Adaptive echo cancellation for an on-frequency RF repeater using a weighted power spectrum

1. A wireless repeater, comprising:

an input antenna for receiving an input signal;

an output antenna for outputting an amplified signal;

an amplifier for amplifying the received input signal and providing the output amplified signal to the output antenna;

a filter for applying a weighting function to a power spectrum of a measured signal in the wireless repeater thereby obtaining a weighted power spectrum of the measured signal; and

an internal feedback path for adaptively canceling an echo between the output antenna and the input antenna by implementing an adaptive algorithm based on an autocorrelation of the input signal employing the weighted power spectrum of the measured signal,

wherein the filter reduces the width of the autocorrelation of the input signal.

2. A wireless repeater as set out in claim 1 , wherein the input signal and the output amplified signal have the same frequency.

3. A wireless repeater as set out in claim 1 , wherein the internal feedback path comprises a digital gain block, and wherein the measured signal is measured before the digital gain block.

4. A wireless repeater as set out in claim 1 , wherein the internal feedback path comprises a portion of a digital IF stage.

5. A wireless repeater as set out in claim 4 , wherein the digital IF stage comprises a digital signal processor implementing the adaptive algorithm for cancelling the echo.

6. A wireless repeater as set out in claim 1 , wherein the weighting function whitens a power spectrum of the input signal plus noise.

7. A wireless repeater as set out in claim 1 , wherein the weighting function preserves echo ripples in the power spectrum of the measured signal.

8. A wireless repeater as set out in claim 1 , wherein the weighting function adjusts power of a carrier within the measured signal so that when multiple carriers are included, each carrier has on average the same power density, and when a single carrier is included, the power density of the single carrier is reduced to match an ambient noise of the repeater.

9. A method for echo cancellation in a wireless repeater, comprising:

measuring a signal in a signal path of the wireless repeater;

applying a spectral weighting function to a power spectrum of the measured signal to obtain a weighted power spectrum;

obtaining an autocorrelation of the signal in the signal path of the repeater based on the weighted power spectrum;

detecting an echo in the signal path based on the autocorrelation; and

adaptively cancelling the echo in the signal path based on the detected echo,

wherein the weighted power spectrum reduces the width of the autocorrelation.

10. A method as set out in claim 9 , wherein applying the spectral weighting function comprises filtering the measured signal.

11. A method as set out in claim 9 , wherein the signal in the signal path comprises a narrowband signal having an overlapping autocorrelation between the echo and measured signal prior to applying said spectral weighting function.

12. A method as set out in claim 11 , wherein the narrowband signal comprises an Enhanced Data rates for GSM Evolution (EDGE) signal.

13. A method as set out in claim 9 , further comprising:

obtaining the spectral weighting function based on an input spectrum without echo.

14. A method as set out in claim 13 , further comprising:

estimating the input spectrum by fitting the power spectrum of the measured signal to a model based on the modulation format of the signal in the signal path.

15. A method as set out in claim 14 , further comprising quantizing the power spectrum of the measured signal to a plurality of levels.

16. A method as set out in claim 15 , wherein quantizing the power spectrum comprises logarithmic quantizing.

17. A method as set out in claim 16 , wherein the power spectrum is configured as a function of a plurality of frequency bins, the method further comprising grouping bins in the power spectrum to form bands wider than said frequency bins.

18. A method as set out in claim 17 , further comprising:

obtaining a mean power from said bands; and

calculating the spectral weighting function using an inverse of the mean power.

19. A method as set out in claim 9 , wherein the spectral weighting function is based on an input signal and a noise signal spectra without effects of the echo.

20. A method as set out in claim 9 , further comprising partitioning the power spectrum into disjoint bands by grouping frequency bins into contiguous bands based on a measured power density.

21. A method as set out in claim 20 , further comprising normalizing a power of each band so that a power spectral density of each band equals a reference level.

22. A wireless communication system, comprising:

a base station; and

an on-frequency repeater for extending the base station coverage, wherein the on-frequency repeater comprises:

an input antenna for receiving an input signal;

an output antenna for outputting an amplified signal;

an amplifier for amplifying the received input signal and providing the amplified output signal to the output antenna; and

an internal feedback path for adaptively cancelling an echo between the input antenna and the output antenna,

wherein the internal feedback path comprises:

means for measuring a signal in the feedback path;

means for obtaining a weighted power spectrum of the measured signal;

means for obtaining a signal autocorrelation in the feedback path based on the weighted power spectrum; and

means for adaptively cancelling the echo based on the obtained signal autocorrelation.

23. A wireless communication system of claim 22 , wherein the means for obtaining the weighted power spectrum comprises a filter for reducing the width of the signal autocorrelation.

24. A wireless communication system of claim 22 , wherein the means for obtaining the weighted power spectrum whitens the power spectrum.