Telemetry method and apparatus

摘要

The invention performs coarse phase synchronisation until the received signal has positive in-phase and quadrature parts 702. It then performs fine phase synchronisation by calculating the vector product of the received signal with a quantised symbol output from a 2D slicer 705. A look up table of phase correction values is referenced with the cross product value 706. This value is fed through a loop filter to an oscillator/signal synthesiser which generates in-phase and quadrature signals for demodulation (See Fig. 6). This process may be repeated until the phase error/offset is less than a threshold 707. The process is carried out on a preamble signal of a QAM signal. The system may be used for wellbore telemetry communications. The description also discloses initialisation schemes for power, gain and equalisation filter settings.