System and method for determining and controlling gain margin in an RF repeater

Abstract

An apparatus for repeating signals includes a receive antenna for capturing a receive signal, processing circuitry for processing the receive signal to form a repeated signal, and a transmit antenna for transmitting the repeated signal. The processing circuitry includes gain circuitry for gain in the repeated signal and decorrelation circuitry configured for modifying the repeated signal with respect to the receive signal to thereby decorrelate the repeated signal from the receive signal. The processing circuitry further comprises circuitry configured for calculating a gain margin for the apparatus utilizing the decorrelated receive and repeated signals.

What is claimed is: 
     
       1. An apparatus for repeating signals, the apparatus comprising:
 a receive antenna for capturing a receive signal that includes an input signal and a feedback signal; 
 processing circuitry coupled with the receive antenna for processing the receive signal to form a repeated signal; 
 a transmit antenna coupled with the processing circuitry for transmitting the repeated signal; 
 the processing circuitry for processing the receive signal including:
 gain circuitry to provide gain in the repeated signal; 
 decorrelation circuitry including frequency shifting circuitry that is configured for decorrelating the input signal of the receive signal and the repeated signal by introducing a frequency shift in the repeated signal to form the repeated signal that is decorellated and frequency-shifted from the input signal of the receive signal; 
 gain margin circuitry configured for calculating a gain margin for the apparatus by utilizing samples of the decorrelated receive signal and the frequency-shifted repeated signal and utilizing samples of the repeated signal wherein the frequency shift that is used to decorrelate the receive and repeated signals has been removed. 
 
 
     
     
       2. The apparatus of  claim 1  wherein the frequency shifting circuitry is operable for creating the frequency shift by multiplying the input signal with a complex sinusoid. 
     
     
       3. The apparatus of  claim 1  wherein the processing circuitry is further operable for adjusting the gain based upon the calculated gain margin. 
     
     
       4. The apparatus of  claim 1  wherein the gain margin circuitry determines the gain margin by comparing a cross-correlation of the receive signal and the repeated signal with a cross-correlation of the receive signal and the repeated signal wherein the frequency shift used to decorrelate the receive signal has been removed. 
     
     
       5. The apparatus of  claim 4  wherein the receive signal includes both the input signal and the feedback signal, cross-correlations being performed over a sufficient correlation length so that an average phase of the feedback signal relative to the input signal is around zero degrees. 
     
     
       6. The apparatus of  claim 4  wherein cross correlations are performed over a correlation length that is an integer number of periods of the frequency shift. 
     
     
       7. The apparatus of  claim 4  wherein cross correlations are windowed, the windowing being performed so that an average phase of the cross correlations is around zero degrees. 
     
     
       8. The apparatus of  claim 4  wherein the processing circuitry normalizes the input signal to have generally a constant envelope. 
     
     
       9. The apparatus of  claim 5  wherein the processing circuitry is further configured for determining additional frequency shifting in the feedback signal and providing a compensating amount of frequency shift for cross-correlations to reduce the effect of the additional frequency shifting. 
     
     
       10. The apparatus of  claim 1  wherein the processing circuitry is configured to dynamically increase or decrease the amount of frequency shift provided by the frequency shifting circuit to the input signal. 
     
     
       11. The apparatus of  claim 1  wherein the decorrelation circuitry is selectively turned ON and OFF for selectively calculating the gain margin. 
     
     
       12. The apparatus of  claim 1  wherein the processing circuitry is implemented at least partially with digital circuitry. 
     
     
       13. A method for repeating signals comprising:
 capturing a receive signal with a receive antenna, the receive signal including an input signal and a feedback signal; 
 processing the receive signal with processing circuitry to form a repeated signal; 
 transmitting the repeated signal; 
 the processing steps including:
 providing gain in the repeated signal; 
 decorrelating the input signal of the receive signal and the repeated signal by introducing a frequency shift in the repeated signal to form the repeated signal that is decorrelated and frequency-shifted from the input signal of the receive signal; 
 calculating a gain margin for the apparatus by utilizing samples of the decorrelated receive signal and the frequency-shifted repeated signal and utilizing samples of the repeated signal wherein the frequency shift that is used to decorrelate the receive and repeated signals has been removed. 
 
 
     
     
       14. The method of  claim 13  further including creating a frequency shift by multiplying the input signal with a complex sinusoid. 
     
     
       15. The method of  claim 13  further comprising adjusting the gain based upon the calculated gain margin. 
     
     
       16. The method of  claim 13  wherein calculating the gain margin includes comparing a cross-correlation of the receive signal and the repeated signal with a cross-correlation of the receive signal and the repeated signal wherein the frequency shift used to decorrelate the receive signal has been removed. 
     
     
       17. The method of  claim 16  wherein the receive signal includes both the input signal and the feedback signal, and further comprising performing cross-correlations over a sufficient correlation length so that an average phase of the feedback signal relative to the input signal is around zero degrees. 
     
     
       18. The method of  claim 16  further comprising performing cross correlations over a correlation length that is an integer number of periods of the frequency shift. 
     
     
       19. The method of  claim 16  further comprising windowing cross correlations so that an average phase of the cross correlations is around zero degrees. 
     
     
       20. The method of  claim 16  further comprising normalizing the input signal to have generally a constant envelope. 
     
     
       21. The method of  claim 16  further comprising determining additional frequency shifting in the receive signal and providing a compensating amount of frequency shift for cross correlations to reduce the effect of the additional frequency shifting. 
     
     
       22. The method of  claim 13  further comprising dynamically increasing or decreasing the amount of frequency shift provided by the frequency shifting circuit to the input signal. 
     
     
       23. The method of  claim 13  further comprising selectively turning the decorrelation circuitry ON and OFF for selectively calculating the gain margin. 
     
     
       24. An apparatus for repeating signals, the apparatus comprising:
 a receive antenna configured to capture a receive signal;   a transmit antenna configured to transmit a repeated signal formed from the receive signal;   gain circuitry configured to provide gain in the repeated signal;   decorrelation circuitry configured to modify the repeated signal and including frequency shifting circuitry operable to create a frequency shift in the repeated signal with respect to the receive signal, wherein the repeated signal is frequency shifted and decorrelated from the receive signal; and   gain margin circuitry configured to calculate a gain margin for the apparatus utilizing the decorrelated receive and repeated signals, the gain margin circuitry utilizing a repeated signal that is shifted in frequency by the negative of the frequency shift used to decorrelate the receive and repeated signal.   
     
     
       25. The apparatus of claim 24, further comprising processing circuitry configured to adjust the gain based upon the calculated gain margin. 
     
     
       26. The apparatus of claim 24, wherein the gain margin circuitry is configured to calculate the gain margin by comparing a cross-correlation of the receive signal and the repeated signal with a cross-correlation of the receive signal and the repeated signal that is shifted in frequency by the negative of the frequency shift used to decorrelate the receive signal and repeated signal. 
     
     
       27. The apparatus of claim 26, wherein the receive signal includes both an input signal and a feedback signal, the cross-correlations being performed over at least one of a length of the correlation that is an integer number of periods of the frequency shift or a length of the correlation that is a sufficient length so that an average cross-correlation phase of the feedback signal relative to the input signal is around zero degrees. 
     
     
       28. The apparatus of claim 26, wherein the cross-correlations are windowed, the windowing being performed so that an average phase of the cross-correlations is around zero degrees. 
     
     
       29. The apparatus of claim 26, further comprising processing circuitry configured to normalize the receive and repeated signals to have generally a constant envelope. 
     
     
       30. The apparatus of claim 26, further comprising processing circuitry configured to determine additional frequency shifting in the feedback signal and provide a compensating amount of frequency shift for the cross-correlations to reduce the effect of the additional frequency shifting. 
     
     
       31. The apparatus of claim 24, further comprising processing circuitry configured to dynamically increase or decrease the amount of frequency shift provided by the frequency shifting circuitry to the repeated signal. 
     
     
       32. The apparatus of claim 24, wherein the gain circuitry, the decorrelation circuitry, and the gain margin circuitry are implemented in different circuits. 
     
     
       33. The apparatus of claim 24, wherein at least two of the gain circuitry, the decorrelation circuitry, and the gain margin circuitry are implemented in the same circuit. 
     
     
       34. The apparatus of claim 24, wherein the gain circuitry, the decorrelation circuitry, and the gain margin circuitry are implemented in the same circuit. 
     
     
       35. The apparatus of claim 24, further comprising:
 a first mixer configured to down-convert the receive signal from a radio frequency to an intermediate frequency or baseband frequency;   an analog-to-digital converter configured to convert the down-converted receive signal to a digital signal, wherein the gain circuitry provides gain to the digital signal, wherein the decorrelation circuitry shifts the frequency of the digital signal; and   a digital-to-analog converter configured to convert the digital signal to an analog signal;   a second mixer configured to up-convert the analog signal to a radio frequency signal, wherein the radio frequency signal is provided to the transmit antenna for transmission as the repeated signal.   
     
     
       36. The apparatus of claim 24, wherein the gain circuitry, decorrelation circuitry, and the gain margin circuitry are implemented in the analog domain. 
     
     
       37. A method for repeating signals comprising:
 capturing a receive signal;   transmitting a repeated signal formed from the receive signal;   providing gain in the repeated signal;   modifying the repeated signal by creating a frequency shift in the repeated signal with respect to the receive signal, wherein the repeated signal is frequency shifted and decorrelated from the receive signal;   calculating a gain margin for the apparatus utilizing the decorrelated receive and repeated signals and utilizing a repeated signal that is shifted in frequency by the negative of the frequency shift used to decorrelate the receive signal and repeated signal.   
     
     
       38. The method of claim 37, further comprising adjusting the gain based upon the calculated gain margin. 
     
     
       39. The method of claim 37, wherein calculating the gain margin includes comparing a cross-correlation of the receive signal and the repeated signal with a cross-correlation of the receive signal and the repeated signal that is shifted in frequency by the negative of the frequency shift used to decorrelate the receive signal and repeated signal. 
     
     
       40. The method of claim 39, wherein the receive signal includes both an input signal and a feedback signal, and further comprising performing the cross-correlations over at least one of a length of the correlation that is an integer number of periods of the frequency shift or a length of the correlation that is a sufficient length so that an average cross-correlation phase of the feedback signal relative to the input signal is around zero degrees. 
     
     
       41. The method of claim 39, further comprising normalizing the receive and repeated signals to have generally a constant envelope. 
     
     
       42. The method of claim 39, further comprising determining additional frequency shifting in the receive signal and providing a compensating amount of frequency shift for the cross-correlations to reduce the effect of the additional frequency shifting. 
     
     
       43. The method of claim 37, further comprising dynamically increasing or decreasing the amount of frequency shift provided by the frequency shifting circuit to the repeated signal. 
     
     
       44. The method of claim 37, further comprising:
 down-converting the receive signal to an intermediate frequency or baseband frequency;   converting the down-converted receive signal to a digital signal, wherein gain is provided to the digital signal, wherein the digital signal is frequency shifted;   converting the digital signal to an analog signal; and   up-converting the analog signal to a radio frequency signal, wherein the radio frequency signal is transmitted as the repeated signal.   
     
     
       45. The method of claim 37, wherein providing gain in the repeated signal, modifying the repeated signal, and calculating the gain margin are implemented in the analog domain. 
     
     
       46. An apparatus for repeating signals, the apparatus comprising:
 a receive input to couple the apparatus to a receive antenna, wherein the receive antenna is configured to capture a receive signal, wherein the receive input is configured to obtain the receive signal from the receive antenna;   a transmit output to couple the apparatus to a transmit antenna, wherein the transmit output is configured to provide a repeated signal formed from the receive signal to the transmit antenna, wherein the transmit antenna is configured to transmit the repeated signal;   gain circuitry configured to provide gain in the repeated signal;   decorrelation circuitry configured to modify the repeated signal and including frequency shifting circuitry operable to create a frequency shift in the repeated signal with respect to the receive signal, wherein the repeated signal is frequency shifted and decorrelated from the receive signal; and   gain margin circuitry configured to calculate a gain margin for the apparatus utilizing the decorrelated receive and repeated signals, the gain margin circuitry utilizing a repeated signal that is shifted in frequency by the negative of the frequency shift used to decorrelate the receive and repeated signal.   
     
     
       47. The apparatus of claim 46, further comprising processing circuitry configured to adjust the gain based upon the calculated gain margin. 
     
     
       48. The apparatus of claim 46, wherein the gain margin circuitry is configured to calculate the gain margin by comparing a cross-correlation of the receive signal and the repeated signal with a cross-correlation of the receive signal and the repeated signal that is shifted in frequency by the negative of the frequency shift used to decorrelate the receive signal and repeated signal. 
     
     
       49. The apparatus of claim 48, wherein the receive signal includes both an input signal and a feedback signal, the cross-correlations being performed over at least one of a length of the correlation that is an integer number of periods of the frequency shift or a length of the correlation that is a sufficient length so that an average cross-correlation phase of the feedback signal relative to the input signal is around zero degrees. 
     
     
       50. The apparatus of claim 48, wherein the cross-correlations are windowed, the windowing being performed so that an average phase of the cross-correlations is around zero degrees. 
     
     
       51. The apparatus of claim 48, further comprising processing circuitry configured to normalize the receive and repeated signals to have generally a constant envelope. 
     
     
       52. The apparatus of claim 48, further comprising processing circuitry configured to determine additional frequency shifting in the feedback signal and provide a compensating amount of frequency shift for the cross-correlations to reduce the effect of the additional frequency shifting. 
     
     
       53. The apparatus of claim 46, further comprising processing circuitry configured to dynamically increase or decrease the amount of frequency shift provided by the frequency shifting circuitry to the repeated signal. 
     
     
       54. The apparatus of claim 46, wherein the gain circuitry, the decorrelation circuitry, and the gain margin circuitry are implemented in different circuits. 
     
     
       55. The apparatus of claim 46, wherein at least two of the gain circuitry, the decorrelation circuitry, and the gain margin circuitry are implemented in the same circuit. 
     
     
       56. The apparatus of claim 46, wherein the gain circuitry, the decorrelation circuitry, and the gain margin circuitry are implemented in the same circuit. 
     
     
       57. The apparatus of claim 46, further comprising:
 a first mixer configured to down-convert the receive signal from a radio frequency to an intermediate frequency or baseband frequency;   an analog-to-digital converter configured to convert the down-converted receive signal to a digital signal, wherein the gain circuitry provides gain to the digital signal, wherein the decorrelation circuitry shifts the frequency of the digital signal; and   a digital-to-analog converter configured to convert the digital signal to an analog signal;   a second mixer configured to up-convert the analog signal to a radio frequency signal, wherein the radio frequency signal is provided to the transmit antenna for transmission as the repeated signal.   
     
     
       58. The apparatus of claim 46, wherein the gain circuitry, decorrelation circuitry, and the gain margin circuitry are implemented in the analog domain.