By John Edler
Wireless technology is familiar to anyone who uses a cellular phone, laptop, or PDA, and it's gaining in popularity for use in building management for many of the same reasons we use these devices: convenience.
Wireless access to building controls makes troubleshooting easier, allowing building operators to access the systems from anywhere in the building or remotely via the Web. In new construction, wireless saves the cost of wiring and enhances performance, and different network systems can be connected to the same backbone. In older or hard-to-wire locations (such as museums or historic buildings), or locations that require frequent configuration changes, such as a warehouse, wireless gives you greater flexibility at minimal cost. You can even connect multiple buildings into the same building-management network.
The Advantage of Wireless Mesh
A wireless mesh is flexible and scales to larger areas by letting devices connect beyond their radio ranges and hop over intermediary links. Consider that a typical WiFi device has an indoor range of 100 to 300 feet and an outdoor range of 300 to 1,000 feet. Multiple radio devices can be used to relay data over longer distances in a multihop network. In many cases, three to five hops can cover a large building. However, deficiencies in the underlying media access control (MAC) protocol lower data throughput with each hop, so you need to make sure that your equipment is robust enough to handle the data traffic.
A wireless mesh also gives you mobility. As you move walls and configurations inside the building, it changes the radio-frequency environment. But, by creating a wireless mesh, you can easily adjust to accommodate such changes; it also means that you can place equipment, such as thermostats, literally anywhere inside the grid.
One Wireless Mesh for Many Uses
When you design your wireless mesh, consider that it can offer more than just support for building-management protocols. Support for IP video or Voice-over-Internet Protocol can be built into the same wireless systems, but you need sufficient bandwidth and support for Quality of Service (QoS) for multiple networks.
For example, building-automation controllers that run BACnet typically operate at 10 to 100 kilobits per second, but you will need more bandwidth to support additional protocols. Also, the simple act of enabling building personnel to wirelessly access the network using a standard laptop computer requires both a higher data rate and interoperability with common 802.11 WiFi protocol. If you are thinking about running multiple protocols over the same wireless mesh, you need to plan accordingly. An effective data throughput should be kept to 30 percent of the maximum attainable radio rate. And, as you connect more devices and sub-networks, the aggregated throughput multiplies. So, to set up multiple networks over one wireless architecture, make sure the hardware delivers sufficient bandwidth and multihop capability to sustain the level of data traffic.
John Edler is vice president and general manager, building systems, at Kiyon Inc. (www.kiyon.com), the San Diego-based creator of high-performance wireless mesh routers for wireless building automation.
