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1. Application requirements
Digital management is the key to improving the level of logistics management. However, as far as logistics management is concerned, the concept of digital management should include: A. The electronic management of cargo documents (including block building and transmission); B. The position of the goods in transit Informatization. The former is mainly realized by reading the identification code (bar code or RFID) of the goods being shipped; while the latter is realized by GPS positioning system and wireless mobile network. Therefore, in the data collection and transmission of the logistics management system, ensuring effective data identification and data transmission is the key to the entire system.
Second, the status quo of the industry
Many people should be very familiar with barcode labels and RFID. The former uses optical scanning, and there can be no physical obstruction between the scanner and the barcode; the latter uses “electromagnetic field scanning”, and there can be obstruction between the two. But in the final analysis, the data read by both is just an identity code. The real data must be consulted in the pre-established database through the identification code read by the barcode reader. Secondly, because the barcode and RFID reading methods are realized through weak reflection or passively coupled signals of the barcode and RFID tag (the RFIDs that are active and can store a small amount of data are actually beyond the definition of RFID itself), Therefore, the reading distance is very limited. In addition, since these two types of tags do not store data themselves, the signal reader must be connected to the database, which results in poor flexibility. These limitations greatly limit its role.
Therefore, the logistics management system based on the combination of ZIGBEE and RFID is an application system based on the combination of Zigbee and RFID, which is the latest wireless communication technology in the communication field. Its main features are as follows: long-distance information reading; self-contained data; long-distance data writing; reading and writing equipment is very simple and reliable, and the price is very low. Therefore, it has the advantages of flexible and convenient use and low construction cost.
3. Introduction to Zigbee and RFID technology
Zigbee is a commercialized name for a wireless connection technology, which mainly solves the application of low-cost, low-power, low-complexity, low-transmission rate, and short-distance device networking.
The ZigBee standard is established based on the 802.15.4 protocol stack and has a powerful device networking function. It supports three main types of self-organizing wireless networks, namely, star structure, mesh structure (Mesh) and cluster tree (Cluster tree) , Especially the mesh structure, has strong network robustness and system reliability.
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Figure 1 ZIGBEE star network structure
Star network structure characteristics
Support point-to-point and point-to-multipoint communication
The central node is the ZIGBEE coordinator, and the terminal node is the ZIGBEE terminal equipment
All data passes through the central node
Suitable for networking of devices that are scattered in a circle and close to each other
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Figure 2 ZIGBEE mesh network structure
MESH mesh network structure characteristics
The system uses multi-hop routing communication
Large network capacity
It can span a large physical space and is suitable for structures that are far away and dispersed
The mesh network topology of the MESH network has powerful functions. All entities in the network can communicate with each other only within the communication range. If there is no direct path, they can also communicate through “multi-hop” mode; this topology It can also form a very complex network; in addition, the network also has self-organization and self-healing functions.
According to different energy supply methods, RFID tags can be divided into passive tags, semi-passive tags, semi-active tags and active tags. The communication between the passive tag and the reader depends on the reader The energy emitted by the antenna; the energy required for communication between the active tag and the reader is provided by the battery attached to the tag, and the active tag can actively send out radio frequency signals.
Four, Zigbee technical characteristics
Equipment power saving
The zigbee technology uses a variety of power-saving working modes, which can ensure that two AA batteries can support up to 6 months to 2 years of use;
Reliable communication
Zigbee adopts the collision avoidance mechanism of CSMA-CA, and reserves dedicated time slots for communication services that require fixed bandwidth to avoid competition and conflicts when sending data; the MAC layer adopts a fully confirmed data transmission mechanism. All data packets must wait for the receiver’s confirmation message;
Strong network self-organization and self-healing ability
Zigbee’s self-organizing function: without manual intervention, network nodes can perceive the existence of other nodes and determine the connection relationship to form a structured network;
Zigbee self-healing function: add or delete a node, the location of the node changes, the node fails, etc., the network can repair itself, and adjust the network topology accordingly, without manual intervention, to ensure that the entire system can still work normally.
A wireless communication network with self-organization and self-healing capabilities is the most ideal communication method for automatic meter reading systems.
low cost
The complexity of the equipment is low, and the Zigbee protocol is royalty-free, which can effectively reduce equipment costs;
Zigbee’s working frequency band is flexible. It is 2.4GHz, which is a license-free frequency band, which is wireless communication without usage fees.
Large network capacity
A ZigBee network can accommodate up to 254 slave devices and a master device, and more than 200 ZigBee networks can exist in an area at the same time;
Data Security
ZigBee provides data integrity checking and authentication functions, the encryption algorithm adopts AES-128, and each application can flexibly determine its security attributes.
5. Logistics management system based on ZigBee and RFID technology
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Figure 1 Reading RFID data when the car enters the field
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Figure 2 Reading RFID data at the cargo yard
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Figure 3 Reading RFID data in supermarket stores
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