Predistorted modulation system for bandwidth efficient satellite links

• US 6,775,330 B2
• Filed: 11/06/2002
• Issued: 08/10/2004
• Est. Priority Date: 04/29/2002
• Status: Active Grant

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Bach, Susan E., Strodtbeck, Andrew L.
• Primary Examiner(s): Ghebretinsae, Temesghen
• Application Number:
  US10/289,043
• Publication Number:
  US 20030202615A1
• Time in Patent Office: 643 Days
• Field of Search: 375/296, 375/297, 375/285, 375/284, 455/126, 330/149
• US Class Current: 375/296
• CPC Class Codes: H04B 7/18517 Transmission equipment in earth stations
• CPC Class Codes: H04L 25/03343 Arrangements at the transmitter end
• CPC Class Codes: Y02D 30/00 Reducing energy consumption in communication networks

Abstract

The present invention discloses a predistortion modulation system for use in satellite systems. A typical apparatus of the invention includes a predistortion processor for predistorting a digital data source signal to reduce transmission distortion and an adaptive algorithm processor for controlling the predistortion processor according to a received a feedback signal derived from the transmitted data source signal. In further embodiments, the non-linear and linear predistortion is adaptively controlled. The invention is particularly useful in a digital cinema satellite system.

Claims

1. An apparatus for transmitting signals, comprising:

a predistortion processor for applying predistortion to a digital data source signal to reduce transmission distortion; and

an adaptive algorithm processor for controlling the predistortion processor according to a received a feedback signal derived from the transmitted data source signal;

wherein the predistortion processor includes a linear predistortion processor and the linear predistortion processor employs a zero forcing equalization (ZFE) algorithm.

2. The apparatus of claim 1, wherein the predistortion processor and adaptive algorithm processor operate in a digital cinema system.

3. The apparatus of claim 1, wherein the feedback signal is derived from the transmitted data source signal before transmission.

4. The apparatus of claim 1, wherein the feedback signal is derived from the transmitted data source signal after transmission.

5. The apparatus of claim 4, wherein the feedback signal is derived by a receiver of the transmitted data source signal and communicated to the adaptive algorithm processor via a low data rare return path.

6. The apparatus of claim 4, wherein the low data rare return path comprises a back channel of a digital cinema system.

7. The apparatus of claim 1, further comprising

a modulator including a digital to analog converter for producing a transmission signal of the digital data source signal, and

a high power amplifier for amplifying the transmission signal to produce the transmitted data source signal;

wherein the transmission distortion comprises effects of the high power amplifier.

8. The apparatus of claim 7, further comprising:

a demodulator including an analog to digital converter for producing the feedback signal derived from the transmitted data source signal; and

a local oscillator providing a lining signal for both the demodulator and modulator.

9. The apparatus of claim 1, wherein the predistortion processor includes a non-linear processor.

10. The apparatus of claim 9, wherein the non-linear processor comprises a complex gain multiplying the digital data source signal, the complex gain depending upon an instantaneous magnitude of the data source signal.

11. The apparatus of claim 10, wherein the magnitude is a monotonic function of a power measurement and the power measurement is applied to a lookup table to determine the complex gain.

12. The apparatus of claim 11, wherein the adaptive algorithm processor adjusts the lookup table using a gradient technique to update values of the lookup table.

13. The apparatus of claim 1, wherein the linear processor comprises an asymmetric finite impulse response digital filter using filter coefficients controlled by the adaptive algorithm processor.

14. The apparatus of claim 13, wherein the asymmetric finite impulse response digital filter comprises four independent real finite impulse response functions.

15. The apparatus of claim 1, further comprising a pulse shaping digital filter applied to the digital data source signal.

16. The apparatus of claim 15, wherein the pulse shaping digital filter comprises a symmetric finite impulse response filter.

17. The apparatus of claim 16, wherein the symmetric finite impulse response filter comprises two substantially identical real finite impulse response functions.

18. A method of transmitting data, comprising the steps of:

applying predistortion to a digital data source signal with a predistortion processor to reduce transmission distortion; and

controlling predistortion of the digital data source signal with an adaptive algorithm processor according to a received a feedback signal derived from the transmitted data source signal;

wherein the predistortion processor includes a linear predistortion processor and the linear predistortion processor employs a zero forcing equalization (ZFE) algorithm.

20. The method of claim 18, wherein the feedback signal is derived from the transmitted data source signal before transmission.

21. The method of claim 18, wherein the feedback signal is derived from the transmitted data source signal after transmission.

22. The method of claim 21, wherein the feedback signal is derived by a receiver of the transmitted data source signal and communicated to the adaptive algorithm processor via a low data rate return path.

23. The method of claim 22, wherein the low data rate return path comprises a back channel of a digital cinema system.

24. The method of claim 18, further comprising:

producing a transmission signal of the digital data source signal with a modulator including a digital to analog converter; and

amplifying the transmission signal with a high power amplifier to produce the transmitted data source signal;

wherein the transmission distortion comprises effects of the high power amplifier.

25. The method of claim 24, further comprising:

producing the feedback signal derived from the transmitted data source signal with a demodulator including an analog to digital converter; and

providing a timing signal for both the demodulator and modulator with a local oscillator.

26. The method of claim 18, wherein the predistortion processor includes a non-linear processor.

27. The method of claim 26, wherein the non-linear processor comprises a complex gain multiplying the digital data source signal, the complex gain depending upon instantaneous magnitude of the data source signal.

28. The method of claim 27, wherein the magnitude is a monotonic function of a power measurement and the power measurement is applied to a lookup table to determine the complex gain.

29. The method of claim 28, wherein the adaptive algorithm processor adjusts the lookup table using a gradient technique to update values of the lookup table.

30. The method of claim 18, wherein the linear processor comprises an asymmetric finite impulse response digital filter using filter coefficients controlled by the adaptive algorithm processor.

31. The method of claim 30, wherein the asymmetric finite impulse response digital filter comprises four independent real finite impulse response functions.

32. The method of claim 18, further comprising a pulse shaping digital filter applied to the digital data source signal.

33. The method of claim 32, wherein the pulse shaping digital filter comprises a symmetric finite impulse response filter.

34. The method of claim 33, wherein the symmetric finite impulse response filter comprises two substantially identical real finite impulse response functions.

19. The method of the predistortion processor and adaptive algorithm processor operate in a digital cinema system.