ZigBee technology is considered to be one of the most possible communication technologies that can change our current life like WiFi and Bluetooth. ZigBee is a technology that allows some devices, especially sensors, to access the Internet.
In the field of home automation control and industrial telemetering and remote control, the demand for wireless data communication is becoming more and more intense, and this wireless data transmission must be highly reliable and resistant to various electromagnetic disturbances in the field.
Zigbee is characterized by its lower power consumption, real-time online access, large number of accesses from the same gateway, and self-organizing network, which has broad application space in the development of the Internet of Things.
Zigbee technology
The term Zigbee is derived from the fact that when honeybees discovered a pollen position, they used a ZigZag dance to inform their peers and exchange information. It can be said that a small animal realizes "wireless" communication through a simple method. People call this a short-range wireless network communication technology that focuses on low power, low cost, low complexity, and low speed.
It is a short-range wireless communication technology developed based on the IEEE802.15.4 protocol. It has low power consumption and is considered by the industry to be the wireless method most likely to be used in industrial control applications. Zigbee is a wireless data transmission network platform composed of up to 65,000 wireless data transmission modules. In the entire network, each Zigbee network data transmission module can communicate with each other, and the distance between each network node can be Standard 75m unlimited expansion.
ZigBee Technical Features and Performance
ZigBee is a wireless connection that can operate in the 2.4GHz (global epidemic), 868MHz (European popular) and 915MHz (U.S. popular) 3 frequency bands with transmissions of up to 250kbit/s, 20kbit/s, and 40kbit/s, respectively Rate, its transmission distance is in the range of 10-75m, but it can continue to increase.
As a wireless communication technology, ZigBee has the following characteristics:
Low power consumption
Because ZigBee's transmission rate is low, the transmission power is only 1mW, and the sleep mode is adopted, and the power consumption is low, so the ZigBee device is very power-saving. According to estimates, ZigBee devices can maintain up to six months to two years of usage time with just two AA batteries, which is beyond the reach of other wireless devices.
low cost
The initial cost of the ZigBee module is around US$6 and it is estimated that it will soon drop to US$1.5-2.5, and the ZigBee protocol is royalty-free. Low cost is also a key factor for ZigBee.
Low complexity
The size of the zigbee protocol is generally 4-32 KB, while Bluetooth and Wi-Fi generally exceed 100 KB.
Short delay:
Both the communication delay and the time delay from the sleep state are very short. The typical search device delay is 30 ms, the sleep activation delay is 15 ms, and the active device channel access delay is 15 ms. Therefore, ZigBee technology is suitable for wireless control (such as industrial control applications, etc.) applications with time-delay requirements.
Large network capacity
A star-type Zigbee network can accommodate up to 254 slave devices and one master device. Up to 100 ZigBee networks can exist in a zone at the same time, and the network composition is flexible. And there can be up to 65,000 node connections in a network.
Network establishment
Zigbee can automatically create the network it wants.
reliable
A collision avoidance strategy is adopted, and a dedicated time slot is reserved for communication services that require a fixed bandwidth, avoiding the competition and collision of data transmission. The MAC layer adopts a fully-confirmed data transmission mode. Each transmitted data packet must wait for a confirmation message from the receiver. Retransmissions can occur if there is a problem during transmission.
Safety
ZigBee provides packet integrity check function based on cyclic redundancy check (CRC), which supports authentication and authentication. AES-128 encryption algorithm is adopted. Each application can flexibly determine its security attributes.
Zigbee's technical performance
1, ZigBee frequency band and data transmission rate
There are three frequency bands that can be used by ZigBee wireless, namely, the 2.4GHz ISM frequency band, the European 868MHz frequency band, and the US 915MHz frequency band, and the available frequency channels for different frequency bands are 16, 1 and 10 respectively.
ZigBee adopts the 2.4G ISM band in China, which is an application-free and royalty-free frequency. It has 16 channels in the 2.4G band and has a bandwidth of 250K.
2. Short-range wireless network standards
Both ZigBee and 802.15.4 standards are suitable for low-rate data transmission with a maximum rate of 250K. Compared with other wireless technologies, they are suitable for relatively close transmission distances. ZigBee wireless technology is suitable for setting up a WPAN network, which is the networking of wireless personal devices for data acquisition. The transmission of control signals is very suitable. Its application location is low speed, complex network, low power consumption and low cost applications.
3. Comparison of wireless network standards
ZigBee wireless transmission bandwidth is in the range of 20-250KB/s, suitable for sensor data acquisition and transmission of control data. Large-scale networks can be set up. The network node capacity reaches 65535, which has a very strong networking advantage; unique low-power design , can guarantee the battery work for a long time.
4, Zigbee physical channel
ZigBee has 16 channels in the 2.4G band, distributed from 2.405GHz to 2.480GHz, and the channel spacing is 5M, which has strong channel crosstalk immunity.
5, Zigbee protocol stack
ZigBee has adopted all the advantages stipulated by IEEE 802.15.4's powerful wireless physical layer, added logic network, network security, and application software, which is more suitable for the unification of product technology and facilitates the interconnection and interoperability of products; ZigBee continues to The IEEE closely integrates to ensure a complete integrated solution to the market.
6, ZigBee network topology
ZigBee technology has powerful networking capabilities and can form star, tree and mesh mesh networks. It can select the appropriate network structure according to actual project needs.
The MESH network topology network has powerful functions. The network can communicate through “multi-hopâ€; this topology can also form an extremely complex network; the network also has self-organizing and self-healing functions; The family tree network is suitable for applications with many points and relatively close distances.
7, ZigBee network device type
7.1 Network Coordinator:
Including all network messages is the most complex of the 3 device types, with the largest storage capacity and strong computer capabilities. Send network beacons, establish a network, manage network nodes, store network node information, find routing messages between a pair of nodes, and continuously receive information.
7.2 Full-function device (FFD):
Can act as a network coordinator, form a network, let other FFD or RFD links, FFD has the function of the controller, can provide two-way transmission of information.
Comes with all 802.15.4 features and all features specified by the standard
More memory and computer power allow it to act as a network router when it is idle.
It is also possible to do terminal equipment
7.3 Reduced Function Device (RFD):
The RFD can only send information to or receive information from the FFD.
Comes with limited features to control cost and complexity
Used as a terminal device in the network.
The relatively simple implementation of ZigBee naturally saves money.
RFD reduces ZigBee component costs by eliminating memory and other circuitry, while a simple 8-bit processor and small protocol stack also help reduce costs.
8, Zigbee anti-interference ability
ZigBee uses direct sequence/frequency (F/D) technology with high processing gain at the physical layer. ZigBee has the highest processing gain, and has the strongest immunity to interference and multi-path delay propagation. The rapid change in frequency is the ability to change the frequency to avoid influence from a known source or signal source;
Experiments prove that the IEEE 802.15.4/ZigBee bit error rate, especially when the signal to noise ratio is 4dB can reach 10 -9; reach the same bit error rate, Bluetooth/802.15.1 signal to noise ratio to reach 16dB, WLAN For 802.11b to achieve 10dB, Zigbee's anti-interference performance is significantly higher than Bluetooth and WLAN technology.
9, ZigBee reliable link
9.1 Physical Layer RF Communication Links
Direct-sequence spread spectrum uses high processing gain
Clear channel detection
Detection of interference energy
Using frequency hopping technology Freqency agility
9.2 agreement
CRC-based error detection/correction
Strategies to avoid conflicts CSMA/CA
Allows professional guaranteed time slots for fixed-bandwidth communications services
Packets sent are subject to confirmation by the recipient. If there is a problem, retransmission
Keep data packets in time Packet data freshness
9.3 Communication Reliability Mechanism
ZigBee uses the collision avoidance mechanism of CSMA-CA, and at the same time reserves dedicated time slots for communication services that require fixed bandwidth, avoiding sending data to make contention and conflict, and clear channel detection.
The MAC layer adopts a fully-confirmed data transmission mechanism, and each transmitted packet must wait for the recipient's confirmation message.
9.4 Network self-organization and self-healing ability
ZigBee's self-organizing function: Without human intervention, network nodes can sense the existence of other nodes, and determine the connection relationship, forming a structured network;
ZigBee self-healing function: Add or delete a node, node location changes, node failure, etc., the network can repair itself, and adjust the network topology accordingly, without manual intervention, to ensure that the entire system can still work properly.
The design of the ZigBee technology RF physical layer ensures strong anti-jamming capability and communication reliability. The reliable design of ZigBee technology in communication protocols ensures strong anti-jamming capability and communication reliability.
ZigBee Alliance
The ZigBee Alliance was established in August 2001. So far, in addition to internationally renowned big companies such as Invensys, Mitsubishi Electric, Motorola, Samsung, and Philips, the alliance has approximately 100 member companies and is growing rapidly. It covers semiconductor manufacturers, IP service providers, consumer electronics manufacturers and OEMs, and industrial control and home automation companies such as Honeywell, Eaton and Invensys Metering Systems, and even toy companies like Mattel.
All of these companies participate in the IEEE802.15.4 working group responsible for developing the ZigBee physical and media control layer technology standards. In the areas of industry, agriculture, automotive electronics, home networking, medical sensors, and servo actuators, the requirements for wireless networks are very different from those for civilian use. It usually requires low data throughput and low power consumption.
In addition, there are a large number of wireless devices that are easy to use and can be used at will, and a large number of wireless access points need to be deployed, and low prices will play a key role. Therefore, the problem to be solved by the ZigBee standard is to design a communication link that maintains minimum traffic and a low-complexity wireless transceiver. The core issues to consider are the low power consumption and low price design, which requires that the standard should provide low bandwidth, low data rate applications.
The IEEE 802.15.4 team and the ZigBee Alliance jointly developed the ZigBee standard. The ZigBee standard is a developing low-cost, low-power, low-power short-range wireless communication standard. It is a wireless network specification designed for low-rate sensors and control networks.
The IEEE established the 802.15.4 group in December 2000 to develop physical layer (PHY) and media access control (MAc) layer specifications. In May 2003, IEEE 802.15 and 4 standards were adopted; the ZigBee Alliance is a global one. Enterprise Alliance aims to collaborate to implement a wireless network monitoring product based on global open standards, reliability, low cost, and low power consumption. It was jointly established by Honeywell, Mitsubishi, Motorola, philips, and Invensys and is responsible for the development of network layer, security management, and applications. Interface specification, adopted in December 2004 version 1.0 specification.
Zigbee technology application
1, the data type suitable for ZigBee transmission
Cyclical data
Sensor data, water and electricity meter data, instrumentation data
Intermittent data
Industrial Control Commands, Remote Network Control, Home Appliance Control
Repetitive low response time data
Such as mouse and keyboard data, data of joystick
2, for ZigBee technology applications
Low equipment cost, small amount of transmission data, and small device size make it inconvenient to place a large rechargeable battery or power module. There is no sufficient power supply support, and only disposable batteries are used. A large range of communication coverage is required, and there are many devices in the network, but only for the monitoring or control environment.
3, typical application of Zigbee technology
3.1 Combining Zigbee and GPRS Wireless Data Transmission
The use of GPRS network to transmit complete wireless network design based on Zigbee wireless sensor sink node data, and the network adopts the star topology or the mesh network topology and the communication mode of waking up the Zigbee module when required, effectively reducing the power consumption of each Zigbee sensor node and reducing the The probability that the sensor node collides with each other when reporting data to the sink node, and uses the GPRS network to transmit the data of the sink node, which changes the limitation that the traditional wireless sensor network needs to rely on the wired public network for data transmission, so that the network has very significant advantages.
The remote management center realizes long-distance communication with the ZIGBEE network through public channels such as GPRS, and obtains related information collected through the GPRS network to realize effective control and management on the site.
3.2 Medical Monitoring System
Using ZIGBEE technology to form a mesh routing network, set up a suitable routing node in the corridor to carry out data transfer. The call nodes in the room use a star network connection. One of the nodes is used as a ZIGBEE router and is responsible for the connection and data with the central network. Relay forwarding. All ZIGBEE routers form a cellular mesh network, and then connect with the ZIGBEE center node. The central node is set in the management center to form a complete ZIGBEE wireless network, which is a very reliable network structure.
3.3 Wireless Ordering System
Restaurant ZigBee wireless node network forms a complete wireless communication network through ZigBee node devices deployed in restaurants, bar tables, kitchens, checkout counters, and processing centers, and automates information processing. The waiter handles customer's points through a handheld ordering terminal. The user orders are automatically uploaded to the kitchen and checkout counters through the ZigBee network in the terminal and lobby. The ZIGBEE center node, wireless ZIGBEE routing, and wireless ordering terminals of the wireless communication system constitute a cellular communication network, any node Implement communications in a multi-tone manner.
Any one of the ZIGBEE routers is responsible for the connection with the center network and data relay forwarding; all ZIGBEE routers form a cellular mesh network, which is connected with the ZIGBEE center node, and the central node is set up at the total service station to form a complete ZIGBEE wireless network. The network is a very reliable network structure for communications.
3.4 Intelligent Traffic Control System
The wireless control system using ZIGBEE combined with solar energy eliminates the need for digging up control lines and enables wireless automatic networking between devices. This reduces system installation costs and, more importantly, avoids the traditional installation methods that cause traffic disturbances. The economic loss, but also to avoid the rapid development of the city, road expansion and other changes to the original embedded pipeline interference.
With the continuous improvement of ZigBee technology, it will become the most advanced digital wireless technology in the world today. ZigBee's remarkable advantages such as low power consumption, low cost, low speed, and ease of use make it sure to have a broad application prospect. The ZigBec Alliance predicts that in the next four to five years, each home will have 50 ZigBee devices and will eventually reach 150 per home. We believe that in the near future, more and more products with ZigBee functionality will enter our lives, bringing great convenience and speed to our lives and work.
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