Fighting over the future of P25
Started more than 10 years ago, the APCO Project 25 Standards Committee is now facing a number of issues to finalize a second group of open public-safety radio specifications in what has been simply dubbed “Phase 2.” Chief among them is that Motorola and the European Aeronautic Defense and Space Co., or EADS, have squared off with different technical solutions for P25 TDMA radios to enable more efficient sharing of spectrum to reduce usage from the current 12.5 KhZ per channel to 6.25 kHz.
In addition, public-safety organizations are aggressively pushing for the finalization of standards for fixed base stations, digital consoles and Inter RF Subsystem Interface, or ISSI, so they can start to see more competition and lower prices from suppliers.
Motorola’s proposal for P25 TDMA is relatively straightforward. “The general approach is to build off the 12.5 [kHz] FDMA standard, using the same control channel, same modulation,” said Mary Pittman, Motorola’s representative on the Project 25 Committee. “It’s a much easier migration with currently deployed system, and you’re also able to facilitate interoperability for folks who never deploy TDMA. You’ll never throw out your FDMA system. TDMA is not for everyone.”
She said that TDMA systems would be deployed in dense urban areas where there are a lot of users and not a lot of available spectrum. “We’ve seen a customer need for this increasing over time for increased capacity.”
The Motorola proposal would use a vocoder that should work both with legacy P25 radios built to the Phase 1 specifications and next-generation TDMA radios. A changeover to TDMA essentially doubles the number of available channels with few hardware changes. “We like the approach using the same modulation,” Pittman said. “Frequency planners, customers and vendors have the coverage area and interference patterns well-understood, so we can hit the ground running.
“The way we are incorporating the vocoder, you can essentially have mixed talk groups of legacy P25 radios and radios capable of operating on the TDMA systems. And you can integrate those two types of channels into the same system if the customer would request it and the vendor would provide.”
One area of debate concerns what vocoders to use in the final implementation and how well they might actually work under real-world conditions. Both EADS and Motorola have submitted vocoders that are undergoing testing at the NTIA Institute for Telecommunications Sciences (ITS) facility in Boulder, Colo. “There’s a number of different vocoder thoughts on the table,” Pittman said. Motorola’s half-rate vocoder has undergone testing in a controlled benign environment and is “better than the baseline [Phase 1 vocoder],” she said. The P25 steering committee has requested additional testing in non-clean conditions, introducing errors in transmissions as well as background noise.
“I’d say there is a concern with the vocoder, and something that is a milestone [when finalized],” Pittman said. “[P25 committee members] are from Missouri, they all need to see test results. We would like to see the testing move quickly so the committee can move forward with test results. The work they yet have to do is the half-rate vocoder in less than ideal conditions with background noises.”
While relatively new to the radio world, EADS poses a unique challenge to Motorola’s historic leadership in the public-safety arena and is one of the few companies in the world with both the technical expertise and corporate resources to give Motorola a good workout, as EADS is a global leader in aerospace, defense and related services. Last year, the company generated revenues of 31.8 billion euros with a staff of 110,000 worldwide employees, manufacturing everything from Airbus commercial passenger aircraft to earth observation satellites. It used its financial strength this year to acquire Nokia’s Professional Mobile Radio business consisting of 325 employees, adding more than 130 customers in 56 countries to its portfolio.
Operating in North America since 2001, EADS Public Safety has sold two radio systems, based on the European TETRAPOL standard, one to the U.S. Army Training Center at Ft. Irwin, Calif., and the other to an undisclosed public-safety organization in Canada. “TETRAPOL is similar to P25,” said Peter MacLaren, president and CEO of EADS Public Safety. “It has similar signal reach and capacity, but with richer features.”
MacLaren is not sure when the P25 community will finally choose between the EADS and Motorola approach. “I think they hope for a miracle to occur, and there’ll be a compromise. But there’s no magic solution.”
EADS has proposed a different modulation scheme under its TDMA implementation that would provide more throughput, 16 kb/s, whereas the existing modulation scheme only delivers 9.6 kb/s. “The main implication is we can support two channels with today’s [existing] codecs and just add to that [EADS’] enhanced full rate codec available today, whereas Motorola has to change codecs,” he said.
Motorola’s proposal keeps the same 9.6 kb/s throughput, but introduces other problems. “The enhanced half-rate codec doesn’t provide the same quality and makes internetworking difficult. You can’t have a half-rate codec talk to a full-rate codec,” MacLaren said.
According to MacLaren, EADS’ proposal provides a full-rate codec that won’t break current encryption methods. It also would open the door to introducing improved vocoders for better voice quality in the narrower bandwidth.
One industry executive, not wanting to be named because of his company’s work with both companies, said that the choice between Motorola’s and EADS’ solutions was a toss-up. “The stakes are big for both of them. Motorola’s proposals are easier to implement and don’t require as much work. EADS’ would require more work overall, but is more elegant and offers some extras,” he said. “From a commercial point of view, Motorola is more attractive. From the user perspective, EADS is more the APCO for the future.”
He went on to assert that the APCO Project 25 Committee had slowly lost patience with Motorola for having dragged out the decision on a new air interface and that EADS had come to meetings prepared to challenge Motorola. “EADS is, technically, extremely competent, extremely well-prepared. They are well-prepared for critics. Motorola finds this hard to deal with. Motorola has had to engage far more actively than it intended.”
Pittman believes that the P25 committee will agree on a single TDMA solution next year. “I’m hoping for sometime in 2006,” she said. “Based on the current rate of progress, it is unlikely that there’ll be anything in 2005.”
Once the standard is published, there is no clear timetable for vendors to produce equipment that meets it. “It’s anyone’s guess,” Pittman said. “The steering committee members use the figure of 18 months. I know from a company perspective, we’re making strategic decisions so we can get to the market with the right product. Everyone has to make their own gamble.”
Regardless, both vendors and the P25 Committee are going to face increasing pressure from public-safety users and the government to finalize other parts of the Phase 2 specifications. “I wouldn’t say we’re comfortable with things the way they are today,” said Don Pfohl, co-director of APCO Project 25. “The U.S. Congress has gotten concerned enough to pass legislation to see what can be done to speed up the ISSI specification.”
Pfohl believes that development of the console interface and fixed system interface have been slowed down because of the delay in the ISSI.
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|Channel bit rate||9.6 kb/s|
|Frame Format||Includes error correction|
|Phase I standards were formalized in 1995 and published under the ANSI/TIA 102 series of documents.|
|Phase I||Phase II|
|Bandwidth||12.5 kHz||6.25 kHz|
|Modulation||QPSK-c||To be determined|
|Vocoder||IBME||To be determined|
|*The three other parts of Phase II currently in process of definition are: Inter RF subsystem interface (ISSI), console interface and fixed station interface|
|Bandwidth||6.25 kHz||6.25 kHz|
|Channel bit rate||9.6 kb/s||16 kb/s|
|A single-Phase 2 TDMA specification may not be finalized until 2006 at the earliest.|