Detection of unknown symbol rate in a digitally modulated signal

1. A symbol rate detector comprising:

a nonlinear device coupled to received a pass band signal, the nonlinear device adapted to provide a signal that includes a sum of (a) a square of a Hilbert transform of the received signal, and (b) a square of the received signal phase shifted by an amount substantially the same as an amount of phase shift introduced by the Hilbert transform;

a component to apply a Fourier Transform to the signal provided by the nonlinear device; and

logic to select a peak frequency component from results of applying the Fourier Transform to the nonlinear device signal and to apply the peak frequency component as a symbol rate of a base band signal corresponding to the pass band signal.

2. The symbol rate detector of claim 1 , wherein the Hilbert transform comprises:

a substantially all-pass finite impulse response filter producing a substantially ninety degree phase shift in the pass band signal.

3. The symbol rate detector of claim 1 , wherein the component to apply a Fourier Transform to the nonlinear device signal comprises:

a fast Fourier Transform.

4. The symbol rate detector of claim 1 , wherein the nonlinear device comprises:

logic of a field programmable gate array.

5. The symbol rate detector of claim 1 , wherein the nonlinear device comprises:

at least one of a square-law, fourth-law, and absolute value device.

6. The symbol rate detector of claim 1 , further comprising:

a filter to remove frequency components of the signal provided by the nonlinear device before the Fourier Transform is applied to the nonlinear device signal.

7. A method comprising:

applying a pass band signal to a nonlinear device;

producing with the nonlinear device a signal that includes a sum of (a) a square of a Hilbert transform of the applied signal, and (b) a square of the applied signal phase shifted by an amount substantially the same as an amount of phase shift introduced by the Hilbert transform;

filtering the signal produced by the nonlinear device;

applying a Fourier Transform to the filtered signal to produce a frequency spectra; and

selecting as a symbol rate a peak frequency component of the frequency spectra from within a pre-selected frequency range for the pass band signal.

8. The method of claim 7 , wherein the Hilbert transform comprises:

a substantially all-pass finite impulse response filter producing a substantially ninety degree phase shift in the pass band signal.

9. The method of claim 7 , wherein applying a Fourier Transform to the filtered signal comprises:

applying a fast Fourier Transform.

10. The method of claim 7 , wherein the nonlinear device comprises:

logic of a field programmable gate array.

11. The method of claim 7 , wherein the pre-selected frequency range for the pass band signal comprises:

a range of frequencies between substantially a full pass band signal bandwidth and a substantially half the pass band signal bandwidth.

12. The method of claim 7 , wherein the nonlinear device comprises:

at least one of a square-law, fourth-law, and absolute value device.

13. A receiver comprising:

a symbol rate detector to apply a nonlinear transformation to a preprocessed pass band signal and to provide a frequency spectra of the transformed preprocessed pass band signal, the transformed signal including a sum of (a) a square of a Hilbert transform of the preprocessed pass band signal, and (b) a square of the preprocessed pass band signal phase shifted by an amount substantially the same as an amount of phase shift introduced by the Hilbert transform; and

logic to apply as a base band symbol rate a peak frequency component of the frequency spectra provided by the symbol rate detector.

14. The receiver of claim 13 , wherein the frequency spectra of the transformed preprocessed pass band signal comprises:

a discrete line cross-power spectral density of the preprocessed pass band signal.

15. The receiver of claim 13 , wherein the symbol rate detector to apply a nonlinear transformation to the preprocessed pass band signal comprises:

logic to produce a squared envelope of the preprocessed pass band signal.

16. The receiver of claim 15 , wherein the logic to produce a squared envelope of the preprocessed pass band signal comprises:

logic to produce an expectation of the squared envelope.

17. The receiver of claim 13 , further comprising:

pass band pre-processing logic.