Stability recovery for an on-frequency RF repeater with adaptive echo cancellation

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; and

an internal feedback path for adaptively cancelling an echo between the output antenna and the input antenna by measuring echo cancellation and implementing an adaptive algorithm employing one or more measured repeater settings and a list having a plurality of list elements, each list element comprising one or more adaptively updated echo cancellation parameters and one or more analog repeater settings.

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 list comprises past successful echo cancellation parameters and corresponding repeater settings.

4. A wireless repeater as set out in claim 1 , wherein the repeater settings comprise analog gain settings of the amplifier.

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

6. A wireless repeater as set out in claim 5 , wherein the digital IF stage comprises a digital signal processor implementing the adaptive algorithm for dynamically updating the list and iteratively cancelling the echo.

7. A wireless repeater as set out in claim 6 , wherein the algorithm further comprises pruning the list for redundant elements.

8. A wireless repeater as set out in claim 1 , wherein the list is indexed using multi-dimensional attribute vectors.

9. A wireless repeater as set out in claim 1 , wherein each of the list elements further comprises a region number indicating a region of an attribute space of which the element is a member.

10. A wireless repeater as set out in claim 9 , wherein the region number corresponds to a region marker in the attribute space, and wherein the element is a member of the attribute space of a closest marker to the element.

11. A wireless repeater as set out in claim 1 , further comprising:

means for monitoring a signal autocorrelation in the repeater; and

means for detecting an echo within the repeater based on the monitored signal autocorrelation.

12. A method for recovering stability of a repeater in a wireless communication system, comprising:

providing a list having a plurality of list elements employing an adaptive algorithm employing measured echo cancellation, each list element comprising one or more echo cancellation parameters and one or more associated analog repeater settings;

detecting a current analog repeater setting;

comparing the current detected repeater setting to those in the list; and

selecting an echo cancellation parameter associated with the most similar repeater setting in the list.

13. A method as set out in claim 12 , wherein the repeater settings are configured as a multi-dimensional attribute vector in an attribute space, and wherein the attribute space is divided into a plurality of regions.

14. A method as set out in claim 13 , wherein each of the list elements further comprises a region number indicating a region of the attribute space of which the element is a member.

15. A method as set out in claim 14 , wherein the region number corresponds to a region marker in the attribute space, and wherein the element is a member of the attribute space of a marker closest to the element.

16. A method as set out in claim 12 , further comprising:

pruning the list for redundant list elements based on a minimum distance between list elements.

17. A method for stabilizing a wireless repeater, comprising:

obtaining an autocorrelation of a signal in a signal path of the repeater;

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

providing a list of elements indicating past successful echo cancellation coefficients and associated past measured analog repeater settings; and

adaptively employing the echo cancellation coefficients to cancel the echo in the signal path employing measured echo cancellation.

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

dynamically updating the list.

19. A method as set out in claim 18 , wherein dynamically updating the list comprises adding current repeater settings for successful echo cancellation to the list.

20. A method as set out in claim 19 , further comprising:

obtaining distances between elements in the list,

wherein dynamically updating the list further comprises pruning the list based on the obtained distances.

21. A method as set out in claim 20 , wherein if instability is detected as determined from comparing the autocorrelation with a first predetermined threshold, the method further comprises:

finding a nearest list element based on distances between the list elements and a current setting of the repeater;

reducing a gain of the repeater to the next lowest gain setting based on the nearest list element;

retrieving an element from the list with echo cancellation coefficients corresponding to the next lowest gain setting; and

pruning the retrieved element from the list.

22. A method as set out in claim 21 , further comprising:

successively reducing the gain using the remaining list elements until stability is restored or the list is empty.

23. A method as set out in claim 22 , further comprising:

if the list becomes empty, setting the echo cancellation coefficients to zero and reducing the gain until stability is restored.

24. A method as set out in claim 20 , wherein if echo is suppressed as determined from comparing the autocorrelation with a second predetermined threshold, the method further comprises:

adding current repeater settings to the list.

25. A method as set out in claim 24 , further comprising;

pruning the list by employing a minimum distance between elements within the list.

26. A method as set out in claim 25 , wherein the distance is an attribute distance, and wherein pruning the list comprises:

selecting an oldest element from the list;

computing attribute distances from the selected oldest element to the remaining elements with a same region of the list;

selecting a minimum attribute distance from the computed attribute distances and comparing the minimum attribute distance with a predetermined attribute distance threshold; and

deleting an older element among an element pair having the minimum attribute distance if the minimum attribute distance is smaller than or equal to the predetermined attribute distance threshold until the whole list is checked.

27. A method as set out in claim 25 , wherein the distance is an echo cancellation coefficient distance, and wherein pruning the list comprises:

selecting an oldest element from the list;

computing attribute distances from the selected oldest element to the remaining elements with a same region of the list;

finding a pair of neighboring elements by selecting a minimum attribute distance from the computed attribute distances;

computing a coefficient distance between the pair of neighboring elements; and

deleting an older element among the pair of neighboring elements if the computed coefficient distance is smaller than or equal to a predetermined coefficient distance threshold until the whole list is checked.

28. A method as set out in claim 20 , wherein pruning the list based on the obtained distances comprises pruning the list for redundant elements among neighboring elements.

29. A method as set out in claim 20 , wherein if the obtained autocorrelation is between a first threshold above which the repeater is considered unstable, and a second predetermined threshold below which the echo is considered suppressed, the method further comprises:

estimating an error in the echo cancellation coefficients; and

updating the echo cancellation coefficients.

30. A method as set out in claim 17 , further comprising reducing coupling between the input antenna and the output antenna by adaptively cancelling the echo.

31. A method as set out in claim 30 , further comprising increasing a forward gain of the repeater if the echo is suppressed.

32. A method as set out in claim 17 , wherein the repeater settings are configured as an attribute space, the method further comprising dividing the attribute space into a plurality of regions to avoid over pruning.

33. A method as set out in claim 32 , wherein each of the list elements further comprises a region number indicating a region of an attribute space of which the element is a member.

34. A method as set out in claim 33 , wherein the region number corresponds to a region marker in the attribute space, and wherein the element is a member of the attribute space of a marker closest to the element.

35. 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 and for stabilizing the on-frequency repeater employing measured echo cancellation,

wherein the internal feedback path comprises:

means for providing a list having a plurality of list elements, each list element comprising one or more echo cancellation parameters, and one or more associated measured analog repeater settings;

means for monitoring a signal autocorrelation in the feedback path; and

means for adaptively cancelling the echo based on the autocorrelation signal and the list.

36. A wireless communication system of claim 35 , wherein the one or more repeater settings are configured as attribute vectors in an attribute space.

37. A wireless communication system of claim 36 , wherein each of the list elements further comprises a region number indicating a region of the attribute space of which the list element is a member.