Despite the emergence of digital radio systems for public safety in the 800 MHz and soon-to-be-available 700 MHz bands, the vast majority of public-safety licensees still operate in the UHF and VHF bands below 512 MHz.

In 2003, the FCC mandated that all public-safety systems in these bands transition from traditional 25 kHz-wide channels to more spectrally efficient 12.5 kHz channels by Jan. 1, 2013 — an expected progression, given that the commission mandated a decade ago that manufacturers build 12.5 kHz capability into equipment operating in the bands.

But the FCC in March ordered vendors to manufacture equipment that can operate on 12.5 kHz channels and 6.25 kHz channels by Jan. 1, 2011 — two years before the 12.5 kHz mandate is effective. The FCC did not establish a deadline for licensees to migrate to 6.25 kHz channels, but the commissioners' long-term intent was clear.

“We reiterate … that 12.5 kHz technology is a transitional step in the eventual migration of [private land mobile radio] systems to 6.25 kHz technology,” the FCC order states.

Although improving spectral efficiency always is an FCC priority, the March ruling was a surprise to many in the public-safety communications sector, leaving many licensees using the UHF, VHF and UHF T-band frequencies with more to consider as they develop their narrowbanding strategies.

“6.25 [kHz] really wasn't on anybody's horizon before this, so this really confuses people,” said John Facella, M/A-COM's director of public-safety markets. “I don't think it's obvious what people could or should do.

“They did not mandate when the licensees will have to move to 6.25 kHz operation. So the confusion among the licensees is, ‘I know I've got to move to 12.5 kHz channels in six years, but I'm going to be able to buy 6.25 kHz equipment before that, so I don't know what to do.’”

Joe Watts, product manager for Kenwood USA — manufacturer of a 6.25 kHz-capable portable radio and a 6.25 kHz-capable base station that will be announced in the fall — echoed this sentiment.

“These large entities are saying, ‘I've got all of these base stations, and I'm now transitioning to 12.5. But if they're going to turn around and mandate 6.25 after 2013, what do I do?’ It's caused several of [licensees] to take a major pause and consider whether they should go to 6.25 immediately,” Watts said.

Alan Tilles, a partner in the law firm of Shulman Rogers Gandal Pordy & Ecker who filed comments with the FCC on behalf of radio vendor ICOM, said he believes the commission's ruling provides licensees in the affected bands desirable options. It also is a fortuitous decision for ICOM, which has developed frequency division multiple access-based portable radios that can operate at channel widths of 6.25 kHz, 12.5 kHz or 25 kHz.

“With a mandate to go to 12.5, licensees that are in the process of making that conversion should take a look at … buying equipment that operates at 12.5 kHz now and at 6.25 kHz-equivalent later,” Tilles said. “The beauty of it is that there is equipment today that's backward-compatible, so anyone who has 12.5 today could integrate it into their systems so that, over time, they can migrate from 12.5 kHz to 6.25 kHz.

“So you could start feeding those radios into your system right now and, when you're ready to [make the transition], all you have to do is the infrastructure.”

The transition process to 6.25 kHz channels described by Tilles is virtually the same one some public-safety licensees have pursued over the past decade to meet the FCC's 12.5 kHz mandate, by systematically purchasing radios that could work on 25 kHz or 12.5 kHz channels, so only the network infrastructure would have to be changed.

“What we're trying to tell people is, ‘Don't wait until the last minute,’” said Harlin McEwen, chairman of the International Association of Chiefs of Police's communications and technology committee.

While such an approach is a logical way to execute the transition to 12.5 kHz channels, it could undermine the ability of licensees to pursue 6.25 kHz technology in the near term. After all, most of these public-safety entities have limited funding resources, so a typical network upgrade is expected to last 15 to 18 years, in order to pay off the loans used to pay for such a large capital expenditure.

That means many public-safety entities still have not fully amortized the 12.5 kHz-capable radios purchased during the past five years, making it difficult to justify paying for new 6.25 kHz-capable equipment in the near term.

“The FCC is saying, ‘We know this is a 10- to 15-year investment, and that's why we're giving you this warning that we are going to move to 6.25 someday — although we don't know when, [so] you might not want to go to 12.5,’” M/A-COM's Facella said. “The people who went to 12.5 are a little bit stuck, and I can understand their frustration.”

Kenwood USA's Watts said this reality is why his company is lobbying the FCC to establish a firm date for the transition to 6.25 kHz. “For business and industry, getting a return on their 12.5 kHz systems is a matter of tax depreciation,” he said. “But for public safety, it's a political and budgetary issue that has a long cycle. Changing to new technology is not as simple as just obtaining money, it's about “getting the approvals and getting the money through the political machines,” Watts said.

For licensees that have not committed to a 12.5 kHz plan, there are options for migrating directly to 6.25 kHz channels, but even those present their own set of challenges to consider. For instance, many UHF and VHF licensees use conventional systems, but the only 6.25 kHz industry standard so far is for Project 25 trunking systems.

“The bottom line is that, for trunking systems, we have a way, in theory — using TDMA technologies and certain data signaling rates — to get to 6.25 equivalent operation,” Facella said. “For conventional systems, there is no standard for creating narrowband operation.”

The absence of a standard for conventional 6.25 kHz operations could prove to be a big inhibitor for licensees that want to increase interoperability and leverage multi-vendor equipment sources. In addition, because conventional 6.25 kHz operation has not been standardized, there is no assurance that coverage patterns from these solutions will mirror the coverage of existing 25 kHz-channel systems, which could require the public-safety entity to invest in additional base-station sites.

“It's not at all clear what the range penalty will be,” Facella said. “A lot of work has been done with P25 Phase II to make sure the coverage is similar to Phase I, so you don't have to add lots of extra sites. That does not necessarily map … to other solutions that might be used with conventional systems.”

Watts said Kenwood has not observed any range degradation in testing its 6.25 kHz-compliant equipment.

Facella also noted that the UHF and VHF spectrum allocations were not designed for trunking systems, so M/A-COM has suggested rechannelizing the bands; the FCC has asked the company to provide greater detail.

Although the stated goal for the narrowbanding transition is to use spectrum more efficiently in order to create new additional channels, that desired result might prove difficult in some of the bands below 512 MHz, said Ron Haraseth, director of automated frequency coordination for APCO.

“This is particularly true in high-band VHF, where everyone is packed so tight,” Haraseth said, adding that a transition to 6.25 kHz channels in the band will generate “at best” a 20% increase in assignable channels. “Just by going to narrowband doesn't necessarily open up new channels.”

With so much uncertainty, there is considerable question as to whether many public-safety licensees operating on spectrum below 512 MHz will opt to migrate directly to 6.25 kHz channels. Regardless, Tilles said the FCC ruling mandating the availability of such spectrally efficient gear would provide licensees with much-needed options as the 2013 narrowbanding deadline approaches.

“You couldn't have asked for a better time for this kind of equipment to be available,” Tilles said.

NARROWBANDING THROUGH THE YEARS

From 25 kHz to 6.25 kHz in spectrum below 512 MHz

1997

FCC ceases certifying radio equipment for bands below 512 MHz unless it can operate on both 25 kHz channels and 12.5 kHz channels.

2003

FCC passes order requiring industrial/business pool licensees to migrate to 12.5 kHz channels by 2013 and for public-safety licensees to do the same by 2018.

2004

FCC revises order to require public-safety licensees to migrate to 12.5 kHz channels by the same 2013 date as industrial/business pool licensees.

2007

FCC requires manufacturers to ensure that all 12.5 kHz equipment also is able to operate on 6.25 kHz channels by 2011. The FCC does not decide when licensees must migrate to 6.25 kHz channelization.

Source: FCC