The origin and development of ZigBee technology
In today's world, communication technology is developing rapidly. With the rapid development of the Internet and the rapid growth of personal data communication requirements, the development of global communication industry technology has three major trends: wireless, broadband and IP. The development of the Internet business has driven the market demand for broadband networks, and the number of broadband users has shown a very strong growth trend around the world. Among many broadband technologies, wireless technology, especially mobile communication technology, has become the biggest bright spot in the communication technology market in recent years, and is an important part of the future communication technology.
Zigbee is a low-power personal area network protocol based on the IEEE802.15.4 standard. The technology specified under this protocol is a short-range, low-power wireless communication technology. The name comes from the bee's splay, because bees rely on flying and "zig" to shake the wings of the "dance" to convey the position of the pollen with the companion, that is, the bee relies on this way It constitutes a communication network in the group. It is characterized by close proximity, 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.
The origin and development of ZigBee technology
Before introducing ZigBee, I would like to mention his predecessor, Bluetooth. During the use of Bluetooth technology, people found that Bluetooth technology has many shortcomings despite its many advantages. For industrial, home automation control and industrial telemetry and remote control, Bluetooth technology is too complicated, power consumption, distance is too close, network size is too small, and industrial automation, the demand for wireless data communication is more and more intense, and For industrial sites, this wireless data transmission must be highly reliable and resistant to various electromagnetic interferences at the industrial site. Therefore, after long-term efforts, the Zigbee agreement was officially released in the United States in 2003.
Zigbee's predecessor was the "Homerflite" technology from the giant hairs of INTEL and lBM in 1998.
A working group was formed in December 2000 to draft the EEE802.154 standard. The Zigbee Alliance was established in August 2001.
In the second half of 2002, the four giants of British vensys, Japan's Mitsubishi Electric Corporation, Motorola of the United States and Philips Semiconductors of the Netherlands jointly announced the joining of the "Zigbee Alliance" to develop the next-generation wireless communication standard called "Zigbee". A milestone in the development of this technology.
In December 2004, the Zigbee10 standard (also known as Zigbee2004) was finalized, which gave Zigbee its own basic standards for development.
The Zig bee 1.0 standard was released in September 2005 and is available for download. During the year, Huawei Technologies Co., Ltd. and BM Corporation joined the Zigbee Alliance. However, there are very few applications based on this version, and it is not compatible with the later versions.
The standard revision was carried out in December 2006, and Zigbee version 1.1 (also known as Zigbee 2006) was launched. Although the agreement is named Zigbee1.1, it is not compatible with Zigbee10.
Completed revision in October 2007 (called Zigbee2007/PRO). Compatible with the previous Zigbee 2006 version and joined the Zibgeepro section, the Zig beel Alliance is more focused on three areas: home automation, building commercial building automation, and advanced meter reading infrastructure.
The technical principle of ZigBee
ZigBee is a wireless data transmission network platform consisting of up to 65,000 wireless data transmission modules. It is very similar to the existing mobile communication CDMA network or GSM network. Each ZigBee network data transmission module is similar to a mobile network base station. Throughout the network, they can communicate with each other; the distance between each network node can be from the standard 75 meters, to the extended hundreds of meters, or even several kilometers; in addition, the entire ZigBee network can also be compared with the existing Other various network connections. For example, you can monitor a ZigBee control network in a certain place in Yunnan via the Internet.
The ZigBee network is mainly established for automatic control of data transmission, and 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 "base station" is less than 1,000 yuan. RMB; each ZigBee network node can not only directly collect and monitor data with monitoring objects, such as sensor connections, it can also automatically transfer data data transmitted by other network nodes; in addition, each ZigBee network node (FFD) can also be wirelessly connected to multiple isolated child nodes (RFDs) that do not undertake network information relay tasks within the scope of their 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 have 8 different interfaces. Digital and analog quantities can be acquired and transmitted.
ZigBee technology features
ZigBee technology is a two-way wireless communication technology with close proximity, low complexity, low power consumption, low speed and low cost. It is mainly used for data transmission between various electronic devices with short distance, low power consumption and low transmission rate, and typical applications with periodic data, intermittent data and low response time data transmission.
Since Marconi invented the radio, wireless communication technology has been moving toward increasing data rates and transmission distances. For example, the third generation mobile communication network (3G) within the WAN is intended to provide multimedia wireless services ranging from 1 Mbit/s of IEEE 802.11 to 54 Mbit/s of IEEE 802.11g. ZigBee technology is dedicated to providing a low-cost wireless communication technology that is inexpensive, fixed, portable, or mobile devices with extremely low complexity, cost, and power consumption.
This wireless communication technology has the following characteristics:
Low power consumption
In the working mode, the ZigBee technology has a low transmission rate and a small amount of transmitted data, so the signal transmission and reception time is short. Secondly, in the non-operation mode, the ZigBee node is in the sleep mode. The device search delay is generally 30 ms, the sleep activation delay is 15 ms, and the active device channel access delay is 15 ms. Due to the short working time, low power consumption of the sending and receiving information, and the sleep mode, the ZigBee node is very power-saving. The battery working time of the ZigBee node can be as long as 6 months to 2 years. At the same time, because battery time depends on many factors, such as battery type, capacity and application, ZigBee technology also optimizes battery usage in terms of protocol. For typical applications, alkaline batteries can be used for years, and for some working hours and total time (working time + sleep time) ratio of less than 1%, the battery life can even exceed 10 years.
Reliable data transmission
ZigBee's media access control layer (MAC layer) uses a talk-when-ready collision avoidance mechanism. Under this fully-confirmed data transmission mechanism, when there is a data transmission demand, it is transmitted immediately, and each data packet sent must wait for the confirmation information of the receiver, and reply the confirmation information. If no reply is received, 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 requiring fixed bandwidth, which avoids competition and conflicts when transmitting data. At the same time, ZigBee is optimized for delay-sensitive applications, and the latency of communication delay and sleep state activation is very short.
Large network capacity
ZigBee's low-rate, low-power, and short-range transmission make it ideal for supporting simple devices. ZigBee defines two devices: a full-featured device (FFD) and a simplified functional device (RFD). For full-featured devices, it is required to support all 49 basic parameters. For simplified functional devices, only minimal basic parameters are required to support 38 basic parameters. A full-featured device can talk to simplified functional devices and other full-featured devices and can operate in three ways: individual domain coordinators, coordinators, or devices. Simplified functional devices can only talk to full-featured devices for 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. If the network coordinator is used, the entire network can support more than 64,000 ZigBee network nodes, and each Network Coordinator can be connected to each other. The number of ZigBee network nodes will be considerable.
ZigBee technology integrates seamlessly with existing control network standards. The network is automatically established through a Coordinator, and channel access is performed by Carrier Sense/Collision Detection (CSMA-CA). For reliable delivery, a full handshake protocol is also provided.
Zigbee provides data integrity checking and authentication capabilities that provide three levels of security in data transfer. The first level is actually no security. For an application, if security is not important or the upper layer has provided sufficient security protection, the device can choose to transfer data in this way. For the second level of security, the device can use an access control list (ACL) to prevent unauthorized devices from acquiring data, and no encryption is taken at this level. The third level of security uses a symmetric cipher belonging to the Advanced Encryption Standard (AES) in data transfer. AES can be used to protect data payloads and prevent attackers from impersonating legitimate devices, and each application can flexibly determine its security attributes.
Low implementation cost
The initial cost of the module is estimated to be around $6, and will soon drop to $1.5-2.5, and the Zigbee agreement is free of patent fees. The current low-speed, low-power UWB chipset is priced at least $20. The price target for ZigBee is only a few cents. Low cost is also a key factor for ZigBee.
Both the communication delay and the delay from the sleep state are very short. The typical search device delay is 30ms, the sleep activation delay is 15ms, and the active device channel access delay is 15ms. Therefore, ZigBee technology is suitable for applications with time-critical wireless control (such as industrial control applications).
The difference between ZigBee and WiFi
1. Both are short-range wireless communication technologies;
2, both use the 2.4GHz band
3, are using DSSS technology;
1. The transmission speed is different. ZigBee's transmission speed is not high (<250Kbps), but the power consumption is very low. It can be used for more than 3 months when using battery power. WiFi is the wireless LAN that is often said to be high (11Mbps), and the power consumption is also large. power supply;
2, the application is different. ZigBee is used in low-speed, low-power applications, such as wireless sensor networks, for industrial control, environmental monitoring, smart home control and other fields. WiFi is generally used to cover a certain range (such as a building) wireless network technology (covering about 100 meters). The form of expression is the wireless router we use. A wireless router is installed in a building, and a laptop (with a wireless network card) in the building can basically be wirelessly connected.
3. The market status is different. As an emerging technology, ZigBee has been in the rapid development and promotion since the release of the first version of the standard in 2004. At present, due to cost and reliability reasons, there has not been a large-scale promotion; WiFi, technology is mature, There are also many applications. Generally speaking, the difference between the two is large, the market positioning is different, and the competition between them is not great. However, the two have technical commonality, and the mutual interference between the two is relatively large, especially the interference of WiFi to ZigBee.
Comparison of hardware memory requirements: ZigBee: 32~64KB+; WiFi: 1MB+; ZigBee hardware requirements are low.
The sustainable battery life comparison between the two batteries: ZigBee: 100~1000 days; WiFi: 1~5 days; ZigBee power consumption is low. Transmission distance comparison (general usage, no high-power antenna transmitter): ZigBee: 1~1000M; WiFi: 1~100M; ZigBee transmission distance is long. ZigBee disadvantages: Network bandwidth comparison: ZigBee: 20~250KB/s; WiFi: 11000KB/s; ZigBee has low bandwidth and slow transmission.
ZigBee technology application
As a low-rate short-range wireless communication technology, ZigBee has its own characteristics, so there are applications tailored for it, although it may overlap with other technologies in some applications. Some of ZigBee's possible applications include smart home, industrial control, automatic meter reading, medical monitoring, sensor network applications and telecom applications.
There may be many electrical and electronic equipment in the home, such as electric lights, televisions, refrigerators, washing machines, computers, air conditioners, etc. There may also be smoke sensors, alarms and cameras. In the past, we may have achieved peer-to-peer control at most. However, if ZigBee technology is used, these electronic and electrical devices can be connected to form a network, and even connect to the Internet through a gateway, so that users can easily monitor their homes anywhere and eliminate wiring at home. The troubles.
There are a large number of sensors and controllers in the factory environment, which can be connected to a network for monitoring using ZigBee technology to enhance job management and reduce costs.
Automatic meter reading
Meter reading may be familiar to everyone, such as gas meters, electricity meters, water meters, etc., every month or quarter may have to count the readings, report to gas, electricity or water companies, and then charge according to the readings. Nowadays, in most places, it is still inconvenient to use manual methods for meter reading. ZigBee can be used in this area to convert readings from tables into digital signals and send readings directly to companies that provide gas or hydropower via the ZigBee network. Using ZigBee for meter reading can also bring other benefits. For example, gas or hydropower companies can send some information directly to users, or combine with energy saving, and automatically reduce the speed of use when it is found that energy is used too fast.
Electronic medical monitoring is a recent research hotspot. Many sensors are installed on the human body, such as measuring pulse and blood pressure, monitoring health status, and placing some monitors and alarms in the surrounding environment of the human body, such as in the ward environment, so that the physical condition of the person can be monitored at any time. , can respond in a timely manner, such as notifying the hospital's duty staff. These sensors, monitors and alarms can be combined into a monitoring network via ZigBee technology. Because of the wireless technology, there is no need for wired connections between the sensors, and the monitored person can also be free to move, which is very convenient.
Sensor network application
Sensor networks are also a recent research hotspot, such as cargo tracking, building monitoring, and environmental protection. Sensor networks require nodes to be low-cost, low-power, and capable of automatic networking, easy maintenance, and high reliability. ZigBee's advantages in networking and low power make it a good technology choice for sensor network applications.
In early 2006, Telecom Italia announced that she had developed a SIM card with integrated ZigBee technology and named it "ZSIM" . In fact, this SIM card is just a means of integrating ZigBee on a telecom terminal. The ZigBee Alliance also released a news in April 2007, saying members of the alliance are developing telecommunications-related applications . If ZigBee technology can really be launched in the field of telecommunications, users can use mobile phones to make mobile payments in the future, and can get some interesting information in hotspots, such as news and discount information. Users can also know their own through location service. position. Although the current GPS location service has done a good job, it is difficult to support indoor positioning, and ZigBee's positioning function just makes up for this defect.
Current Zigbee technology still has problems
Although Zigbee technology was listed as one of the ten fastest growing and most promising new technologies in the world in 2004, there have been many discussions about the advantages of Zigbee technology. So far, many manufacturers at home and abroad We have also developed and produced a wide variety of Zigbee products, and have done a lot of work in application promotion. However, in fact, the Zigbee technology is completely used to solve specific practical problems, and the meaningful cases are very limited.
Zigbee seems to be a fashion, but it is not yet a real new technology. For the reason, in addition to being a new technology, it needs a technology improvement and maturity, as well as the process of market cultivation. In the practice of long-term application of Zigbee technology to solve practical problems, we also found the following important. In the short term, we think it is very difficult to solve:
1. One of Zigbee's core technologies is dynamic networking and dynamic routing. That is, the Zigbee network considers the increase and decrease of nodes in the network. Each node in the network is separated by a certain time and needs to be re-wired by means of wireless signal communication. And every time you send information from one node to another, you need to scan for all possible paths, starting with the shortest path, which involves the management of the wireless network. All of these require a large amount of bandwidth resources and increase the delay of data transmission. In particular, as the number of network nodes increases and the number of transfers increases. Therefore, although Zigbee's RF transmission rate is 250 kbps, the actual available rate after multiple transits will be greatly reduced, and the data transmission delay will be greatly increased, and the wireless network management will become more troublesome. This is the main problem of the current Zigbee network in data transmission.
2, the word Zigbee, from the perspective of English, it is composed of the words "Zig" and "bee". The former "Zig" Chinese means "the path of the glyph". The latter English word "bee" is the meaning of the bee. Our understanding, Zigbee network technology, is to imitate the way of bee information transmission, through the information between the network nodes. Interspersed with each other to transfer a message from one node to another in the distance. According to the general standard Zigbee node, in the open space, the data transmission average increases by 50 meters linear transmission distance calculation, the transmission of 500 meters linear distance needs to be transferred ten times; indoors, due to the transmission frequency of 2.4 G used by Zigbee, generally pass Signal reflection for transmission, due to the occlusion of the building, to transmit a certain distance, often need to use more network nodes for data transfer, as in the analysis in the first article above, this is for a Zigbee network, and Not a simple thing. Of course, we can also use amplifiers to increase the transmission distance of Zigbee network nodes. However, this will inevitably increase the power consumption and cost of network nodes, and lose the original purpose of Zigbee low cost and low power consumption. Moreover, using this method indoors to increase the transmission distance has a limited effect. Obviously, a star-shaped network communication structure with a terminal point outside the center and a terminal module outside is more reasonable.
3. One of Zigbee's core technologies is that each network node, in addition to its own information collection point and execution of commands from the center, also undertakes the data transfer task from the network at any time, so that the transceiver of the network node must be at any time. It is in the receiving and receiving state, which means that its minimum power consumption is at least 20mA. Generally, the long-distance network node of the amplifier is used, and its power consumption is generally around 150mA. It is obviously difficult to use battery drivers to ensure the normal operation of the network nodes;
4. Since each node in Zigbee participates in the work of automatic networking and dynamic routing, the single-chip microcomputer of each network node is relatively complicated, 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 Zigbee networks, in many cases, sacrifice network transmission efficiency, bandwidth, and power consumption of node modules in exchange for dynamic networking and dynamics that are not important in many practical applications. The function of routing, because, in general, our network nodes and data transmission paths are often fixed. Therefore, the current power consumption problem of nodes that Zigbee technology has not solved, the problem of low efficiency of network data transmission and long delay, and the problem of limited data transmission distance are the fundamental reasons why Zigbee technology is difficult to be promoted.