ZigBee to improve wireless mesh networks in 2007

Staff -- Control Engineering, 11/1/2006

ZigBee networks connect control nodes and target nodes wirelessly in a mesh structure. Each node communicates with its nearest neighbors, so command signals propagate across the network via multiple paths rather than directly. Should one path become unusable (because a node fails or a communication link becomes blocked), the command can reach its target via other paths. ZigBee's purpose is to provide a means of passing low-level control signals into a common "mesh" network.

The advantage of a mesh is that control signals can propagate through the net from node to node. Thus, the control point node need not have a direct link to all of the controlled nodes.

Brent Hodges, vice president marketing and business development of the ZigBee Alliance, told Control Engineering about some major enhancements to the ZigBee standard that the Alliance expects to make available during first-quarter 2007:

• Grouping devices—OEMs may create groups of devices, while allowing individual devices to belong to multiple groups. This simplifies configuring networks by allowing large groups of devices (such as all the lights on one floor of a building) to be connected to a control point with one command, rather than having to connect them individually.
• Easy maintenance—ZigBee technology prevents a single point-of-failure on the network and allows for easy replacement or repair of devices through a simple process of storing a device's information onto a nearby device. While a failed node may no longer function (that is, a certain light may not turn on), control signals have alternate paths to bypass that node, so the net as a whole functions.
• Targeted broadcasts—Broadcasts of commands can be specified for specific types of devices: routers, "awake" or "sleeping" devices. For example, a signal might turn on all of the lights in a certain group that are initially in an off state without affecting those that are already on. This feature reduces RAM requirements, lowering the total cost of the components for ZigBee products.
• Over-the-air setup—Opens the door for an array of new setup tools to facilitate adding devices to a network. The setup tools can be used to bind specific devices, such as a light fixture and a corresponding switch, and professional installers may use the tools to modify a network on a larger scale.

Enhanced ZigBee continues use of mesh networking and digital spread spectrum technology to communicate over the globally available 2.4 GHz frequency. The protocol is designed to accommodate more than 65,000 devices on one network.

www.zigbee.org