Frequency offset correction

Abstract

Various methods and systems are provided for frequency offset correction. In one example, among others, a method includes determining a phase estimation of a RF signal, rotating a sample of the RF signal based at least in part upon the phase estimation, and determining a channel estimation based upon the rotated sample. The channel estimation may be derotated based at least in part upon the phase estimation. In another example, a communication device includes a phase rotator configured to rotate RF signal samples based upon a rotation offset, a channel estimation filter configured to determine channel estimates, and a phase derotator configured to rotate the channel estimates based upon another rotation offset. Another example of a communication device includes a differential detector configured to determine conjugate multiply results, an averaging filter configured to sum the results, and a phase estimator configured to determine a phase estimation based upon the sum.

Therefore, at least the following is claimed: 
     
         1 . A method, comprising:
 receiving a plurality of fingers of a radio frequency (RF) signal;   determining a phase estimation based upon samples corresponding to each of the plurality of fingers, the phase estimation corresponding to a carrier frequency offset associated with the received RF signal;   rotating a sample corresponding to at least one finger of the RF signal based at least in part upon the determined phase estimation; and   determining a channel estimation corresponding to the at least one finger based upon the rotated sample.   
     
     
         2 . The method of  claim 1 , comprising determining conjugate multiply results for the at least one finger based upon the samples corresponding to the at least one finger, wherein the phase estimation is determined based at least in part upon a sum of the conjugate multiply results. 
     
     
         3 . The method of  claim 2 , comprising determining conjugate multiply results for each of the plurality of fingers based upon the samples corresponding to the corresponding one of the plurality of fingers, wherein the phase estimation is determined based at least in part upon a sum of the conjugate multiply results for each of the plurality of fingers. 
     
     
         4 . The method of  claim 3 , wherein the conjugate multiply results for each of the plurality of fingers is weighted before summing. 
     
     
         5 . The method of  claim 4 , wherein the weighting is determined based at least in part upon a signal-to-noise ratio of the corresponding one of the plurality of fingers. 
     
     
         6 . The method of  claim 1 , comprising determining a phase accumulation based at least in part upon a series of determined phase estimations, wherein rotating the sample corresponding to at least one finger of the RF signal is based at least in part upon the phase accumulation. 
     
     
         7 . The method of  claim 1 , comprising derotating the channel estimation based at least in part upon the determined phase estimation. 
     
     
         8 . The method of  claim 7 , wherein derotating the channel estimation is based at least in part upon a phase accumulation based at least in part upon a series of determined phase estimations and a phase rotation corresponding to a group delay associated with the channel estimation. 
     
     
         9 . The method of  claim 8 , wherein the channel estimation is determined by a N-tap finite impulse response (FIR) filter with a group delay of (N−1)/2. 
     
     
         10 . The method of  claim 1 , wherein the RF signal is from a neighbor cell. 
     
     
         11 . A communication device, comprising:
 a circuit that determines a channel estimation for a finger of a received radio frequency (RF) signal, the circuit comprising:
 a phase rotator configured to rotate samples of the finger of the RF signal based upon a first rotation offset corresponding to a carrier frequency offset associated with the received RF signal; 
 a channel estimation filter configured to determine channel estimates based upon the rotated samples; and 
 a phase derotator configured to rotate the channel estimates based upon a second rotation offset corresponding to the carrier frequency offset. 
   
     
     
         12 . The communication device of  claim 11 , wherein the circuit comprises a phase accumulator configured to determine the first rotation offset and the second rotation offset based at least in part upon a series of phase estimates corresponding to the carrier frequency offset associated with the received RF signal. 
     
     
         13 . The communication device of  claim 12 , wherein the phase accumulator comprises an infinite impulse response (IIR) filter configured to determine the first rotation offset based upon the series of phase estimates. 
     
     
         14 . The communication device of  claim 13 , wherein the first rotation offset is wrapped around between −pi to pi. 
     
     
         15 . The communication device of  claim 13 , wherein the phase accumulator determines the second rotation by scaling a current phase estimate by a group delay associated with the channel estimation filter and adding the scaled phase estimate to a current output of the IIR filter. 
     
     
         16 . A communication device, comprising:
 a circuit that provides a phase estimation based upon a carrier frequency offset associated with a received radio frequency (RF) signal, the circuit comprising:
 a differential detector configured to determine a series conjugate multiply results for a series of samples associated with the received RF signal; 
 an averaging filter configured to sum the series of conjugate multiply results; and 
 a phase estimator configured to determine the phase estimation based upon the sum of the conjugate multiply results. 
   
     
     
         17 . The communication device of  claim 16 , wherein the circuit comprises an accumulator configured to provide the series of samples associated with the received RF signal to the differential detector. 
     
     
         18 . The communication device of  claim 16 , wherein the circuit comprises a plurality of differential detectors, each differential detector corresponding to a finger of the RF signal, and wherein the averaging filter is configured to sum a series of conjugate multiply results from each of the plurality of differential detectors. 
     
     
         19 . The communication device of  claim 16 , wherein the circuit comprises a plurality of differential detectors, each differential detector corresponding to an antenna of the communication device, wherein conjugate multiply results of the plurality of differential detectors are summed to determine the series conjugate multiply results. 
     
     
         20 . The communication device of  claim 16 , wherein the phase estimator comprises a cordic polar circuit configured to determine the phase estimation based upon the sum of the conjugate multiply results.