Carrier recovery in a QAM receiver
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United States of America Patent
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Oct 18, 2016
Grant Date -
Jan 7, 2016
app pub date -
Feb 28, 2014
filing date -
Feb 28, 2013
priority date (Note) -
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Abstract
The present invention relates to inspection apparatus for use in wellbores in the oil and gas industries. In particular the invention relates in general to the field of transmission of data between downhole module in a wellbore and a controlling module at the surface. The invention provides a method an apparatus for receiving data from a telemetry module, the data being modulated according to a quadrature amplitude modulation coding scheme, in which a receiver has a carrier recovery circuit comprising a phase detector, a loop filter and a signal synthesizer generating an inphase and a quadrature demodulation signal. The method comprises receiving a preamble sinusoidal signal representing a symbol; determining the cross product of the received inphase and quadrature components and ideal inphase and quadrature components; indexing a look up table with said cross product to determine a phase adjustment and adjusting the phase of the demodulation signals in accordance with said determined phase adjustment.
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