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User Manual
Airbridge cBTS3612 CDMA Base Station
2.4.3 Dual-Satellite Synchronization Antenna & Feeder
I. Overview
Many important features of CDMA system are closely related with global satellite
navigation system and are much dependent on it. If global satellite navigation
system does not work for a long time, the whole network will collapse. In
consideration of the system security and reliability, BTS receives the signals of GPS
system or of GLONASS system through the dual-satellite synchronization antenna &
feeder, to implement radio synchronization. In this way, the whole network can
operate normally without any adverse effect when GPS or GLONASS system is not
available. The following describes the application of GPS and GLONASS in CDMA
system.
1) GPS
CDMA network can be synchronized with GPS. GPS is a high precision global
positioning system set up by American Navy Observatory. It is a all-weather satellite
navigation system based on high frequency radio. It provides 3D-position
information, so users can attain high precision information about position, speed and
time. The 3D-position is accurate to less than 10 yard (approx. 9.1m) in space and
less than 100ns in time. The received signal is processed and used as the master
reference frequency.
The whole system consists of three parts: space part, land control part and user
part.
Space part is a group of satellites 20,183 kilometers high, orbiting the earth at a
speed of 12 hours/circle. There are 24 satellites together, running on 6 orbits. The plane of
each orbit is at a 55â angle with the equator.
The land control part consists of a main control center and some widely distributed
stations. The land control network tracks the satellites and controls their orbits
accurately. It also corrects astronomical data and other system data from time to
time and transmits to users through the satellites.
The user part includes the GPS receivers and their supporting equipment. The
CDMA system is actually a GPS user utilizing the timing function of GPS. GPS
satellites are synchronized with a cesium atom clock group on the land. Therefore,
GPS timing signal is steady and reliable. The frequency is in a long-term stability of
cesium atom clock level. BTS provides a highly stable crystal clock, which is stable
on a short-term base. The crystal clock together with GPS signals ensures the clock
absolute stability and reliability of CDMA system.
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System Description
2 Hardware Architecture
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