Patent ID: 8036319

Claim:
A method for correcting phase imbalance in a direct conversion receiver, the method comprising: receiving an input signal at an in-phase channel and at a quadrature channel of the direct-conversion receiver, wherein the input signal comprises a Radio frequency (RF) signal having a plurality of pilot carriers; obtaining an in-phase zero intermediate frequency (IF) signal in the in-phase channel and a quadrature zero-IF signal in the quadrature channel from the input signal; filtering the in-phase zero-IF signal and the quadrature zero-IF signal to obtain a fixed band zero-IF signal in the in-phase channel and a fixed band zero-IF signal in the quadrature channel respectively; sampling the fixed-band zero-IF signal in the in-phase channel and the fixed-band zero-IF signal in the quadrature channel; determining a phase imbalance correction value for the fixed band zero-IF signal in the quadrature channel, wherein the phase imbalance correction value is a function of the frequency of the fixed-band zero-IF signal in the in-phase channel and the fixed-band zero-IF signal in the quadrature channel, wherein determining the phase imbalance correction value comprises: extracting the plurality of pilot carriers from the in-phase zero-IF signal and the quadrature zero-IF signal; calculating a phase imbalance value for each pilot carrier of the plurality of pilot carriers by using the following equation: E(IQ)/E(I 2 +Q 2 ) where: E (IQ) is an average of a product of the fixed-band zero-IF signal in the in-phase channel and the fixed-band zero-IF signal in the quadrature channel, and E (I 2 +Q 2 ) is an average value of a sum of a square of the fixed-band zero-IF signal in the in-phase channel and the fixed-band zero-IF signal in the quadrature channel; and determining the phase imbalance correction value from the phase imbalance value of each pilot carrier of the plurality of pilot carriers by determining the gradient with reference to frequency of the phase imbalance value using a least square fit; applying the phase imbalance correction value to the sampled fixed-band zero-IF signal in the quadrature channel or to the sampled fixed-band zero-IF signal in the in-phase channel to correct the phase imbalance in the direct conversion receiver; and applying the phase imbalance correction value using an interpolation of the quadrature or in-phase components of the zero-IF signal.