Measuring the phase of received signals

摘要

The present disclosure relates to a method to determine the phase of a signal when transmitter and receiver circuits use separate clocks. A discrepancy between the separate clocks is determined, as is a correction factor between the separate clocks. The phase is determined using a measured time of arrival of the signal, the determined discrepancy, and the determined correction factor. A drift factor and an expected start time of a pulse sequence may be used to determine the discrepancy. A start time of a pulse within the pulse sequence is determined and used to determine the correction factor. The method works by either absolute synchronization of the separate clocks, or by making the measurements independent of clock synchronization.

主权项

1. A method to determine a phase of a signal with transmitter and receiver modules each having circuits that use separate clocks comprising:
disposing the transmitter and the receiver modules into a borehole in a subsurface formation; sending a synchronizing signal from the transmitter module to the receiver module while the transmitter and receiver modules are in the borehole;determining a clock difference between the separate clocks from the synchronizing signal;
performing a hardware adjustment to at least one of the circuits to adjust at least one of the separate clocks by the clock difference to synchronize the separate clocks; and determining the phase with the synchronized separate clocks; wherein the determining the clock difference comprises:
determining a drift factor between the separate clocks;determining expected start times of a synchronizing pulse sequence relative to each of the separate clocks; anddetermining the clock difference using the determined expected start times of the synchronizing pulse sequence and the drift factor; and wherein determining the expected start time of the synchronizing pulse sequence comprises:
determining a time of occurrence of a final pulse in the synchronizing pulse sequence relative to each of the separate clocks;determining, for an adjacent, subsequent pulse sequence, a time of occurrence of a synchronization pulse of the adjacent, subsequent pulse sequence relative to each of the separate clocks;determining the difference between the determined time of occurrence of the final pulse in the pulse sequence and the determined time of occurrence of the synchronization pulse of the adjacent, subsequent pulse sequence relative to each of the separate clocks; anddetermining the expected start time using the determined differences.