Wireless sensor networks looking to Zigbee Alliance

Imagine a golf course that can sense rainfall, and adjust the automatic sprinkler system to delay a scheduled watering session or focus on parts of the course that didn't get as much rain as others. Or a hotel that can detect when a room is vacant, and turn off the heating or cooling systems in that room to save energy.

Later this year, vendors will start releasing products based on a wireless standard called Zigbee that enable these types of sensor networks. The Zigbee Alliance plans to certify products with a Zigbee logo to ensure that products from different vendors are interoperable and easy to manage, said Bob Heile, chairman of the Zigbee Alliance, at a briefing for reporters and analysts at the Zigbee Alliance Member Meeting in Boston Wednesday.

Zigbee is a set of networking, security and application software standards that sits atop the 802.15.4 low-data wireless standard approved by the Institute of Electrical and Electronics Engineers. Unlike other wireless standards such as 802.11 or 802.16, Zigbee and 802.15.4 are designed to carry limited amounts of data at a maximum rate of 250K bps (bits per second), Heile said.

Backers of the technology take great pains to avoid overselling Zigbee as a wireless panacea, but many think the technology can find a home as a replacement for wiring that connects electrical system controllers or passive asset management tags.

Zigbee will allow users to construct mesh networks that can send data back to a central repository, respond to changes in their environment and monitor themselves for failures or redundancies, said Jon Adams, director of radio technology and strategy at Freescale Semiconductor Inc.

Other popular wireless standards are overkill for the types of applications envisioned by Zigbee supporters. Wi-Fi and Bluetooth use far more power than a Zigbee radio would consume, Heile said. The Zigbee Alliance thinks radios built with the standard should be able to operate on standard household batteries for years, he said.

Wi-Fi and Bluetooth chips are also much too expensive to justify setting up the large networks that would allow some of these applications to work, said Jack Gold, an industry analyst with Meta Group Inc. Semiconductor makers, such as Freescale, will have to produce chips that cost less than US$1 to convince companies that there is a need for this type of information.

After addressing the cost issues, Zigbee products should be an easy sell to any factory or distribution outlet that wants to assimilate as much information as possible, said Glen Allmendinger, president of Harbor Research Inc.

Most businesses develop operations or capacity plans using historical data that only presents users with a sense of what has happened in the past, Allmendinger said. Sensor networks would allow companies to gather data as it happens, and therefore predict where problems might occur, he said.

For example, a Zigbee tag could be placed on a pallet of chocolate bars and provide more data than whether that pallet arrived at its destination, Adams said. These tags could tell the chocolate manufacturer whether the temperature around that pallet has risen steadily for the past hour because it was left on a runway in the sun. Armed with that data, the manufacturer could call the airport and have that pallet moved before its merchandise melted away.

Some companies are starting to experiment with passive RFID (radio frequency identification) tags that do little more than store a unique identification number. Zigbee radios hold some promise as active RFID tags that can sense more complicated information and distribute that information on its own, said Ian McPherson, president of the Wireless Data Research Group.

"(Zigbee products) are not meant to replace passive RFID, but they can change the economics of active RFID by using more sensors and less gateways," McPherson said. Right now, even passive RFID tags are too expensive for most companies to consider implementing, but costs are expected to come down over the next few years, he said.

Despite Zigbee's promise, the technology will face hurdles as users try to scale their networks to massive sizes, McPherson said. Mesh networks are an emerging technology that users are still evaluating and troubleshooting, he said. The technology will probably be used on less-important applications until users get comfortable with the technology, he said.

Freescale will introduce Zigbee-based products in the fourth quarter, Adams said. The company is a promoter of the Zigbee Alliance along with companies such as Samsung Electronics Co. Ltd., Honeywell International Inc., Ember Corp., Koninklijke Philips Electronics NV, Mitsubishi Electric Corp. and Invensys PLC.

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