Science and technology
Zigbee: for the interconnection of smart home
Wireless Internet of Things technology can be differentiated in different ways, mainly by communication distance, such as 5G, eMTC, NB-IoT, LoRa, WiFi, Bluetooth and Zigbee, and also by network topology, such as point-to-point network Bluetooth Classic, star network W Classic. IFi; and network Zigbee, Thread and so on; there are also power consumption, transmission rate and so on.
The scenario of smart home requires a system: an "end" consisting of smart devices; a "management" that connects devices to home networks by wired and wireless technologies, and a "management" that connects home networks to the Internet; and a local control center that implements basic application and service scenarios, and even further deepens and enriches them. Use the "cloud" platform of the scene. And all kinds of wireless technology are mainly used in the interconnection and interoperability between devices. Familiar smart home scenarios include home security, intelligent lighting, environmental control, video entertainment and so on. The smart home field is realized by collecting environmental and arbitrary information through many sensors, and then processing the information through preset logic or advanced in-depth learning and artificial intelligence. The basic mechanism of scenery. Zigbee is particularly suitable for building the sensor control network for smart home, mainly in:
Multi-node mesh network: Typical smart home environments often require 50-100 devices. A single Zigbee network can connect hundreds to hundreds of devices, and self-repairing mesh network can ensure that network communication is not affected even when some nodes fail.
Appropriate transmission distance: indoor single-hop transmission distance is 75-100 meters, through the network routing mechanism can easily cover hundreds of meters, to meet the needs of smart home;
Various types of equipment: Different from industrial and commercial applications, smart home involves a variety of devices, and Zigbee stack standard defines more than 40 types of equipment, involving lighting, security, heating, closure and other categories, to meet family needs;
Low power consumption: A great advantage of wireless network is that it can save wiring costs and facilitate the installation of battery power supply equipment in various locations. Low power network can prolong battery life and reduce maintenance costs. Zigbee has a Green Power feature, which allows sensors and switching devices that do not need to change batteries or batteries to join the network without maintenance.
Mature Open Standard, Global Market: Zigbee uses the 2.4 GHz band without authorization, and the standard has been around for more than a decade. After many iterations, Zigbee has been tested by hundreds of millions of devices deployed around the world. Through the testing and certification process, we have created an ecological circle with multiple suppliers (including famous brand enterprises and many start-ups) in all links, which provides a good market environment for reducing costs and promoting innovation.
What's the problem with Zigbee's ad hoc network? Why do we communicate in this way?
First, jump out of Zigbee and talk about why ad hoc networks are needed.
Ad hoc networks are not a "happy" technology. Compared with peer-to-peer networks, ad hoc networks add a lot of communication mechanisms and management work, such as equipment networking, off-network, parameter allocation, node management, path selection, path recovery and so on. These operations are not needed in point-to-point communication. But why develop such a complex mesh protocol? The reason is the contradiction between low power consumption and large network.
The power requirements of Internet of Things devices are extremely stringent, and the scale of applications is often very large (think of sensors deployed on a large scale). Low power consumption inevitably limits the transmission power of the device, thereby limiting the effective propagation distance of RF; and large-scale applications usually mean huge geographic space and huge number of devices. How can small energy devices work properly in large networks? We (have to) choose to implement mesh networks. It can be said that mesh network is a helpless move of "short arm, large network", and it is an inevitable choice for any low-power communication to enter the application of the Internet of Things. Zigbee and Thread are born like this, and BLE mesh is an example of adaptive evolution.
Zigbee devices can be divided into three types: terminal devices, routers and coordinators, and two security models: centralized networks with coordinators (trust centers) and distributed networks with only routers and terminal devices. The Zigbee device supports both modes. When the Zigbee network is not found, the router or coordinator device can form a network to generate routing by itself or automatically identify the network mode when the Zigbee network already exists and join the network.
First of all, mesh network can expand the network coverage area under the condition of low power consumption. Through routing mechanism, devices can communicate with devices that are not in their communication range. Secondly, it can increase the stability of the network, i.e. self-repairing function. When a node is moved or powered off, it can not communicate. It can be updated automatically without affecting the communication of other nodes.
Why is Zigbee better than Wi-Fi and Bluetooth?
Zigbee includes carrier monitoring multiple access (CSMA-CA) protocol defined by IEEE 802.15.4 and direct sequence spread spectrum technology (DSSS), including conflict avoidance, receiving energy detection, link quality indication, idle channel evaluation, message confirmation, security, support guarantee slot mode and data packet timeliness, which can reduce interference to other users. In addition, Zigbee also uses automatic data re-transmission to ensure the robustness of the network.