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Project 25

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P25 (Project 25) (also APCO-25) is a standard for digital radio communications for use by federal, state/province and local public safety agencies in North America to enable them to communicate with other agencies and mutual aid response teams in emergencies. In this regard P25 fills the same role as the European Tetra protocol (although it is not compatible with Tetra).

Project 25 (P25) Suite of Standards

Recognizing the need for common standards for First Responders and Homeland Security/Emergency Response professionals, representatives from the Association of Public Safety Communications Officials International (APCO), the National Association of State Telecommunications Directors (NASTD), selected Federal Agencies and the National Communications System (NCS) established Project 25 (P25), a steering committee for selecting voluntary common system standards for digital public safety radio communications. TIA TR-8 facilitates such work through its role as the ANSI-accredited Standards Development Organization (SDO).

P25-compliant systems are being increasingly adopted and deployed. Radios can communicate in analog mode with legacy radios and in either digital or analog mode with other P25 radios. Additionally, the deployment of P25-compliant systems will allow for a high degree of equipment interoperability, compatibility and economy of scale. Specifically, P25 systems can be maintained and upgraded cost effectively over the system's life cycle, thus meeting user requirements, achieving interoperability and security, promoting committed manufacturers to provide compliant products, fostering competition and achieving cost-effective emergency/safety communication solutions. In light of recent worldwide terrorist activities, interoperability among first responders is a key initiative of many countries.

The P25 suite of standards involve digital Land Mobile Radio (LMR) services for local, state and national (federal) public safety organizations and agencies. P25 is applicable to LMR equipment authorized or licensed, in the U.S., under the National Telecommunications and Information Administration (NTIA) or Federal Communications Commission (FCC) rules and regulations. However, use of such equipment is not limited to public safety, and P25 equipment has also been selected and deployed in other private system applications, for example, to serve the needs for a high-quality, secure digital radio system for a railroad system, including rolling stock, personnel, and transportation vehicles.

P25-compliant technology is being deployed in several phases, based on TIA Engineering Committee work and the P25 standards TIA ultimately publishes. Vendors are currently shipping

  • Phase I: 12.5 kHz FDMA channel spacing 4 level FM (C4FM) at 4800 baud and 2 bits per symbol, yielding 9600 bits per second total channel throughput.
  • Phase II: 6.25 kHz channel spacing Compatible Quadrature Phase Shift Keying (CQPSK), also at 4800 baud and 2 bits per symbol.

Both standards use the IMBE vocoder to encode the voice signal.

Receivers designed for the C4FM standard can also demodulate the CQPSK standard, as the parameters of the CQPSK signal were chosen to yield the same signal deviation at symbol time as C4FM.

APCO-25 may be used in "conventional" mode without any intervening equipment between 2 radios, or in a trunked mode where traffic is automatically assigned to one or more voice channels by a Repeater.

APCO-25 signaling may also be used on the voice channels of a Motorola Smartnet® system.

The protocol supports the use of DES encryption (56 bit), Triple-DES encryption (112 bits), or AES encryption at up to 256 bits keylength (or no encryption).

Adoption

Adoption of these standards has been slowed by budget problems in the US, however funding for communications upgrades from the Department of Homeland Security usually requires migrating to APCO-25. It is also being used in other countries world wide.


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