RECEIVER-BASED FREQUENCY RESPONSE ESTIMATION

• US 20090180573A1
• Filed: 01/10/2008
• Published: 07/16/2009
• Est. Priority Date: 01/10/2008
• Status: Active Grant

• Current Assignee: ViaSat Incorporated
• Original Assignee: ViaSat Incorporated
• Inventors: Thesling, William H.
• Granted Patent: US 8,625,659 B2
• Time in Patent Office: Days
• 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

Methods, systems, and devices are described for estimating a frequency response using a received signal. A first spectral estimation is performed on a digitized representation of an initial version of a wireless signal. A second spectral estimation is performed on the digitized representation of the wireless signal as received from the transmitter. The first spectral estimation is compared with the second spectral estimation to estimate a frequency response. A later signal transmitted from the transmitter may be pre-distorted to compensate for the estimated frequency response. The disclosed frequency response estimation techniques may be used in a satellite communications system.

Claims

1. A system for pre-distorting a signal, the system comprising:

a subscriber terminal configured to;

receive a first wireless signal transmitted from a gateway device via a satellite;

buffer a digitized representation of the first wireless signal comprising a sequence of symbols;

decode the sequence of symbols to recover a set of data;

compare a first spectral estimate for the buffered sequence of symbols to a second spectral estimate generated from the recovered set of data to create comparison data; and

transmit the comparison data; and

a gateway device, in communication with the subscriber terminal via the satellite, and configured to;

receive the comparison data; and

pre-distort a second signal to be transmitted based at least in part on the comparison data.

2. The system of claim 1, wherein the subscriber terminal is configured to generate comparison data comprising one or more measurements of amplitude differences between the first spectral estimate and the second spectral estimate.

3. The system of claim 1, wherein the subscriber terminal is configured to generate comparison data comprising one or more measurements of phase differences between the first spectral estimate and the second spectral estimate.

4. The system of claim 1, wherein the gateway device is configured to pre-distort the second signal by filtering the second signal to modify an amplitude and phase of a subset of spectral components of the second signal.

5. The system of claim 1, wherein the subscriber terminal is configured to transmit the comparison data to the gateway device via a landline.

6. The system of claim 1, wherein the subscriber terminal is configured to transmit the comparison data to the gateway device via the satellite in a pad portion of a data packet.

7. The system of claim 1, wherein the gateway device is configured to:

receive additional spectral estimate comparisons from the plurality of additional subscriber terminals, wherein the pre-distortion of the second signal is based at least in part on the received additional spectral estimate comparisons.

8. The system of claim 7, wherein the gateway device is configured to:

receive additional spectral estimate comparisons from a plurality of additional subscriber terminals; and

exclude additional spectral estimate comparisons when the second signal is not directed at any of the plurality of additional subscriber terminals.

9. The system of claim 1, wherein the satellite transmits the first wireless signal from the gateway device in a spot beam not covering the gateway device.

10. A method of pre-distorting a signal, the method comprising:

buffering a digitized signal comprising a sequence of symbols received from a transmitter;

decoding the digitized sequence of symbols to recover a set of data;

comparing a spectral estimate for the buffered sequence of symbols to a spectral estimate of data generated from the recovered set of data; and

pre-distorting a signal to be transmitted from the transmitter based at least in part on the comparison of spectral estimations.

11. The method of claim 10, further comprising:

generating the spectral estimate for the buffered sequence of symbols; and

generating the spectral estimate of data generated from the recovered set of data.

12. The method of claim 11, wherein,

the spectral estimate for the buffered sequence of symbols and the spectral estimate of data from the recovered set of data are each generated using a fast Fourier transform.

13. The method of claim 10, wherein the pre-distorting step comprises:

filtering the signal to be transmitted from the transmitter to modify an amplitude of at least a subset of spectral components of the second signal.

14. The method of claim 10, wherein each of the steps of the method are performed by a gateway device comprising the transmitter.

15. The method of claim 10, further comprising:

estimating a frequency response of channel using the comparison of spectral estimations.

16. The method of claim 15, further comprising:

determining that the frequency response comprises a nonlinear output; and

identifying pre-distortion filter coefficients using a look-up table, wherein the identified pre-distortion filter coefficients are used in the pre-distorting step.

17. A subscriber terminal for use in determining a frequency response, the subscriber terminal comprising:

a receiver unit configured to receive and digitize a first wireless signal transmitted from a transmitter;

a decoder unit, communicatively coupled with the receiver unit, and configured to decode a sequence of symbols of the digitized wireless signal to create a recovered set of data;

a regeneration unit, communicatively coupled with the decoder unit, and configured to regenerate a version of the transmitted signal using the recovered set of data; and

a spectral estimation unit, communicatively coupled with the receiver unit and regeneration unit, and configured to;

generate a first spectral estimate for the sequence of symbols of the digitized wireless signal;

generate a second spectral estimate for the regenerated version; and

compare the first spectral estimate and the second spectral estimate to generate comparison data.

18. The subscriber terminal of claim 17, wherein,

the comparison data includes measurements phase and amplitude differences between the first spectral estimate and the second spectral estimate.

19. The subscriber terminal of claim 17, wherein,

the first spectral estimate and the second spectral estimate are each generated using a fast Fourier transform.

20. The subscriber terminal of claim 17, further comprising:

a transmitter unit, communicatively coupled with the receiver unit, and configured to transmit the comparison data.

21. A method of determining a frequency response, the method comprising:

buffering a sequence of symbols comprising a digitized representation of a wireless signal received from a transmitter;

decoding the buffered sequence of symbols to recover a set of data;

regenerating a version of the wireless signal using the recovered set of data; and

comparing a spectral estimate for the buffered sequence of symbols to a spectral estimate for the regenerated version of the first signal to estimate a frequency response.

22. The method of claim 21, further comprising:

pre-distorting a signal to be transmitted from the transmitter based at least in part on the comparison of spectral estimations, wherein the pre-distortion includes a phase modification.

23. The method of claim 21, further comprising:

transmitting the estimated frequency response to a gateway device comprising the transmitter,

wherein the method is performed by a dedicated frequency response estimation terminal.

24. A method of determining a frequency response, the method comprising:

performing a first spectral estimation of a first digitized representation of a wireless signal received from a transmitter;

performing a second spectral estimation of a second digitized representation of the wireless signal, the second digitized representation approximating an ideal version of the wireless signal as transmitted from the transmitter; and

comparing the first spectral estimation and the second spectral estimation to estimate a frequency response.

25. The method of claim 24, further comprising:

receiving the wireless signal from the transmitter via the satellite;

digitizing the received wireless signal to create the first digitized representation;

decoding the first digitized representation to recover a set of data; and

modulating and coding the recovered set of data to generate the second digitized representation.