Case Study: Simulcast Expands Channel Availability and Cuts Expenses for Public Safety

There simply are not enough channels to go around, especially for public safety use. Agencies have been forced to apply for new channels and upgrade to very elaborate systems in order to communicate. However, thanks to analog simulcast agencies can use the same channel to cover a wide geographic area, while continuing to use their existing mobile and portable units. Simulcast is more popular in the public safety field than anywhere else.

Although P25 digital communication is currently a major topic of discussion, it is also a big-ticket item many rural entities cannot afford; this is another reason they turn to simulcast analog communications, instead. However, simulcasting requires the latency, or time delay, across the microwave backhaul to be fixed. P25 does not require fixed latency like analog systems do. Therefore, most P25 systems use IP backhaul. An IP-based data stream can also work if all you want is analog backhaul, as long as it is not contingent on critical timing. Conversely, if you’re using multiple sites, IP-based systems are not viable solutions, because they vary too much.

CommTech, a division of Communications Group, Inc., is a wireless communications provider in Nashville, TN. It provides complete communications infrastructure, which runs the gamut from building towers to outfitting the equipment at the base of the towers for radio systems to integrating into 9-1-1 centers when necessary.

The core of CommTech’s business is public safety entities throughout middle Tennessee. Most of the customers CommTech caters to are county agencies. As such, they do not have the financial resources of most metropolitan agencies. Therefore, CommTech delivers many simulcast radio systems with multiple towers transmitting at the same time. Because these are analog systems, timing is critical and the latency cannot vary, which is why CommTech started working with Arcata, CA-based Carlson Wireless Technologies, Inc. more than 10 years ago.

Brad Adams, service manager at CommTech says, “Carlson fits into our business because in multisite systems, you need backhaul from tower to tower. Fixed latency is something Carlson’s Trailblazer radio does that’s really important. The latency cannot change, it always has to be the same; and that is the primary reason that we use the Trailblazer.”

Affordability is another reason CommTech turned to Carlson for a simulcast solution.

“Carlson was the least expensive solution and it met our needs better,” says Adams. “A lot of microwave solutions are way more than you need for an analog application; whereas, Carlson’s Trailblazer, which we use exclusively for these types of applications, is just enough and not too much.”

Steve Rich, vice president at CommTech says, “Carlson is the only one in their price point/class that provides analog fixed latency. The next step up, you’re looking at a much higher tier radio system and you are into three to four times the price. The Trailblazer is a very good radio with very good quality for its price point.”

The following is an example of how CommTech’s simulcast system solves a communications crunch. A county sheriff 30–50 miles outside the metropolitan area may not have millions to spend on a P25 radio system, so CommTech builds the county a simulcast analog system using Carlson’s Trailblazer for backhaul. The agency can keep all of its legacy equipment in its cars as well as their portables, all the while improving their coverage. Ultimately, they are able to achieve the same goal even though they are still using analog. Hence, there’s still a valuable place in the market for true TDM microwave.

“One of the other things I like about the Trailblazer is it offers the best of both worlds,” says Adams. “We can have analog, true TDM, fixed latency, microwave, with a little bit of Ethernet. We only use a portion of the Trailblazer’s 512 KB bandwidth for connectivity to different sites to do diagnostics requiring Ethernet.”

Although you can purchase the Trailblazer with a 2.4 GHz, 4.9 GHz or 5.8 GHz radio, CommTech uses the 4.9 GHz Trailblazer. It is then able to change the band range from 4.9 to 5.8 or to 2.4 GHz without changing the radio. As many as 10 Trailblazers have been placed at a site with almost no degradation, because CommTech found a way to successfully eliminate localized interference by using the Trailblazer to spread the usage over various frequencies.

For those agencies considering P25 for the future, Carlson’s Trailblazer offers the perfect migration path because the system allows for both IP and TDM analog. If it was being used for analog simulcast and then the agency switched to P25, they could change over the bandwidth to IP and use it to migrate to P25. However, since most agencies using an IP backhaul need higher bandwidth capable of supporting extensive data, such as video traffic cameras or other streams, Carlson also offers its LongHaul family of IP bridges for that purpose.

But for CommTech, the Trailblazer fits its needs “to a T.”

“Carlson’s Trailblazer has found its niche in analog simulcast because it is a true TDM radio. It does exactly what it’s supposed to do,” says Adams. “It does fixed latency backhaul for analog communications, and it does it quite well.”