US 5,705,949 AGranted

Compensation method for I/Q channel imbalance errors

AssigneeU.S. Robotics Access Corp.

InventorsCarl H. Alelyunas, Andrew L. Norrell, Vladimir Parizhsky

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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 I.sub.d and Q.sub.d 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 K.sub.x and K.sub.y 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.

Claims26

Dependent claims

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 .epsilon. related to the phase difference between said I and Q analog signals;
converting said I and Q analog signals to I.sub.d and Q.sub.d digital signals;
compensating for said differential offset errors by averaging the incoming I.sub.d and Q.sub.d 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 K.sub.x and K.sub.y 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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