Improvement of Holdover Characteristics of GPS Timing and Frequency Reference for CDMA System using WAVELET Transform

In the CDMA digital mobile communication network, the system timing of the base stations are generated using GPS Timing and Frequency Reference. It is, however, possible to drop the radio wave in a long tract of time by reason of the location or the failure of the Antenna circuits. In those cases, the reliability of the system will be degraded because of the drift, such as the aging, of the system clock. This paper describes a technique, based on the Wavelet transformation, to reduce the phase error and frequency drift of the GPS Timing and Frequency Reference when the GPS carrier signals could not be received. By simulations and experiments, we have achieved that the phase error is less than 10 microsecond within 48 hour in the state without GPS carrier signals, demonstrating the validity of the proposed technique.