Zigbee is a low-cost, low-power, wireless mesh network standard targeted at battery-powered devices in wireless control and monitoring applications.
Zigbee is a short-distance, low-power wireless communication technology name. The origin of this name is the horoscope dance of bees. Its characteristics are close range, low complexity, low power consumption, low data rate, and low cost. It is mainly suitable for automatic control and remote control and can be embedded in various devices.
Zigbee technical advantages
① Low power consumption
In the low-power standby mode, two AA batteries can support a node to work for 6 to 24 months, or even longer. This is the outstanding advantage of Zigbee. In comparison, Bluetooth can work for several weeks and WiFi can work for several hours.
② Low cost
By greatly simplifying the protocol (less than 1/10 of Bluetooth), the requirements for the communication controller are reduced. According to the predictive analysis, the 8051 8-bit microcontrollers are used to calculate, the full-featured master node requires 32KB of code, and there are fewer sub-function nodes. Up to 4KB code and Zigbee are free of protocol patent fees. The price of each chip is approximately US$2.
③ Low speed
④ Close range
The transmission range is generally between 10 and 100m. After increasing the RF transmission power, it can also be increased to 1 to 3km. This refers to the distance between adjacent nodes. If through the relay of routing and communication between nodes, the transmission distance will be farther.
⑤ Short-time delay
Zigbee’s response speed is relatively fast. Generally, it only takes 15ms to switch from sleep to working state, and it only takes 30ms for nodes to connect to the network, which further saves power. In comparison, Bluetooth requires 3-10s, and WiFi requires 3s.
⑥ High capacity
Zigbee can adopt star-shaped, sheet-shaped, and mesh network structures. A master node can manage several sub-nodes, and at most one master node can manage 254 sub-nodes; at the same time, the master node can also be managed by the upper network node, which can form up to 65,000 A large network of nodes.
⑦ High security
Zigbee provides a three-level security mode, including no security settings, the use of access control lists (ACL) to prevent illegal access to data, and the use of advanced encryption standards (AES 128) symmetric passwords to flexibly determine its security attributes.
⑧ License-free frequency band
Use direct sequence spread spectrum in the Industrial Scientific Medical (ISM) frequency band, 2.4 GHz (global), 915 MHz (US), and 868 MHz (Europe).
The development of Zigbee
Zigbee is similar to Bluetooth. It is an emerging short-range wireless technology for sensor and control applications.
This idea was put forward in the IEEE 802.15 working group, so the TG4 working group was established and the standard IEEE 802.15.4 was formulated.
In 2002, the Zigbee alliance was established.
In 2004, Zigbee V1.0 was born. It was the first specification of Zigbee. However, due to the hasty launch, there were some errors.
In 2006, Zigbee 2006 was launched, which is relatively complete.
At the end of 2007, Zigbee 2007 was launched, and some new features appeared.
Zigbee technical characteristics
The underlying technology of Zigbee is based on IEEE 802.15.4.
The physical layer and MAC layer directly reference IEEE 802.15.4.
Three frequency bands of Zigbee
1) 868MHZ transmission rate is 20KB/S suitable for Europe
2) 915MHZ transmission rate is 40KB/S applicable to the United States
3) 2.4GHZ transmission rate is 250KB/S universal
Since the physical layers of these three frequency bands are not the same, their respective channel bandwidths are also different, respectively 0.6MHZ, 2MHZ, and 5MHZ. There are 1 10 and 16 channels respectively. The spread spectrum and modulation methods of different frequency bands are different. Although Both use the direct spread spectrum (DSSS) method, the conversion method from bit to the chip is quite different.
The modulation method uses phase modulation technology, but the 868MHZ and 915MHZ frequency bands use BPSK while the 2.4GHZ frequency band uses When OQPSK has a transmit power of 0dBm, Bluetooth can usually use a range of 10M. The Zigbee based on IEEE 802.15.4 can usually reach a range of 30-50 meters indoors. Outdoors, if there are few obstacles, can even be used. Reaching a range of 100 meters. So Zigbee can be classified as a low-speed short-range wireless communication technology.
Zigbee performance analysis
1. The data rate is relatively low
In the 2.4GHZ frequency band, it is the only 250KB/S, and it is only the rate on the link. After removing the frame header overhead, channel competition response, and retransmission, the rate that can be actually utilized by the application may be less than 100KB/S, and the remaining rate maybe It is divided by multiple neighboring nodes and multiple applications on the same node. Therefore, it is not suitable for things like video.
Suitable application areas–sensing and control
2. Reliability
In terms of reliability, Zigbee has many aspects to guarantee. The physical layer uses spread spectrum technology, which can resist interference to a certain extent.
MAC used to have a response retransmission function at the application layer (APS part).
The CSMA mechanism of the MAC layer allows the node to monitor the channel before sending, which can play a role in avoiding interference.
When the ZigBee network is interfered with by the outside world and cannot work normally, the entire network can be dynamically switched to another working channel.
3. Delay
Since Zigbee uses random access to the MAC layer and does not support the channel access method of time-division multiplexing, it cannot support some real-time services well.
4. Energy consumption characteristics
Energy consumption characteristics are a technical advantage of Zigbee. Usually, the application data rate carried by the Zigbee node is relatively low. When no communication is required, the node can enter a low-power sleep state.
At this time, the energy consumption may only be one-thousandth of the normal working state. , Sleep time accounts for most of the total running time, and sometimes the normal working time is less than one percent, so it achieves a high energy-saving effect.
5. Networking and routing-characteristics of the network layer
Zigbee’s large-scale networking capability: 60000 nodes per network
Bluetooth: Each network has 8 nodes.
Because the bottom layer of Zigbee uses direct expansion technology, if the non-beacon mode is adopted, the network can be expanded greatly, because there is no need to synchronize and the process of nodes joining the network and rejoining the network is very fast, generally within 1 second, or even faster. And Bluetooth usually takes 3 seconds.
In terms of routing, Zigbee supports the routing of a highly reliable mesh network, so it can deploy a wide range of networks and supports multicast and broadcast features, which can bring strong support to rich applications.
What are the Zigbee applications?
Zigbee is an IEEE 802.15.4-based specification for a suite of high-level communication protocols used to create personal area networks with small, low-power digital radios, such as for home automation, medical device data collection, and other low-power low-bandwidth needs, designed for small-scale projects which need wireless connection. Hence, Zigbee is a low-power, low data rate, and close proximity (i.e., personal area) wireless ad hoc network.
Its application areas mainly include the following.
Home and building network: Temperature control of the air-conditioning system, automatic control of lighting, automatic control of curtains, gas metering control, remote control of household appliances, etc.;
Industrial control: Automatic control of various monitors and sensors;
business: Smart tags, etc.;
Public places: Smoke detectors, etc.;
Agricultural control: Collect various soil information and climate information;
Medical treatment: Emergency pagers and medical sensors for the elderly and people with reduced mobility.