## 3 Performance Evaluations
### Fiber Channel
#### 3.2.3 Lab Experiment  
In this experiment, we explore the performance of the proposed ISAC system. The setup is built based on photonics technology, following the model depicted in Figure 9. The system employs a transmit signal with a bandwidth of 700 MHz, which is designed to support a data rate of 50 Mbits per second for communication purposes. For the radar functionality, the waveform utilized has a duration of 8 microseconds. This signal is transmitted over a carrier frequency of 28 GHz. Figure 15 presents the experimental setup. In our experiment, we introduced two distinct targets into the scene, positioned with a separation distance of 43 cm. The channel fiber's length for both transmission and reception within the ISAC system is carefully set to 10 km (one way), ensuring consistency across the setup. Because of the unavailability of optical equipment required to receive the reflection of the transmitted signal, the echo of the radar signal is captured using OSC.  
Figure 16 shows the reconstructed image observed at the output of the communication receiver. As can be seen, the image can be correctly recovered with a 0-BER. Figure 17 illustrates the performance of the communication system at various levels of received optical power at the PD input in the transmitter part for a fiber channel of 10 km. Figure 17a shows the constellation diagram and the corresponding error vector magnitude (EVM) for different levels of the received optical power. An EVM value of 12 is achieved at a transmitted power of \(-3.8\) dB. Figure 17b shows the EVM values versus received optical power in the transmitter part.  
Figure 14: The radar’s correlator output with two targets separated by 43 cm and for fiber lengths 10, 25, 50, and 75 km.  
Figure 18, on the other hand, illustrates the correlator's output at the radar receiver. Encouragingly, the results from both figures align closely with those obtained through simulations, validating the efficacy of our proposed ISAC system. The results show that when the distance between the two targets is 21 cm (which is less than the range resolution), the radar identifies them as a single target. However, when the separation between the two targets precisely equals the range resolution at 43 cm, the radar distinguishes two clear peaks, representing two targets. Moreover, when the separation between the two targets exceeds the range resolution at 128 cm, the radar can still detect two clear peaks. The second target exhibits weaker received power due to its greater distance from the receiver antenna.  
These findings highlight the versatility and robustness of the proposed ISAC framework, which seamlessly integrates communication and sensing functionalities. The experimental validation serves as a pivotal milestone, affirming the practical viability of our approach for diverse applications requiring concurrent communication and sensing capabilities.  
Figure 16: The reconstructed image at the communication receiver for a fiber channel of 10 km.  
Figure 17: Performance of the communication system for a fiber channel of 10 km. **(a)** The constellation diagram versus different received optical power values. **(b)** EVM values versus the received optical power.  
Figure 15: The experimental setup for **(a)** communication system; **(b)** radar system.