Dusting Off ZigBee
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So-called "smart dust" networking has not yet hit the mainstream, but it is coming soon, and it could have big implications for the Wi-Fi community.
The term refers to tiny sensors, perhaps as small as one cubic millimeter. They would be scattered over an industrial space, for example, and would form an ad hoc wireless network to report back on conditions such as temperature or pressure in a production facility. They might be rigged up across a person's chest to monitor heart rate and blood pressure. The various possibilities are only just being discussed.
The nodes would be easy to deploy. They would report back to a central hub via IEEE's 802.15.4 wireless personal area network (WPAN) protocol-- also known as ZigBee. ZigBee will be a standard for extremely low power wireless used for monitoring and control.
While the setup may sound familiar -- small independent nodes reporting to a central hub -- experts say smart dust will not give Wi-Fi a run for its money. Rather, the two networking paradigms likely will complement each other, once the researchers have finished their work and brought smart dust to the mass market.
In the first place, early iterations of smart dust won't allow for heavy lifting. The microscopic chips will be used mainly as to gather and relay minute quantities of information, as compared to Wi-Fi's more robust data capacity. The cheaper and more pervasive dust network might therefore pass on its findings to a Wi-Fi network, which could gather together data from multiple points as pass it on as a whole.
"You have the sensor network at one end, and that network talks to your devices. Then the sensors connects it to a gateway which then will connect it to Wi-Fi. They all will coexist," predicts Sokwoo Rhee, chief technical officer at Millennial Net, a maker of wireless sensor networks.
For a concrete example, consider an industrial scenario:
"Let's say you are doing electric motor monitoring," says Peter Stein, vice president of marketing and business development at Sensicast Systems, which develops products in support of dust-type networks. "You can collect the low-bandwidth data from a dozen wireless sensors on a plant floor, and then all you need is a gateway that converts [that data] from 802.15.4 to the 802.11 standard. That way you can take the data from your battery-powered sensors with a limited life and pass it on to the Wi-Fi device, which is already powered."
This issue of power is one that plagues smart dust developers. It's one of the prime concerns that has so far keep these miniature networking devices out of the mainstream market.
With hundreds of devices at play in any given situation, it will be impractical to try and change every few weeks. How, then, to juice up the network? There are several ideas on the table. One is to make the devices slightly bigger, maybe the size of the thumbnail, and then to power them with a watch-battery sized power source. At low output levels such a setup could last as long as 10 years without a battery change.
At the University of Glasgow , Professor Iain Thayne is striving for a mix of optical and radio connectivity in order to minimize battery consumption. At Philips Research, researchers in the Small Autonomous Network Devices (SANDs) project are working on systems that will power themselves through ambient energy: Feeding batteries with light outdoors, or through vibration energy in an industrial setting. (Philips dedication to ZigBee, after an early push of support, might be wavering according to recent reports.)
Assuming the power problem will be solved eventually, radio interference would seem to be another issue in the realm of dust-to-Wi-Fi connectivity. While network administrators may point to this as an obvious stumbling block, dust researchers say the problem has already been solved. Both systems will operate at 2.4 GHz, Stein explained, but they will utilize different areas within the band.
Thus, in theory, dust networks and Wi-Fi connectivity will be able to live together in happy coexistence, each one adding value to the other by extending the range and capabilities of the overall system.
"The Wi-Fi standard is going for higher and higher data bits per dollar, whereas the wireless sensor networks are really focused on low bandwidth, low power consumption and low cost," Stein says.
"If you look at the flexibility that 802.11 has given people, this is really just going that step further, in that the whole computational activity becomes distributed as well," says Prof. Thayne.