Codan Radio P25 Training Guide - Manual (Page 19)

P25 RADIO SYSTEMS | TRAINING GUIDE
Chapter 1: Introduction To P25 Page 11
Improved Audio Quality
With 2800 bits per second of the total 9600 bits per second channel capacity allocated to error correction,
Phase 1 P25 digital signals have improved voice quality over standard analog signals, especially at low
or noisy RF carrier levels. The IMBE™ voice coder converts voice information into digital data and then
the data is protected using error correction codes. The error correction is able to correct for small errors
in the received signal. Since the audio is digitally encoded, the background noise typically present in
analog systems is also removed.
Figure 1-7: Analog to P25 Channel Comparison
Enhanced Functionality
Phase 1 P25 radio systems use 2400 bits per second for signaling and control functions. The signaling
capabilities include selective calling (Source and Destination ID), talk groups (TGID), network (repeater)
access codes (NAC) and emergency fl ags all as standard P25 digital features.
Other P25 signaling includes; Manufacturers identifi cation codes (MFID) which uniquely identifi es
different manufacturers to customize radio capabilities, Low Speed Data for user applications, encryption
keys and algorithms for secure transmission and many other standard signaling formats.
1 25 kHz Channel 2 x 12.5 kHz Channels
Voice
Signaling
4400 bits/s voice
20 ms of speech =
88 bits of
information to be
transmitted over
the radio link
2800 bits/s error
correction
2400 bits/s
signaling
Total 9600 bits/s