Case Study of Colorado DOT microwave backhaul system for highway system
The Colorado Department of Transportation (CDOT) is responsible for a 9,134 mile highway system throughout the state, including 3,406 bridges. Each year, this system of highways handles over 48 billion vehicle miles of travel. CDOT maintenance forces take care of the highway system, plowing snow and repairing pavement. In fact, during the winter of 2009-2010, CDOT personnel plowed 7.2 million miles of highway. They also repaired road damage and potholes, using more than 248,000 tons of asphalt and 178,800 gallons of liquid asphalt in preservation activities.
Information about road conditions often comes to CDOT from its own workers or the Colorado State Patrol, but in some areas the agency has begun deploying video surveillance systems to reduce costs and provide real-time information. In 2006, CDOT developed a plan to install a high resolution video-based traffic surveillance and data collection system along a 30-mile stretch of US Highway 36 between Denver and Boulder. The information would give CDOT monitoring personnel up-to-date information on the highway’s congestion and other conditions, and it could also feed into a public web site for consumers seeking traffic information about this busy commuter route.
Searching for the Right Signal
With no existing fiber available along the route, CDOT and nationwide network engineering firm MSN Communications of Englewood, Colorado designed a system of high resolution pan/tilt/zoom video cameras to monitor the roadway. There was no available fiber along the route, so the design included a wireless backhaul network to transport the video and traffic statistics back to the CDOT operations center in Lakewood, Colorado.
It was a good plan, but wireless was initially the weak link. The initial plan called for Wi-Fi radios in the 2.4 and 5 GHz spectrum, and these proved inadequate to the task.
“We had scoped out the project based on the vendor’s claim that their radios could reach up to 22 miles,” said Jill Scott, project engineer at CDOT. “Once we started deploying the first systems, though, they wanted us to deploy 18 hops, which was totally impractical.” In addition, the high resolution video-based application required high bandwidth, and the Wi-Fi system couldn’t deliver sufficient capacity.
Looking for alternatives, MSN Communications consulted Exalt partner KNS Communications of Denver, a worldwide provider of microwave systems for utilities, governments, and enterprises, about a better wireless solution. KNS recommended Exalt all-outdoor microwave backhaul systems configured for the 5.8 GHz frequency.
Reliable performance from Day One
The Exalt systems were set up to deliver 100 Mbps of Ethernet data, and thanks to the Exalt systems’ superior performance, only seven hops were needed to cover the entire length of the project. Each microwave system was configured for 100 megabits per second (Mbps) of Ethernet, and Exalt’s throughput symmetry control feature allowed CDOT network operators to assign 80 percent of the bandwidth to the upstream direction from the video cameras to the operations center.
After extensive testing, the project went live in 2009, and it has worked flawlessly from the first day. Technicians from CDOT and their consultants used Exalt’s remote management system and built-in spectrum analyzer to optimize the performance of each link while minimizing the impact of interference.
The results were excellent. “The video we get from this system is very valuable,” says Scott. “You can’t tell that it’s not coming in over a fiber link.”
Once at the operations center, CDOT personnel monitor the video 24 hours a day, and the data is also sent to CDOT’s traffic web site so consumers can determine current traffic conditions.
Now, after a year of operations in all weather conditions, the Exalt microwave backhaul system has proven its reliability and performance. At one point a new source of interference crept into one of the links, but Scott’s team was able to work with KNS technicians to resolve it using the spectrum analyzer built into each Exalt radio, along with Exalt’s remote management and configuration capabilities.
Challenges of this project
- Deliver mission-critical backhaul on hilly route with high winds and limited power availability
- Provide required capacity for video surveillance application
- Simplify deployment
- Deploy Exalt all outdoor microwave backhaul systems featuring mission-critical reliability and Power over Ethernet
- Configure systems for 100 Mbps Ethernet with throughput symmetry control to assign most of the system’s bandwidth to the upstream direction coming from the video cameras
- Use Exalt remote management and the spectrum analyzer built into every Exalt radio to optimize link performance and mitigate interference.