The South Metro Fire Rescue Authority provides emergency-medical, fire-suppression and fire-prevention services to the people living and working in Colorado's Arapahoe and Douglas counties. The agency, which exists as the result of a merger between the South Metro Fire Rescue and Parker Fire Protection districts, covers 176 square miles south of Denver.

Emergency services require ultra-reliable communications for the delivery of dispatch information, and that means having a fast and equally reliable network. To this end, South Metro upgraded its legacy, Wi-Fi-based radio network with microwave technology to increase available capacity and provide reliable communications, to ensure the timely arrival of fire and rescue personnel to a crisis scene.

Before South Metro was formed, the Parker Fire Protection District wanted to increase network capacity and eliminate monthly recurring charges for the leased T1 and ISDN lines that connected its fire stations and its headquarters building. After consulting with KNS Communications of Denver, the district chose point-to-point Wi-Fi-based radios that used the 5.3 GHz and 5.8 GHz frequency bands to connect its seven facilities. The distances between these facilities range from one to seven miles.

Though this approach eliminated Parker Fire's dependence on leased lines, it hardly was a panacea. The district had hoped for throughput of 10 Mbps, but even light radio interference in the license-exempt 5.3 and 5.8 GHz frequency bands could reduce throughput to a small fraction of that. This is because Wi-Fi is a "best-effort" radio technology — the performance of any given connection can vary widely, and because it uses license-exempt frequencies, it is possible — or even likely — that other users in the area will be using those same frequencies. Lacking a strong ability to resist such interference, Wi-Fi systems often struggle to deliver reliable point-to-point performance.

When Steve Macaulay, South Metro's network and communications manager, arrived at Parker Fire in 2005, he immediately began researching better solutions for the wireless network. At the time, Parker Fire was participating in an FCC test of the 4.9 GHz public-safety band, dubbed The Colorado 4.9GHz Project. Because 4.9 GHz is a licensed frequency band reserved for public-safety use, it would not be affected by other nearby radios using the same band, as is sometimes the case in the aforementioned license-exempt bands.

"We liked the idea of using the dedicated 4.9 GHz frequency because we knew it would be an easy way to minimize the likelihood of interference," Macaulay said.

KNS Communications has installed dozens of radio systems for municipal governments, public-safety organizations and enterprises. Although there are Wi-Fi-based systems for the 4.9 GHz band, KNS recommended a microwave backhaul system for the network upgrade because such systems have been used for decades to reliably deliver point-to-point voice and data traffic across long distances. In contrast, Wi-Fi technology migrated into point-to-point use from its origin as an enterprise and home-access technology.

What now makes microwave systems especially attractive for public-safety organizations like South Metro is that the prices have come down into the same range as enterprise-class Wi-Fi systems (roughly $5,000 per link), and that the newer microwave units are smaller and easier to deploy than in the past.

KNS and Macaulay deployed the microwave system in nine locations beginning in 2006. It carries 52 Mbps of Ethernet data traffic — more than enough throughput to support all of the district's current and anticipated applications — among them five fire stations, two headquarters buildings and two communications towers. This backbone supports not only South Metro's computer-aided emergency dispatch system, but also its voice-over-IP telephone system, e-mail, file-sharing and video-conferencing applications.

Since South Metro replaced its Wi-Fi radio links with microwave systems, Macaulay reports that traffic moves more quickly over the network and that performance issues have been eliminated.

"We have two radio links that were almost impossible to keep running when we were using Wi-Fi radios in the 5.3 and 5.8 GHz bands," he said. "One link between a fire station and a tower in Parker was completely overshadowed by interference from a small ISP using the same frequencies to do some of its backhaul. The 4.9 GHz microwave backhaul system completely solved that problem."

Macaulay also likes the idea that the all-indoor microwave systems are protected from snow and ice — an important consideration in Colorado. The older radio systems were outdoor units with integrated antennas, so their performance suffered during the winter as snow and ice formed on them. With the new systems, only the antennas are exposed to the weather, and the other system electronics are in weatherproof enclosures. "We've had virtually no impact on the network from weather since we switched to the new systems," he said.

Another important difference was that South Metro's microwave systems feature synchronization technology that makes it easy to co-locate several of them on one tower, something that is extremely difficult to do with Wi-Fi due to interference between radios. In fact, South Metro built a new tower in 2008 that now hosts five of the microwave systems.

Microwave systems often are used in remote locations. For that reason, the microwave systems deployed by South Metro can be configured and managed remotely via a Web interface. Additionally, each system includes a spectrum analyzer that is used to monitor performance and potential interference sources, which are far less common in the 4.9 GHz band than in the license-exempt 5 GHz bands, but occasionally are present.

While wireless systems look like an obvious choice for public-safety organizations looking to reduce recurring costs by eliminating leased lines, not all wireless systems are created equal. As the South Metro Fire Rescue Authority discovered, microwave technology delivers performance and reliability that Wi-Fi just can't match. Using a licensed, protected frequency band that minimizes interference issues makes it that much better.

Charles Rubin is a freelance writer based in Northern California. This article was contributed by Exalt Communications.

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