Doppler estimator for OFDM systems

1. A computer-implemented method of estimating a Doppler spread of a channel of a communication system, the method comprising:

computing, using the computer, a first sum defined by a difference between a plurality of pilot tones of a first group of N symbols and a corresponding plurality of pilot tones of a second group of N symbols preceding the first group of N symbols, wherein N is an integer greater than one;

computing, using the computer, a second sum defined by the plurality of pilot tones of the second group of N symbols; and

computing, using the computer, a ratio of the first sum and the second sum for each of the N symbols of the first and second group of symbols thereby to generate N ratios representative of the Doppler spread of the channel.

2. The computer implemented method of claim 1 wherein said first sum is further defined by a square of the difference between the plurality of pilot tones of the first group of N symbols and the corresponding plurality of pilot tones of the second group of N symbols.

3. The computer implemented method of claim 2 wherein said first plurality of pilot tones of each symbol of the first group of N symbols comprises an entire set of pilot tones of the symbol of the first group of N symbols, and wherein said second plurality of pilot tones of each symbol of the second group of N symbols comprises an entire set of pilot tones of the symbol of the second group of N symbols.

4. The computer implemented method of claim 2 wherein said plurality of pilot tones of the first group of N symbols comprise in-phase and quadrature-phase pilot tones, and wherein said plurality of pilot tones of the second group of N symbols comprise in-phase and quadrature-phase pilot tones.

5. The computer implemented method of claim 2 further comprising:

normalizing the N ratios.

6. A system configured to estimate a Doppler spread of a channel of a communication system, the system comprising:

a first summing block configured to compute a first sum defined by a difference between a plurality of pilot tones of a first group of N symbols and a corresponding plurality of pilot tones of a second group of N symbols preceding the first group of N symbols, wherein N is an integer greater than one;

a second summing block configured to compute a second sum defined by the plurality of pilot tones of the second group of N symbols;

a memory configured to store the first and second sum; and

a processing block configured to compute a ratio of the first sum and the second sum for each of the N symbols of the first and second group of symbols thereby to generate N ratios representative of the Doppler spread of the channel.

7. The system of claim 6 wherein said first sum is further defined by a square of the difference between the plurality of pilot tones of the first group of N symbols and the corresponding plurality of pilot tones of the second group of N symbols.

8. The system of claim 7 wherein said first plurality of pilot tones of each symbol of the first group of N symbols comprises an entire set of pilot tones of the symbol of the first group of N symbols, and wherein said second plurality of pilot tones of each symbol of the second group of N symbols comprises an entire set of pilot tones of the symbol of the second group of N symbols.

9. The system of claim 7 wherein said plurality of pilot tones of the first group of N symbols comprise in-phase and quadrature-phase pilot tones, and wherein said plurality of pilot tones of the second group of N symbols comprise in-phase and quadrature-phase pilot tones.

10. The system of claim 7 wherein said processing block is further configured to normalize the N ratios.

11. A system configured to estimate a Doppler spread of a channel of a communication system, the system comprising:

a processing unit configured to:

compute a first sum defined by a difference between a plurality of pilot tones of a first group of N symbols and a corresponding plurality of pilot tones of a second group of N symbols preceding the first group of N symbols, wherein N is an integer greater than one;

compute a second sum defined by the plurality of pilot tones of the second group of N symbols; and

compute a ratio of the first sum and the second sum for each of the N symbols of the first and second group of symbols thereby to generate N ratios representative of the Doppler spread of the channel; and

a memory configured to store the first and second sums.

12. The system of claim 11 wherein said first sum is further defined by a square of the difference between the plurality of pilot tones of the first group of N symbols and the corresponding plurality of pilot tones of the second group of N symbols.

13. The system of claim 12 wherein said first plurality of pilot tones of each symbol of the first group of N symbols comprises an entire set of pilot tones of the symbol of the first group of N symbols, and wherein said second plurality of pilot tones of each symbol of the second group of N symbols comprises an entire set of pilot tones of the symbol of the second group of N symbols.

14. The system of claim 12 wherein said plurality of pilot tones of the first group of N symbols comprise in-phase and quadrature-phase pilot tones, and wherein said plurality of pilot tones of the second group of N symbols comprise in-phase and quadrature-phase pilot tones.

15. The system of claim 12 wherein said processing unit is further configured to normalize the N ratios.