Alvarion BreezeACCESS II System Manual page 234

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antenna to generate the synchronization signals for the AUs. When
two or more BS-GU modules are daisy-chained, the signals from the
GPS antenna are transferred to all "slave" BS-GU modules via the
SYNC OUT - SYNC IN cable, and all BS-GUs use these signals to
generate synchronization signals for their AUs.
The BS-GU can detect whether a daisy-chaining cable is connected
to its' SYNC IN port; If a daisy-chaining cable is connected to the
SYNC IN port, the unit is a "slave" unit. If a daisy-chaining cable is
not connected to the SYNC IN port, the unit will behave like a
"master".
The BS-GU continuously checks whether it receives proper PPS
(Pulse Per Second) signals from the GPS antenna. Proper PPS
signals are exactly one second apart. When a BS-GU detects that it
does not receive proper timing signals from the GPS antenna, it will
behave as follows:
a. If the BS-GU is a "master", it will start generating
synchronization signals using its internal clock. The
synchronization signals will also be transferred to the SYNC
OUT port.
b. If a BS-GU is a "slave", it will use the synchronization signals it
receives from the "master" via the SYNC IN port. It will also
transfer these signals to its SYNC OUT port for use by the next
slave module if applicable.
A slave module continuously monitors the lines from the GPS
antenna in its SYNC IN port. If it determines that proper PPS signals
are received (at least three consecutive PPS signals one second
apart), it will automatically revert to the regular operating mode,
using the PPS signals for generating its synchronization signals.
A master BS-GU must enter a special antenna recovery mode to
check the validity of the signals it receives from the GPS antenna.
NOTE:
During Antenna Recovery mode the master BS-GU module stops generating
synchronization signals for several seconds. Therefore, the rate of entering this mode
should be minimal.
The antenna recovery mode can be activated either manually or
automatically, using the GPS Antenna Recovery menu:
Manual Recovery Mode - Enables to initiate a single antenna
recovery process during which the unit checks the signals it
receives from the GPS antenna. The manual recovery mode is
completely independent of the automatic recovery mode,
meaning that a manual recovery process can be initiated by the
user regardless of the selected option in Automatic Recovery
Option. Typically, manual recovery will be initiated after
connecting/re-connecting or fixing a problem in the GPS
antenna.
Manual Revision: 3.0
BreezeACCESS Version 4.3 Operations and Administration