Hardly anyone who has something to do with public safety communications agrees about anything when it comes to TETRA's features and capabilities vs. those of Project 25, the definition of "interoperability," the standards-setting process, and who has to license TETRA intellectual property rights and why and when and for what. Ready? Let's begin:

The "Project 25" U.S. standard for public safety digital radio may be the best chance to achieve interoperability among federal, state and local jurisdictions for services that protect life and property.

Interoperability is so important that some detest the idea that at this late date TETRA, a competing digital technology from Europe, might enter the field if it isn't modified for interoperability - whether some potential users want it modified or not.

Interoperability proponents have federal support. The FCC may require the use of Project 25 equipment in the new 700MHz public safety band.

European interoperability Europe can achieve public safety and commercial interoperability throughout the continent on its new private mobile radio service band (380MHz-400MHz) and its commercial mobile radio service band (410MHz-430MHz), among other frequencies. The fastest-growing inter-operable systems use a European standard originally called Trans-European Trunked Radio and renamed as Terrestrial Trunked Radio (TETRA). Yet, a competing, non-compliant digital technology has won 500,000 users in Europe and elsewhere, and it is not interoperable with TETRA. More about that later.

Some European governments interpret a European Union Treaty provision as requiring them to deploy only TETRA. In 1996, the United Kingdom's Home Office limited bids for its national police and emergency service network to TETRA suppliers. It awarded the $2.1 billion contract to British Telecom.

Matra Nortel, the French manufacturer of TETRAPOL, the competing and similarly named - though fundamentally different - digital technology, is challenging the exclusive procurement of TETRA and has some support from the European Commission. Matra Nortel argues that TETRAPOL's frequency-division, multiple-access (FDMA) technology is "equivalent" to the TETRA standard. As such, the company argues that government contractors must evaluate their tenders or they would breach European Union Treaty rules on the free movement of goods and services.

Despite separate European and U.S. decisions that favor interoperability with home-grown standards, some European manufacturers want the North American market opened up.

The interesting twist to all of this involves the different performance and capacity of time-division, multiple-access (TDMA) and FDMA technologies. TETRA is TDMA; Project 25 (Phase I) and TETRAPOL are FDMA.

Europe is more densely populated than the United States. It has few areas of sparse population as compared to our western states. Most of its public safety agencies, especially police departments, are organized into larger departments at federal and state levels. It doesn't have the many small municipal departments (those with only a few officers) that are common in this country.

This difference is important because a persuasive case has been made that FDMA serves small user groups and sparsely populated areas better, in part because it can be implemented with fewer channels when a small system fits the need. TETRA produces the equivalent of four channels in a 25kHz bandwidth as a minimum. Its infrastructure may require more sites for equivalent coverage to FDMA. TETRA reuses frequencies in multisite networks (and thus, might need more frequencies), either reducing the need for simulcast or compensating for its inability to simulcast, depending on how you look at it.

Which is better - and why? According to an older report written by an ETSI working group, for fewer than 10 channels per site and wide-area coverage, FDMA is superior. For more than 15 channels per site and limited area coverage, TDMA is superior. Even so, systems with few channels and increasingly sophisticated data applications could benefit from TETRA's ability to aggregate, on demand, four time-slots for 28.8kbps "high-speed" data capability.

Some U.S. jurisdictions are densely populated and have large public safety agencies. Several European-based manufacturers want to offer TETRA to them.

These manufacturers want to serve U.S. commercial users, too. TETRA was designed with public safety and commercial users in mind; Project 25 was not.

TETRA can be modified to fit Project 25's Phase II 6.25kHz-and-equivalent narrowband standard. Committees involved with the standard have begun working on the modification. Commercial users don't need the modification.

Manufacturers would rather not modify their products, in part because it will raise the price. The difference in price between FDMA and TDMA products is expected to be a key selling point.

With respect to public safety, it will come down to individual agencies making their own radio communications system procurement decisions based on what's most important to their operations. If some forgo interoperability, it will be despite every effort being spent to make it available.