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The Wireless Lucky Number
by Geoff Mulligan
May 17, 2006

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The new 802.15.4 standard seems big enough for at least two wireless protocols and countless opportunities for improved efficiency.


A lmost no one disputes the enormous potential wireless networks offer in improving the total cost of installing, operating, and maintaining BAS. After all, it’s estimated that fully 60% of new equipment installation costs result from the wiring required to network dozens, even hundreds of sensors and controllers in a building to power sources and each other.

Imagine if many of these devices, particularly sensors, could communicate just as effectively via radio frequency (RF) and require minimal power, such that a simple, low-cost battery could power them. Not only would most of the wiring costs be eliminated, but also building owners would have the flexibility going forward to easily and inexpensively retrofit and enhance their BAS to keep pace with the changing building environment. The basic “drivers” for wireless use are essentially the same for buildings as they are for cell phones, PDAs, and PCs: more design flexibility, freedom of movement, lower total installed cost, and lower total cost of operation.



RF comes into its own

Of course, theory and practice are two different things. The use of RF in the building environment has, in the past, been difficult to implement effectively. The building structure itself can act as an impediment to adequate signal quality, particularly over long distances. The signal must be “heard” despite co-existing with, and perhaps facing interference from, other RF devices and the building’s own infrastructure. Those that have adapted RF to the building environment generally have developed proprietary networks that are expensive to implement, require more power, and are neither open nor interoperable.

Now, however, all of that is changing. RF is poised to become a low-cost, low-power, highly effective and, most importantly, open and interoperable solution, thanks to the Institute of Electrical and Electronics Engineers, Inc.’s (IEEE) new RF open standard, 802.15.4. This standard follows on the heels of other IEEE RF standards such as 802.11, commonly known as WiFi and 802.15.1, or Bluetooth. Both 802.15.4 and 80.2.11 use direct sequence spread spectrum (DSSS) technology, which, unlike the conventional narrow band of FM radio, spreads the data out over a very wide band so that competing noise will not ultimately cause any significant interference.

Many vendors (Freescale, TI, Renesas, Atmel) seeing the potential are already jumping on the 802.15.4 bandwagon, thus ensuring that the cost for all network components will be competitive with their wired counterparts. In addition, several alliances are now working to define protocols for 802.15.4 — just as WiFi (802.11) and Bluetooth (802.15.1) were built to run on top of their respective frequencies.



Zigbee on the move

The best known of these is “Zigbee.” The Zigbee alliance of manufacturers has made it possible for any number of low-power, often battery-operated, wireless devices to communicate over even considerable distances via a “mesh” network. The fact that each device is designed to transmit just a very short distance minimizes the potential for interference and reduces power requirements, thus making battery application much more practical — and ideal for building application.

Yet, despite the limited range of individual devices, their data is easily, and automatically, relayed in multiple “hops” across the mesh network of Zigbee devices, allowing reduced function devices (RFDs) like temperature or occupancy sensors to communicate with full function devices (FFDs) such as VAV or plant controllers.

The Internet Engineering Task Force’s (IETF) 6 LoWPAN (Wireless Personal Area Network for IPv6) is another promising protocol built on 802.15.4 — but takes it a step further than Zigbee, making it now possible for a wireless mesh network to be open, interoperable, and IP-compatible and allowing the use of existing tools, technology, and knowledge, and more easily integrating into and using existing networks and systems such as BACnet/IP and Ethernet.

In addition, 6LoWPAN is designed to work around “packet loss,” and to be self-configuring and self-healing should physical changes — planned or unplanned — be made to the building environment. For example, if a building owner decides to re-configure an office area with partitions that now block the transmission of a temperature sensor to its VAV controller, the network can automatically, and seamlessly, route the signal in a different direction around the interference, rather than having to re-install the sensor in a new location.

A year or two ago, we could only dream of low-cost, low-power wireless devices operating in an open, interoperable network — all “future proofed” with IP compatibility. Now, we’re just months away from seeing the first products available to customers using 802.15.4. Stay tuned …



Geoff Mulligan
Mulligan is technology director with Invensys Building Systems and chairman for the Zigbee IPv6 Task Group, and the IETF 6LoWPAN Working Group.

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