With the development of mobile internet technology, automated warehousing technology has become more mature and has been widely used. Among them, the typical automatic guided transport vehicle (AGV) equipment greatly improves the operation efficiency, improves the quality and reduces the operating cost in the process of picking and sorting of logistics and storage. The fast and stable operation of AGV equipment relies on highly reliable Wi-Fi networks, especially for the roaming capabilities of Wi-Fi networks. This article will delve into the Wi-Fi network for automated warehousing.
Figure 1: Schematic diagram of the AGV
Exploring the need for automated warehousing for Wi-Fi networks
The AGV belongs to the category of Wheeled Mobile Robots, and the more direct point is the driverless transporter. The AGV is characterized by wheeled movement. Compared with walking, crawling or other non-wheeled mobile robots, it has the advantages of quick action, high work efficiency, simple structure, strong controllability and good safety. It does not need to lay rails and supports. Fixing devices such as racks are not restricted by site, road and space. Therefore, in the automated storage system, AGV is the most fully embossed for its autonomy and flexibility, enabling efficient, economical and flexible unmanned production.
Having said so many features of AGV, we can't help but ask: What is the direct relationship between this and the seamless roaming of Wi-Fi networks? With this question, let's first analyze the real network requirements in automated warehousing.
From the analysis of the working mode of the AGV, the AGV must control its travel route and behavior by computer through wireless communication, which is destined to be inseparable from the support of the wireless network, and the Wi-Fi network is the most important wireless used by the AGV. Communication means. Then, according to the traditional office network Wi-Fi idea, deploying a wireless network can support the AGV business needs? the answer is negative.
As shown in Figure 2 below, in actual automated storage, AGV loading and unloading operations need to travel to and from different work areas. A single wireless access point (AP) cannot completely cover the entire area. Therefore, an AGV actually needs to roam between multiple AP signals. communication.
Figure 2: Automated warehousing diagram
Compared with the moving speed of people in the office network, the moving speed of the AGV is much faster. As shown in Table 1, the AGV of visual two-dimensional code navigation is widely used in the e-commerce logistics industry, and its driving speed can be as high as 150m/min. Therefore, the AGV will actually perform fast roaming between multiple APs. However, during this roaming process, it is still necessary to ensure that the communication between the AGV and the background is accurate, that is, to ensure that the AGV does not drop the line and avoid AGV congestion. Seriously affect production operations.
Table 1: AGV operating speed
However, in the current automated warehousing scenario, customers generally use traditional WLAN technology to deploy Wi-Fi networks and integrate traditional roaming technology, but the actual effect of AGV is not ideal.
Below, we analyze the technical difficulties of Wi-Fi roaming, and why the traditional roaming method can not meet the needs of AGV.
Analyze the weakness of automated warehousing traditional Wi-Fi roaming solutions
Analysis of automated warehouse roaming problem
1. The traditional roaming process is generally divided into three steps:
Pre-roaming status: as shown in Figure 3 below.
· Entry conditions: signal strength ≤ pre-roaming threshold;
· Operational behavior: scan the channel and store it in the roaming list;
· Duration: The signal strength rises after the threshold is restored;
· Experience impact: no packet is received during scanning, communication is interrupted, resulting in increased delay/loss.
Figure 3: Pre-roaming state diagram
The terminal is out of state: as shown in Figure 4 below.
· Entry conditions: signal strength ≤ diffuse threshold;
· Operational behavior: disconnect the old AP connection;
· Duration: instantaneous behavior;
· Experience impact: The terminal is disconnected and does not receive or send packets.
Figure 4: Diffuse state diagram
Terminal flooding status: as shown in Figure 5 below.
· Entry conditions: APs with good signals in the roaming list;
· Operational behavior: the terminal is re-associated with the AP;
· Duration: The general terminal completes the association within 300ms;
• Experience impact: Before the association is completed, the terminal network is in a disconnected state and does not send and receive packets.
Figure 5: Diffuse state diagram
2. Analysis of problems in the traditional roaming process:
Pre-roaming phase: Due to the incompleteness of the current terminal roaming algorithm, the pre-roaming effect is poor. When the terminal leaves the current wireless network area, the terminal often loses time to access the new wireless network.
· The diffuse phase: It may be due to the large coverage area of the AP. Although the quality of the signal received by the current terminal is already poor, it cannot be switched to the new AP, which causes roaming stickiness.
In the flooding phase: the area covered by the AP signal is small, which may result in the terminal being unable to access the AP when it leaves the AP. This causes the terminal to drop the line for a short period of time and affects the stable operation of the entire service. .
In addition, in the traditional roaming scheme, for the action of roaming handover, the initiative right is not directly controlled by the AP end on the terminal wireless network card, and there is always a state in which the wireless network is temporarily interrupted.
So, what are the optimization options for wireless device vendors for traditional roaming problems? Let's take a look at the traditional wireless vendors based on AP-level optimization.
Roaming optimization scheme for traditional Wi-Fi networks
In view of the problems existing in traditional roaming, traditional wireless vendors have made a lot of efforts to solve many problems of AP-side roaming in the automated warehousing traditional roaming solution. In the following, through a terminal, AP1 roams to AP2 in three different states: pre-roaming, flooding, and flooding, to learn more about the traditional roaming optimization scheme.
Pre-roaming status: As shown in Figure 6, using DWO (Distributed Wireless Optimize), the coverage of the AP is adjusted to allow the terminal to enter its roaming state machine earlier, mainly including three levels of optimization:
· Channel scan logic optimization;
· Channel scan time optimization;
· Roaming state machine optimization.
Figure 6: Pre-roaming state optimization map
Diffuse state: as shown in Figure 7, based on the strength of the terminal RSSI signal by intelligent roaming means, when the AP detects that the RSSI signal strength of the terminal reaches the threshold (the different parameters of the terminal are different), it is generally about -70dBm. Line, forcing the terminal to roam.
Figure 7: Diffuse state optimization diagram
Diffuse state: As shown in Figure 8, the DWO technology is used to actively adjust the coverage, transmit power, channel width, and optimized switching time of the AP.
Figure 8: Diffuse state optimization diagram
As described above, for the traditional Wi-Fi problem, the AP can only indirectly affect the roaming behavior of the terminal through optimization means. For the traditional office network, the problem can be basically solved, thereby improving the terminal experience. However, in the automated warehousing scenario, the traditional roaming optimization solution cannot solve the problem completely because the AGV quickly roams between multiple APs. In addition, because the wireless network card capabilities and quality of the AGV equipment are uneven, the Wi-Fi roaming effect is better and cannot be controlled.
In summary, if you want to completely solve the AGV fast roaming experience, you need to start from the following two aspects:
· The AGV-side Wi-Fi network card is decoupled from the host, and the hardware capabilities are unified to control the Wi-Fi roaming behavior on the terminal side.
· Design a new roaming mechanism based on the existing Wi-Fi protocol.
Automated warehousing Wi-Fi network seamless roaming solution to bring you answers.
Automated warehousing Wi-Fi network seamless roaming solution to help automate the rapid development of warehousing business
Automated warehousing Wi-Fi network seamless roaming solution architecture
The seamless roaming scheme for automated warehousing Wi-Fi networks is shown in Figure 9, where the network product components and application technologies and the achievable effects are as follows:
· Network product components: wireless controller (AC), AP, Wi-Fi converter, etc.;
· Application technology and achievable results: based on dual radio aggregate link technology (DRAL, Dual Radio Aggregate link) and pre-roam (Pre-Roam) technology. Through the vehicle Wi-Fi converter, combined with the above two technologies, the wireless signal is converted into a wired signal to provide a network to the terminal, which not only improves signal stability but also solves compatibility problems;
Figure 9: Automated warehousing Wi-Fi network seamless roaming solution architecture diagram
Detailed technical principles
1. DRAL technology, as shown in Figure 10 below.
· The Wi-Fi converter establishes the linkA and link B dual data links between the primary RF card and the backup RF card and the AP, and simultaneously switches the wireless network to wired access, replacing the traditional Wi-Fi network card, and providing an uplink network connection for the AGV;
Figure 10: Dual link setup, wireless to wired diagram
· Adopt deduplication technology. As shown in Figure 11 below, the wireless loop problem is solved while establishing dual link data.
When a loop occurs: a link A and link B dual data link are established between the primary RF card and the backup RF card. If the two links are connected to the Wi-Fi switch and the AP successfully establishes a communication link. When communication occurs, a loop occurs on the entire link.
A link A and link B dual data link are established between the primary RF card and the backup RF card and the AP. The two wireless links are in a dual-protected state at the same time. At this time, the primary link is used for data transmission. When the primary link is normally communicating, the backup link establishes a connection between the Wi-Fi converter and the next AP signal in a backup state. When the primary radio link is roaming, the primary link is disconnected and switched to the backup link for communication.
Figure 11: Dual-link keep-alive diagram
2. The Pre-Roam technology, that is, the dual-link pre-roaming solution, mainly solves the problem of signal reception of the terminal device during the roaming process.
· In the pre-roaming phase, the Wi-Fi converter scans the signal according to the backup link in the two links established in advance, and the other stabilizes the communication, and actively detects the most suitable flooding signal source in advance, as shown in Figure 12 below. Show.
Figure 12: Pre-roaming state diagram with Pre-Roam technology
· In the diffuse phase: the Wi-Fi converter has proactively detected the most suitable diffuse signal source in advance. At this point, one link performs normal communication and the other link performs flooding, as shown in Figure 13 below.
Figure 13: Using the Pre-Roam technology to pop out the state diagram
· In the flooding phase: one link of the Wi-Fi converter has switched the most suitable diffuse source. At this point, you need to ensure that one of the links is successfully roamed, and the other link is switched, as shown in Figure 14.
Figure 14: Using the Pre-Roam technology to map into the state diagram
As described above, the automated warehousing Wi-Fi network seamless roaming design, on the one hand through the Wi-Fi converter to achieve AGV-side Wi-Fi network card and host decoupling, through the unified hardware capabilities, to achieve terminal-side Wi-Fi roaming behavior control. On the other hand, based on the existing Wi-Fi protocol, a dual-radio aggregation link, an efficient pre-roaming mechanism, and a wired-to-wireless approach provide a stable and reliable Wi-Fi network for intelligent terminals such as AGVs in an automated storage environment.
to sum up
Automated warehousing Wi-Fi network seamless roaming solution is simply a converged network solution. It is based on different problem sources and is dedicated to solving the traditional roaming solution of automated warehousing and the wireless network experience of intelligent devices in automated warehousing. . Through the wireless to wired mode, the Wi-Fi roaming of the terminal side can be controlled by the Wi-Fi converter. At the same time, combined with dual-link and Pre-Roam technology, it effectively guarantees the reliability of network quality and meets the needs of AGV fast and seamless roaming, thus ensuring the smooth operation of automated warehousing services that rely on the quality of wireless networks.