Patent ID: 9574441
Date: 2017-02-21
CPC Classifications: E21B,H04B,H04L

Claim:
1. A method for modulating a downhole telemetry signal using a fluid pressure pulse generator that generates pressure pulses of multiple pulse heights in a drilling fluid including a low amplitude pressure pulse and a high amplitude pressure pulse having an amplitude that is greater than the amplitude of the low amplitude pressure pulse, the method comprising: (a) generating the low and high amplitude pressure pulses and measuring and determining the amplitudes thereof; (b) converting measurement data into a bitstream comprising symbols of a selected symbol set; (c) only when the low and high amplitude pressure pulses have determined amplitudes that are between a low amplitude reference pressure and a high amplitude reference pressure, encoding the bitstream into a pressure pulse telemetry signal using a modulation technique that includes amplitude shift keying wherein each symbol of the selected symbol set is assigned a pressure pulse having a unique amplitude and that is selected from the low and high amplitude pressure pulses; and (d) generating pressure pulses in the drilling fluid corresponding to the telemetry signal.