User's Manual Part 2

Node B Rack Mount Installation Guide
Version 0.0.3 Page 34 of 39
Step 12 GPS Installation & Operation
The Node B has an external/remote GPS antenna and receiver. The connection for the
antenna (N-Type) is located on the Digital Shelf, Figure 6-17.
The GPS timing signal is used by the Node B for the TDD frame timing, so that all Node B's
in a network are synchronized. The GPS signal is also used by the master oscillator for a
frequency reference. The Node B can operate for two hours after a loss of GPS timing but a
gradual drift of the frame timing will result in system interference and a loss of Node B
selection / reselection capability.
A suitable Node B GPS antenna is shipped with every Node B. This antenna should be used
with a maximum of 15 metres cable of RG6 type cable plus male N-type connectors at each
end. For longer runs, the cable losses will affect signal strength and could impede GPS
signal performance.
For proper operation of the GPS receiver, the Node B GPS Antenna must have a clear
southern view of the sky. A site survey should be done before Node B installation to verify
that the Node B installation location is suitable for GPS reception.
A simple survey method is to take a handheld GPS receiver to the site and verify that GPS
lock is obtained in the location of the Node B installation. The handheld GPS should be able
to obtain a "locked" condition within 2 minutes of power-on, and should be able to see a
minimum of 4 satellites at all times.
The GPS receiver, integral to the Node B Digital shelf, is automatically enabled when the
Node B is powered and there are no adjustments or settings to be made by the user.
Note: When the Node B installation is on or near a tower or building wall, the GPS survey
should replicate the configuration.
When tower space is at a premium, or when long cable runs are involved, it may be
preferable to use a single GPS antenna to feed multiple Node Bs. It is possible to use one
GPS antenna with up to three units, providing that a passive splitter is used.
Caution:
It is essential that in a ‘single GPS antenna supporting multi-Node B’ installation
only one of the Node B’s is designated and configured to supply the GPS antenna with +5V
via the GPS antenna cable as in a standard single installation.
The remaining subordinate Node Bs are provided their GPS signal through a DC block
device. Failure to do this may result in damage to the Node B. It should also be noted that in
the event of power failure to the DC supplying Node B, GPS reception to all Node B’s will be
affected.
Figure 6-17 : GPS Antenna
GPS Antenna
Field of Vision No
Obstructions