Codan Radio P25 Training Guide User Manual
Page 98
TRAINING GUIDE | P25 RADIO SYSTEMS
Chapter 7: P25 Phase 2
Page 90
The use of an FDMA Phase 1 Control Channel provides backwards compatibility to Phase 1 systems,
as it can control and manage both Phase 1 FDMA and Phase 2 TDMA subscribers (using the TRC) as
shown in Figure 7-5. A Phase 2 trunking system must have Phase1 traffi c channels available for this
backwards compatibility and for any data capability.
Figure 7-5: P25 Phase 1 and 2 Trunking System
Subscriber TDMA capabilities are registered with the TRC during the registration process on the control
channel. When Phase 2 subscribers make a voice call to other Phase 2 subscribers (in the talk group),
the TRC will identify the TDMA capability of the subscribers and assign a TDMA traffi c channel (and
time slot). When a Phase 2 subscriber makes a data call, or a voice call to a Phase 1 subscriber, the
TRC will assign an FDMA traffi c channel. Phase 1 subscribers will ignore any messages relevant only
to TDMA subscribers. Phase 1 FDMA is used by all Phase 1 and Phase 2 subscribers for Talk-Around,
direct subscriber to subscriber communications.
Phase 2 trunking systems do not synchronize the FDMA control channel to the TDMA traffi c channels.
Phase 2 TDMA subscribers, when monitoring the Phase 1 FDMA control channel, use the Phase
1 control channel (with TDMA extensions) to synchronize and align with the inbound TDMA traffi c
channel. The Phase 2 standard allows for low latency switching between the FDMA control channel
and TDMA traffi c channels.
H-DQPSK
Phase 2
Subscriber Unit
Phase 2
Talk Group
Control
Channel
FDMA
Phase 1
12.5 KHz
Phase 2 to Phase 2 Voice Call
Assigned any Phase 2 TDMA
Traffic Channel (with time slot)
for all Voice Communications
Traffic (Voice or
Data) Channel
FDMA
Phase 1
12.5 KHz
Traffic (Voice)
Channel
TDMA
Phase
2
12.5 KHz
TDMA
Phase
2
Traffic (Voice)
Channel
TDMA
Phase
2
12.5 KHz
TDMA
Phase
2
Phase 2
Subscriber Unit
Phase 1
Talk Group
Phase 2 to Phase 1 Voice or Data Call
(or vice versa)
Assigned any Phase 1 FDMA
Traffic Channel for all
Voice or Data Communications
Traffic (Voice or
Data) Channel
FDMA
Phase 1
12.5 KHz
Trunking Resource Controller (TRC)
C4FM
H-CPM
H-DQPSK
H-CPM
C4FM
C4FM
C4FM