Asymmetric multi-channel adaptive equalizer
View Patent ↗An apparatus is disclosed to compensate for non-linear effects resulting from the transmitter, the receiver, and/or the communication channel in a communication system. A receiver of the communication system contains an image cancellation module that compensates for images generated during the modulation and/or demodulation process. The image cancellation module includes a fine carrier correction loop to correct for frequency offsets between the transmitter and receiver. The image cancellation module includes a coarse acquisition mode and a decision directed mode. The decision directed mode allows for a larger signal-to-noise ratio for the receiver when compared against the coarse acquisition mode.
1. An adaptive image canceler, comprising:
a feed forward equalizer (FFE) configured to receive a communication signal, the communication signal including a signal of interest and an image of the signal of interest;
an image canceler module configured to produce an output that is a substantially close replica of the image; and
a summer module configured to combine an output of the FFE with the output of the image canceler module to substantially suppress the image from the communication signal.
2. The adaptive image canceler of claim 1 , wherein the FFE is further configured to compensate for distortion present within the communication signal.
3. The adaptive image canceler of claim 1 , wherein the image canceler module comprises:
an adaptive filter, having multiple equalization taps, configured to adjust its impulse response by adjusting equalization coefficients corresponding to the multiple equalization taps.
4. The adaptive image canceler of claim 3 , further comprising:
a switch configured to select between a coarse acquisition mode of operation and a decision directed mode of operation,
wherein the image canceler module is further configured to adjust the equalization coefficients based upon an output of the summer module in the coarse acquisition mode of operation, and
wherein the image canceler module is further configured to adjust the equalization coefficients based upon an estimation of the signal of interest in the decision directed mode of operation.
5. The adaptive image canceler of claim 1 , wherein the communication signal is a multi-channel communication signal having a plurality of information channels, and
wherein the signal of interest occupies at least one information channel from among the plurality of information channels.
6. The adaptive image canceler of claim 1 , wherein the image canceler module is further configured to receive an estimate of the image that is correlated with the image and uncorrelated with the signal of interest.
7. The adaptive image canceler of claim 6 , wherein the image canceler module is further configured to filter the estimate of the image to produce the output that is a substantially close replica of the image.
8. The adaptive image canceler of claim 1 , further comprising:
a decision feedback equalizer (DFE) configured to receive an output of the summer module.
9. An adaptive image canceler, comprising:
a feed forward equalizer (FFE) configured to receive a communication signal, the communication signal including a signal of interest and a residual signal, the communication signal being a multi-channel communication signal having a plurality of information channels, the signal of interest and the residual signal occupying at least one information channel from among the plurality of information channels;
an image canceler module configured to produce an output that is a substantially close replica of the residual signal; and
a summer module configured to combine an output of the FFE with the output of the image canceler module to substantially suppress the residual signal from the communication signal.
10. The adaptive image canceler of claim 9 , wherein the residual signal is an image of the signal of interest, or one or more neighboring channels from among the plurality of information channels.
11. The adaptive image canceler of claim 9 , wherein the FFE is further configured to compensate for distortion present within the communication signal.
12. The adaptive image canceler of claim 9 , wherein the image canceler module comprises:
an adaptive filter, having multiple equalization taps, configured to adjust its impulse response by adjusting equalization coefficients corresponding to the multiple equalization taps.
13. The adaptive image canceler of claim 12 , further comprising:
a switch configured to select between a coarse acquisition mode of operation and a decision directed mode of operation,
wherein the image canceler module is further configured to adjust the equalization coefficients based upon an output of the summer module in the coarse acquisition mode of operation, and
wherein the image canceler module is further configured to adjust the equalization coefficients based upon an estimation of the signal of interest in the decision directed mode of operation.
14. The adaptive image canceler of claim 9 , wherein the communication signal is a multi-channel communication signal having a plurality of information channels, wherein the signal of interest occupies at least one information channel from among the plurality of information channels.
15. The adaptive image canceler of claim 9 , wherein the image canceler module is further configured to filter the residual signal to produce the output that is a substantially close replica of the image.
16. The adaptive image canceler of claim 9 , further comprising:
a decision feedback equalizer (DFE) configured to receive an output of the summer module.
17. The adaptive image canceler of claim 9 , wherein the output of the image canceler module is correlated with the residual signal and uncorrelated with the signal of interest.
18. A method for canceling images embedded onto a communication signal, comprising:
compensating, by an adaptive image canceler, for distortion present within the communication signal to provide an equalized communication signal, the communication signal including a signal of interest and an image of the signal of interest;
producing, by the adaptive image canceler, a correlated signal that is substantially correlated with the image and substantially uncorrelated with the signal of interest; and
subtracting, by the adaptive image canceler, the correlated signal from the equalized communication signal to substantially suppress the image from the communication signal.
19. The method of claim 18 , wherein the producing the correlated signal comprises:
receiving, by the adaptive image canceler, a second image that is correlated with the image and uncorrelated with the signal of interest; and
adaptively filtering, by the adaptive image canceler, the second image to provide the estimate.
20. The method of claim 18 , wherein the adaptively filtering the second image comprises:
adjusting, by the adaptive image canceler, equalization coefficients corresponding to multiple equalization taps of an adaptive filter; and
filtering, by the adaptive image canceler, the second image using the adjusted equalization coefficients to adaptively filter the second image.