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ZigBee an RF wireless signal is desperatly trying to bome the backbone of the connected home up against a lot of traditional wireless technology.

  Many in the Zibee alliance believe that Zigbee has the potential to out-sell Ethernet in the home, however I believe that this is wishful thinking as Ethernet is a very mature technology. In addition there are several other Wireless options.

The ZigBee Alliance – consisting of more than 68 members – has recently defined the ZigBee standard for wireless communication. It’s based on the IEEE 802.15.4 standard, and is for low-data-rate communication in the 2.4GHz spectrum. It’s expected that ZigBee will be used in a wide range of everyday devices with embedded wireless technology, as well as for medical instruments, industrial sensors and building automation. ZigBee is specifically for large networks of low-cost, low-power, short range devices, connected in a mesh or star network that is self-organising and self-healing. It’s optimised for timing-critical applications, with fast network join times, and includes a “sleep” mode for devices to encourage minimal power usage. ZigBee is set to replace proprietary designs and become widely used in sensor networks, encouraging interoperability between different manufacturer’s products and thereby widening the market.

ZigBee and Ethernet

It’s taken thirty years for Ethernet to reach the volume shipments we see today, but ZigBee has the potential to overtake it within a year, according to Bob Metcalfe, inventor of the Ethernet, and now chairman of Ember (a member of the ZigBee alliance). Metcalfe noted that just 2% of the eight billion embedded microprocessor shipments a year are currently networked, highlighting what Ember thinks is a huge market opportunity. The distributed nature and openness of Ethernet helped it beat competing technologies – vendors who originally used Ethernet to improve their own product performance found that interoperability with other vendor’s equipment opened up larger markets, and Metcalfe thinks the same kind of model will be true for ZigBee.

ZigBee itself is a platform adding logical network, security and application software to a powerful physical radio standard specified by IEEE 802.15.4. A ZigBee network has enough addresses to support 65,000 nodes (but using the full MAC address, it would be possible in theory to have 264). Mesh or star configurations are possible, along with combinations of the two, allowing more robust networks since mesh topologies are more resistant to broken links and topology changes. Self-organising and self-healing technology means that ZigBee networks should be essentially plug-and-play – they won’t need configuring by the user and can adapt to network changes automatically.

A ZigBee network may contain a device that acts as a controller or co-ordinator, along with full-function devices and reduced-function devices.Full-function devices are always on and will maintain a “backbone” through a mesh network, even when all the reduced-function (power-saving) devices are in “sleep” mode.

Typical network joining times are of the order of 30ms, with a channel access time of 15ms. Typically it might take 15ms for a node to emerge from “sleep” mode.The “sleep” mode and the very low duty cycle of active nodes, typically as low as 0.1%, will ensure extensive battery life. The low duty cycle also reduces the chances of overcrowding the assigned frequency band (868MHz in Europe).

ZigBee and Bluetooth

The idea is for ZigBee to be complementary to Bluetooth, the wireless standard for replacing cables between laptops, PDAs, mobile phones and the like. ZigBee addresses different product requirements – it’s for low-cost, low power wireless devices, such as remote controls.

Bluetooth devices are usually power-hungry and expect regular recharging, but ZigBee devices will rarely need new batteries and will be optimised for mostly static devices that are used infrequently, like monitoring or control sensors. Where Bluetooth sends large packets over a small network (it can support eight devices with a ten metre range at 1Mbps), ZigBee sends small packets over a large network (216 devices over a 70 metre range at a link rate of 250kbps). ZigBee is optimised for timing critical applications, with fast network-join times of 30ms versus Bluetooth’s comparatively slow join time of around 3 seconds.

Applications

Typical products using ZigBee range from home security and automation systems (lighting controls, garage door closers and numerous others), to medical sensing and monitoring applications. A multitude of sensor types for the home are available, with Ember leading the way, to enable many types of automation and control in the home – everything from “is my cellar flooded?” to “are the curtains closed?” to “have I locked the front door?”, a sector Ember is calling “home awareness”. Home Heartbeat is Eaton’s Ember-enabled scaleable technology for monitoring and controlling comfort, safety and security with sensors in the home.

It allows unobtrusive sensors to monitor and control ordinary household devices and systems – doing everything from locking the doors to shutting the curtains, from turning on the TV to opening the windows. The entire network is controlled from a key-fob device with a small LCD screen and a scrollable, clickable wheel-button. Wirelessly switching off un-needed lights in office buildings and hotels to save energy may become commonplace. Medical instruments can be made to wirelessly communicate with data logging systems and sensors worn on the patient can transmit to bedside stations and alert doctors when necessary. Ember expects that ZigBee will take longer to reach industrial sectors since it takes longer to infiltrate the lengthier industrial design cycles.
 

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