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Article - July 2000
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Wireless Data Technology Emerges GraphicWireless
Data Technology
Emerges

Richard Desmarais
VP Engineering,
Teletrol Systems Inc.


"The best advice is to try the technology at a typical job site before you buy."

At the turn of the last century, wireless - as early radio was called - was a point of discussion in parlors and at parties. As we open this century, wireless is again a hot topic, but the technology is well developed and companies are busy trying to determine how to use it to create value for their customers. A little understanding of the technology can go a long way in helping building owners and system integrators determine whether a wireless technology can be of value to them in their building automation applications.

Wireless technologies can be clearly understood based on their technological differences (modulation schemes, power output, protocols); however, before you decide to implement a wireless system, you should consider how and where the technology would be used. Generally, wireless technologies can be described in the context of a LAN (Local Area Network) or a WAN (Wide Area Network). LAN wireless technologies allow you to connect a handheld communication device to a server on-site or let PCs in the same office communicate without wires. With WAN wireless technology, your in-house PCs can talk with a base station located miles away. With a LAN, data is typically passed from one point to another directly; with a WAN, all the data is passed to a central site where the data packet is checked for a destination address and then dispatched. In building automation, a room sensor could link to a unitary controller and a monitoring PC over a local LAN, but the system controller that aggregates data from all of these unitary controllers could transmit its data to a location across the country over a wireless WAN. LAN data is carried between local nodes; WAN data is received by a carrier and re-sent, and for that service, the WAN carrier typically charges based on the amount of data transmitted or the transmission time used. If you want to see data updated more frequently, this may affect your monthly service costs.

Control Solutions, Inc In any wireless installation, interference control is essential. This is very important in building automation given the types of equipment used to run a building and its potential to generate electrical interference. Point-to-point LAN radios frequently use spread spectrum techniques to combat this interference. Spread spectrum allows a radio to dynamically change frequencies and coordinate that frequency change with other equipment in the local network. In other situations with LANs and WANs, moving the radio is the most effective method of interference reduction.

Since WANs require each radio to transmit data back to a central antenna, each radio must be able to receive signals from the antenna and those signals must be received reliably by the central antenna. The challenge in building automation to consider is the potential for radio reception when the mechanical and control system are installed. To improve coverage in low signal areas, the WAN radio's antenna can be moved, as can the radio itself. As more carriers deploy more towers and antennas, this will be less of a problem, but for now, it is an important point to consider when reviewing wireless systems.

Some of the more popular wireless data technologies that are making their way into commercial buildings today are:

LAN Technologies

Wireless Ethernet 802.11 - This standard covers a variety of transmission media and data rates, but is typically implemented using radio transceivers that transmit data at 1 Mbps or 2 Mbps; a newer version of the standard supports a data rate of 11 Mbps. All network nodes in the LAN can operate wirelessly or an access point can be provided that links the wireless Ethernet nodes with the wired nodes.

Bluetooth and HomeRF - These new, competing standards link devices together wirelessly and can manage access to and interaction with other devices, such as a cell phone, organizer, or PC as you enter and leave local networks. If you have a portable PC equipped with one of these technologies, it would automatically notify you when you approached a controller.

In addition, there are some vendors who have created proprietary wireless LANs that can connect many nodes together. Other vendors market wireless devices to allow you to create a "virtual wire" between two points, replacing your RS-232 or RS-485 wired connection entirely.

WAN Technologies

Analog Cellular - Analog cellular can be used with a low-speed modem to transmit data over a cellular voice channel. There are also technologies that use the call progress control channels to exchange data.

Digital Cellular - Digital cellular systems already transmit voice as digitized data, so data from another source is easily accommodated. Popular digital technologies include CDMA, TDMA, and GSM.

CDPD - CDPD is a technology dedicated exclusively to the transmission of wireless data and shares frequencies with analog cellular.

Two-Way Paging - Paging has been around for decades but two-way paging is a wireless data service marketed to existing pager users as an upgrade. It is a specialized application of two-way wireless data rather than a unique technology.

Satellite - Satellites are used for data transmission and reception but are typically subject to the limitation that the antenna has to have a clear view of the sky.

In addition to these technologies, there are other vendors that offer their own national and local WANs and implement proprietary protocols for wireless data.

Questions like "how far will it operate" and "where will the antenna be placed" cannot be answered properly without reviewing a typical installation site. As discussed, there are many factors to be addressed to produce a successful installation and they vary in importance depending on the job site. The best advice is to try the technology at a typical job site before you buy.

Conclusion

Wireless has emerged as a technology of interest in building automation because of the lower costs of new hardware and the emergence of standards that allow a wireless node to easily access a larger network, such as the Internet. While applying wireless technology in building automation is certainly more challenging than in an office environment, understanding the problems to be addressed with each technology and trying the equipment on-site can ensure a successful installation. 

Teletrol Systems Inc., located in Manchester, NH, is a manufacturer of Web based BACnet compliant building automation systems.


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