Channel state information (CSI) estimation and applications for in-band on-channel radio receivers

1. A method for estimating channel state information in an in-band on-channel radio signal including a plurality of digitally modulated reference subcarriers, the method comprising:

receiving symbols transmitted on the reference subcarriers;

combining the reference subcarrier symbols with a known reference sequence conjugate to produce a plurality of samples;

median filtering the samples to produce filtered samples;

smoothing the filtered samples for each of the reference subcarriers over the plurality of reference subcarriers to produce a complex channel gain estimate for each of the subcarriers; and

using a bias correction function to compensate for estimation bias error in the complex channel gain estimate due to the median filtering.

2. The method of claim 1 , wherein the bias correction function includes a noise variance bias correction component.

3. The method of claim 1 , further comprising:

using the plurality of samples and the complex channel gain estimate for each of the subcarriers to produce noise squared samples;

filtering the noise squared samples to produce a noise variance estimate;

selecting between the noise squared samples and the noise variance estimate to determine a selected noise variance estimate;

smoothing the selected noise variance estimate for each of the reference subcarriers over the plurality of reference subcarriers to produce a noise variance estimate for each of the subcarriers; and

compensating for bias error in the noise variance estimate.

4. The method of claim 3 , wherein the step of compensating for bias error in the noise variance estimate compensates for bias error due to the step of nonlinear processing of the noise squared samples.

5. The method of claim 4 , wherein the step of compensating for bias error in the noise variance estimate compensates for the median filter bias error in the noise squared samples.

6. The method of claim 3 , wherein the step of compensating for bias error in the noise variance estimate compensates for the excess noise feedforward nonlinear bias error in the noise variance estimate.

7. The method of claim 1 , wherein the bias correction function comprises a multiplicative factor compensation function.

8. The method of claim 1 , further comprising:

estimating an effective signal-to-noise ratio of the in-band on-channel radio signal by averaging the signal-to-noise ratios of the reference subcarriers in the in-band on-channel radio signal and subtracting an approximation of a standard deviation of the signal-to-noise ratios of the reference subcarriers.

9. The method of claim 8 , further comprising:

using the effective signal-to-noise ratio to derive an effective carrier-to-noise density ratio.

10. The method of claim 1 , wherein data subcarriers were used in addition to the reference subcarriers.

11. A receiver for an in-band on-channel radio signal including a plurality of digitally modulated reference subcarriers, the receiver comprising:

an input for receiving symbols transmitted on the reference subcarriers; and

processing circuitry for estimating channel state information, the processing circuitry being configured to combine the reference subcarrier symbols with a known reference sequence conjugate to produce a plurality of samples; median filter the samples to produce filtered samples; smooth the filtered samples for each of the reference subcarriers over the plurality of reference subcarriers to produce a complex channel gain estimate for each of the subcarriers; and use a bias correction function to compensate for estimation bias error in the complex channel gain estimate due to the median filtering.

12. The receiver of claim 11 , wherein the bias correction function includes a noise variance component.

13. The receiver of claim 11 , wherein the processing circuitry is further configured to use the plurality of samples and the complex channel gain estimate for each of the subcarriers to produce noise squared samples; filter the noise squared samples to produce a noise variance estimate; select between the noise variance estimate and the noise squared samples to determine a selected noise variance estimate; smooth the selected noise variance estimate for each of the reference subcarriers over the plurality of reference subcarriers to produce a noise variance estimate for each of the subcarriers; and compensate for bias error in the noise variance estimate.

14. The receiver of claim 13 , wherein the processing circuitry is further configured to compensate for bias error in the noise variance estimate by compensating for bias error due to the step of filtering the noise squared samples.

15. The receiver of claim 14 , wherein processing circuitry is further configured to compensate for bias error in the noise variance estimate by compensating for bias error in the noise variance estimate.

16. The receiver of claim 13 , wherein the processing circuitry is further configured to compensate for bias error in the noise variance estimate by compensating for bias error in the noise variance estimate.

17. The receiver of claim 11 , wherein the bias correction function comprises a multiplicative factor compensation function.

18. The receiver of claim 11 , wherein the processing circuitry is further configured to estimate an effective signal-to-noise ratio of the in-band on-channel radio signal by averaging signal-to-noise ratios of reference subcarriers in the in-band on-channel radio signal and subtracting an approximation of a standard deviation of the signal-to-noise ratios of the reference subcarriers.

19. The receiver of claim 18 , wherein the processing circuitry is further configured to use the effective signal-to-noise ratio to derive an effective carrier-to-noise density ratio.

20. The receiver of claim 11 , wherein data subcarriers were used in addition to the reference subcarriers.