So far, so good

Nov 1, 2008 12:00 PM, By Doug Mohney

Consensus on 6.25 kHz frequency coordination procedures comes easy.

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The de-rating factors will be reviewed in two years and increased by 3 dB unless harmful interference cases are documented. “If there are any problems, we want to review that two years from now to see if we cause any problems or if those [guidelines] can be loosened up further,” Ittner said.

Using a less rigid process to implement coordination procedures is a faster way to come to agreement than a more formalized one, according to Ittner

“In the FCC, the rules process is a lengthy one, so we're not trying to define rules,” he said. “We're trying to coordinate the community to come to a consensus. … We don't want to overburden the issue.”

And what does the FCC think of the LMCC's work? The agency wouldn't comment on the record, but a spokesperson noted that the FCC has granted LMCC coordinators the opportunity to police themselves and that the proposed coordination procedures already are in accord with existing FCC rules.

“We wanted the FCC to get the word out to let users know what LMCC is doing,” Ittner said. “We requested a Public Notice, but they didn't see a need for one at this time. … I think it's largely because this effort is one that LMCC has been engaged in, not one specifically requested by FCC. We're taking the initiative here.”

Though the transition to 6.25 kHz is still well in the future as the FCC has yet to set a hard date for the migration, manufacturers already are working with the end-user community to ensure they can sell commercial products today without interfering with — or receiving interference from — existing or future systems. Right now, the action is in the private sector, which is expected to establish precedents for the first-responder community when it eventually makes its move to greater spectrum efficiency.

“Initial systems going in are the mid- and lower-tier kinds of radios best-suited for private businesses,” Ittner said.

“[6.25 kHz] solutions are in the marketplace today,” agreed Donald Vasek, executive director EWA, which represents enterprise business users, dealers, service providers and technology vendors. (EWA also is an FAC that coordinates more than 6000 business and industrial/land transportation radio licenses annually.)

“We worked with a couple of manufacturers,” Vasek said. “They came to us, helped us to make sure the technologies that our customers are acquiring can be implemented and can be implemented such that they don't cause interference with existing systems.”

It is expected that Project 25, the North American public-safety standard for interoperable digital radios, ultimately will implement a 6.25 kHz equivalent bandwidth scheme for better spectrum efficiency. Indeed, the APCO Project 25 Interface Committee, or APIC, in August sent the physical-layer proposal for the second phase of the standard — which includes a harmonized, industry-consensus, two-slot time division multiple access, or TDMA, common air interface standard for 12.5 kHz channels — to TIA for review. (Two-slot TDMA meets the FCC's requirement for 6.25 kHz channel equivalency by creating two voice paths within a 12.5 kHz channel, which is achieved by using an enhanced half-rate IMBE vocoder in a 12 kb/s air link data stream.)