The APCO Project 25 Interface Committee, or APIC, has sent the physical-layer proposal for the second phase of the standard — including a harmonized, industry-consensus two-slot time division multiple access, or TDMA, common air interface standard for 12.5 kHz channels — to the Telecommunications Industry Association's TR8-12 committee, said Roy McClellan, director of standards development for EADS North America.

The proposal will be vetted in the committee, for which McClellan recently was elected vice chairman. McClellan said that he's not anticipating any major glitches. He also said he is comfortable that major issues have been addressed and that participating North American radio vendors — including Motorola, Tyco Electronics M/A-COM, Tait Communications, EFJohnson Technologies, Thales, ICOM America, Kenwood USA, RELM Wireless and EADS — are on board concerning the selection of two-slot TDMA as the technology platform for Phase 2.

“It's not a fait accompli, but it's moving in the right direction,” McClellan said. “There are positive indications that the standard is headed in the right direction. It's all positive right now.”

Assuming that no hiccups occur during the vetting stage, the proposal could be put to a vote by TIA in October, he said.

A lot of hard work was accomplished at the APIC stage, as various vendor and user concerns had to be addressed. Considering what is at stake, that was expected, he said.

Two-slot TDMA doubles system capacity and 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.