The U.S. Responds: Project 25 Technology Is Forged.
The Project 25 initiative brought together a wide array of local, state, and government agencies with support from the U.S. Telecommunications Industry Association (TIA) to evaluate and develop a new standard for digital two-way radio.
Co-chaired by APCO International and the National Association of State Telecommunications Directors (NASTD), a steering committee was given the job of evaluating the plethora of technologies. Several sub-committees, in-turn, provide the technical expertise to research a number of specialized areas. The objective of the steering committee was to establish an open narrowband digital radio standard. Such an open standard would stimulate competition among multiple vendors for contracts to supply compliant networks with interoperable products. Secondary principles include achieving maximum radio spectrum efficiency, and simplifying P25 equipment.
A Phase-in Approach to Deployment.
The final documents establishing the Project 25 Standard were signed in Aug. 1995. Today, the Project 25 standard calls for a two–phased implementation. Phase I, specifying a 12.5 kHz bandwidth and using the C4FM modulation scheme, is nearly complete. With an eye toward smoothly migrating from 25-kHz analog to 12.5-kHz digital, Phase I radios are capable of both 25 kHz analog FM and 12.5-kHz digital C4FM operation. This allows operators to procure radios as budgets allow.
Similarly, Project 25 Phase II involves a well-planned migration strategy, both in the forward and backward direction. Phase II calls for a 6.25-kHz bandwidth specification, using a CQPSK modulation scheme. Just as in the case of the migration from analog to digital in Phase I, the Phase II implementation allows the use of Phase I radios. Again, since C4FM and CQPSK radios may share a common receiver design, users are allowed the flexibility to gradually replace Phase I radios, base stations and repeaters. Alternative TDMA technologies have been proposed for Phase II and are currently under consideration to ensure they provide the level of functionality required.
Project 25 Technology Basics.
Project 25 was envisioned as a unique approach to developing a common digital radio standard that provided public safety professionals with a new level of performance, efficiency and security. Project 25 standards were also designed with special consideration given to enhancing interoperability, and providing the capability to handle high bandwidth data applications (e.g. transmit photos, criminal records, fingerprints and limited-motion video).
The basic characteristics of Project 25 radios are:
Phase I—Emission designator 8K10F1E (C4FM, compatible four-level frequency modulation) in a 12.5 kHz channel.
Phase II—Emission designator of 5K76G1E (CQPSK, compatible quadrature phase shift keying) in a 6.25 kHz channel.
Common receiver for both C4FM and CQPSK to ensure full interoperability.
Encryption—As defined in the U.S. Data Encryption Standard (DES) algorithms.
Improved Multiband Excitation vocoder—Provides 4400 bits/s of digitized voice.
The first true P25-compliant system is expected to be the statewide P25 trunked system of the Michigan State Police.