Project 25 Documents & Standards Reference

Common Air Interface

The P25 (Project 25) CAI (Common Air Interface) uses two access methods:

• FDMA (Frequency Division Multiple Access) using a 12.5 KHz (kilohertz) channel — mandatory for all P25 Phase 1 systems. Phase 1 refers to P25 requirements and standards for a digital CAI that provides for channel reduction from 25 kHz to 12.5 kHz.

• TDMA (Two-Slot Time Division Multiple Access) using two 6.25 kHz equivalent channels or slots in a single 12.5 kHz channel — optional (mandatory if supporting Two-Slot TDMA Trunked Digital features) for all P25 Phase 2 systems. Phase 2 refers to P25 requirements and standards for a digital CAI that provides two 6.25 kHz equivalent channels or two slots in a single 12.5 kHz channel.

Operation in a conventional mode is mandatory for Project 25, while operation using a trunked mode is optional. The PSCR program’s P25 DSR (Project 25 Documents & Standards Reference) breaks down P25 CAI documents as follows:

• General CAI Documents

• FDMA Air Interface Documents

o FDMA Conventional Digital—Phase 1

o FDMA Trunked Digital—Phase 1

• TDMA Air Interface Documents

o Two-Slot TDMA Trunked Digital—Phase 2