Frequency and phase offset compensation of modulated signals with symbol timing recovery

Abstract

Systems and methods are provided in which a wireless receiver can be configured to compensate frequency and phase offsets with joint symbol timing recovery of modulated signals transmitted across a channel, and it can include a transformation module configured to generate an error signal for an information signal representing the modulated signal received by the receiver. The transformation module can include a squaring module configured to square the information signal, thereby generating a squared signal, and a mixer configured to perform a complex multiplication of the squared signal by the local reference signal, and a downsampler. The transformation module can also be configured to extract and compensate frequency and phase offsets with joint symbol timing recovery.

The invention claimed is:  
     
       1. A radio frequency receiver configured to receive a modulated signal transmitted across a channel, the radio frequency receiver comprising:
 one or more transformation modules, each of the one or more transformation modules configured to generate an error signal for a digital information signal representing a digitized version of the modulated signal received by the receiver, each transformation module comprising:
 a squaring module configured to square the digital information signal, thereby generating a squared digital information signal; and 
 a first mixer configured to perform a complex multiplication of the squared digital information signal by a local reference signal; 
 
 a symbol timing estimator module, configured to estimate a symbol timing of the received signal based on an error signal generated by the one or more transformation module, and to generate a symbol timing signal; 
 a frequency offset estimator module, configured to estimate a frequency offset of the received signal based on an error signal generated by the one or more transformation modules; 
 a phase offset estimator module configured to estimate a phase error in the received signal based on an error signal generated by the one or more transformation modules. 
 
     
     
       2. The radio frequency receiver of  claim 1 , wherein the symbol timing estimator module, frequency offset estimator module, and phase offset estimator module are each configured to perform their respective estimation using an error signal calculated based on the same digital information signal. 
     
     
       3. The radio frequency receiver of  claim 1 , wherein a first transformation module of the one or more transformation modules is configured to generate a first error signal based on the digital information signal, and wherein a second transformation module of the one or more transformation modules is configured to generate a second error signal for the received signal based on a frequency correction of the digital information signal; and further wherein the symbol timing estimator module and frequency offset estimator module are configured to perform their respective estimation using the first error signal calculated based on the same digital information signal, and the and phase offset estimator module is configured to perform phase offset estimation using the second error signal calculated based on the frequency corrected digital information signal. 
     
     
       4. The radio frequency receiver of  claim 1 , further comprising a second mixer configured to apply the estimated frequency offset to the digital information signal resulting in a frequency corrected digital information signal, and a third mixer configured to apply the estimated phase offset to the frequency corrected digital information signal. 
     
     
       5. The radio frequency receiver of  claim 1 , wherein each of the one or more transformation modules further comprises a shift register module configured to receive an output signal from the mixer and to delay the output signal; and a downsampler configured to perform spectrum folding of the mixed, delayed signal in order to select delayed samples of the output error signal. 
     
     
       6. The radio frequency receiver of  claim 1 , wherein each of the one or more the transformation modules further comprises a shift register module configured to delay the digital information signal, and a downsampler module configured to down sample the delayed digital information signal prior to squaring, and wherein squaring the digital information signal comprises squaring the downsampled delayed digital information signal. 
     
     
       7. The radio frequency receiver of  claim 1 , wherein the digital information signal comprises a digitized and downconverted version of the modulated signal received by the receiver. 
     
     
       8. The radio frequency receiver of  claim 7 , wherein the transformation, symbol timing estimator, frequency offset estimator and phase offset estimator modules comprise computer readable program code stored on a non-transitory storage medium. 
     
     
       9. The radio frequency receiver of  claim 1 , wherein the digital information signal comprises a digital baseband signal. 
     
     
       10. The radio frequency receiver of  claim 1 , wherein the error signal generated by the one or more transformation modules comprises:
     e ( m )= e   2j|(−1)     b     mωTε+ΔωTm+θ     0     }   
 wherein the ε component represents the symbol timing estimate, the Δω component represents the frequency offset estimate, and the θ 0  component represents the phase offset estimate. 
 
     
     
       11. The radio frequency receiver of  claim 1 , wherein estimating symbol timing by the symbol timing estimator module comprises performing a plurality of transformations, each transformation operating on a version of the digital information signal delayed by a different amount, comparing results of the plurality of transformations, and determining, based on the comparison, which amount of delay represents the delay between the received signal and local reference signal. 
     
     
       12. The radio frequency receiver of  claim 11 , wherein comparing comprises comparing mean power from each of the plurality of transformations to determine which one has the maximum power. 
     
     
       13. A method for estimating frequency and phase offset and symbol timing for a modulated signal transmitted across a channel and received by a receiver, the method comprising:
 applying a first transformation to a digital information signal representing a digitized version of the modulated signal received by the receiver to generate a first error signal, wherein the transformation comprises squaring the digital information signal, thereby generating a squared digital information signal, and multiplying by complex multiplication the squared digital information signal by a reference signal; 
 estimating a symbol timing of the received signal based on the error signal generated by the first transformation, and generating a symbol timing signal for the information signal; 
 estimating a frequency offset of the received signal based on an error signal generated by a transformation of the digital information signal; and 
 estimating a phase error in the received signal based on an error signal generated by a transformation of the digital information signal. 
 
     
     
       14. The method of  claim 13 , wherein estimating the symbol timing, frequency offset, and phase offset are performed using the first error signal calculated based on the same digital information signal. 
     
     
       15. The method of  claim 13 , further comprising: applying a second transformation of the digital information signal that generates a second error signal for the received signal based on a frequency corrected version of the digital information signal; and further wherein estimating the symbol timing and frequency offset are performed using the first error signal calculated based on the digital information signal, and the and estimating the phase offset is performed using the second error signal calculated based on the frequency corrected digital information signal. 
     
     
       16. The method of  claim 13 , further comprising mixing the estimated frequency offset with the digital information signal resulting in a frequency corrected digital information signal, and mixing the estimated phase offset with the frequency corrected digital information signal. 
     
     
       17. The method of  claim 13 , wherein applying the first transformation further comprises delaying a signal output from the multiplication and down sampling the delayed signal to generate the first error signal. 
     
     
       18. The method of  claim 13 , wherein applying the first transformation further comprises delaying the digital information signal, and down sampling the delayed digital information signal prior to squaring, and wherein squaring the digital information signal comprises squaring the downsampled delayed digital information signal. 
     
     
       19. The method of  claim 13 , wherein in the digital information signal comprises a digitized and downconverted version of the modulated signal received by the receiver. 
     
     
       20. The method of  claim 13 , wherein the digital information signal comprises a digital baseband signal. 
     
     
       21. The method of  claim 13 , wherein the first error signal comprises:
     e ( m )= e   2j|(−1)     b     mωTε+ΔωTm+θ     0     }   
 wherein the ε component represents the symbol timing estimate, the Δω component represents the frequency offset estimate, and the θ 0  component represents the phase offset estimate. 
 
     
     
       22. The method of  claim 13 , wherein estimating symbol timing by the symbol timing estimator module comprises performing a plurality of transformations, each transformation operating on a version of the digital information signal delayed by a different amount, comparing results of the plurality of transformations, and determining, based on the comparison, which amount of delay represents the delay between the received signal and local reference signal. 
     
     
       23. The method of  claim 22 , wherein comparing comprises comparing mean power from each of the plurality of transformations to determine which one has the maximum power.