Codan Radio P25 Training Guide - Manual (Page 11)

P25 RADIO SYSTEMS | TRAINING GUIDE
Chapter 1: Introduction To P25 Page 3
Phase 2
The P25 Phase 2 Standards are based on a two-slot TDMA channel access method within 12.5 kHz
channel bandwidth and is used for P25 trunking systems. P25 Phase 2 two-slot TDMA trunking is an
addition to the P25 Standard and does not replace P25 Phase 1 FDMA. The P25 two-slot TDMA for
Phase 2 doubles the spectrum effi ciency of Phase 1 (12.5 kHz).
The P25 Phase 2 TDMA CAI uses two different modulation schemes for over-the-air transmission of
the 12 kbps data stream, Harmonized Continuous Phase Modulation (H-CPM), is a common constant-
envelope non-linear modulation and is transmitted by the subscriber equipment. Harmonized Differential
Quadrature Phase Shift Keyed modulation (H-DQPSK), is a non-coherent modulation scheme and is
transmitted by the fi xed site equipment.
A P25 Phase 2 FDMA solution was fi nalized (CQPSK), but never widely used.
The majority of this guide primarily deals with P25 Phase 1. More detailed information about P25
Phase 2 can be found in Chapter 7.
CONVENTIONAL VS. TRUNKED
In general, radio systems can be separated into conventional and trunked systems. A conventional system
is characterized by relatively simple geographically fi xed infrastructure (such as a repeater network)
that serves to repeat radio calls from one frequency to another. A trunked system is characterized by
a controller in the infrastructure which assigns calls to specifi c channels. P25 supports both trunked
and conventional radio systems. While this document deals primarily with conventional radio systems,
more detailed information about P25 trunking can be found in Chapter 6.