Migrating to a Project 25 trunked system (Part 2)
After assessing the myriad issues surrounding its legacy VHF analog simulcast system, it became clear that the Multi Agency Communications Center (MACC) needed to migrate to digital technology, according to Dean Hane, the agency’s radio communications manager, who recently spoke on the topic.
The primary motivation was the FCC’s mandate that required all radio systems operating below 470 MHz to convert to 12.5 kHz channels from 25 kHz channels to achieve greater spectrum efficiency. But Hane said that the MACC—an entity that provides emergency communications services for 30 agencies—also desperately needed more channels, something that it wasn’t going to find, if it stayed with analog technology. An analog system also wasn’t going to be able to take advantage of some of the rich features, such as encryption and advanced network-management functionality, that digital systems provide.
“We needed more, and we wanted more,” Hane said. “We were going to shell out close to 10 million bucks here [for a system upgrade], and we didn’t want to do that to sit on analog. That seemed kind of silly.”
Hane’s first inclination was to move to a Project 25 VHF system, but he quickly decided that scenario wasn’t going to be much better than what the MACC was experiencing with its analog system.
“It’s still VHF spectrum—you’re not going to any more channels, regardless of whether it’s P25 or analog,” he said.
“So, number one, we had to get out of VHF and, number two, we had to get out of analog.”
Ultimately, the MACC decided to implement a Project 25 trunked system that operates on 800 MHz spectrum. But, because Washington is a border state, there were a few issues associated with that band that had to be considered carefully before taking the leap, according to Hane.
“We had the [800 MHz Transition Administrator] to deal with, we had Sprint Nextel to deal with, and we had border issues with Canada,” Hane said, referring to the ongoing effort to reconfigure the 800 MHz band along the U.S./Canada border in order to solve interference issues.
Despite those issues, Hane believed that the 800 MHz band offered the best chance to solve some of the agency’s coverage and frequency issues. But it created another big obstacle—interoperability—because the MAAC serves Grant County, Wash., which is surrounded by nine counties that operate VHF analog systems.
“They’re not going to upgrade to digital radios just to listen to their neighbors,” Hane said. “It would be fine, if they didn’t have to spend any money—but, if they had to spend money, it wasn’t going to happen.”
Hane described the workaround to this dilemma as a “sour pill”—two radios in every vehicle.
“We didn’t want any individual carrying two portables—that’s a train wreck,” he said. “There’s not enough rope on the belt already for all the tools and materials a cop or a firefighter has to carry. So, we knew that we only wanted them to carry the 800 MHz portable radio. In the vehicles, we didn’t have a choice—it had to be both radios. …
“In Washington state, all of the interoperability stuff happens in VHF analog—we get that, we know that, we planned for it,” Hane continued. “But that still doesn’t make that pill go down any easier about having two radios. Users complain about cost, they complain about maintenance, they complain about not having enough space in the vehicle, they complain about having too many microphones.”
Interoperability is an especially big issue in the eastern part of Washington State, because the region is prone to wildfires. To ensure that agencies can communicate with each other during such multijurisdictional events, Hane decided to create a console patch that operates continuously for certain channels.
“In the VHF world, on the fire side, we have Fire 1 and Fire 2—countywide channels,” he said. “We made mirror-image talk groups on the 800 [MHz] side—800 Fire 1 and 800 Fire 2. We patch them together at the console, and that patch is running all the time.”
Hane said that he got some grief for creating the patch at the console, rather than hardwiring it or making it permanent through punch-downs or equipment cross-connects. But he had a ready answer for his decision.
“I had made that mistake before,” Hane said. “It showed up pretty quick when there was a problem on one side of the patch or the other, and it would manifest across the entire system
“Here’s an example: Our terrain is very flat, and signals carry a long, long way on VHF over terrain like that. So, we would get other people’s traffic … and that interference would get patched over to the trunked side, and—all of a sudden—we’d have this mess on the trunked side when we were supposed to have clear communications.”
There were other implementation issues. One was that the coverage was a little less than what the agency experienced with its VHF system. Another was that users sometimes experienced coverage anomalies—something they weren’t expecting.
“At 800 [MHz], it only takes a subtle move of the portable to make your coverage go up or down [in fringe areas],” Hane said. “A guy would say, ‘I’m having trouble with my portable,’ and a small adjustment to his body made some differences. That’s a big culture change between the 800 [MHz] wavelength and the VHF wavelength.”
In addition, the radios being used in the field were unable to decode the control channel in certain conditions, and it would take up to 30 seconds for the radios to resume decoding—far too long, according to Hane.
“The user could forcefully restart everything by hitting his push-to-talk, but we didn’t want him doing that,” he said. “This is a giant simulcast system, so I get Rayleigh fading and all of that. I get that there are times when we’re going to have high bit-error rates and delay-spread areas, and we’re not going to be able to decode the control channel. But that should only last for a few seconds.”
Also, mixed-mode scan—the ability to scan both trunked and conventional channels at the same time—was a “gigantic train wreck,” Hane said.
“We implemented it, mostly at the pressure of the fire guys—and I totally get that,” Hane said. “Fire guys for the most part are going to use a trunked system to dispatch on, and they will use simplex tactical channels in certain cases, like when they’re in the basement of a building.
“But it was a mess for us. It caused radios to look for conventional channel activity more often and longer than it should have. … We had to work with our vendor, and it cost us another three months to solve this problem. They rewrote the hunting algorithm that [governs] how the radio scans, and it’s a 10 times better product today than it was when we got it—but it cost us time.”
Hane said that the biggest blunder the MACC made was putting all of its traffic on the TDM side of its microwave backhaul system.
“I did it because, at our level, we protect the individual T1,” he said. “For troubleshooting purposes, I could easily troubleshoot the same method for analog traffic and digital traffic. [But] we have grown very fast already—we already have added channels, and we’re going to add sites. Now that T1 is filled up, and we’re in the process of migrating all of our P25 traffic to Ethernet. …
“If you have the ability for some bandwidth on the Ethernet side of your transport, take it. We did it on the TDM side, but it was tight, and I’m paying for it now.”
TheMACC’s P25 800 MHz trunked system has been live for about nine months now, and things still are getting smoothed out, according to Hane. He described the migration process as “a little bit aggravating”—one in which the MACC seemed to continually take two steps forward, and then one step backward. But Hane believes the aggravation was worth it.
“This system still is better today than it was two to three years ago,” he said.