ZIGBEE is a wireless technology developed as an open global standard to address the needs of low-cost, low-power, wireless sensor networks. The standard takes full advantage of the IEEE 802.15.4 physical radio specification and operates in unlicensed bands worldwide at the following frequencies: 2.400-2.484 GHz, 902-928 MHz and 868.0-868.6 MHz.
The 802.15.4 specification, developed at the Institute of Electrical and Electronics Engineers (IEEE), is a packet-based radio protocol. The protocol allows devices to intercommunicate and be powered by batteries that last for years instead of hours.
The ZigBee protocol carries all the benefits of the 802.15.4 protocol with added networking functionality.
The protocol was engineered by the ZigBee Alliance, a non-profit consortium of leading semiconductor manufacturers, technology providers, OEMs and end-users worldwide. The protocol was designed to provide OEMs and integrators with an easy-to-use wireless data solution characterised by low-power consumption, support for multiple network structures and secure connections.
Also, the protocol was designed to carry data through the hostile RF environments that routinely exist in commercial and industrial applications.
The protocol features: low duty cycle (provides long battery life); low latency; support for multiple network topologies (static, dynamic, star and mesh); Direct Sequence Spread Spectrum (DSSS); up to 65,000 nodes on a network; 128-bit AES encryption (provides secure connections between devices); collision avoidance; link quality indication; clear channel assessment; retries and acknowledgements; and support for guaranteed time slots and packet freshness.
The ZigBee specification’s security toolbox approach ensures reliable and secure networks. Access control lists, packet freshness timers and 128-bit encryption based on the NIST Certified Advanced Encryption Standard (AES) help protect transmitted data.
ZIGBEE enables the broad-based deployment of wireless networks that can run for years on inexpensive batteries for monitoring applications such as lighting controls, AMR (automatic meter reading), smoke and CO detectors, wireless telemetry, HVAC control, heating control and environmental control.
Here’s an example: It’s 4 a.m. on a farm. Sensors in the fields report the moisture content in the soil and humidity in the air. Farm personnel use this data to decide where and when to water for optimum effect. The information also serves as an early warning system for environmental issues, such as frost. Precious resources are used more efficiently and productivity increases. The sensors in the field are interconnected in a “mesh” network. If a sensor node goes down, the network is self-healing; the nodes are able to connect with one another dynamically, finding another route to stay connected within the network.
A key component of the ZigBee protocol is the ability to support mesh networks.
In a mesh network, nodes are interconnected with other nodes so that at least two pathways connect each node. Connections between nodes are dynamically updated and optimised in difficult conditions. In some cases, a partial mesh network is established with some of the nodes only connected to one other node.
Mesh networks are decentralised in nature: each node is self-routing and able to connect to other nodes as needed. The characteristics of mesh topology and ad-hoc routing provide greater stability in changing conditions or failure at single nodes.
A member of the ZigBee Alliance, MaxStream has developed OEM solutions based on the ZigBee architecture. These comprise the XBee and XBee-Pro modules.
Their features include a small form factor, plug-and-communicate wireless capability, suitability for low cost, low data rate applications, long battery life, robust security, high data reliability, and product interoperability (modules are interchangeable and pin-for-pin compatible with each other). The communications range of XBee-Pro modules is up to 1,200 metres. XBee standard modules communicate at up to 300 metres.
* Commentary by Conlab