The development of global communications industry technology presents three major trends: wireless, broadband and IP. Among the many broadband technologies, wireless, especially mobile communication technology, has become the biggest highlight of the communication technology market in recent years and is an important part of future communication technology.
Zigbee is a low-power personal area network protocol based on the IEEE802.15.4 standard. The technology specified under this agreement is a short-range, low-power wireless communication technology. The name comes from the eight-character dance of bees, because bees rely on the "dance" of flying and zig-zagging wings to communicate the location of pollen to their companions. That is to say, bees rely on this method. constitutes the communication network in the group. It is characterized by short range, low complexity, self-organization, low power consumption, and high data rate. It is mainly suitable for use in the fields of automatic control and remote control and can be embedded in various devices. In short, ZigBee is a cheap, low-power short-range wireless networking communication technology.
Technical principles of ZigBee
ZigBee is a wireless data transmission network platform composed of up to 65,000 wireless data transmission modules, which is very similar to the existing CDMA network of mobile communications. Or GSM network, each ZigBee network data transmission module is similar to a base station of the mobile network. They can communicate with each other within the entire network; the distance between each network node can range from the standard 75 meters to the expanded Hundreds of meters or even several kilometers; in addition, the entire ZigBee network can also be connected to various other existing networks. For example, you can monitor a ZigBee control network somewhere in Yunnan via the Internet in Beijing.
The ZigBee network is mainly established for automatic control of data transmission, while the mobile communication network is mainly established for voice communication; the value of each mobile base station is generally more than one million yuan, and each ZigBee" The "base station" is less than 1,000 yuan; each ZigBee network node can not only directly connect to the monitoring object, such as a sensor, for data collection and monitoring, but it can also automatically transfer data from other network nodes; in addition In addition, each ZigBee network node (FFD) can also be wirelessly connected to multiple isolated sub-nodes (RFD) that do not undertake network information transfer tasks within the range of its own signal coverage.
Each ZigBee network node (FFD and RFD) can support up to 31 sensors and controlled devices, and each sensor and controlled device can ultimately have 8 different interface methods. Can collect and transmit digital and analog quantities.
Characteristics of ZigBee technology
ZigBee technology is a short-range, low-complexity, low-power, low-speed, low-cost two-way wireless communication technology. It is mainly used for data transmission between various electronic devices with short distance, low power consumption and low transmission rate, as well as typical applications with periodic data, intermittent data and low response time data transmission.
Since Marconi invented the radio, wireless communication technology has been developing towards continuously increasing data rates and transmission distances. For example: The third generation mobile communication network (3G) within the wide area network aims to provide multimedia wireless services. The standards within the local area network range from IEEE802.11's 1Mbit/s to IEEE802.11g's 54Mbit/s data rate. ZigBee technology is committed to providing a low-cost, low-rate wireless communication technology with extremely low complexity, cost and power consumption for fixed, portable or mobile devices.
This wireless communication technology has the following characteristics:
1. Low power consumption
In working mode, ZigBee technology has a low transmission rate and a large amount of transmitted data. Small, so the signal sending and receiving time is very short. Secondly, when in non-working mode, the ZigBee node is in sleep mode. The device search delay is generally 30ms, the sleep activation delay is 15ms, and the active device channel access delay is 15ms. Due to the short working time, low power consumption for sending and receiving information and the adoption of sleep mode, ZigBee nodes are very power-saving. The battery working time of ZigBee nodes can be as long as 6 months to about 2 years. At the same time, since battery time depends on many factors, such as battery type, capacity and application, ZigBee technology also optimizes battery usage in the protocol. For typical applications, alkaline batteries can last for several years, and for some cases where the ratio of operating time to total time (working time + sleep time) is less than 1%, the battery life can even exceed 10 years.
2. Reliable data transmission
ZigBee’s media access control layer (MAC layer) adopts a talk-when-ready collision avoidance mechanism.
Under this fully confirmed data transmission mechanism, when there is a need for data transmission, it will be transmitted immediately. Each data packet sent must wait for confirmation information from the receiver and reply with confirmation information. If no confirmation information is received, it will be sent. Indicates that a collision has occurred and will be transmitted again. This method can improve the reliability of system information transmission. At the same time, dedicated time slots are reserved for communication services that require fixed bandwidth to avoid competition and conflicts when sending data. At the same time, ZigBee is optimized for delay-sensitive applications, and the communication delay and sleep state activation delay are very short.
3. Large network capacity
ZigBee’s low speed, low power consumption and short-distance transmission characteristics make it very suitable for supporting simple devices. ZigBee defines two types of devices: full-function devices (FFD) and reduced-function devices (RFD). For a fully functional device, it is required to support all 49 basic parameters. For simplified function devices, it is only required to support 38 basic parameters in the minimum configuration. A full-function device can talk to reduced-function devices and other full-function devices, and can work in three ways: personal area network coordinator, coordinator or device. Reduced function devices, on the other hand, can only talk to full function devices and are only used in very simple applications. A ZigBee network includes up to 255 ZigBee network nodes, one of which is the master device and the rest are slave devices. Through the Network Coordinator, the entire network can support up to more than 64,000 ZigBee network nodes. In addition, each Network Coordinator can be connected to each other, and the number of ZigBee network nodes will be considerable.
4. Compatibility
ZigBee technology is seamlessly integrated with existing control network standards. The network is automatically established through the network coordinator (Coordinator), and the carrier sensing/collision detection (CSMA-CA) method is used for channel access. For reliable delivery, a full handshake protocol is also provided.
5. Security
Zigbee provides data integrity checking and authentication functions, providing three levels of security in data transmission. The first level is actually no security method. For certain applications, if security is not important or the upper layer has provided sufficient security protection, the device can choose this method to transfer data. For the second level of security, devices can use access control lists (ACLs) to prevent unauthorized devices from obtaining data. No encryption measures are taken at this level. The third level of security uses symmetric ciphers belonging to the Advanced Encryption Standard (AES) during data transfer. AES can be used to protect data payloads and prevent attackers from impersonating legitimate devices. Each application can flexibly determine its security attributes.
6. Low implementation cost
The initial cost of the module is estimated to be around US$6, which will soon be reduced to US$1.5-2.5, and the Zigbee protocol is patent-free. Current low-speed, low-power UWB chipsets cost at least $20. The price target for ZigBee is only a few cents. Low cost is also a key factor for ZigBee.
7. Short delay
Communication delay and activation delay from sleep state are very short. The typical search device delay is 30ms, and the sleep activation delay is 15ms. The delay for active device channel access is 15ms. Therefore, ZigBee technology is suitable for wireless control applications with stringent latency requirements (such as industrial control situations, etc.).
The difference between ZigBee and WiFi
Similarities:
1. Both are short-range wireless communication technologies;
2 , both use the 2.4GHz frequency band
3. Both use DSSS technology;
Differences:
1. The transmission speed is different. The transmission speed of ZigBee is not high (<250Kbps), but the power consumption is very low. It can generally be used for more than 3 months when powered by batteries; WiFi, often referred to as wireless LAN, has a high speed (11Mbps) and high power consumption, and is generally used externally. Power supply;
2. The application scenarios are different. ZigBee is used in low-speed, low-power applications, such as wireless sensor networks, and is suitable for industrial control, environmental monitoring, smart home control and other fields. WiFi is generally a wireless network technology used to cover a certain range (such as a building) (coverage range is about 100 meters). The form of expression is our commonly used wireless router. Install a wireless router in a building, and basically all laptops (with wireless network cards) in the building can access the Internet wirelessly.
3. The market status is different. As an emerging technology, ZigBee has been undergoing rapid development and promotion since the first version of the standard was released in 2004; currently, it has not been promoted on a large scale due to cost and reliability reasons; WiFi technology is much more mature. There are many applications. Generally speaking, there is a big difference between the two. They have different market positioning and the competition between them is not very big.
It's just that the two have the same technical similarities, but the mutual interference between the two is still relatively large, especially the interference of WiFi to ZigBee.
Comparison of hardware memory requirements between the two: ZigBee: 32~64KB+; WiFi: 1MB+; ZigBee hardware requirements are low.
Comparison of the sustainable time of battery power supply between the two: ZigBee: 100~1000 days; WiFi: 1~5 days; ZigBee has low power consumption. Transmission distance comparison (general usage, no high-power antenna transmitting device): ZigBee: 1~1000M; WiFi: 1~100M; ZigBee has long transmission distance. ZigBee disadvantages: Network bandwidth comparison: ZigBee: 20~250KB/s; WiFi: 11000KB/s; ZigBee has low bandwidth and slow transmission.
Technical applications of ZigBee
As a low-rate short-distance wireless communication technology, ZigBee has its own characteristics, so there are applications tailor-made for it. Although in certain Some application aspects may overlap with other technologies. Some possible applications of ZigBee include smart homes, industrial control, automatic meter reading, medical monitoring, sensor network applications and telecommunications applications.
1. Smart Home
There may be many electrical appliances and electronic equipment in your home, such as lights, TVs, refrigerators, washing machines, computers, air conditioners, etc., and there may also be smoke sensors, In the past, we could only achieve point-to-point control of equipment such as alarms and cameras, but if ZigBee technology is used, these electronic and electrical equipment can be connected to form a network, and can even be connected to the Internet through a gateway, so that users can You can conveniently monitor your home situation from anywhere and save yourself the trouble of wiring at home.
2. Industrial control
There are a large number of sensors and controllers in the factory environment. ZigBee technology can be used to connect them into a network for monitoring, strengthen operation management, and reduce costs.
3. Sensor network applications
Sensor networks are also a recent research hotspot, and have good application prospects in aspects such as cargo tracking, building monitoring, and environmental protection. Sensor networks require nodes with low cost, low power consumption, automatic networking, easy maintenance, and high reliability. ZigBee's advantages in networking and low power consumption make it a good technology choice for sensor network applications.
There are still problems with Zigbee technology
Although Zigbee technology was listed as one of the top ten new technologies with the fastest development and the most market prospects in the world in 2004; There has been a lot of discussion about the advantages of Zigbee technology. So far, many manufacturers at home and abroad have developed and produced a variety of Zigbee products and done a lot of work in application promotion. However, to be honest, , Zigbee technology is truly fully used to solve specific practical problems, and there are very limited meaningful cases.
Zigbee seems to have become a fashion, but it is not yet a truly practical new technology. For this reason, in addition to being a new technology, which itself requires a process of technological improvement and maturity, as well as market cultivation, in our long-term practice of applying Zigbee technology to solve practical problems, we have also found the following to be very important: Problems that we think are very difficult to solve in the short term:
1. One of the core technologies of Zigbee is dynamic networking and dynamic routing, that is, the Zigbee network takes into account the changes in the number of nodes in the network, and the network Each node in the network needs to reorganize the network through wireless signal communication after a certain period of time, and each time information is sent from one node to another node, it needs to scan various possible paths and try from the shortest path. Since then, this involves wireless network management issues. All of these require a large amount of bandwidth resources and increase data transmission delays. Especially as the number of network nodes increases and the number of transfers increases. Therefore, although the radio frequency transmission rate of Zigbee is 250kbps, the actual available rate after multiple transfers will be greatly reduced, and the data transmission delay will also be greatly increased, making wireless network management more troublesome. This is the main problem in data transmission of Zigbee network at present.
2. From an English perspective, the word Zigbee is composed of the two words "Zig" and "bee". The former "Zig" in Chinese means "Zig"-shaped path, and the English word "bee" behind it means bee. Our understanding is that Zigbee network technology imitates the way bees transmit information, through the transmission of information between network nodes. Mutual transmission to transmit a message from one node to another distant node.
If calculated according to the general standard Zigbee node, each data transfer in an open space increases the straight-line transmission distance by an average of 50 meters, and ten transfers are required to transmit a straight-line distance of 500 meters; indoors, due to the 2.4 G transmission frequency used by Zigbee, it is generally transmitted through The signal is transmitted by reflection. Due to the obstruction of buildings, it is often necessary to use more network nodes for data transfer in order to transmit a certain distance. As analyzed in the first article above, this is not suitable for a Zigbee network. Not a simple matter. Of course, we can also use amplifiers to increase the transmission distance of Zigbee network nodes. However, this will inevitably greatly increase the power consumption and cost of the network nodes, losing the original purpose of Zigbee's low cost and low power consumption. Moreover, using this method indoors to increase transmission distance has limited effect. Obviously, a star network communication structure with the central point outdoors and the terminal modules outdoors is more reasonable.
3. One of the core technologies of Zigbee is that each network node, in addition to serving as an information collection point and executing commands from the center, also undertakes the task of transferring data from the network at any time. In this way, The transceiver of the network node must be in the receiving and transmitting state at all times, which means that its minimum power consumption is at least about 20mA. Generally, the power consumption of long-distance network nodes using amplifiers is generally about 150mA. It is obviously difficult to use battery drive to ensure the normal operation of network nodes;
4. Since each node in Zigbee participates in automatic networking and dynamic routing, the microcontroller of each network node It is relatively complex and the cost is naturally higher. In addition, the amount of development work for specific applications based on the Zigbee network is larger.
In summary, we believe that the Zigbee network, in fact, in many cases, sacrifices network transmission efficiency, bandwidth and node module power consumption in exchange for in many practical applications, it does not Important dynamic networking and dynamic routing functions, because, under normal circumstances, our network nodes and data transmission paths are often fixed. Therefore, the current Zigbee technology has not yet solved the node power consumption problem, the low efficiency of network data transmission and the long delay problem, as well as the problem of limited data transmission distance, which are the fundamental reasons why the current Zigbee technology is difficult to be well promoted.