Digital data-aided frequency offset estimation
Techniques are provided herein for digital data-aided frequency offset estimation offering better performance and increased accuracy over existing solutions. These new techniques also allow a trade-off between complexity and accuracy to be performed. The embodiments of the techniques for frequency offset estimation can be used for correction in both feedback and feed-forward control.
1. A method for estimating frequency offset in a signal received through a radio propagation channel, comprising:
estimating the frequency offset from at least one phase derived from the received signal, wherein a weight dependent on characteristics of a transmitted signal is applied to the phase,
wherein the characteristics of the transmitted signal are derived from a set of estimated transmitted samples resulting from a demodulation process, and
wherein a second set of samples is calculated by scaling and de-rotating the received signal where the de-rotation is configured to be dependent on phase contributions from at least one of the transmitted signal and the radio propagation channel, and the at least one phase used in the frequency offset estimation is derived from the second set of samples.
2. The method of claim 1 , wherein the transmitted signal comprises a known training sequence from which the characteristics of the transmitted signal are derived.
3. The method of claim 2 , wherein the weight is pre-computed independently of the received signal.
4. The method of claim 1 , wherein the weight is dependent on the power of the transmitted signal.
5. The method of claim 1 , wherein the at least one phase used in the frequency offset estimation is derived from a plurality of correlation terms that are calculated on the second set of samples.
6. The method of claim 5 , wherein at least one of the at least one phase is calculated as a sum of the correlation terms.
7. The method of claim 1 , further comprising:
grouping adjacent samples from the second set of the samples to form a plurality of groups, in a way that the frequency offset estimate is generated from the at least one phase calculated using a value derived from each group.
8. The method of claim 7 , wherein the number of samples in each group is adapted to a maximum value of the frequency offset to be estimated.
9. The method of claim 7 , wherein the number of samples in each group is adapted according to properties of the received signal.
10. An apparatus for estimating frequency offset in a signal received though a radio propagation channel, the apparatus comprising:
a radio frequency processing stage configured to process a received signal that is received through a propagation channel;
a mixed signal processing stage configured to receive an output from the radio frequency processing stage; and
a digital signal processing stage configured to receive an output from the mixed signal processing stage and to estimate the frequency offset from at least one phase derived from the received signal, wherein a weight dependent on characteristics of a transmitted signal is applied to the phase,
wherein the characteristics of the transmitted signal are derived from a set of estimated transmitted samples resulting from a demodulation process, and
wherein the digital signal processing stage is further configured to calculate a second set of samples by scaling and de-rotating the received signal where the de-rotation is configured to be dependent on phase contributions from at least one of the transmitted signal and the radio propagation channel, and the at least one phase used in the frequency offset estimation is derived from the second set of samples.
11. The apparatus of claim 10 , wherein the transmitted signal comprises a known training sequence from which the characteristics of the transmitted signal are derived.
12. The apparatus of claim 11 , wherein the weight is pre-computed independently of the received signal.
13. The apparatus of claim 10 , wherein the weight is dependent on the power of the transmitted signal.
14. The apparatus of claim 10 , wherein the at least one phase used in the frequency offset estimation is derived from a plurality of correlation terms that are calculated on the second set of samples.
15. The apparatus of claim 14 , wherein at least one of the at least one phase is calculated as a sum of the correlation terms.
16. The apparatus of claim 10 , wherein the digital signal processing stage is further configured to:
group adjacent samples from the second set of the samples to form a plurality of groups, in a way that the frequency offset estimate is generated from the at least one phase calculated using a value derived from each group.