User's Manual

CSM System Time – GPS & LFR/HSO Verification
08/01/2001
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1X SCt4812ET Lite BTS Optimization/ATP
PRELIMINARY
Clock Synchronization
Manager (CSM) System Time
The primary function of the Clock Synchronization Manager (CSM)
cards is to maintain CDMA system time. The CSM card in SCCP shelf
slot CSM–1 is the primary timing source while the card in slot CSM–2
provides redundancy. The second generation CSM card (CSM2) is
required when using the remote GPS receiver (R–GPS). R–GPS uses a
GPS receiver in the antenna head that has a digital output to the CSM2
card. A CSM2 card can have a local GPS receiver daughter card to
support an RF–GPS signal.
Each CSM2 card features a temperature–stablized, crystal oscillator that
provides 19.6608 MHz clock, even second pulse, and 3 MHz reference
signals to the synchronization source selected from the following (refer
to Table 3-20 for source selection/verification procedures):
S GPS: local/RF–GPS or remote/R–GPS
S LORAN–C Low Frequency Receiver (LFR) or High Stability
Oscillator (HSO)
S External reference oscillator sources
CDMA Clock Distribution Cards (CCDs) buffer and distribute
even–second reference and 19.6608 MHz clock signals from the CSM
cards. CCD 1 is married to the card in slot CSM–1, and CCD 2 is
married to the card in slot CSM–2.
The BTS switches between the primary and redundant units (card slots
CSM–1 and CSM–2, respectively) upon failure or command. A failure
in CSM–1 or CCD 1 will cause the system to switch to the
CSM–2–CCD 2 redundant card pair.
Fault management has the capability of switching between the GPS
synchronization source and the LFR/HSO backup source in the event of
a GPS receiver failure in CSM–1. During normal operation, the card in
CSM–1 selects GPS as the primary timing source (Table 3-20). The
source selection can also be overridden via the CDMA LMF or by the
system software.
In addition to providing GPS synchronization to the LFR or HSO
back–up sources, synchronization between the primary and redundant
CSM–CCD pairs increases reliability.
Low Frequency Receiver/
High Stability Oscillator
The CSM performs the overall configuration and status monitoring
functions of the LFR/HSO. In the event of GPS failure, the LFR/HSO is
capable of maintaining synchronization initially established by the GPS
reference signal.
The LFR requires an active external antenna to receive LORAN–C RF
signals. Timing pulses are derived from this signal, which is
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