Receiver for an Acoustic Telemetry System

Abstract

One embodiment includes a method comprising receiving an acoustic signal that is propagated along a drill string. The method also includes correlating the acoustic signal to a first stored acoustic signal representing a first symbol, wherein the first stored acoustic signal is acquired from a propagation along the drill string in an approximately noise free environment.

1 - 22 . (canceled) 
     
     
         23 . A system comprising:
 a drill pipe that includes:
 an acoustic telemetry transmitter to transmit an acoustic signal along the drill pipe, wherein the acoustic signal includes a first symbol in a first symbolic interval and a second symbol in a second symbolic interval; and 
 an acoustic telemetry receiver that includes a tail subtract logic to receive the acoustic signal that is propagated along the drill pipe, wherein the tail subtract logic is to subtract a tail of the first symbol that is within the second symbolic interval from the second symbol to generate a corrected second symbol. 
   
     
     
         24 . The system of  claim 23 , wherein the tail subtract logic is to receive the acoustic signal during a drilling operation. 
     
     
         25 . The system of  claim 23 , wherein the tail subtract logic is to receive the acoustic signal during a drill stem test operation. 
     
     
         26 . The system of  claim 23 , wherein the acoustic telemetry receiver includes a training logic to determine a representation of a symbol in an approximately noise free acoustic signal during a training period. 
     
     
         27 . The system of  claim 26 , wherein the acoustic telemetry receiver includes a correlation logic to correlate the corrected second symbol with the representation of the symbol in the approximately noise free acoustic signal. 
     
     
         28 . The system of  claim 27 , wherein the acoustic telemetry receiver includes a detection logic to determine whether the corrected second symbol is the representation of the symbol in the approximately noise free acoustic signal based on a threshold. 
     
     
         29 . The system of  claim 23 , wherein the acoustic telemetry receiver includes a timing recovery logic to locate the first symbolic interval and the second the second symbolic interval. 
     
     
         30 . The system of  claim 29 , wherein the timing recovery logic includes an early-late-gate correlation timing circuit. 
     
     
         31 . The system of  claim 23 , wherein the drill pipe includes a drill string. 
     
     
         32 . The system of  claim 31 , wherein the drill string includes a sensor to monitor a downhole parameter. 
     
     
         33 . The system of  claim 32 , wherein the acoustic signal is to carry communication related to the downhole parameter. 
     
     
         34 . The system of  claim 32 , wherein the downhole parameter is from a group consisting of a resistivity of a subsurface formation, porosity of the subsurface formation, density of the subsurface formation, a diameter of a borehole and the shape of the borehole. 
     
     
         35 . The system of  claim 23 , wherein the drill pipe further includes an acoustic telemetry repeater between the acoustic telemetry transmitter and the acoustic telemetry receiver. 
     
     
         36 . The system of  claim 23 , wherein the acoustic telemetry transmitter is located downhole of a borehole. 
     
     
         37 . The system of  claim 23 , wherein the acoustic telemetry received is located at the surface of the borehole. 
     
     
         38 . A machine-readable medium that provides instructions, which when executed by a machine, cause said machine to perform operations comprising:
 receiving a telemetry signal along a transmission channel having a transmission channel characteristic; and   correlating the telemetry signal to a first stored telemetry signal that includes the transmission channel characteristic.   
     
     
         39 . The machine-readable medium of  claim 38 , further correlating the telemetry signal to a second stored telemetry signal that includes the transmission channel characteristic. 
     
     
         40 . The machine-readable medium of  claim 39 , wherein correlating the telemetry signal to the first stored telemetry signal outputs a first degree of correlation and wherein correlating the telemetry signal to the second stored telemetry signal outputs a second degree of correlation. 
     
     
         41 . The machine-readable medium of  claim 40 , further comprising marking the telemetry signal as a symbolic value based on the first degree of correlation and the second degree of correlation. 
     
     
         42 - 61 . (canceled) 
     
     
         62 . A method comprising:
 determining a training tone pulse, during a training period, at a first frequency of a frequency shift key (FSK) acoustic signal that is propagated along a drill pipe;   determining a training tone pulse, during the training period, at a second frequency of the FSK acoustic signal that is propagated along the drill pipe;   receiving the FSK acoustic signal, during a drilling operation, that is propagated along the drill pipe at at least the first frequency or the second frequency;   subtracting a tail of a previous symbol from a previous symbolic interval at the first frequency in the FSK acoustic signal from a current symbol in a current symbolic interval of the FSK acoustic signal to generate a corrected current symbol, if the previous symbol from the previous symbolic interval is at the first frequency; and   subtracting a tail of the previous symbol from the previous symbolic interval at the second frequency in the FSK acoustic signal from a current symbol in a current symbolic interval of the FSK acoustic signal to generate the corrected current symbol, if the previous symbol from the previous symbolic interval is at the second frequency.   
     
     
         63 . The method of  claim 62 , further comprising correlating the corrected current symbol with the training tone pulse at the first frequency and the training tone pulse at the second frequency. 
     
     
         64 . The method of  claim 63 , further comprising marking the corrected symbol as a first data value or a second data value based on the correlating of the corrected current symbol. 
     
     
         65 . The method of  claim 63 , wherein correlating the corrected current symbol with the training tone pulse at the first frequency and the training tone pulse at the second frequency comprises:
 correlating the corrected current symbol with the training tone pulse at the first frequency to generate a first correlated output;   correlating the corrected current symbol with the training tone pulse at the second frequency to generate a second correlated output; and   subtracting the second correlated output from the first correlated output to generate a subtract output.   
     
     
         66 . The method of  claim 65 , further comprising:
 marking the corrected symbol as a data value associated with the first frequency upon determining that a polarity of the subtract output is positive; and   marking the corrected symbol as a data value associated with the second frequency upon determining that a polarity of the subtract output is negative.   
     
     
         67 . The method of  claim 62 , further comprising performing a bandpass filter operation of the acoustic signal prior to the subtracting of the tail of the previous symbol. 
     
     
         68 . An apparatus comprising:
 a tail subtract logic to receive a current symbol in a current symbolic interval within a frequency shift key (FSK) acoustic signal that is propagated along a drill string; during a non-training period, wherein the tail subtract logic is to subtract a tail of a previous symbol in a previous symbolic interval of the FSK acoustic signal from the current symbol to generate a corrected current symbol;   a first frequency correlation logic to correlate the corrected current symbol to an approximately noise free acoustic signal propagated along the drill string at a first frequency; and   a second frequency correlation logic to correlate the corrected current symbol to an approximately noise free acoustic signal propagated along the drill string at a second frequency.   
     
     
         69 . The apparatus of  claim 68 , further comprising a detection logic to mark the corrected current symbol as a value associated with the first frequency or a value associated with the second frequency based on the correlations. 
     
     
         70 . The apparatus of  claim 68 , further comprising a timing recovery logic to locate the previous symbolic interval and the current symbolic interval. 
     
     
         71 . The apparatus of  claim 70 , wherein the timing recovery logic includes an early-late-gate correlation timing circuit. 
     
     
         72 . A machine-readable medium that provides instructions, which when executed by a machine, cause said machine to perform operations comprising:
 determining a training tone pulse, during a training period, at a first frequency of a frequency shift key (FSK) acoustic signal that is propagated along a drill pipe;   determining a training tone pulse, during the training period, at a second frequency of the FSK acoustic signal that is propagated along the drill pipe;   receiving the FSK acoustic signal, during a drilling operation, that is propagated along the drill pipe at at least the first frequency or the second frequency;   subtracting a tail of a previous symbol from a previous symbolic interval at the first frequency in the FSK acoustic signal from a current symbol in a current symbolic interval of the FSK acoustic signal to generate a corrected current symbol, if the previous symbol from the previous symbolic interval is at the first frequency; and   subtracting a tail of the previous symbol from the previous symbolic interval at the second frequency in the FSK acoustic signal from a current symbol in a current symbolic interval of the FSK acoustic signal to generate the corrected current symbol, if the previous symbol from the previous symbolic interval is at the second frequency.   
     
     
         73 . The machine-readable medium of  claim 72 , further comprising correlating the corrected current symbol with the training tone pulse at the first frequency and the training tone pulse at the second frequency. 
     
     
         74 . The machine-readable medium of  claim 73 , further comprising marking the corrected symbol as a first data value or a second data value based on the correlating of the corrected current symbol. 
     
     
         75 . A method comprising:
 determining training tone pulses, during a training period, at at least two different phases of a phase shift key (PSK) acoustic signal that is propagated along a drill pipe;   receiving the PSK acoustic signal, during a non-training period, that is propagated along the drill pipe at at least two different phases; and   subtracting a tail of a previous symbol from a previous symbolic interval at the phase of the previous symbolic interval to generate a corrected current symbol.   
     
     
         76 . The method of  claim 75 , further comprising correlating the corrected current symbol with the training tone pulses at the at least two different phases. 
     
     
         77 . The method of  claim 76 , further comprising marking the corrected symbol as one of a number of data values based on the correlating of the corrected current symbol. 
     
     
         78 . The method of  claim 75 , wherein determining the training tone pulses, during the training period, at the at least two different phases of the PSK acoustic signal comprises determining the training tone pulses, during the training period, at a first phase and a second phase of the PSK acoustic signal, wherein the first phase is shifted approximately  180  degrees relative to the second phase. 
     
     
         79 . An apparatus comprising:
 a tail subtract logic to receive a current symbol in a current symbolic interval within a phase shift key (PSK) acoustic signal that is propagated along a drill pipe;   during a non-training period, wherein the tail subtract logic is to subtract a tail of a previous symbol in a previous symbolic interval of the PSK acoustic signal from the current symbol to generate a corrected current symbol;   a first phase correlation logic to correlate the corrected current symbol to an approximately noise free acoustic signal propagated along the drill pipe at a first phase; and   a second phase correlation logic to correlate the corrected current symbol to an approximately noise free acoustic signal propagated along the drill pipe at a second phase.   
     
     
         80 . The apparatus of  claim 79 , further comprising a detection logic to mark the corrected current symbol as a value associated with the first phase or a value associated with the second phase based on the correlations. 
     
     
         81 . The apparatus of  claim 79 , further comprising a timing recovery logic to locate the previous symbolic interval and the current symbolic interval. 
     
     
         82 . The apparatus of  claim 81 , wherein the timing recovery logic includes an early-late-gate correlation timing circuit. 
     
     
         83 . The apparatus of  claim 79 , wherein the first phase is shifted approximately  180  degrees relative to the second phase. 
     
     
         84 . A machine-readable medium that provides instructions, which when executed by a machine, cause said machine to perform operations comprising:
 determining training tone pulses, during a training period, at at least two different phases of a phase shift key (PSK) acoustic signal that is propagated along a drill pipe;   receiving the PSK acoustic signal, during a non-training period, that is propagated along the drill pipe at at least two different phases; and   subtracting a tail of a previous symbol from a previous symbolic interval at the phase of the previous symbolic interval to generate a corrected current symbol.   
     
     
         85 . The machine-readable medium of  claim 84 , further comprising correlating the corrected current symbol with the training tone pulses at the at least two different phases. 
     
     
         86 . The machine-readable medium of  claim 85 , further comprising marking the corrected symbol as one of a number of data values based on the correlating of the corrected current symbol. 
     
     
         87 . The machine-readable medium of  claim 84 , wherein determining the training tone pulses, during the training period, at the at least two different phases of the PSK acoustic signal comprises determining the training tone pulses, during the training period, at a first phase and a second phase of the PSK acoustic signal, wherein the first phase is shifted approximately 180 degrees relative to the second phase.