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Wireless Technology: Overcoming Obstacles
Thermostats. Occupancy sensors. Lighting controls.
In a large facility, there may be hundreds, even thousands, of devices that should communicate with one another. Linking disparate devices into a harmonious whole has long been a topic of interest for facility executives.
But creating a connected facility remains a challenge. Cabling and the labor cost associated with it can be expensive. It is a barrier that can make adding new technology to existing buildings prohibitively expensive.
One solution drawing increasing interest from facilities executives is wireless technology.
“In the world of facility management, wireless will begin replacing labor with radio frequency links,” says Jeff Raimo, product manager for Siemens. “And copper costs are now a significant factor for wired solutions.”
But the use of wireless systems is not always straightforward. Some wireless technologies use a significant amount of power — so much so that batteries must be changed frequently, creating a potential maintenance hassle. And then there are concerns about the reliability of wireless networks.
A wireless standard known as ZigBee is designed specifically to address those concerns.
Just what is ZigBee? It’s a comparatively new wireless network standard being adopted by a growing number of building controls manufacturers.
While plenty of tech-savvy people have heard of Wi-Fi or say that they understand how a wireless network functions, the lexicon of wireless engineers can be confusing. Before delving into the benefits and challenges of ZigBee — and how it differs from existing wireless technology — it’s useful to examine a bit of technical background.
A ZigBee Primer
ZigBee is a wireless personal area networking standard (WPAN) that conforms to the IEEE standard 802.15.4-2003, which is similar to other WPAN networks operating in the 802.15 family — of which the best known is Bluetooth (802.15.1).
For beginners, 802.15.4 is a radio frequency — much like radio stations that incorporate AM or FM frequencies in their names. A ZigBee module, which can be smaller than the size of a paper matchbook, contains the radio chip, microprocessor and application software that allows devices to receive and transmit information over the air.
Three ZigBee devices make up a network.
- Coordinator: This full-function device initiates the network. Once the network is up and running, the coordinator behaves as just another device on the network, meaning there is no single point of failure in a well-designed ZigBee network. There is only one ZigBee coordinator in each network.
- Full Function Device: Full function devices have the ability to act as routers on the wireless network and pass data packets between devices on the network. Any ZigBee device could be a full function device on the network, although they are typically powered devices such as controls or sensors.
- Reduced Function Device: Typically, this device is an end device on the network and could be a control or sensor (e.g., light switch or thermostat). This device can send and receive information to other devices on the network, but it does not act as a router to relay data from other devices.
Globally, ZigBee uses the 2.4 GHz frequency band; additionally, 915 MHz is available in North America and 868 MHz can be used in Europe.
While many networks on the 802 standard can transmit data faster than ZigBee, those approaches cost significantly more and use greater amounts of power. In addition, only ZigBee has mesh networking as part of the standard to enable greater reliability and easier commissioning of wireless networks. ZigBee is also capable of handling hundreds to thousands of devices per network, where other approaches are limited to dozens of devices or only offer point-to-point communication.
Most proprietary wireless solutions also communicate point-to-point or have a very limited number of devices allowed within a network. When one device along the chain fails, the entire message being transmitted may not reach its destination.
Unlike Bluetooth, ZigBee devices are arrayed in self-healing mesh networks. That means it is more reliable than the point-to-point communication of other 802-frequency wireless networks. Bluetooth also can support only seven active devices on its network, rather than the 65,000 devices that a ZigBee network can host.
While ZigBee is designed for short-range use at low power, some member companies are supplying modules with special designs capable of boosting ranges to hundreds of meters or even kilometers. However, given ZigBee’s mesh networking capabilities, devices at normal low power settings can join together to expand the network over vast expanses. Currently, thermostats, lighting systems, access control, temperature sensors, smoke alarms and security devices are among the many devices that can be controlled via a ZigBee network.
Less Power, More Reliability
Because ZigBee devices typically are not required to share much information — the temperature of a room, or whether a light is switched on, for example — they draw very little power. In addition, some manufacturers have designed their sensors to stay dormant unless a change in state is noted, further reducing battery drain.
This is one of ZigBee’s greatest advantages, according to Ravi Sharma, marketing director for Ember. “ZigBee’s greatest virtue as an application is its ability to dramatically reduce energy consumption and energy waste,” he says.
“ZigBee devices can run unattended for years on cheap batteries,” says Sharma. “Other power-hungry wireless standards would be extremely high-maintenance in sensor network applications.”
“ZigBee modules draw very little power. In fact, a standard AA alkaline battery can power a module for up to five years. Lithium ion batteries can last up to 10 years.
But Raimo says network reliability is ZigBee’s most laudable characteristic. “A ZigBee network has intelligence, in that the modules select an optimal path,” he says. “Redundancy is the biggest benefit over older wireless technologies, because if a device experiences a failure, ZigBee’s mesh network automatically sends the message using other devices on the network.”
The ability to reliably communicate data across a network is further enhanced through ZigBee’s use of direct sequence spread spectrum communications. “ZigBee was designed for the hostile RF environments that routinely exist in mainstream commercial and industrial facilities,” says Sharma. “It can overcome competing wireless ‘noise,’ data collisions and other problems.”
Its mesh networking enables it to re-route traffic around temporary physical obstacles, radio-frequency interference, router error or other failures.
“By providing multiple pathways for data to travel, a mesh network eliminates single points of failure and affords transparent recovery of devices on the network,” says Brent Hodges, vice president of marketing and business development for the ZigBee Alliance.
ZigBee has also proven highly scalable and not limited just to battery-powered solutions.
“ZigBee also enables AC powered devices,” says Hodges. “But battery-powered devices have been engineered to last for years, allowing them to be installed in difficult or out of the way places.”
The addressing scheme is capable of supporting thousands of nodes per network and multiple networks can easily be linked together to support extremely large networks, says Sharma.
The standard also enables security in ZigBee devices, based on a 128-bit algorithm.
ZigBee solutions are comparatively low cost, and Alliance members say they believe costs will continue to decrease as greater numbers of members begin building ZigBee-enabled devices. “Depending on the vendor, chip prices are in the low dollars and will continue to fall as the market volume ramps up,” says Sharma.
Making Itself Known
For facilities executives who already have a reliable wired system in place, there’s little reason to tear out the cabling and replace it with wireless. But for new construction, or for facilities executives contemplating installing their first facility monitoring or control system, wireless can make a great deal of sense. Nevertheless, wireless technologies like ZigBee are not the first option that many facilities executives think of.
“Many facilities executives still favor wired solutions for remote monitoring and control applications,” says Hodges. “People are not well educated about recent advancements in wireless technologies, which make wireless systems more reliable, cheaper and easier to deploy.”
Even though the standard is fairly recent — ratification took place in December 2004 and the latest revision was released in December 2006 — the more than 200 members of the ZigBee Alliance have made available many traditional devices with ZigBee certification.
In fact, many commercial ZigBee products are being used in real world facility applications today, particularly in the areas of building automation, automatic meter reading and industrial automation. ZigBee products are also available for residential use.
“More than 10 billion products are built each year with microcontroller-based intelligence inside them, yet the vast majority can’t communicate with each other,” says Hodges. “Adding ZigBee is the easiest way to wirelessly enable the world’s products and devices.”
About The Zigbee Alliance
The ZigBee Alliance got its informal start in the late 1990s, when RF engineers began to realize that existing wireless networks would not meet the needs of facilities executives. The first members joined in 2002, and the standard for 802.15.4 was finalized in 2003. The standard was ratified in December 2004, and the Alliance has since grown into an organization with more than 220 member companies. Members include original equipment and semiconductor manufacturers, and technology providers, all of whom collaborate to produce ZigBee-certified devices.