The increasing presence of Project 25

Papers on various radio technologies were presented at last year’s RadioComms Connect event in Melbourne. This article looks at another of the technologies discussed - P25 - and charts some of its evolving features.

The Project 25 radio system has scalable networks and terminals - from conventional to voting, simulcast and trunking, analog compatibility and a breadth of competing vendors providing options and value for users, and it is claimed to be the only open digital radio technology that provides all these benefits.

In addition, its adoption in countries such as Australia, New Zealand, Brazil, Canada, Russia and the Middle East adds further strength to its versatility as its uses have now gone beyond public safety to include utilities, transport, general services and public works.

These strengths and others were discussed by Trevor Laughton, who is the strategy and innovation manager of Tait Radio Communications. He called his presentation ‘The Increasing Presence of Project 25’.

Looking briefly at the history of the system, he said that it was initiated in 1989 by the US Association of Public Safety Communication Officials (APCO). Twelve years later, following the attack on the World Trade Centre, the need for interoperability was further accelerated among public safety agencies.

P25 is a suite of standards that defines interoperable communications for emergency services and although the initial standards were released in 1995, they continue to evolve beyond the initial US focus and into the world arena.

The standard is becoming incredibly comprehensive, specifying not just the common air interface and encryption methods, but also all the wired interfaces in the network.

Standards require a purpose as does the radio system itself he said. Some of these objectives include ensuring competition in life cycle procurements and product choices, proving user-friendly equipment, efficiently using radio spectrum, allowing efficient and reliable intra-agency and inter-agency communications.

Tait, as one of the prime movers in the development of P25, saw early on that it was better to provide coverage rather than capacity. As a result, the system is a natural choice for low-density, wide-area applications for countries such as Australia.

It also uses existing spectrum and is backwards compatible with FM analog, dual mode digital and FM, and it makes migration between them easy.

Other advantages include its scalability from conventional to voting to simulcast and to trunking. It also has an open standard that is user-driven and its features are clearly defined.

Phase 1 of the P25 requirements and standards call for a digital common air interface using FDMA 12.5 kHz channels that also had to be backwards compatible with FM analog.

Under phase 2 a new vocoder has been approved, the channel bandwidth will be reduced to 6.25 kHz equivalency and units must be compatible with phase 1 equipment.

Also, under phase 2, the final trunking definition document is due to be published this year as are a number of test documents still to be completed. Meanwhile, work is beginning on defining the conventional application phase 2.

The availability of phase 2 technologies in the future does not supersede phase 1 technology. Phase 1 will continue to be available for new purchases and will be supported by phase 2 technology so that interoperability between them is possible with the appropriate system design.

With the main advantage of phase 2 being extra channel capacity, it may not always be necessary or practical to roll out phase 2 equipment in the regional areas that emergency services often operate in.

Ensuring the future development of P25 has resulted in the Compliance Assessment Program (CAP) that recognises manufacturers and independent laboratories that any vendor can access to test their P25 products to the standard and publish a Supplier’s Declaration of Compliance (SDoC).

The CAP is currently focused on ensuring interoperability between participating manufacturers’ phase 1 equipment and the process allows multiple manufacturers to work together to improve the technology of the system.

Trevor’s paper more than clearly illustrates that P25 is anything but a static system waiting to be superseded by another one. Developments in standards are an ongoing process to ensure that the system meets users’ ambitions.

Technical innovation is incorporated where it is believed to be useful but underlining all this is the need and realisation that P25 must provide interoperability for customers.