Codan Radio P25 Training Guide - Manual (Page 93)

P25 RADIO SYSTEMS | TRAINING GUIDE
Chapter 7: P25 Phase 2 Page 85
CHAPTER 7: P25 PHASE 2
INTRODUCTION
This chapter describes the U
m2
over the air interface, the P25 Phase 2 two-slot Time Division Multiple
Access (TDMA) Common Air Interface. 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.
The Project 25 Statement of Requirements (SoR) defi nes a key goal to achieve spectrum effi ciency in
Phase 2 equivalent to one voice channel per 6.25 KHz. The P25 two-slot TDMA Standard for Phase
2 doubles the spectrum effi ciency of Phase 1 (12.5 kHz) operation to achieve this goal. The two-slot
TDMA Standard also maintains interoperability and compatibility with the Phase 1 Standard, including
support for the Inter-RF Sub-System Interface (ISSI), backwards compatibility with Phase 1 subscribers,
and encryption capability.
The P25 two-slot TDMA Standard is based on P25 trunking systems and does not support P25
conventional systems.
A P25 Phase 2 Frequency Division Multiple Access (FDMA) solution was fi nalized using Compatible
Differential Offset Quadrature Phase Shift Keying (CQPSK) modulation but is not in use. Phase 2
FDMA required transmitter linearization on subscriber units and infrastructure equipment to pass the
amplitude component of the CQPSK signal.
The P25 Phase 2 two-slot TDMA trunking Common Air Interface (CAI) is an addition to the P25 Standard
and does not replace the P25 Phase 1 FDMA CAI. The Inter Sub-System Interface (ISSI) has been
updated to include Phase 2 two-slot TDMA trunking messages. The Console Sub-System Interface
(CSSI) and Fixed Station Interface (FSI) are defi ned for conventional systems only. Phase 1 and
Phase 2 trunking systems connect to a Console Sub-System using the ISSI interface.