# Formation Control of Dual Auto Guided Vehicles Based on Compensation Method in 5G Networks
## 2 5G Networks Characteristics
### 5G Networks Delay Measurement and Analysis  
The time delay is one of the most important factors that determines the efficiency of the NCS. Affected by time delay, the control command sent by the controller cannot take effect in time, and the controller cannot get accurate feedback. Before designing the  
Figure 1: Structure of 5G physical private networks.  
control system in 5G networks, it is necessary to measure delay and analysis characteristics. To obtain the characteristic of 5G networks delay, some researchers have made effort on measurement and analysis of the 5G networks delay [25; 26]. They both used clock-synchronized devices to measure air interface delay or E2E delay in laboratory conditions. However, it is difficult to synchronize the clocks of 2 AGV through wireless networks in factory. E2E delay cannot be measured directly without clock synchronization. Therefore, Round Trip Time (\(RTT\)) is used to characterize the delay. In this paper, \(RTT\) refers to the time it takes for AGV1 from send information to AGV2 and receive the reply. For measuring the \(RTT\), one controller sends the data packet to another and records the sending time and receiving reply time by system clock. \(RTT\) is the difference between sending time and receiving time.  
The measurements are carried out in a physical private network in factory. The network parameters are shown in Table 1. The 2 AGV are in the same room and the distance between 2 AGVs is 1200 mm. The 5G Customer Premise Equipment (5G CPE) is a product of Lierda MX880 while the \(RTT\) is calculated by Beckhoff embedded PC CX5010 with Intel Atom Z510 processor, 512 MB RAM, and a Windows Embedded CE 6 operating system. The 5G CPE is connected to CX5010 through the EtherCAT EAP protocol.  
This paper constantly measured 1546 sets of \(RTT\) in 30 s and the results are shown in Figure 2. Define  
\[\Delta RTT(k)=RTT(k)-RTT(k-1) \tag{1}\]  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Value** \\ \hline Frequency & 2.6 GHz \\ Bandwidth & 100 MB \\ Signal to Noise Ratio & 20 dB \\ Reference Signal Receiving Power & \(-\)85 dBm \\ \hline \hline \end{tabular}
\end{table}
Table 1: Parameters of 5G networks.  
Figure 2: \(RTT\) measurement results (**a**) Timing diagram; (**b**) \(RTT\) distribution histogram.  
Figure 2 shows that the \(RTT\) of the 5G network has randomness and multi-peak characteristics. The peak-to-peak intervals are approximately 5 ms. \(RTT\) is mainly concentrated around 19 ms (17-22 ms, 90.89%). The \(RTT\) measured consists of the terminal processing delay, core network processing delay, and air interface delay. There are some factors such as time-division duplex (TDD) uplink-downlink conversion cycle and retransmission which could cause the multi-feature feature. The TDD uplink-downlink conversion usually causes jitters in 0-5 ms and retransmission in MAC layer also bring jitters in 5-20 ms.  
Figure 3 shows the distribution of \(\Delta RTT\) to reflect the delay changes. A total 88.1% of the data are in 0 \(\pm\) 2 ms and 90.3% in 0 \(\pm\) 3 ms. There are still some large jitters but it occurs less frequently. With the development of 5G, network technologies such as network slicing and resource scheduling can further improve network quality and reduce jitter [7].  
In summary, the \(RTT\) of 5G transmission has randomness, but most of them are still concentrated in 19 \(\pm\) 3 ms. The jitter of \(RTT\) is relatively gentle and mainly concentrated in 0 \(\pm\) 3 ms.