User's Manual

CSM System Time – GPS & LFR/HSO Verification
68P64115A18–1
Mar 2003
1X SC 4812T Lite BTS Optimization/ATP Software Release R2.16.1.x
DRAFT
3-44
CSM System Time – GPS & LFR/HSO Verification
Clock Synchronization Manager (CSM) Sub–system Description
Overview – Each BTS CSM sub–system features two CSM boards per
RFMF. The primary function of the CSM cards is to maintain CDMA
system time. GPS is used as the primary timing reference and
synchronizes the entire cellular system. In typical operation, the primary
CSM locks its Digital Phase Locked Loop (DPLL) circuits to GPS
signals. These signals are provided by either an on–board GPS receiver
module (RF–GPS) or a remote GPS receiver (RGPS). RGPS uses a GPS
receiver in the antenna head that has a digital output. The second
generation CSM card (CSM–II) is required when using the RGPS. A
CSM–II card can also be equipped with a local GPS receiver daughter
card to support an RF–GPS signal.
SCCP Shelf CSM Card Slot Assignments – The GPS receiver is
interfaced to the board in SCCP shelf slot CSM 1. This card is the
primary timing source, while the card in slot CSM 2 provides
redundancy. The redundant card, does not have a GPS receiver.
CSM–II Card Type Description – Each CSM–II card features a
temperature–stabilized 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 3-19
for source selection/verification procedures):
S GPS: local/RF–GPS or remote/RGPS
S LORAN–C Low Frequency Receiver (LFR) or High Stability
Oscillator (HSO)
S External reference oscillator sources
CDMA Clock Distribution Card (CCD) Description – CCD cards
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.
CSM Card Redundancy – 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. GPS timing
synchronization is continually maintained between the primary and
redundant CSM–CCD pairs.
Secondary Timing References – The BTS may be equipped with a
LORAN–C Low Frequency Receiver (LFR), a High Stability Oscillator
(HSO), or external 10 MHz Rubidium source which the CSM can use as
a secondary timing reference. Continuous GPS synchronization is
maintained for the LFR or HSO secondary timing references. The CSM
monitors and determines what reference to use at a given time.