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RFID is an emerging technology, especially RFID based on the 900MHz UHF EPC Gen2 standard is a technology that will affect and change people’s lifestyles in the next few years. Compared with traditional automatic identification technology, such as bar code, magnetic recording, IC card and other technologies, UHF RFID has the characteristics of long reading distance, fast speed, readable and writable, and high efficiency. And also compared with other RFID technologies, its cost is much lower. This makes UHF RFID technology increasingly popular, and many new applications of RFID have emerged.
RFID vehicle management is a very good example based on passive UHF RFID technology. The reading distance of UHF is relatively long, and it can realize label reading of about 3 to 6 meters, which is suitable for reading at entrances and exits or key points; and through the management system and GIS geographic information system for vehicle movement tracking and positioning.
In the existing RFID passive applications and wireless environments, there are three types of solutions that can solve the purpose of vehicle key point positioning and movement tracking, namely: using vehicle-mounted RFID readers for landmark tracking; using vehicle tags for key point recording; and According to pure wireless network (non-RFID technology) and mobile computer WiFi tracking and positioning method.
The application principles of the three methods are now introduced as follows:
1. Car RFID reader for landmark tracking
The landmark tag is identified by the on-board RFID reader. When the vehicle passes the tag, the RFID reader can identify the content of the landmark tag within a distance of about 1.5 meters, and pass it to the background management system through the wireless network, and the location can be passed The GIS geographic information system is reflected on the monitoring screen to realize the tracking and positioning of the vehicle.
In the plan, both landmark tags and vehicle readers must be strictly coded for definition.
The landmark label must be unique: each landmark represents a location in a site, and the location must be unique in the GIS information system. Landmarks can only indicate a location, but not the direction in which the vehicle is moving.
The identification of the vehicle reader: the vehicle reader also needs to be uniquely identified, that is, when the reader reads the RFID data, it must be transmitted to the network together with the number information of the machine, and the vehicle is analyzed by the GIS as the moving point The form is reflected on the monitor screen.
Wireless network: In order to realize the real-time and reliable transmission of collected data, a wireless communication network must be built in the site.
2. Use vehicle tags to record key points
The key point refers to the passage point using a fixed reading device. When a vehicle passes by, the fixed reading device obtains the information of the on-board tag and transmits the data to the GIS system. After software analysis, the information about the movement of the vehicle is obtained. Key points are usually only set up at some doorways, passages or junctions to provide signs of vehicle travel routes.
The vehicle needs to install an RFID tag, which represents the unique information of the vehicle. When the vehicle-mounted tag passes through the doorway or passage, the fixed reader can identify the tag within a range of 3-6 meters. To determine the location of the vehicle.
Application of vehicle tags: Metal tags must be used for vehicle tags and have a certain strength to be suitable for use in a forklift environment. The tag is affixed to the side of the vehicle, so that only one side of the reader antenna on the door or both sides of the door can read the tag. Through the identification of the antenna, the vehicle’s travel route can be determined without software analysis.
Landmarks are UHF RFID tags that are buried underground and can be identified by reading devices. Once the landmark tags are buried, it is no longer inconvenient to replace them. Therefore, the best solution for landmark tags is to use passive tags. UHF Gen2 tags can better adapt to landmark applications.
Door passage reader: The door passage uses XR440 fixed readers and high-performance reading antennas. The antennas are set up on both sides of the passage. Each reading antenna has a different identification. This identification can be provided to the back-end system for analysis of vehicle location and travel .
The solution does not require a wireless network, and the fixed reader can be directly connected to the system through a wired network.
Three, wireless network and mobile computer for WiFi positioning
The method of WiFi positioning is to locate the location of a mobile device through the signal level provided by the wireless network in the venue, and the mobile device must have a WiFi communication module.
The principle of WiFi positioning is to use a three-point positioning method, that is, to identify the location of the mobile device through the wireless signal exchange between the mobile device and three wireless network access points, because the distance between the mobile device and the three wireless access points is different Therefore, the field strength of the wireless signal of the mobile device reflected on the wireless access point will be different, and the position of the vehicle can be determined more accurately through the differential algorithm.
Requirements for wireless networks: Generally, WiFi positioning places higher requirements on wireless networks. The denser the network access points, the higher the positioning accuracy.
Requirements for mobile computers: mobile computers must have wireless network WiFi communication capabilities.
Analysis system: The analysis system for WiFi positioning is a third-party software system. AutoCAD-based site drawings must be provided to run the analysis system. Before application, a professional site survey is required to determine the landmark information.
The purpose of determining the mark point is to measure the field strength of the wireless signal in the area, and this information is the judgment condition in the future application. When the marker point information is measured, when the mobile computer moves around the location and vicinity, its field strength information will be used as the value analyzed by the management software to compare with the reference point value.
The accuracy of WiFi positioning is about 0.5 meters when the wireless network meets the requirements.
4. Comparison of three positioning and tracking methods
1. Comparison items: single analysis of vehicle RFID and landmark vehicle tags and key points WiFi positioning. The positioning accuracy is based on the buried density of the landmarks, and the buried density depends on the complexity of the project. The overall positioning accuracy is medium. For reading on the door channel, the positioning accuracy depends on the number of fixed reading points and the investment cost, and the positioning accuracy is low. The positioning accuracy is high, and precise positioning within 0.5 meters can be achieved. In terms of accuracy, WiFi is the best application solution.
2. Investment budget: It is necessary to install RFID reading equipment on each vehicle, and the investment cost is high. RFID passive tags are installed on vehicles, and the number of fixed points is limited, so the overall investment cost is low. A wireless network must be set up, and the vehicle must be equipped with a mobile computer, which is costly. From an investment perspective, the vehicle label is the lowest. But in terms of the overall system, it is more appropriate to invest in a wireless network, because mobile services must run on the wireless network.
3. Engineering complexity: it depends on the density of buried tags, and the engineering complexity is high. Only need to install the door passage, the project is the least difficult. Need to build a wireless network and Site Survey, the complexity is medium.
4. System integration: It depends on the GIS system, can be independently developed, and the integration is better. Depending on the GIS system, it can be developed independently and has good integration. The third-party analysis system is difficult to integrate.
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