System and method for feedback cancellation in repeaters
An apparatus for repeating signals includes a receive antenna for receiving input signals, processing circuitry for processing the input signals to form repeated signals, and a transmit antenna for transmitting the repeated signals. The processing circuitry includes an adaptive digital filter configured to generate cancellation signals that are added to the input signals to cancel unwanted feedback signals from the input signals. A frequency shifting circuit adds a frequency shift to the input signals, after the addition of the cancellation signals, to form repeated signals that are frequency shifted from the input signals. A digital signal processor is coupled to the adaptive digital filter for digitally adapting the filter. The digital signal processor utilizes the frequency shift of the transmission signals to adapt the adaptive digital filter.
1. A system for repeating signals, the system comprising:
at least one receive antenna for receiving input signals;
processing circuitry for processing the input signals to form repeated signals;
at least one transmit antenna for transmitting the repeated signals;
the processing circuitry including:
an adaptive digital filter configured to generate cancellation signals that are added to the input signals to attenuate feedback signals in the input signals;
a digital signal processor coupled to the adaptive digital filter and operable for adapting the filter;
the processing circuitry configured for modifying the repeated signals with respect to the received input signals to differentiate the repeated signals that are received as feedback from the input signals and configured for utilizing the modified repeated signals for de-correlating, from the input signals, the repeated signals that are received as feedback signals by the receive antenna;
a control circuit configured to dynamically modulate how the repeated signals are modified;
the digital signal processor using the de-correlation to adapt the adaptive digital filter.
2. The system of claim 1 , the processing circuitry further comprising a frequency shifting circuit configured for modifying the repeated signals by adding a frequency shift to the repeated signals to form repeated signals that are frequency shifted from the input signals, the processing circuitry configured for utilizing the frequency shift of the repeated signals for de-correlating, from the input signals, repeated signals that are received as feedback signals.
3. The system of claim 1 wherein the adaptive digital filter has multiple taps to generate cancellation signals that attenuate feedback signals that have a plurality of path lengths.
4. The system of claim 1 wherein the adaptive digital filter is a FIR filter.
5. The system of claim 3 wherein the adaptive digital filter is configured to generate cancellation signals to address previous repeated signals that are received directly from the transmit antenna and previous repeated signals that are reflected from surfaces remote from the transmit antenna.
6. The system of claim 2 wherein the control circuit is configured to evaluate the input signals and determine the frequency at which the input signals and the repeated signals beat together, the control circuit operable for slowing down, in real time, the adapting of the adaptive digital filter during the time when the signals beat together.
7. The system of claim 2 wherein the control circuit is configured to evaluate the input signals and determine the frequency at which the input signals and the repeated signals beat together, the control circuit operable for pausing, in real time, the adapting of the adaptive digital filter during the time when the signals beat together.
8. The system of claim 1 wherein the processing circuitry is configured to evaluate the modification of the repeated signals and to synchronize the adaptation of the adaptive digital filter by the digital signal processor based on the modification.
9. The system of claim 1 wherein the control circuit is operable to determine the level of signal traffic in the system, the control circuit dynamically modulating the signal modification based on the signal traffic level.
10. The system of claim 2 wherein the processing circuitry further includes:
a delay element for introducing a delay to the input signals to form repeated signals that are both time delayed and frequency shifted from the input signals;
the processing circuitry configured for utilizing the time delay and the frequency shift of the repeated signals to adapt the adaptive digital filter.
11. The system of claim 10 wherein the processing circuitry is operable for de-correlating, from the input signals, repeated signals that are received as feedback signals using the time delay and frequency shift, the digital signal processor relying on this de-correlation to adapt the adaptive digital filter.
12. The apparatus of claim 1 wherein the digital signal processor is operable to determine if the modification of the repeated signals is sufficient to de-correlate the input signals and repeated signals, the digital signal processor adapting the adaptive digital filter if the modification is sufficient and not adapting the adaptive digital filter if the modification is not sufficient.
13. A circuit for reducing the effect of feedback signals in a signal repeating system that repeats input signals received by at least one receive antenna and transmits the repeated signals with at least one transmit antenna, the circuit comprising:
an adaptive digital filter configured to generate cancellation signals to be added to input signals to attenuate feedback signals in the input signals, the cancellation signals configured to cancel feedback signals received by the repeater apparatus along with the input signals;
a digital signal processor coupled to the adaptive digital filter and operable for adapting the filter;
processing circuitry configured for modifying the repeated signals with respect to the received input signals to differentiate the repeated signals that are received as feedback from the input signals and configured for utilizing the modified repeated signals for de-correlating, from the input signals, the repeated signals that are received as feedback signals by the receive antenna;
a control circuit configured to dynamically modulate how the repeated signals are modified;
the digital signal processor configured for utilizing the de-correlation to adapt the adaptive digital filter.
14. The circuit of claim 13 further comprising a frequency shifting circuit configured for modifying the repeated signals by adding a frequency shift to the repeated signals to form repeated signals that are frequency shifted from the input signals, the processing circuitry configured for utilizing the frequency shift of the repeated signals for de-correlating, from the input signals, repeated signals that are received as feedback signals.
15. The circuit of claim 13 wherein the adaptive digital filter has multiple taps to generate cancellation signals that cancel feedback signals that have a plurality of path lengths.
16. The circuit of claim 14 wherein the control circuit is configured to evaluate the input signals received by a signal repeating system and determine the frequency at which the input signals and the repeated signals beat together, the control circuit operable for slowing down, in real time, the adapting of the adaptive digital filter during the time when the signals beat together.
17. The circuit of claim 14 wherein the control circuit is configured to evaluate the signals received by a signal repeating system and determine the frequency at which the input signals and the repeated signals beat together, the control circuit operable for pausing, in real time, the adapting of the adaptive digital filter during the time when the signals beat together.
18. The circuit of claim 13 wherein the circuit is further configured to evaluate the modification of the repeated signals and to synchronize the adaptation of the adaptive digital filter based on the modification.
19. The circuit of claim 13 wherein the control circuit is operable to evaluate input signals to determine the level of signal traffic of the system, the control circuit dynamically modulating the signal modification based on the signal traffic level.
20. The circuit of claim 14 further comprising:
a delay element for introducing a delay to the input signals to form repeated signals that are both time delayed and frequency shifted from the input signals;
the processing circuitry configured for utilizing the time delay and the frequency shift of the repeated signals to adapt the adaptive digital filter.
21. A method of repeating signals comprising:
receiving input signals;
processing the input signals to form repeated signals;
transmitting the repeated signals;
the processing of the input signals including:
generating cancellation signals with an adaptive digital filter and adding the cancellation signals to the input signals to attenuate feedback signals in the input signals;
modifying the repeated signals with respect to the received input signals to differentiate the repeated signals that are received as feedback from the input signals;
utilizing the modified repeated signals for de-correlating, from the input signals, the repeated signals that are received as feedback signals by the receive antenna;
dynamically modulating how the repeated signals are modified;
utilizing the de-correlation to adapt the adaptive digital filter.
22. The method of claim 21 further comprising adding a frequency shift to the repeated signals to form repeated signals that are frequency shifted from the input signals, utilizing the frequency shift of the repeated signals for de-correlating, from the input signals, repeated signals that are received as feedback signals.
23. The method of claim 21 wherein the adaptive digital filter has multiple taps, the method including generating cancellation signals that attenuate feedback signals that have a plurality of path lengths.
24. The method of claim 22 further comprising determining the frequency at which the input signals and the repeated signals beat together and then at least one of slowing down or pausing, in real time, the adjusting of the adaptive filter during the time when the signals beat together.
25. The method of claim 21 further comprising synchronizing the adaptation of the adaptive digital filter with the modulation of the modification.
26. The method of claim 21 further comprising determining if the modification is sufficient to de-correlate the input signals and repeated signals and adapting the adaptive digital filter if the modification is sufficient and not adapting the adaptive digital filter if the modification is not sufficient.