User's Manual
BTS Configuration – continued
DRAFT
SC300 1X BTS Hardware Installation, ATP, and FRU Procedures
JAN 2002
7-26
Synchronization Background
GPS
GPS is typically used as the primary timing reference for CDMA BTSs.
In applications where RGPS is used, the BTS is said to be synchronous
with CDMA system time. The RGPS provides a 1 Pulse Per Second
timing reference and Time Of Day information to allow the BTS to
synchronize to CDMA system time.
HSO
A High Stability Oscillator (HSO) within the BTS provides a backup
timing reference in the event of a GPS outage. Using only the HSO, the
BTS can maintain CDMA system time for up to 24 hours. The BTS can
also use the HSO as the primary timing reference (non–synchronous
operation). However, synchronization to CDMA system time is not
possible. The HSO provides a 1 Pulse Per Second timing reference to
allow the BTS to remain synchronized to CDMA system time in the
event of a GPS outage (synchronous operation) or to provide a stable
frequency reference (non–synchronous operation).
The HSO must be installed with GPS tracking for at least
24 hours before the HSO can provide 24 hours of backup
for CDMA system time synchronization.
NOTE
BTS
The BTS uses a Digital Phase Locked Loop (DPLL) to track the RGPS
and/or HSO and generate a 19.6608 MHz CDMA timing reference. This
timing reference, in conjunction with Time Of Day information provided
by the RGPS, allows the BTS to synchronize to CDMA system time. A
2 Second reference is also generated by the BTS to allow alignment of
Pilot offsets for the BTS and external test equipment. Both the 19.6608
MHz (19 MHz) and 2 Second (2 Sec) references are available via SMA
connectors located in the Diagnostic Access Area.
In order for the DPLL to begin the RGPS tracking process, the RGPS
must be tracking GPS satellites. In order for the DPLL to begin the
HSO tracking process, the BTS must be powered up (warmed) for at
least 15 minutes.
The DPLL status is defined as being in one of five states: Init, Warm,
A1, A2 and TK.
The Init state is the starting state of the DPLL.
The Warm state is the condition during the 15 minute BTS warm up
time.
The A1 and A2 states are acquisition states when the DPLL is
adjusting the 19.6608 MHz frequency based on the available reference
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