October 25, 2012 by Nakul
Author: Srijana K
ZigBee is a low-power wireless technology designed to interact with remote controlled devices, which are put under a single standardized control interface that can interconnect a network .Once associated with a network, a ZigBee node can wake up and communicate with other ZigBee devices and return to sleep.
Zigbee’s key technical features include three license free frequency bands-2.4GHz, 868MHz, 915MHz; multiple channels; up to 100mts range; CSMA-CA channel access; low power, long battery life; supporting up to 255 devices per network.
Zigbee is used in home security systems where wireless sensors are easily installed than sensors that need wiring. The same is true in industrial environments, where wiring typically accounts for 80% of the cost of sensor installations. And then there are applications for sensors where wiring isn’t practical or even possible. ZigBee promises to put wireless sensors in everything from factory automation systems to home security systems to consumer electronics.
The network name comes from the zigzagging path a bee (a data packet) takes to get from flower to flower (or node to node). The technique that honey bees use to communicate new-found food sources to other members of the colony is referred to as the ZigBee Principle. Using this silent, but powerful communication system, whereby the bee dances in a zigzag pattern, they are able to share information such as the location, distance, and direction of a newly discovered food source to her fellow colony members.
The various features which make it reliable are:
- Low cost — Extends wireless to virtually any sensor
- Low power consumption — Ideal for battery operation
- Small size, light weight — Easy to integrate
- Ease of implementation
- Reliable data transfer
- Appropriate levels of security
- Direct sequence spread spectrum — Fast acquisition time
- Range- 50m typical (5-500m based on environment)
- Multiple topologies- star, peer-to-peer, mesh
- Data rates of 250 kbps (@2.4 GHz), 40 kbps (@ 915 MHz), and 20 kbps (@868 MHz)
A ZigBee network can have three types of nodes: Zigbee Coordinator (ZBC), Zigbee router (ZBR) and Zigbee End Device (ZBE) each having some unique property. ZigBee Network Coordinator is a smart node that automatically initiates the formation of the network. ZigBee Router isanother smart node that links groups together and provides multi-hoping for messages. It associates with other routers and end-devices. ZigBee EndDevices is where the rubber hits the road—sensors, actuators, monitors, switches and dimmers.
Zigbee’s self-forming and self-healing mesh-network architecture lets data and control messages pass from one node to another by multiple paths. This feature extends the network range and improves data reliability. It may also be used to build large, geographically dispersed networks with smaller networks linked to form a ‘cluster-tree’ network.
The NWK layer supports multiple network topologies including star, cluster tree, and mesh, all of which are shown in Figure above.
In a star topology, one of the FFD-type devices assumes the role of network coordinator and is responsible for initiating and maintaining the devices on the network. All other devices, known as end devices, directly communicate with the coordinator. In a mesh topology, the ZigBee coordinator is responsible for starting the network and for choosing key network parameters, but the network may be extended through the use of ZigBee routers. The routing algorithm uses a request-response protocol to eliminate sub-optimal routing. Ultimate network size can reach 264 nodes (more than we’ll probably need). Using local addressing, you can configure simple networks of more than 65,000 (216) nodes, thereby reducing address overhead.
An example where Zigbee can be used is in a home automation system. There can be only one ZBC in a network, the one that initiates the network in the first place and stores the information about the network. This would be the main control panel or remote control in the living room of each storey. All the devices in the network communicate with this ZBC. It has routing capabilities and acts as a bridge to other networks on other floors. A ZBR is an optional component used to extend the coverage, say, providing access to the Zigbee receivers controlling the garage lighting and shutter which is in the nearby shed. The router itself may host an application like a CC Camera which is continuously in active monitoring state. It can also handle local address allocation or de-allocation. A ZBE is optimized for low power consumption and is the cheapest among the three node types. It communicates only with the coordinator and is the point where sensors are deployed. Any end device like lighting units, air conditioning elements etc. can be Zigbee End Devices. When a car enters the premises, the radio transmitter inside the car broadcasts its presence to the Zigbee Coordinator through routers. The coordinator then binds the garage shutter’s receiver with the Car’s transmitter and all packets from the Car transmitter are routed to the Shutter, which can then open and close without stepping out of the car. The whole transaction can be automated such that by the time the car reaches the garage door, it automatically opens.
Zigbee promises to put wireless sensors in everything from factory automation systems to home security systems to consumer electronics. Zigbee is a new standard that still needs to pass through the circles or rigorous technology critics and establish its own place in the industry.