Questions, dissent mark new stage in wireless sensing

The starry-eyed have given way to the hard-eyed at this year's Wireless Sensing Solutions Conference.

Questions from attendees, mainly systems integrators and software developers, are more pointed, more skeptical and more demanding than last year. Faced with extravagant promises about the benefits of sensors married to low-power wireless mesh networks, they want to know about security, management, interference, reliability and total cost of ownership.

A wireless sensor mesh project being studied for Ronald Reagan Airport in Washington, D.C., was outlined in one session by Srini Krishnamurthy, vice president of business development for Airbee Wireless. Every door in the airport could be outfitted with 900 MHz wireless sensors and automated locks, networked to a central point where rules could be set for when the door could be opened, by whom, by time of day, without the need for guards to be stationed.

But that simply raised more questions for Samuel Reed, an electrical engineer with Key Technologies, a Baltimore, Md., engineering design company that works with sensors and various kinds of wireless nets. "Can a terrorist walk in to the airport with a 900 MHz jammer and shut the whole place down?" he wonders.

Another attendee wanted to know how many products had actually shipped with the ZigBee Alliance's mesh networking software stack. "There are some prototype projects with 100 to 150 nodes," said William Craig, program manager for wireless communications at ZMD America. "But you can't point to a [ZigBee] thermostat today." He said ZigBee-based products will start to hit the market late in 2005.

Another questioner wanted to know whether large-scale wireless mesh nets could overwhelm the available RF spectrum. None of the speakers answered with an unqualified "No." They did point out that the ZigBee specification and the underlying IEEE 802.15.4 radio standard had various features to avoid collisions and find open channels; and that sensors could be set to transmit only occasionally, and when they do transmit send only small amounts of data.

At the same time, the fledging industry itself is facing dissension over the still emerging specifications. The IEEE 802.15.4 standard defines, in effect, the basic radio for a low-power wireless mesh, the media access control layer and the physical layer. The ZigBee Alliance, a group of start-ups, integrators and manufacturers, has crafted higher level specifications for security and networking, as well as a set of application level profiles, which are sort of like outlines for programmers.

But in several conference sessions, even vendors made it clear they were not wedded to Zigbee or even 802.15.4. "The most important thing is to come up with applications that work, to validate the [wireless sensing] technology," says Mark Goodman, director of sales, for Crossbow Technology, which offers the Smart Dust wireless sensors. "Sometimes that's [using] Zigbee and 802.14.5 and sometimes it's not."

"Today, most protocol stacks are proprietary [software] over 802.15.4 radios," says Bernd Grohmann, vice president of alliances for Zensys, a German company that has launched its own Z-Wave wireless mesh protocol through the Z-Wave Alliance. The company says over a hundred manufacturers, including Honeywell and Leviton, are incorporating Z-Wave into various products for home and building control applications.

And one group of enterprising Canadian engineers, Newtrax Technologies, showed up this year to promote a complete alternative to both Zigbee and 802.14.5: a frequency hopping spread spectrum radio, and a mesh software stack that extends even to the sensors themselves. Together, the Canadians say, the result is better range, greater resistance to interference, and higher reliability.

Key Technologies' Samuel Reed says he was impressed by the capabilities outlined for ZigBee networks. "But it's the Cadillac," he says. "For something simple, there are lots of other alternatives that are cheaper and simpler."

"If you're not doing a network, there are lots of alternatives out there," says Airbee's Krishnamurthy. "[But] if you're doing a network, then ZigBee is key."

Now all Krishnamurthy has to do is convince a whole lot of people like Reed.

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