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As an open international standard, ZigBee is a wireless communication technology developed to meet the unique needs of low-cost and low-power wireless sensor networks. This standard has absorbed all the advantages of the IEEE 802.15.4 radio specification and can work in different frequency ranges without a license around the world. ZigBee wireless mesh networks (ZigBee-WMNs) are recognized as an economical and flexible solution for building automation and control systems. They may unify the data communication methods of sensors, actuators, home appliances, and asset tracking devices. They provided a set of solutions to build a reliable, reasonably priced, and can support low data rate and low duty cycle battery-powered equipment backbone network to facilitate building automation and control systems (BACs).
1. Application of wireless network in building automation
A wireless sensor network can be defined as a network composed of sensor nodes, which covers a wide range and provides regional environmental information monitored by wireless communication protocols. It can be used in many fields, including healthcare, environmental monitoring, home automation, and military industries. Wireless sensor networks have greater market potential due to their ease of installation and low cost. Building automation and control systems (BACs) are characterized by a large number of sensors and controlled objects distributed in the building. Figure 1 shows some of the subsystems included in BACs, such as heating, ventilation and air conditioning (HVAC), lighting, electricity, hot water, fire fighting, access control, closed-circuit monitoring, and public address systems.
The connection of the wireless sensor eliminates the related costs of hard wiring. An additional benefit is that it reduces obstacles from residents and facilities in the renovation project. Compared with the sensor installed in an easy-to-wire position, the wireless sensor can be installed where it is really needed to optimize the performance and keep the match on the same floor plan.A large number of documents have recorded the use of wireless technology in buildings[3-8].Early research[10]An overview of how the wireless network supports the wireless communication of field devices, such as the use of room or area controllers and related temperature sensors in different places, such as schools, hospitals and universities, etc.
Figure 1 Structure of building automation and control system
The wireless sensor network opened a new chapter in its application in BACs. Compared with wired networks, wireless sensing systems in BACs will be more convenient and faster, with lower risks and costs. It can integrate lighting, air-conditioning, security, security systems and other monitoring networks into a single platform, reduce the energy consumption of air-conditioning through optimized management, distribute public utility expenses fairly according to actual consumption, reconfigure the lighting system with minimal effort, and establish self-consumption Adapt to the work area and expandable and upgradeable construction infrastructure. Many organizations can reduce wasted lighting and heating expenditures by 50% by installing wireless control networks in a wide range.
2. Application advantages of Zigbee
ZigBee wireless mesh networks (ZigBee-WMNs) are self-organizing, self-repairing and easy to maintain networks. Each device in the network contains a microcontroller router, allowing the network to be reconfigured or expanded. If the device loses contact with the neighboring node, the self-healing performance of the network allows the node to find other nodes that can establish communication. This feature helps to improve the reliability of the network.
ZigBee technology is a wireless communication protocol based on IEEE (Institute of Electrical and Electronics Engineers) 802.15.4. It is a short-distance, low-power protocol, especially suitable for design and application in small building automation In equipment, such as automatic temperature adjustment devices, lighting control equipment, environmental sensors, etc. ZigBee technology can provide short-distance, low-speed data transmission with low power consumption. ZigBee wireless sensors using ordinary dry batteries can continue to operate for 2 to 3 years.
In addition, the excellent networking capabilities of ZigBee technology make it particularly incomparable compared with other wireless communication technologies in the application of building automation systems.
3 ZigBee technical analysis
ZigBee technology is developed and promoted by a group between enterprises-the ZigBee Alliance (ZigBee Alliance). The ZigBee Alliance is sponsored by seven internationally renowned companies including Honeywell, Invensys, Mitsubishi Electric, Samsung, Motorola, Philips and Ember. As of 2004 In November 2011, the alliance has participated in more than 100 corporate members, all of which have significant influence in the industry.
ZigBee technology is based on IEEE802.15.4 standard technology. IEEE802.15.4 is a wireless network standard that supports low power consumption and low data transmission rate. It is mainly designed for remote monitoring and control applications. In May 2003, the IEEE802.15.4 standard was formally approved. IEEE802.15.4 is a simple but very powerful data packet protocol. It uses confirmation, error detection, prioritized communication, and DSSS (Direct Sequence Spread Spectrum-direct sequence spread spectrum technology). It has the ability to change the frequency to eliminate interference. Capability) and the user’s choice of security level and other technologies to provide high reliability of wireless communication. The IEEE802.15.4 standard also only specifies the physical layer and medium access sublayer in the open system interconnection reference model. The physical layer defines three permitted frequency bands. They are 2.4GHz (the highest transmission rate is 250kbps), 915MHz ( The highest transmission rate is 40kbps) and 868MHz (the highest transmission rate is 20kbps).
ZigBee technology adds network layer, security layer and application profile layer (Application Profiles) on the basis defined by IEEE802.15.4. ZigBee supports star, mesh and tree cluster network topologies. There can be up to 65,535 nodes in each ZigBee network, and the address of each node is allocated by the ZigBee Network Coordinator. In addition, the transmission range of each node is between 30 and 100m, and the transmission distance can also be extended by using power amplifiers and multi-hop mesh network structures.
ZigBee technology has broad development and application prospects in the field of building automation. First of all, ZigBee technology is a low-cost, low-power wireless solution. Wireless sensors using ZigBee technology can work for 2 to 3 years using ordinary dry batteries. , And the price of the ZigBee chip will be reduced to about US$2 within 1 to 2 years; secondly, ZigBee technology supports the mesh network structure, which makes the ZigBee network self-organizing and self-repairing, and improves the reliability of the network; Third, the ZigBee network supports a large number of nodes, which is very important for occasions that require a large number of sensors and controllers in a large-scale building automation system.
4. The application prospects of ZigBee technology in the field of building automation
According to ABI Research[1]Forecast: Products with built-in ZigBee wireless devices will grow from 1 million units in 2005 to 80 million units in 2006. The huge room for development of ZigBee lies in its obvious technical advantages and clear market positioning. At present, international experts in building automation have basically reached a consensus that the application of wireless communication technology in building automation will be unstoppable. The wireless network will not only be a beneficial supplement and expansion to the wired network, but may be a substitute.
In a building automation system using ZigBee technology, the wireless network framework is a mesh structure. A certain number of ZigBee router nodes can cover the entire building interior area, and the more nodes there are, the more reliable the system will be. In addition, since the mesh network structure has the function of self-configuration, it is very convenient when adding new nodes or re-arranging nodes. The edge of the wireless network is a star structure. A large number of sensors or actuators with built-in ZigBee wireless devices are connected to the network. These sensors can work for 2 to 3 years using ordinary dry batteries. Although ZigBee technology has unparalleled advantages, its application in building automation still faces the problem of fusion with international standardized communication protocols such as BACnet, LonTalk, and EIB, which mainly use wired networks. At present, building control systems that use these communication protocols The products are very mature and occupy a leading position in the building control field. The simpler way to integrate ZigBee technology is to establish related gateways between the ZigBee network and these heterogeneous networks as a bridge between them, then ZigBee will be a useful supplement to these wired networks, and then the entire building automation system will appear wireless and wired The situation of network coexistence, so as to obtain higher economic benefits. A more complete approach is to establish a complete set of wireless communication protocols suitable for building automation similar to BACnet and LonTalk communication protocols on the basis of ZigBee technology. In this case, ZigBee will be able to keep pace with these communication protocols, and it is possible Eventually replace these communication protocols that mainly use wired networks.
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