Compensation method for I/Q channel imbalance errors
First Claim
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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Abstract
A method in which correctable I/Q imbalance errors in a complex receiver can be detected and compensated for digitally without the use of special calibration signals. Differential D.C. offset errors are compensated by averaging the incoming Id and Qd digital signals and subtracting from them an expected value of differential D.C. offset, for example, computed from the long term average of the I and Q signals to create I'"'"' and Q'"'"' signals. Differential gain imbalance errors are corrected by calculating a root means square average of the I'"'"' and Q'"'"' digital signals and applies to them compensation coefficients Kx and Ky determined from either the RMS average or from a Stochastic Gradient Algorithm. The DSP compensates for the quadrature phase errors by calculating a compensation matrix which is independent of the frequency of the carrier and applies the compensation matrix to the I'"'"' and Q'"'"' digital signals. The compensation matrix for quadrature phase errors is completely independent of the frequency of the input carrier signal supplied to the complex receiver, and is not dependent on the use of a calibration signal. The compensation may be performed as a step in calibration of the complex receiver, or continuously.
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Citations
26 Claims
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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:
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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. - View Dependent Claims (2, 3, 4, 5, 6)
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7. In a communication system, a compensation method for I/Q channel quadrature phase errors in I and Q analog signals generated by a complex receiver, comprising the steps of:
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receiving an FM analog carrier input signal with said complex receiver and responsively generating I and Q analog signals having a quadrature phase error; calculating a compensation matrix independent of the frequency of said FM analog carrier input signal and without the use of a calibration signal, said compensation matrix related to said quadrature phase error between said I and Q analog signals; and applying said compensation matrix to said I and Q signals to compensate for said quadrature phase errors present in said I and Q signals to responsively produce I'"'"'" and Q'"'"'" output signals separated in phase by substantially 90 degrees. - View Dependent Claims (8, 9, 10, 11, 12, 13, 14)
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15. A method for detecting gain variations in a complex receiver output, comprising the steps of:
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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 a differential gain imbalance error; converting said I and Q analog signals to Id and Qd digital signals; compensating for said differential gain imbalance errors by calculating a root mean square average of the Id and Qd digital signals and applying to said Id and Qd signals compensation coefficients Kx and Ky derived from either a root mean square average of said Id and Qd signals or from a stochastic gradient algorithm. - View Dependent Claims (16, 17, 18, 19)
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20. Communication apparatus, comprising:
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a complex receiver for receiving an analog input carrier signal and responsively generating I and Q analog signals; means for converting said I and Q analog signals into Id and Qd digital signals; an error compensator means receiving said Id and Qd digital signals for compensating for differential gain, differential D.C. offset and quadrature phase errors in said I and Q analog signals to produce I'"'"'" and Q'"'"'" compensated signals, said error compensator means compensating for said differential gain, differential offset and phase errors substantially independent of changes in frequency of said analog input carrier signal and without the use of a calibration signal. - View Dependent Claims (21, 22, 23, 24, 25, 26)
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Specification