As a wireless communication technology, ZigBee has many applications in modern life. For example, ZigBee plays an important role in the scenario of smart farm. In previous articles, Xiaobian introduced the bottom layer of ZigBee, the difference between ZigBee and Bluetooth. In order to enhance our understanding of ZigBee, this paper will interpret ZigBee standard, ZigBee technical difficulties and ZigBee module software composition. If you are interested in ZigBee, read on.
1、 ZigBee and its standards
ZigBee is a new wireless communication technology, which is suitable for a series of electronic devices with short transmission range and low data transmission rate. ZigBee wireless communication technology can coordinate communication between thousands of micro sensors relying on special radio standards, so it is often called homerflite wireless technology and firefly wireless technology. ZigBee wireless communication technology can also be applied to a small range of control and automation fields based on wireless communication. It can not only save the cable between computer equipment and a series of digital equipment, but also realize the wireless networking between a variety of different digital equipment, so that they can communicate with each other or access to the Internet.
ZigBee technology is a new technology, it appears recently, mainly rely on wireless network transmission, it can be close to the wireless connection, belongs to the wireless network communication technology. In the data information transmission, ZigBee technology is the main technical index, it is safe to use, and its capacity is very strong, it is widely used in human daily communication transmission.
On the basis of IEEE802.15.4 standard, ZigBee alliance has developed a set of industrial standards for networking and application. Unlike IEEE, which only formulates the underlying standards of phy and MAC, ZigBee alliance has standardized the network layer, application layer and its supporting and security sub layers. Therefore, a complete ZigBee product implemented by terminal manufacturer should be composed of high-level application specification, application support sublayer, ZigBee device object (ZDO) sublayer, network layer, MAC and PHY. The standard protocols of network layer and above are formulated by ZigBee alliance, and IEEE802.15.4 is only responsible for phy and MAC standards.
The combination of ZigBee standard and IEEE802.15.4 standard makes its products have the characteristics of low power consumption, easy networking and short distance interconnection. Therefore, it is considered that it has considerable advantages in the application of sensor network / Internet of things. The standard developed by ZigBee alliance covers the whole seven layer protocol of open system interconnection (OSI), which is very conducive to the implementation of manufacturers. Therefore, when it comes to the products and solutions of sensor network / Internet of things, ZigBee is considered as a mature solution.
2、 Difficulties in ZigBee Technology
1. Dynamic networking and dynamic routing
At present, the main problems of ZigBee network in data transmission are dynamic networking and dynamic routing. The nodes of ZigBee network are not static, but dynamic in real time. Each node in the network is separated for a certain period of time. It needs to re network through wireless signal exchange, and each time it needs to send information from one node to another. At this time, we need to scan all possible paths, starting from the shortest path. This takes up a lot of bandwidth resources, and the delay of data transmission is also amplified. Especially when the number of network nodes and transmission increases. Therefore, although the RF transmission rate of ZigBee is 250kbps, the actual available rate will be greatly reduced after multiple transmission.
2. Communication stability is weak
At present, the domestic ZigBee technology mainly uses 2.5G frequency of ISM band, and generally uses signal reflection transmission. But its diffraction ability is not strong. During this period, due to obstacles such as buildings, the signal is greatly weakened.
Therefore, more network nodes are needed for data transmission. The solution to this problem is to use amplifiers to increase the transmission distance of ZigBee network nodes. However, it is impossible to have the best of both worlds. This solution will greatly increase the power consumption and cost of network nodes. ZigBee has the advantages of low cost and low power consumption, which will no longer exist.
3、 Software composition of ZigBee module
The software contains a complete ZigBee protocol stack, and has its own PC configuration tool. It uses serial port to communicate with user products, and can configure the transmission power, channel and other network topology parameters of the module, which is simple and fast to use.
The advantage of transparent transmission module is that users do not need to consider how the program in the module runs. Users only need to send their own data to the module through the serial port, and then the module will automatically send the data out wirelessly. According to the pre configured network structure, the module will send and receive communication with the destination address node in the network, and the receiving module will check the data, If the data is correct, it will be sent out through the serial port.
However, at present, most users will have their own data processing mode when using ZigBee technology, so that each node device will have its own CPU to process the data, so the module can still be regarded as a “chip” that has integrated RF, protocol and program.