| 摘要 |
A communication system utilizes an external signal of high accuracy to maintain a good degree of accuracy of synchronization of base sites. A good example of such a signal is the signal transmitted by the global positioning system (GPS) or, a high accuracy PCM (pulse code modulation) or other high accuracy signal provided by a terrestrial transmission network including the base sites. When the synchronization to the GPS signal on one or more base sites cannot be achieved, the communication system employs an alternate synchronization source on those base sites that are missing the synchronization to the GPS signal. The alternate synchronization source is a separate local oscillator of the base site. To achieve the degree of synchronization accuracy provided by the GPS signal, the communication system learns the behavior of each and every local oscillator. This characterization is performed on each base site, and is done by utilizing the GPS signal when the GPS signal is present. When the synchronization to the GPS signal is lost, the characterized local oscillator is then employed such that synchronization of the base sites is transparent to the base sites. Use of the GPS signal to characterize the local oscillators allows the characterized oscillator to provide the same degree of accuracy as that of the GPS signal. The method of characterizing the alternate synchronization source on a site basis makes it possible to take the local oscillators' individual characteristics, as well as the site specific conditions, into account. |
