## 6 Experimental Evaluation
### Result Analysis  
Figure 16 compares the end-to-end delay for Modbus RTU and 5G by the protocol adaptation scheme and transparent transmission. It can be seen from the figure that the end-to-end delay of using the protocol adaptation scheme is lower than that of using protocol transparent transmission.  
Figure 17 compares the end-to-end delay for Modbus TCP and 5G by the protocol adaptation scheme and transparent transmission. As observed from the figure, the end-to-end delay of using the protocol adaptation scheme is also lower than that of using protocol transparent transmission.  
Furthermore, by comparing Figures 16 and 17, it can be found that the end-to-end delay fluctuates up and down. This instability may be caused by server congestion as a transfer station or instability of commercial 5G. Moreover, when we transmit the same magnitude packets, the end-to-end delay differential value of Modbus RTU data transmitted by two methods is smaller than that of Modbus TCP data transmitted by two methods. The reason should be that the Modbus RTU data resolved by the protocol adaptation scheme has a 3 bytes differential value compared with the original Modbus RTU data. However, the Modbus TCP data resolved by the protocol adaptation scheme have a 7 bytes differential value compared with the original Modbus TCP data.  
Figure 16: The end-to-end delay comparison between protocol adaptation and prototype transparent transmission for Modbus RTU.  
Figure 18 presents the end-to-end delay comparison results of the protocol adaptation scheme between Modbus RTU/Modbus TCP and 5G. From the figure, it can be observed that the end-to-end delay of transmitting Modbus TCP in the protocol adaptation scheme is lower than that of transmitting Modbus RTU in the protocol adaptation scheme when we transmit the same data length. Accordingly, by analyzing and comparing the end-to-end delay of four groups of experiments, it can be found that the end-to-end delay of the protocol adaptation scheme is the best between Modbus TCP and 5G.  
To test the reliability of the wireless PLC prototype, we fit the discrete data of five known test nodes into a curve by the smoothing spline function. By fitting, we can obtain the estimated values of other unknown test nodes. Figure 19 illustrates the reliability comparison results of Modbus RTU and 5G protocol adaptation. According to this figure, the reliability of the Modbus RTU protocol adaptation scheme is lower than that of the Modbus RTU protocol transparent transmission. This is mainly because transparent transmission does not resolve the protocol data and directly encapsulate the data as 5G data.  
Figure 17: The end-to-end delay comparison between protocol adaptation and prototype transparent transmission for Modbus TCP.  
Figure 18: The end-to-end delay comparison between Modbus RTU and Modbus TCP for protocol adaptation.  
Figure 20 depicts the reliability comparison results of Modbus TCP and 5G protocol adaptation. Likewise, the reliability of the Modbus TCP protocol adaptation scheme is lower than that of the Modbus TCP protocol transparent transmission.  
Moreover, based on the overall comparison of Figures 19 and 20, it can be found that with the increase of sending instructions time interval, the reliability is higher.  
To further analyze the reliability, we take three test nodes to compare the reliability of the protocol adaptation scheme between Modbus RTU/Modbus TCP and 5G. As can be  
Figure 19: The reliability comparison between protocol adaptation and prototype transparent transmission for Modbus RTU.  
Figure 20: The reliability comparison between protocol adaptation and prototype transparent transmission for Modbus TCP.  
observed from Figure 21, the reliability of the Modbus TCP protocol adaptation scheme is higher than that of the Modbus RTU protocol adaptation scheme. By analyzing and comparing the reliability of four groups of experiments, it can be found that the reliability of the protocol transparent transmission is the highest between Modbus TCP and 5G.