TB9400/TN9275 Installation and Operation Phase 2 Internal Timing 117
© Tait International Limited May 2023
6 Phase 2 Internal Timing
6.1 Introduction
P25 Phase 2 (trunking) channels require timing synchronization even in
non-simulcast networks. According to the P25 standard:
All outbound two-slot TDMA radio channels at a Site shall be time-
aligned. This means that all superframes on all outbound paths of
TDMA channels at a Site are time-aligned. In addition, there is symbol
and burst alignment on all outbound paths of TDMA channels so that
symbol sync, burst sync, ultraframe sync, and superframe sync on one
TDMA channel gives symbol sync, burst sync, ultraframe sync, and
superframe sync on other TDMA channels at that Site. [TIA.102-
BBAC-A, 3.6]
The reason the standard demands time alignment of channels is that an SU
may more quickly acquire a channel if it knows the timing in advance, thus
reducing the time required to enter a call.
Prior to base station firmware release 3.45, the means of time-aligning
channels at a site was to treat Phase 2 operation as simulcast: Timing must
be co-incident across sites, and a by-product of the simulcast design is that
timing is also aligned between channels at the same site. An unfortunate
by-product of the time-alignment-as-simulcast solution is that non-
simulcast Phase 2 capable networks still require expensive timing units to
provide the timing inputs that ensure channel time-alignment at each site.
6.2 Internal Timing
Beginning with firmware version 3.45, Tait base stations in Phase 2 non-
simulcast sites can exchange timing signals amongst themselves to ensure
timing alignment of the downlink transmitted signals. External timing units
are not required. The following table summarizes the options:
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