Orthogonal frequency digital multiplexing correlation canceller

• US 7,426,242 B2
• Filed: 08/04/2004
• Issued: 09/16/2008
• Est. Priority Date: 08/04/2003
• Status: Active Grant

• Current Assignee: ViaSat Incorporated
• Original Assignee: ViaSat Incorporated
• Inventors: Thesling, William H.
• Primary Examiner(s): Ha; Dac V
• Application Number:
  US10/910,868
• Publication Number:
  US 20050030888A1
• Time in Patent Office: 1,504 Days
• Field of Search: 375/144, 375/146, 375/260, 375/285, 375/295, 375/296, 375/298, 370/203, 370/206, 370/464, 370/465, 370/482, 370/497, 455/46, 455/59, 455/91, 455/103, 455/104, 455/109, 455/114.2, 455/114.3, 455/115.1
• US Class Current: 375/296
• CPC Class Codes: H04L 25/022 of frequency response
• CPC Class Codes: H04L 25/03343 Arrangements at the transmitter end

Abstract

A correlation canceller modulates a communication signal over a plurality of channels and an epoch aperture by a plurality of interference response signals corresponding to linear response by one or more filtering effects to generate an inversely correlated communication signal.

Claims

1. A method of a priori conditioning of a communication signal having a plurality of channels, comprising:

transmitting a data signal over one of the plurality of channels in a first processed data signal;

selecting an epoch aperture;

digitally filtering the plurality of channels;

monitoring the remaining plurality of channels over the epoch aperture to obtain corresponding channel response signals resulting from the transmission of the data signal over the one of the plurality of channels;

generating interference response signals based on the channel response signals, the interference response signals corresponding to the plurality of channels over the epoch aperture; and

modulating a second processed data signal by the interference response signals over the plurality of channels and the epoch aperture prior to digital filtering by a digital filter.

2. The method of claim 1, wherein generating interference response signals based on the channel response signals comprises inverting the channel response signals to obtain the interference response signals corresponding to the plurality of channels over the epoch aperture.

3. The method of claim 2, wherein digitally filtering the plurality of channels comprises filtering the plurality of channels through a finite impulse response (FIR) filter.

4. The method of claim 2, wherein transmitting a data signal over one of the plurality of channels in a first processed data signal comprises transmitting one of an in-phase or quadrature data signal over the one of the plurality of channels.

5. The method of claim 4, wherein the data signal comprises an impulse signal.

6. The method of claim 2, wherein inverting the channel response signals to obtain interference response signals corresponding to the plurality of channels over the epoch aperture comprises multiplying each channel response signal by a negative value.

7. The method of claim 1, wherein the data signal comprises an in-phase and quadrature communication signal, and wherein defining an epoch aperture comprises selecting a symbol aperture of n−

1, n, and n+1.

8. The method of claim 7, wherein the communication signal comprises an orthogonal frequency digitally multiplexed (OFDM) signal.

9. The method of claim 1, wherein modulating a second processed data signal by the interference response signals over the plurality of channels and the epoch aperture prior to digital filtering by a digital filter comprises modulating the output of the one of the plurality of channels by unity at a selected time within the epoch aperture.

10. The method of claim 1, wherein the corresponding channel response signals comprise complex values.

11. The method of claim 1, wherein the corresponding channel response signals comprise real values.

12. A system for a priori conditioning of a communication signal having a plurality of channels, comprising:

a channel modulator operable to receive as input a plurality of data signals and modulate the data signals over a plurality of channels to generate a processed data signal having corresponding plurality of communication channels;

a correlation canceller comprising a data store storing a plurality of interference response signals corresponding to a digital filter transfer function, the plurality of interference response signals defining an epoch aperture, the correlation canceller operable to modulate the processed data signal over the plurality of channels and the epoch aperture prior to digital filtering to generate an inversely correlated data signal;

a carrier modulator operable to modulate the inversely correlated data signal to generate a communication signal; and

a digital filter operable to receive as input the communication signal and filter the communication signal according to the digital filter transfer function to generate a filtered communication signal.

13. The system of claim 12, wherein digital filter comprises a finite impulse response (FIR) filter.

14. The system of claim 13, wherein the processed data signal comprises in-phase and quadrature data signals.

15. The system of claim 14, wherein the epoch aperture defines a symbol aperture of n−

1, n, and n+1.

16. The system of claim 12, wherein the interference response signals are based on channel response signals for the plurality of channels;

the channel response signals responsive to an impulse signal transmitted over at least one of the plurality of channels.

17. The system of claim 16, wherein interference response comprises the channel response signals multiplied by a negative value.

18. The system of claim 16, wherein the correlation canceller is further operable to modulate the processed data signal by modulating the output of the one of the plurality of channels by unity at a selected time within the epoch aperture.

19. The system of claim 12, wherein the correlation canceller comprises a field programmable gate array (FPGA).

20. The system of claim 12, wherein the correlation canceller comprises an application specific integrated circuit (ASIC).

21. The system of claim 12, wherein the interference response signals comprise real values.

22. The system of claim 12, further comprising:

an epoch aperture correlator operable to perform a correlation operation on a demodulation data signal to generate channel response data, the demodulated data signal based on the filtered communication signal; and

an interference response signal generator operable to receive the channel response data from the epoch aperture correlator and generate and update the interference response signals for use in the correlation canceller.

23. The system of claim 22, wherein the correlation operation of the epoch aperture correlator comprises an autocorrelation of the demodulated data signal over the epoch aperture.

24. The system of claim 22, wherein the correlation operation of the epoch aperture correlator comprises a correlation of the processed data signal and the demodulated data signal over the epoch aperture.

25. A signal processing system, comprising:

a processing subsystem;

a data store subsystem in data communication with the processing subsystem; and

a communications subsystem in data communication with the processing subsystem and data store subsystem;

wherein the communication subsystem is operable to receive as input a plurality of data signals and modulate the data signals over a plurality of channels to generate a processed data signal having a corresponding plurality of communication channels; and

wherein the data store subsystem is operable to store processing instruction data to cause the processing subsystem to access a plurality of interference response signals corresponding to a digital filter transfer function and defining an epoch aperture, and to modulate the processed data signal over the plurality of channels and the epoch aperture prior to digital filtering to generate an inversely correlated data signal.

26. The system of claim 25, wherein the processing subsystem and data store comprise a field programmable gate array (FPGA).

27. The system of claim 25, wherein the processing subsystem and data store comprise an application specification integrated circuit.

28. The system of claim 25, wherein the interference response signals are based on a plurality of channel response signals over the epoch aperture.

29. A system for facilitating digital filtering through a digital filter by a priori conditioning of a communication signal having a plurality of channels, comprising:

means for receiving a plurality of input data signals, for modulating the data signals over a plurality of channels, and for generating a processed data signal having a corresponding plurality of communication channels;

means for storing a plurality of interference response signals defining an epoch aperture and corresponding to a digital filter transfer function and channel responses of the plurality of communication channels, and for modulating the processed data signal over the plurality of channels and the epoch aperture prior to digital filtering to generate an inversely correlated data signal; and

means for digitally filtering the inversely correlated communication signal according to the digital filter transfer function to generate a filtered communication signal.

30. A method of a priori conditioning of a communication signal having a plurality of channels, comprising:

generating a processed data signal;

modulating the processed data signal over an epoch aperture and over the plurality of channels by a plurality of interference response signals to generate an inversely correlated data signal;

modulating and filtering the inversely correlated data signal to generate a filtered communication signal;

demodulating the filtered communication signal to generate a demodulated data signal;

correlating the demodulated data signal to obtain channel response data; and

generating and updating the interference response signals based on the channel response data.

31. The method of claim 30, wherein the step of correlating the demodulated data signal comprises correlating the demodulated data signal with the processed data signal.

32. The method of claim 31, wherein the step of correlating the demodulated data signal comprises autocorrelating the demodulated data signal.