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Compensation method for I/Q channel imbalance errors

  • US 5,705,949 A
  • Filed: 09/13/1996
  • Issued: 01/06/1998
  • Est. Priority Date: 09/13/1996
  • Status: Expired due to Term
First Claim
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1. In a communication system, a detection and compensation method for I/Q channel imbalance errors for I and Q analog signals generated by a complex receiver, comprising the steps of:

  • receiving an incoming analog carrier signal at said complex receiver and responsively generating said I and Q analog signals, said I and Q analog signals nominally separated in phase by 90 degrees and having differential offset, differential gain imbalance and quadrature phase errors, said quadrature phase error proportional to a factor ε

    related to the phase difference between said I and Q analog signals;

    converting said I and Q analog signals to Id and Qd digital signals;

    compensating for said differential offset errors by averaging the incoming Id and Qd digital signals and subtracting from them an expected value values of differential D.C. offset to create offset compensated signals I'"'"' and Q'"'"';

    compensating for said differential gain imbalance errors by calculating a root mean square average of the I'"'"' and Q'"'"' digital signals and applying to them compensation coefficients Kx and Ky derived from either said root mean square average or a stochastic gradient algorithm to create gain compensated signals I" and Q";

    compensating for said quadrature phase errors by calculating a quadrature compensation matrix independent of the frequency of the carrier and applying said compensation matrix to said I" and Q" signals to generate I'"'"'" and Q'"'"'" output signals,whereby said I'"'"'" and Q'"'"'" output signals compensate for said differential offset, differential gain and quadrature phase errors without the use of calibration signals, thereby improving the performance of said communication system.

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