CLOSED-LOOP RECEIVER FEEDBACK PRE-DISTORTION

• US 20070153884A1
• Filed: 10/12/2006
• Published: 07/05/2007
• Est. Priority Date: 10/13/2005
• Status: Active Grant

• Current Assignee: ViaSat Incorporated
• Original Assignee: ViaSat Incorporated
• Inventors: Miller, Mark, Pateros, Charles, Balasubramanian, Rama
• Granted Patent: US 8,385,391 B2
• Time in Patent Office: Days
• US Class Current: 375/221
• CPC Class Codes: H03F 1/3247 using feedback acting on predistortion circuits H03F1/3264 takes precedence
• CPC Class Codes: H03F 1/3288 to compensate phase shift as a function of the amplitude
• CPC Class Codes: H03F 2201/3233 Adaptive predistortion using lookup table, e.g. memory, RAM, ROM, LUT, to generate the predistortion
• CPC Class Codes: H03F 3/195 in integrated circuits
• CPC Class Codes: H03F 3/24 of transmitter output stages
• CPC Class Codes: H04L 25/03343 Arrangements at the transmitter end
• CPC Class Codes: H04L 27/368 adaptive predistortion
• CPC Class Codes: H04W 52/08 Closed loop power control
• CPC Class Codes: H04W 52/52 using AGC [Automatic Gain Control] circuits or amplifiers

Abstract

Methods and systems for calculating pre-distortion coefficients in a closed-loop communication system are presented. Transmission terminals that include high power amplifiers are difficult to operate at or near the saturation point without transmitting signals with nonlinear distortions. By pre-distorting the signal prior to amplification the transmitted nonlinear distortions may be decreased. A closed-looped pre-distortion system may include a receiver that calculates the pre-distortion coefficients and transmits these coefficients back to the transmitter. These coefficients may be stored in a pre-distortion coefficient lookup table and may be updated by the receiver terminal.

Claims

1. A two-terminal closed-loop communication system where pre-distortion coefficients are calculated for a first terminal at a second remote terminal, comprising:

a first terminal, wherein said first terminal comprises;

a pre-distortion multiplication module,

a transmitter, and

a receiver; and

a second terminal, wherein said second terminal comprises;

a receiver,

a pre-distortion coefficient calculator, and

a transmitter,

wherein;

said first terminal is located in a geographically distinct location from said second terminal;

said first terminal prepares and transmits a signal to said second terminal;

said signal is distorted by said first terminal prior to transmission to said second terminal;

said transmitted signal is received at the receiver of said second terminal;

said pre-distortion calculator determines the pre-distortion coefficients for said first terminal from the signal received from said first terminal;

said second terminal transmits said pre-distortion coefficients to said receiver at said first terminal;

said receiver at said first terminal receives said pre-distortion coefficients; and

said first terminal applies said pre-distortion coefficients to subsequently received signals.

2. The two-terminal closed-loop communications system recited in claim 1, wherein said first terminal further comprises a lookup table where said pre-distortion coefficients are stored.

3. The two-terminal closed-loop communications system recited in claim 1, wherein said first terminal further comprises a high power amplifier.

4. The two-terminal closed-loop communications system recited in claim 1, wherein said first terminal further comprises a digital-to-analog converter.

5. The two-terminal closed-loop communications system recited in claim 1, wherein said signal comprises a known header.

6. The two-terminal closed-loop communications system recited in claim 1, wherein said pre-distortion calculator calculates said pre-distortion coefficients using a least squares estimation algorithm.

7. The two-terminal closed-loop communications system recited in claim 1, wherein said pre-distortion calculator calculates said pre-distortion coefficients using a least mean squares algorithm.

8. The two-terminal closed-loop communications system recited in claim 4, wherein said pre-distortion coefficient multiplication module modifies said signal prior to conversion at said digital-to-analog converter.

9. The two-terminal closed-loop communications system recited in claim 4, wherein said pre-distortion coefficient multiplication module modifies said signal after conversion at said digital-to-analog converter.

10. A two-terminal closed-loop communications system, said two-terminal closed-loop communications system comprising:

a first terminal; and

a second terminal;

wherein;

said first terminal comprises a receiver, wherein said receiver receives pre-distortion coefficients from said second terminal;

said first terminal comprises a lookup table, wherein said lookup table stores pre-distortion coefficients received at said receiver;

said first terminal comprises a pre-distortion multiplication module, wherein said pre-distortion multiplication module modifies a data signal by applying said pre-distortion coefficients;

said first terminal comprises an amplifier, wherein said amplifier amplifies a signal after modification at said pre-distortion multiplication module;

said first terminal comprises a transmitter antenna, wherein said transmitter antenna transmits said signal;

said second terminal comprises a receiver, wherein said receiver receives a signal from said first terminal;

said second terminal comprises a pre-distortion coefficient calculator, wherein said pre-distortion coefficient calculator, determines pre-distortion coefficients based on said received signal; and

said second terminal comprises a transmitter, wherein said transmitter transmits said pre-distortion coefficients to said receiver located t said first terminal.

11. The two-terminal closed-loop communications system recited in claim 10, wherein said first and second terminals communicate via a full duplex channel.

12. The two-terminal closed-loop communications system recited in claim 10, wherein said first terminal further comprises a digital-to-analog converter.

13. The two-terminal closed-loop communications system recited in claim 10, wherein said signal comprises a known header

14. The two-terminal closed-loop communications system recited in claim 10, wherein said pre-distortion calculator calculates said pre-distortion coefficients using a least squares estimation algorithm.

15. The two-terminal closed-loop communications system recited in claim 10, wherein said pre-distortion calculator calculates said pre-distortion coefficients using a least mean squares algorithm.

16. A terminal for a closed-loop pre-distortion feedback system, wherein said terminal comprises:

a receiver module;

a pre-distortion coefficient calculation module; and

a transmitter module,

wherein;

said receiver module is adapted to receive transmitted signals from at least one source terminal;

said pre-distortion coefficient calculation module determines pre-distortion coefficients for said source terminal based on the signal received at said receiver; and

said transmitter module transmits said pre-distortion coefficients to said source terminal.

17. The terminal for a closed-loop pre-distortion feedback system according to claim 16, wherein said pre-distortion calculation module uses a least squares estimation algorithm to initialize said pre-distortion coefficients.

18. The terminal for a closed-loop pre-distortion feedback system according to claim 16, wherein said pre-distortion calculation module uses a least mean squares adaptation algorithm to calculate said pre-distortion coefficients.

19. A terminal for a closed-loop pre-distortion feedback system, wherein said terminal comprises:

a receiver module;

a pre-distortion multiplication module;

a pre-distortion coefficient look-up table;

an amplifier; and

a transmitter module;

wherein;

said receiver module receives pre-distortion coefficients transmitted from another terminal;

said pre-distortion coefficients received at said receiver module are stored in said pre-distortion coefficient lookup table;

said pre-distortion multiplication module modifies a signal by applying said pre-distortion coefficients stored in said lookup table to said signal

said amplifier amplifies said signal after said pre-distortion coefficients have been applied to said signal at said pre-distortion coefficient multiplication module; and

said signal is transmitter from said transmitter by said transmitter module.

20. The terminal for a closed-loop pre-distortion feedback system as recited in claim 19, wherein said transmitter further comprises a high power amplifier.

21. The terminal for a closed-loop pre-distortion feedback system as recited in claim 19, wherein said transmitter further comprises a digital-to-analog converter.

22. The terminal for a closed-loop pre-distortion feedback system as recited in claim 21, wherein said pre-distortion coefficient calculator modifies said signal prior to conversion at said digital-to-analog converter.

23. The terminal for a closed-loop pre-distortion feedback system as recited in claim 21, wherein said pre-distortion coefficient calculator modifies said signal after conversion at said digital-to-analog converter.

24. A closed-loop satellite communication system, wherein said closed-loop satellite communication system comprises:

a plurality of satellite terminals; and

a gateway terminal;

wherein;

each satellite terminal comprises a pre-distortion multiplication module;

each satellite terminal comprises a high power amplifier;

each satellite terminal comprises a transmitter module;

each satellite terminal comprises a receiver module;

said gateway terminal comprises a pre-distortion coefficient calculation module;

said gateway terminal comprises a transmitter;

said plurality of satellite terminals transmit a signal that is received by said receiver at said gateway terminal;

said pre-distortion calculation module determines pre-distortion coefficients for the unique satellite terminal from which the signal was received;

said second terminal transmits said pre-distortion coefficients to said receiver at said satellite terminal; and

said receiver at said satellite terminal receives said pre-distortion coefficients.

25. A method for calculating closed-loop pre-distortion coefficients at a location for a remote terminal, wherein said method comprises the steps of

receiving a signal from a remote terminal at said location, wherein said location is remote to the remote terminal;

calculating pre-distortion coefficients for application at the remote terminal from the signal received from said remote terminal at said location; and

transmitting said pre-distortion coefficients calculated in said calculating step back to said remote terminal.

26. The method for calculating pre-distortion coefficients for the remote terminal as recited in claim 25, wherein said signal is a wireless signal.

27. The method for calculating pre-distortion coefficients for the remote terminal as recited in claim 25, wherein said signal is a wired signal.

28. The method for calculating pre-distortion coefficients for the remote terminal as recited in claim 25, wherein said calculating step further comprises calculating the least-squares error between said signal and a model signal.

29. The method for calculating pre-distortion coefficients for the remote terminal as recited in claim 25, wherein said calculating step further comprises calculating the least mean squares between said signal and a model signal.

30. The method for calculating pre-distortion coefficients for the remote terminal as recited in claim 25, wherein said calculating step further comprises using a least squares estimation algorithm.

31. The method for calculating pre-distortion coefficients for the remote terminal as recited in claim 25, wherein said calculating step further comprises using a least mean squares algorithm.