## 4 Experimental Results
### Experiment Results in Real Traffic Scenarios  
In this section, we illustrate some experiment results in real traffic scenarios. The sensing waveform is designed under the time division mode, and the sensing waveform looks like the radar pulse as shown in Figure 2. We thus use the radar module to emulate only the sensing waveform timing and verify its sensing performance. Furthermore, we use the IWR1642 radar module to imitate the sensing waveform of the TD-ISAC system. The radar module is not exactly the same with the 5G communication system, as we only use the radar to imitate the designed timing. One more issue to say is that there is CP in communication, but radar does not have it. Generally, in an ISAC system it removes the CP first while receiving the sampled signal, and then processes the signal without CP [41]. Hence, we use the radar module to imitate the sensing waveform without considering the CP.  
Figure 13: Vehicles solved by the DFT-based method. (**a**) Uniform Sensing. (**b**) Dual-PRF uplink-flexible mode. (**c**) Dual-PRF uplink-fixed mode.  
Figure 15 illustrate the real test of traffic scenarios. The IWR1642 radar is produced by Texas Instruments and operates with the carrier frequency of \(f_{c}=77\) GHz. The radar installation height is 8.4m. The specific radar parameters are set as follows: sampling frequency \(f_{s}=5000\) kHz, pulse wide of a chirp \(T_{c}=40\) us, number of chirps in a frame is 128, bandwidth of the sampled radar signal \(B=420\) MHz, and a frequency slope of 14 MHz/ us. From the parameters, there are 128 uniform chirps during a frame. We extract consecutive 80 chirps to emulate the uniform communication slot timing as shown in Figure 16, and extract the dual-PRF sensing waveform according to the timing of the dual-PRF sensing waveform under uplink-flexible mode as shown in Figure 3. As we know, there is timing modification under uplink-fixed mode as shown in Figure 5, and the modification is realized by shifting only to a OFDM symbol. However, the radar works in chirp mode, and there is no signal transmitted between two chirps. It is illustrated in Figure 16 that the modification timing (red pulse) under uplink-fixed mode cannot be emulated by the radar module. Hence, it cannot emulate the designed waveform under the uplink-fixed mode when limited to its parameters. We only compare the sensing performance of the uniform waveform with the dual-PRF sensing waveform under uplink-flexible mode in real traffic scenarios.  
Figure 17 illustrates the detected results for one vehicle, where the rectangle denotes that the detection cell is a real vehicle, and the ellipse denotes the ambiguity targets. It can be seen that the uniform sensing waveform with the DFT method and the dual-PRF sensing waveform under uplink-flexible mode with the IAA and OMP methods can all solve for the vehicle unambiguously. Although the \(2T_{r}\) and \(3T_{r}\) sensing pulses have ambiguous velocity with the DFT-based method, it can also solve for the real vehicle by the CRT method obviously.  
Figure 18 illustrates the detected results of multiple vehicles, where the different colors represent three vehicles, respectively. The shapes of rectangle and ellipse denote the same meaning as that in Figure 17. It has the same results as those of the last experiment in each range cell. Hence, the designed sensing waveform can realize the sensing of multiple vehicles with the three signal processing under real common traffic scenarios.  
Figure 14: Vehicles solved by the IAA and OMP methods. (**a**) Dual-PRF uplink-flexible mode. (**b**) Dual-PRF uplink-fixed mode.  
Figure 16: Sensing symbol timing and radar transmitted timing.  
Figure 17: One vehicle in real traffic scenario. (**a**) DFT-based method. (**b**) IAA and OMP method.  
Figure 15: Real test of traffic scenarios. (**a**) Test scenarios of the radar installation. (**b**) Real traffic scenarios.