Calm after the storm
Grundy County, Ill., is using new microwave radio links to upgrade its emergency communications network. With its county seat in Morris, Ill., (60 miles southwest of Chicago), Grundy County’s government uses its portion of state-mandated telecommunications service fees to operate an Emergency Telephone System Board (ETSB) that dispatches police, fire and emergency medical services for approximately 50,000 residents.
Although the Grundy County ETSB has long relied on legacy microwave systems to transmit voice communications, the damage from a recent storm, coupled with evolving voice and data service demands, led to an upgrade.
The ETSB began developing a microwave radio network in 1998 as a way to consolidate and streamline emergency communications throughout the county. “We had eight different fire departments and police departments with their own radios systems,” said Chris Kindelspire, director of electronics operations for Grundy County ETSB. “It was a hodgepodge that was difficult and expensive to manage.”
To remedy the situation, Kindelspire designed a county-wide microwave radio network that carries traffic for all city and county agencies. The primary infrastructure relies on equipment that uses the licensed 6 GHz, 10.5 GHz and 18 GHz frequency bands, but portions of the network use 5.8 GHz and 4.9 GHz links. The network links the Grundy County Administration Building, which houses emergency management personnel; the Grundy County Courthouse; fire stations, public works offices and police departments in Morris, Minooka and Coal City; and the county’s primary and secondary voice/data transmission sites. (Figure 1).
The network carries voice and data traffic, including mapping information, dispatch records, motor-vehicle re and arrest records, scheduling information, and administrative traffic. This system served the county well until the fall of 2007, when the 5.8 GHz backup link spanning six miles between the administration building and the primary transmission site was damaged in a storm. Kindelspire used the event as an opportunity to upgrade the link’s capacity.
“The link didn’t give us the throughput we wanted because it didn’t handle data, so after it was damaged we looked for something more robust,” he said. “We knew we wanted something in the license-exempt band because the existing link was license-exempt, but we also wanted to use it as a backup for both voice and data.”
After researching systems on the market, Kindelspire chose an Exalt EX-5r-c radio because it delivered both native T1 voice and Ethernet and offered guaranteed availability. The system also incorporates AES 128- or 256-bit encryption to secure public-safety traffic.
Kindelspire and his assistant deployed the system themselves over a period of three days. As with any license-exempt radio system, the Exalt gear required frequency tuning to maximize performance and minimize interference, but the system included a Web-based management interface and a built-in spectrum analyzer that made things easier.
“In the past, we would have had to physically travel to each site to tune the frequencies,” Kindelspire said. “But the Exalt management system allowed us to change from the A to B end of the frequency or adjust power levels remotely.” The system allows for frequency tuning in increments of 1 MHz.
As configured, the 5.8 GHz system provides four T1s and 100 Mb/s Ethernet, which is more than enough bandwidth for the organization’s needs. The biggest bandwidth consumer is the group’s computer-aided dispatch and mapping system, which provides location information to emergency responders in their vehicles. At times, this system uses up to 30 Mb/s of bandwidth on the 5.8 GHz link, but typical traffic is under 10 Mb/s.
After the initial deployment, Kindelspire was happy with the system’s reliability and performance, so he decided to upgrade a second link in the network. This link runs from the primary transmission site to the Minooka Public Works facility — a distance of about 12 miles.
“The existing link was a 6 GHz licensed, and carried only eight T1s for our radio dispatch traffic, so we had to do data by using an Ethernet-to-T1 converter,” he said. “We wanted to run data service out to that site as well, and so we could back up our radio dispatch network.”
Kindelspire and his assistant deployed an Exalt EX-4.9i system, which delivers four T1s as well as up to 55 Mb/s of Ethernet data. As deployed, that link provides 30 Mb/s of data and four T1s for voice radio dispatch traffic.
The ETSB was one of the early applicants for an FCC license for the 4.9 GHz spectrum, so it could deploy the link immediately, although it must file paperwork designating the locations and use of this link as a permanent part of the infrastructure.
Charles Rubin is a freelance writer based in Northern California. This article was contributed by Exalt Communications.
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