposed joint communication jamming signal has very high spectrum use efficiency by making the FBMC chirp jamming signal energy more concentrated in the main lobe, fully reducing the energy of the side lobe of the jamming signal. The radar system also cannot detect the covered target. The FBMC chirp requires less jamming power than chirp or other signals, which can save energy in the joint system and ensure the robustness of communication transmission quality. The third column in Figure 14 illustrates the results of multi-false-target jamming on the threshold relationship of CFAR. Compared with the CFAR detection results of multi-false-target jamming in [24], the jamming signal of our design enters the reference cell of the radar's CFAR detector, increasing the estimated noise power of the CFAR detector. This results in a CFAR detection threshold of about 20 dB higher than the target signal power to achieve the coverage effect on the target. Due to the elevated threshold value of CFAR,  
Figure 14: The results of multi-false-target jamming under the MTD and CFAR. The leftmost column (**a**,**d**,**g**) is the results of target echoes processed by MTD under three cases; the second column (**b**,**e**,**h**) is zoom in MTD results; the third column(**c**,**f**,**i**) is the comparison of CFAR threshold. the jamming signal is also lower than the threshold, and the opponent's radar is unable to detect the jamming signal; thus, the coverage of the intended target is completed.