Glossary 133
P
P25 Project 25. The Association of Public
Safety Communications Officials
(APCO) established Project 25 (P25).
This project was led by United States
Federal, state, and local government
representatives to develop standards
for interoperable digital radios and
systems to meet the needs of public
safety users.
See http://www.project25.org for further
information.
P25 Phase 1 P25 Phase 1 refers to radio systems
operating in 12.5 kHz analog, digital or
mixed mode on conventional networks
or in digital for trunking networks.
Phase 1 digital transmissions are FDMA
(Frequency Division Multiple Access)
based and use Continuous 4 level
Frequency Modulation (C4FM) or LSM,
a linear modulation for simulcast
systems.
P25 Phase 2 P25 Phase 2 refers to the P25 digital
Common Air Interface (CAI), Time
Division Multiple Access (TDMA) based,
which provides one voice channel per
6.25 kHz channel spectrum efficiency.
The current standards effort focuses on
2-slot TDMA which provides two voice
traffic channels in a 12.5 kHz allocation.
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