Hybrid frequency offset estimator

1. A signal processor, comprising:

a channel observer operable for receiving an input signal propagating at an expected carrier frequency experiencing an error offset, the input signal comprising a distorted data signal in which modulating data has been influenced by the error offset, the channel observer further operable for processing the input signal to obtain channel observations for the data signal;

an error estimator operable for removing modulation from the channel observations to obtain a modulation-free resultant signal comprising a representation of the error offset, obtaining a frequency spectrum representation of the modulation-free resultant signal, processing the frequency spectrum representation of the modulation-free resultant signal to identify multiple error offset candidates, and passing the error offset candidates to a decoder for use in decoding the data signal;

wherein the error estimator comprises a data-aided processor and a non-data-aided processor each for removing data modulation to obtain the modulation-free resultant signal.

2. The signal processor of claim 1 , wherein the error estimator is selected from the group consisting of a carrier frequency offset estimator and phase angle offset estimator.

3. The signal processor of claim 1 , wherein the channel observer further comprises a front-end analog processor operable for amplifying the input signal, down-converting the amplified input signal to obtain an intermediate frequency signal, and filtering the intermediate frequency signal.

4. The signal processor of claim 1 , wherein:

the input signal comprises burst-mode multi-frequency time division multiplexed (MF-TDMA) data in which the data signal is encoded using a quadrature phase shift key (QPSK) modulation technique in accordance with the digital video broadcast return channel via satellite (DVB-RCS) standard; and

the channel observer further comprises a digital preliminary processor operable for digitizing a representation of the input signal to obtain a digital MF-TDMA signal, demultiplexing the MF-TDMA signal to obtain a concatenated single-channel TDMA signal, and detecting burst-mode data packets within the single-channel TDMA signal to obtain the channel observations.

5. The signal processor of claim 1 , wherein the error estimator identifies the error offset candidates by identifying multiple local maxima values in the frequency spectrum representation of the modulation-free resultant signal.

6. The signal processor of claim 1 , wherein the channel observations comprise symbols having phase components representing data.

7. The signal processor of claim 6 , wherein the data-aided processor comprises a modulation remover that removes data modulation from known symbols within the channel observations by multiplying the known symbols in the channel observations with conjugate representations of the known symbols to cancel phase modulation due to the known symbols.

8. The signal processor of claim 6 , wherein the non-data-aided processor comprises a modulation remover that removes data modulation from unknown symbols within the channel observations by scaling the phase components of the unknown symbols by a modulation index to cancel the phase components of the unknown symbols.

9. The signal processor of claim 1 , wherein the error estimator obtains the frequency spectrum representation of the modulation-free resultant signal using a Fast Fourier Transform (FFT) technique.

10. A signal processor, comprising:

a channel observer operable for receiving an input signal propagating at an expected carrier frequency experiencing an error offset, the input signal comprising a distorted data signal in which modulating data has been influenced by the error offset, the channel observer further operable for processing the input signal to obtain channel observations for the data signal;

an error estimator operable for removing modulation from the channel observations to obtain a modulation-free resultant signal comprising a representation of the error offset, obtaining a frequency spectrum representation of the modulation-free resultant signal, processing the frequency spectrum representation of the modulation-free resultant signal to identify at least one error offset candidate, and passing the error offset candidates to a decoder for use in decoding the data signal;

wherein the error estimator comprises a data-aided processor operable for processing known data elements in the channel observations to obtain a data-aided frequency spectrum representation comprising a modulation-free representation of the error offset associated with the known data elements, a non-data-aided processor operable for processing unknown data elements in the channel observations to obtain a non-data-aided frequency spectrum representation comprising a modulation-free representation of the error offset associated with the unknown data elements, and a combiner for combining the data-aided and non-data-aided frequency spectrum representations.

11. The signal processor of claim 10 , wherein the data-aided and non-data-aided frequency spectrum representations are converted to a LOG domain, independently scaled, and summed to obtain the frequency spectrum representation of the modulation-free resultant signal.

12. The signal processor of claim 11 , wherein the data-aided and non-data-aided frequency spectrum representations are independently scaled to allow adjustment within the frequency estimator.

13. The signal processor of claim 12 , wherein a scaling factor for either the data-aided or the non-data-aided processor may be independently set to zero or a non-zero value and thereby allow the signal processor to switch between purely data-aided, purely non-data-aided, and hybrid processing modes.

14. The signal processor of claim 10 , wherein the data-aided and non-data-aided processors are frequency aligned to facilitate combining the data-aided and non-data-aided frequency spectrum representations.

15. The signal processor of claim 14 , wherein the channel observations include symbols having phase components representing data, and wherein:

the data-aided processor comprises a modulation remover that removes data modulation from known symbols within the channel observations by multiplying the known symbols in the channel observations with conjugate representations of the known symbols to cancel the phase components of the known symbols;

the non-data-aided processor comprises a modulation remover that removes data modulation from the unknown symbols within the channel observations by scaling the phase components of the unknown symbols by a modulation index to cancel the phase components of the unknown symbols;

the data-aided processor comprises a data-aided pre-transform processing filter;

the non-data-aided processor comprises a non-data-aided pre-transform processing filter; and

the data-aided pre-transform processing filter and the non-data-aided pre-transform processing filter are cooperatively configured to align the data-aided and non-data-aided frequency spectrum representations.

16. The signal processor of claim 15 , wherein:

the data-aided pre-transform processing filter comprises a data-aided decimation filter operating at a data-aided decimation rate;

the non-data-aided pre-transform processing filter comprises a non-data-aided decimation filter operating at a non-data-aided decimation rate; and

the non-data-aided decimation rate is substantially equal to the data-aided decimation rate multiplied by the modulation index to align the data-aided and non-data-aided frequency spectrum representations.

17. The signal processor of claim 10 , wherein the error estimator identifies the error offset candidates for the channel observations by identifying a maximum values in the frequency spectrum representation of the modulation-free resultant signal.

18. The signal processor of claim 10 , wherein:

the data-aided processor comprises a data-aided modulation removal module, a data-aided frequency spectrum module, and a data-aided scaling module; and

the non-data-aided processor comprises a non-data-aided modulation removal module, a non-data-aided frequency spectrum module, and a non-data-aided scaling module.

19. The signal processor of claim 10 , wherein the input signal comprises burst-mode multi-frequency time division multiplexed (MF-TDMA) data in which the data signal is encoded using a quadrature phase shift key (QPSK) modulation technique in accordance with the digital video broadcast return channel via satellite (DVB-RCS) standard.

20. The signal processor of claim 19 , wherein the channel observer further comprises a front-end analog processor operable for amplifying the input signal, down-converting the amplified input signal to obtain an intermediate frequency signal, and filtering the intermediate frequency signal.

21. The signal processor of claim 20 , wherein the channel observer further comprises a digital preliminary processor operable for digitizing the filtered intermediate frequency signal to obtain a digital MF-TDMA signal, demultiplexing MF-TDMA signal to obtain a concatenated single-channel TDMA signal, and detecting burst-mode data packets within the single-channel TDMA signal to obtain the channel observations.

22. A signal processor, comprising:

a channel observer operable for receiving an input signal propagating at an expected carrier frequency experiencing an error offset, the input signal comprising a distorted data signal in which modulating data has been influenced by the error offset, the channel observer further operable for processing the input signal to obtain channel observations for the data signal;

an error estimator operable for removing modulation from the channel observations to obtain a modulation-free resultant signal comprising a representation of the error offset, obtaining a frequency spectrum representation of the modulation-free resultant signal, processing the frequency spectrum representation of the modulation-free resultant signal to identify multiple error offset candidates, and passing the error offset candidates to a decoder for use in decoding the data signal;

wherein the error estimator comprises a data-aided processor operable for processing known data elements in the channel observations to obtain a data-aided frequency spectrum representation comprising a modulation-free representation of the error offset associated with the known data elements, a non-data-aided processor operable for processing unknown data elements in the channel observations to obtain a non-data-aided frequency spectrum representation comprising a modulation-free representation of the error offset associated with the unknown data elements, and a combiner for combining the data-aided and non-data-aided frequency spectrum representations.

23. The signal processor of claim 22 , wherein the data-aided and non-data-aided processors are frequency aligned to facilitate combining the data-aided and non-data-aided frequency spectrum representations.

24. The signal processor of claim 23 , wherein the input signal comprises burst-mode multi-frequency time division multiplexed (MF-TDMA) data in which the data signal is encoded using a quadrature phase shift key (QPSK) modulation technique in accordance with the digital video broadcast return channel via satellite (DVB-RCS) standard.

25. The signal processor of claim 24 , wherein the channel observer further comprises a front-end analog processor operable for amplifying the input signal, down-converting the amplified input signal to obtain an intermediate frequency signal, and filtering the intermediate frequency signal.

26. The signal processor of claim 25 , wherein the channel observer further comprises a digital preliminary processor operable for digitizing the filtered intermediate frequency signal to obtain a digital MF-TDMA signal, demultiplexing MF-TDMA signal to obtain a concatenated single-channel TDMA signal, and detecting burst-mode data packets within the single-channel TDMA signal to obtain the channel observations.

27. The signal processor of claim 26 , wherein the frequency estimator obtains the data-aided and non-data-aided frequency spectrum representations using a Fast Fourier Transform (FFT) technique.

28. A signal processor, comprising:

a channel observer operable for obtaining channel observations for an input signal comprising distorted data;

an error estimator comprising a data aided processor and a non-data-aided processor each for removing modulation from the channel observations to obtain a modulation-free resultant signal;

a data-aided signal distortion analyzer operable for processing known data elements in the resultant signal to obtain a data-aided signal distortion indicator;

a non-data-aided signal distortion analyzer operable for processing unknown data elements in the resultant signal to obtain a non-data-aided signal distortion indicator;

a combiner for combining the data-aided and non-data-aided signal distortion indicators to obtained a combined signal distortion indicator.

29. The signal processor of claim 28 , further comprising a signal distortion candidate selector for processing the combined signal distortion indicator to identify multiple candidates for a parameter associated with the signal distortion.

30. A signal processor, comprising:

a channel observer operable for obtaining channel observations for an input signal comprising a distorted data signal in which modulating data has been influenced by unknown distortion, the channel observer further operable for processing the input signal to obtain channel observations for the data signal; and

a signal distortion candidate estimator operable for removing modulation using data-aided and non-data-aided processing techniques from the channel observations to obtain a modulation-free resultant signal comprising a representation of the distortion, processing the resultant signal to identify multiple candidates for a parameter associated with the signal distortion, and passing the candidates to a decoder for use in decoding the data signal.

31. A method for operating a signal processor of a burst-mode data input signal exhibiting a low signal-to-noise ratio, comprising the steps of:

removing modulation from the data input signal to obtain a modulation-free resultant signal using data-aided and non-data-aided processing techniques;

applying data-aided and non-data-aided signal processing techniques to the resultant signal to create a combined signature representing a signal distortion parameter associated with the data input signal; and

analyzing the combined signature to identify multiple candidate values for the signal distortion parameter and passing the multiple candidates to a decoder for use in decoding the data signal.

32. In or for a signal processor of a burst-mode data input signal operating at a carrier frequency experiencing carrier frequency offset and exhibiting a low signal-to-noise ratio, an improvement comprising:

a carrier frequency offset estimator operable for removing modulation from the data input signal using data-aided and non-data-aided processing techniques to obtain a modulation-free resultant signal and applying data-aided and non-data-aided signal processing techniques to the resultant signal to obtain a combined frequency spectrum comprising a representation of a carrier frequency offset associated with the data input signal; and

a multiple peak selector operable for identifying multiple carrier frequency offset candidates by identifying local maxima values in the combined frequency spectrum representation.