APCO Project 25

Overview

Project 25 trunked radio systems are so named because they follow the open APCO Project 25 standard for public safety trunked radio systems. Multiple vendors make and sell Project 25 systems and compliant radios. Audio on these systems is exclusively digital using the APCO-25 Common Air Interface (CAI) standard.

Motorola's implementation of the Project 25 digital trunking standard is marketed as "ASTRO-25."

Different Types of Digital Trunking/Modulation

Project 25 / APCO-25

Project 25 uses the IMBE Vocoder. IMBE stands for Improved Multi-Band Excitation, and was developed by DVSI Inc. Numerous vendors have produced Project-25 capable subscriber equipment, including Motorola, EF Johnson, Uniden, Racal, and others. There are conventional voice solutions as well as trunking solutions available for this digital voice solution.

Currently, there are two trunking solutions available that use the Project-25 vocoder:

1. Motorola ASTRO IMBE - This is Motorola's APCO-25 compliant digital solution, and is also called the "ASTRO Digital CAI (Common Air Interface) Option". This is a proprietary trunking solution that uses the Project-25 vocoder as it's digital voice solution on top of a standard Motorola Type II Smartzone system. Some agencies using Motorola ASTRO APCO-25 IMBE systems include The City of Baltimore, Jefferson Parrish LA, The Metro Washington Airports Authority, Fairfax County VA, and Sarasota County FL.

The Motorola ASTRO IMBE solution uses the Motorola Type II 3.6 Kb Smartzone control channel.

The Motorola ASTRO IMBE solution can allow both analog and Project-25 digital radios to operate on the same network

2. Project 25 Digital Trunking - This is the Project 25 Digital trunking solution that is vendor independent and designed around the Project-25 Digital Trunking standards. The State of Michigan and the State of Colorado are two of the few systems that uses this format. This is becoming a more popular trunking format for new systems.

Project 25 Trunking uses a 9.6 Kb control channel.

All radios on a Project-25 Digital trunking system must use digital voice - no analog trunking capability is provided.