P25 and TETRA Technology Roundtable on May 3, 2012

“If coverage rather than capacity is your main requirement, then a P25 system will likely require fewer sites and prove a lower overall cost option,” said Tony Gray, regional business director (MENA) on behalf of P3 Communications. “If capacity is your main requirement, then TETRA may require fewer carriers per site for a given traffic capacity or accommodate more total users/calls per site, and may prove a lower overall cost solution.”

Gray addressed the background, properties and benefits of Terrestrial Trunked Radio (TETRA) during the roundtable on Tuesday afternoon, May 1, during the 2012 APCO Global Congress. He presented the vendor perspective.

From the end-user perspective, Chris Kindelspire, director of electronic operations for Grundy County Emergency Telephone System Board in Illinois, U.S., discussed the background, properties and benefits of P25.

The discussion, moderated by APCO International Deputy Executive Director Mark Cannon, centered on how interoperability is achieved for public safety by both standards.

“We both believe that the two systems are entirely complementary,” said Gray, speaking on behalf of Kindelspire.

In general, P25 is predominant in North and South America, Australia and China, and parts of Saudi Arabia and Turkey. TETRA is in wide use in Europe and the Middle East.

TETRA is an open standard developed by the European Telecommunications Standards Institute (ETSI), defining a series of open interfaces as well as services and facilities, which together allow independent manufacturers to develop infrastructure and terminal products that fully interoperate.

In terms of technology, TETRA employs four-slot Time Division Multiple Access (TDMA) technology. It uses 25 kHz spaced RF bearers divided into four time slots each. Thus, TETRA provides four communications channels per 25 kHz channel, an efficient use of spectrum.
According to Gray, TETRA also defines a rich variety of standardized services and functionality. “There’s quite a bit of functionality in sending and receiving data packets,” said Gray.

Benefits for the user include a manufacturer-independent supply of subscriber equipment, a wide selection of products, gateways, special terminals, etc., low prices, constant improvement and increased speed of innovation.

Benefits for the manufacturer include a large, global market, critical mass for special products, faster time to market, increased investment opportunity, and one common specification, thus no vendor bias.

“Security was one of the fundamental driving forces for the development of TETRA,” said Gray.
There are layered security measures built into TETRA, such as mutual two-way authentication between radios and networks, standard air interface encryption (AIE) and an option for end-to-end encryption.

Gray also touted the “extremely good voice quality and elimination of background noise” of TETRA.

Members of the audience who use TETRA indicated that one serious drawback is the assumption that users will use infrastructure from a single company. They would like the open standard to be enforced on manufacturers at that level as well.

Also known as APCO Project 25, the P25 suite of standards was developed via a long-standing partnership between the public safety communications community and industry manufacturers whose goal is to satisfy the complex and evolving mission-critical communication needs of users for interoperable, narrowband land mobile radio equipment and systems.

To accomplish this vital goal, users and manufacturers participating in the P25 process develop voluntary, consensus communications standards under the auspices of American National Standards Institute (ANSI)-accredited Telecommunications Industry Association (TIA). According to the APCO International website, “The P25 process focuses on the practical realization of the significant benefits inherent to digital radio communications technologies and promotes the competitive offering of compliant P25 equipment and systems for effective use by a highly diverse user community on a worldwide basis.”

P25 is an open, user-driven standardization process, with technical and operational requirements established through the participation of its stakeholders, including public safety practitioners from different countries representing different levels of government. The standards published by TIA establish the basis upon which manufacturers develop, implement and competitively offer P25 equipment and systems; recognized laboratories conduct P25 compliance testing; and users specify, procure and operate P25 radios and communications infrastructure.

One key advantage to P25 over TETRA, said Kindelspire, is that you can phase it in. Because it’s backward compatible, you don’t have to replace your entire system all at once.

That backward compatibility also helps meet the goal of interoperability. When agencies from another area or on a different system roam into a P25 system — for a mutual aid response, for example — the connectivity is seamless. Although they cannot operate in P25 mode, the P25 digital radios can still receive and transmit the analog signal.

There’s no backward compatibility in TETRA. “It was never intended,” said Gray. In practice, the only way for a VHF radio to operate in a TETRA system is through a gateway. By doing so, you lose the inherent encryption ability.

Although there’s a growing emphasis on encryption and data, at this time encryption is an option under the P25 standards; it’s not inherent.
Phase 1 P25 radio systems operate in a 12.5 kHz analog, digital or mixed mode, and like TETRA, P25 is a TDMA software-defined solution.
“P25 offers improved voice quality over standard analog signals, especially at low or noisy RF carrier levels,” said Kindelspire.
When considering either option, agencies need to keep in mind that TETRA radios cannot be used on a P25 infrastructure or vice versa. They use completely different signaling.

However, there are gateway devices available so P25 and TETRA can work together.
Another difference: P25 is capable of simulcasting; whereas TETRA is limited to multicasting. “We’re able to cover a larger area because of simulcasting,” said Kindelspire.

TETRA radios also have lower power, thus, reduced coverage area in comparison to P25.

“There’s a fit for one, and there’s a fit for the other,” said Kindelspire. “It comes down to capacity and coverage, and it’s a huge spectrum issue.”

Source: APCO International