Migrating to a Project 25 trunked system (Part 1)

The unquestioned king of buzzwords in public-safety communications right now is “broadband.” It has been that way ever since Morgan O’Brien floated his fantastic notion about a nationwide broadband network for first responders built on 700 MHz spectrum that the federal government would provide.

And the use of this buzzword has grown exponentially over the last couple of years, fueled by Congress’s reallocation of the D Block to public safety and the formation of the First Responder Network Authority (FirstNet), which was created to build this futuristic network.

But it will take many years—perhaps decades—for that network to come to fruition, and even then some agencies may not be able to leverage it, depending on their geographic locations and the economic model that FirstNet ultimately develops.

As a result, there is still plenty of activity involving land-mobile-radio (LMR) technology, and numerous agencies that are contemplating various migrations—for example, analog to digital, digital to Project 25, DMR or TETRA; and conventional to trunking—because their legacy systems have reached end of life, or their needs have changed.

One of those entities is the Multi Agency Communications Center (MACC), which is a consolidated public-safety answering point (PSAP) that serves Grant County, Wash. The county is in the eastern half of the state, between the Cascade mountain range and Spokane. The center has a 3,000-square-mile territory, and provides 911 services to 30 agencies that serve a combined population of 90,000.

Dean Hane, radio communications manager for MACC 911—located in the town of Moses Lake—spoke about the agency’s transition to a P25 trunked system that operates on 800 MHz spectrum, and offered best practices for executing such a project.

Hane said that the agency had no issues regarding the surrounding terrain or topology, as it relates to coverage.

“There are very little trees and no mountains,” he said. “It’s nothing but a big desert—we get less than 10 inches of rain each year.”

But there were coverage issues.

“That big flat terrain causes a problem in a simulcast environment, something called delay spread,” said Hane, who was a project manager for Motorola and a senior consultant for ADCOMM Engineering in Bothell, Wash., before joining MACC 911. “That means that all of those radios out in the field can hear multiple sites at the same time, and it’s not clear which site that radio is listening to.”

A bigger issue was that the agency was operating a wideband VHF simulcast system that had only five sites; according to Hane, this was “nowhere near enough” to provide coverage over a 3,000-square-mile footprint. But Hane said that the big driver for making a change was the FCC’s narrowbanding mandate, which required all radio systems operating below 470 MHz to convert to 12.5 kHz channels from 25 kHz channels to achieve greater spectrum efficiency.

To meet this mandate, the agency settled on what ended up as an interim solution—an 11-site VHF narrowband system.

“And for eight months, the coverage was spectacular, and our users were very, very happy about that,” Hane said.

However, it eventually became clear that the agency needed to scuttle its legacy system, primarily because they needed more channels than they could have with analog technology, according to Hane. He said that Grant County is bordered by nine counties, each of which operates VHF narrowband systems.

“There was no way we were going to get any more workable channels,” Hane said.

A complicating factor was that, of the six VHF channels that MACC 911 operates, the agency is licensed on two of them as secondary users.

“That’s not where we wanted to be in terms of running a 911 communications system,” Hane said. “We were pinched from the beginning.”

Next: What MACC did and learned.