GPS synchronization for wireless communications stations
View Patent ↗A method and system are specified to determine, provide, and exploit the precise time base relations between the distinct signal timings of the Global Positioning System (GPS) and a wireless communications system (WCS) for which the internal WCS downlink time base standards are not inherently synchronized to GPS timing. These downlink signal synchronization facilities are particularly beneficial for a wireless location system (WLS) and related methods and subsystems that provide mobile-station location determination through the exploitation of the time base synchronization information, e.g., to assist a GPS-equipped mobile station in determining its GPS-derived measurements with enhanced efficiency and accuracy.
1. A signal processing method for use in processing a base transceiver station (BTS) downlink signal, comprising:
acquiring a candidate time series from a received BTS downlink burst signal;
correlating a frequency correction channel (FCCH) replica with a candidate broadcast control channel (BCCH) beacon signal to determine a nominal frame time alignment and time of arrival (TOA) for an FCCH burst signal;
correlating a synchronization channel (SCH) extended training sequence to determine a time alignment and TOA for an SCH burst signal;
attempting to demodulate the SCH burst signal;
determining that the SCH demodulation is not acceptable, and in response thereto performing the following steps:
obtaining A-bis monitoring system (AMS)-derived possible partial/modulo frame and associated BSIC information for the candidate BCCH signal;
calibrating the AMS-derived timings to GPS-based times for possible partial/modulo frames, and using the candidate AMS-derived partial/modulo frame information to form the possible complete frame numbers (FNs) with associated reduced frame numbers (RFNs) for the SCH;
applying selected BSIC and FN/RFN to form a complete SCH replica; correlating the SCH replica with a candidate BCCH signal to refine the TOA measurement for the SCH burst signal;
integrating the SCH correlation with an associated FCCH correlation for a refined measurement of TOA;
determining that the correlation results are acceptable and propagating a measured GPS-timebased TOA to a frame boundary, thereby determining a measured GPS-timebased TOA corresponding to a frame boundary; and
forming a record of correlated BCCH carrier identification, BSIC, FN, and GPS-timebased TOA.
2. A signal processing system for use in processing a base transceiver station (BTS) downlink signal, comprising a processor and executable instructions for configuring the processor to perform a sequence of predefined steps, said steps including:
acquiring a candidate time series from a received BTS downlink burst signal;
correlating a frequency correction channel (FCCH) replica with a candidate broadcast control channel (BCCH) beacon signal to determine a nominal frame time alignment and time of arrival (TOA) for an FCCH burst signal;
correlating a synchronization channel (SCH) extended training sequence to determine a time alignment and TOA for an SCH burst signal;
attempting to demodulate the SCH burst signal;
determining that the SCH demodulation is not acceptable, and in response thereto performing the following steps:
obtaining A-bis monitoring system (AMS)-derived possible partial/modulo frame and associated BSIC information for the candidate BCCH signal;
calibrating the AMS-derived timings to GPS-based times for possible partial/modulo frames, and using the candidate AMS-derived partial/modulo frame information to form the possible complete frame numbers (FNs) with associated reduced frame numbers (RFNs) for the SCH;
applying selected BSIC and FN/RFN to form a complete SCH replica; correlating the SCH replica with a candidate BCCH signal to refine the TOA measurement for the SCH burst signal;
integrating the SCH correlation with an associated FCCH correlation for a refined measurement of TOA;
determining that the correlation results are acceptable and propagating a measured GPS-timebased TOA to a frame boundary, thereby determining a measured GPS-timebased TOA corresponding to a frame boundary; and
forming a record of correlated BCCH carrier identification, BSIC, FN, and GPS-timebased TOA.