Project 25 Documents & Standards Reference
Common Air Interface
The P25 CAI uses two access methods:
FDMA using a 12.5 kHz 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 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 breaks down P25 CAI documents as follows:
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
