Multicarrier successive predistortion for digital transmission

Patent metadata

Field	Value
Publication number	US-9614554-B2
Application number	US-201514738812-A
Country	US
Kind code	B2
Filing date	Jun 12, 2015
Priority date	Mar 31, 2014
Publication date	Apr 4, 2017
Grant date	Apr 4, 2017

Abstract

An approach for improved compensation for nonlinear distortion in multicarrier satellite systems is provided. Source reflecting encoded and modulated sequences of source data symbols are received. Each source signal is predistorted, and a transmit filter is applied to each predistorted source signal. Each filtered signal is translated to a carrier frequency, and the translated signals are combined into a composite signal for transmission via a multicarrier transponder. The final predistorted version of each source signal is generated via an iterative process of a number of stages, wherein, for a given stage and for each source signal, the process comprises: receiving a prior predistorted version of each source signal from a preceding stage; processing each prior predistorted source signal based on all of the received prior predistorted source signals, wherein the processing is performed based on a characterization of one or more characteristics of the multicarrier satellite transponder.

First claim

What is claimed is:

1. A method comprising:
receiving a plurality of source signals, wherein each source signal comprises a sequence of source data symbols;
encoding and modulating each source signal for transmission via a multicarrier channel of a wireless communications system;
generating a final predistorted version for each encoded and modulated source signal;
applying a transmit filter to the final predistorted version of each of the source signals;
translating each of the filtered signals to a respective carrier frequency; and
combining the translated signals to generate a composite signal for transmission via the multicarrier channel;
wherein the final predistorted version for each of the encoded and modulated source signals is generated via an iterative process of a number of stages, wherein, for a given stage and for each source signal, the process comprises:
receiving a respective prior predistorted version of each of the source signals from a preceding stage; and
processing the prior predistorted version of the source signal based on the received prior predistorted versions of all of the source signals from the preceding stage, such that, at each stage, the processing of the prior predistorted version of each source signal takes into account the prior predistorted versions of all the encoded and modulated source signals from the preceding stage, wherein the processing of the prior predistorted version of the source signal is performed based on a characterization of one or more characteristics of the multicarrier channel.

2. The method according to claim 1 , wherein the processing of the prior predistorted version of the source signal based on the received prior predistorted versions of all the encoded and modulated source signals from the preceding stage comprises determining a distortion estimate that would result from passing the composite signal through the multicarrier channel, and generating an error signal based on the distortion estimate.

3. The method according to claim 2 , wherein the error signal is driven towards zero by applying the estimation via the iterative process.

4. The method according to claim 1 , wherein, for each source signal and for the given stage of the iterative process for the generation of the final predistorted version for each of the encoded and modulated source signals:
the predistorted version of each of the source signals from the preceding stage is represented as a vector of data symbols associated with the respective carrier frequency;
a further predistorted version of the source signal is generated by applying an estimated predistortion, based on a distortion estimate that would result from passing the composite signal through the multicarrier channel, to the vector representation for the source signal; and
the further predistorted versions of all of the source signals are fed-back for processing via the next stage.

5. The method according to claim 4 , wherein the distortion estimate is represented as a vector based on a vector representation of the further predistorted versions for each of the source signals, and the distortion estimate is used to generate an error vector for the source signal relative to an undistorted version of the encoded and modulated source signal.

6. The method according to claim 5 , wherein the error vector for the source signal is generated by subtracting the distortion estimate vector from the undistorted version of the encoded and modulated source signal.

7. The method according to claim 6 , wherein the error vector for the source signal is driven towards zero by the iterative predistortion process.

8. The method according to claim 1 , wherein for each source signal and for the given stage of the iterative process for the generation of the final predistorted version for each of the encoded and modulated source signals:
the predistorted version of each of the source signals from the preceding stage is represented as a vector of data symbols associated with the respective carrier frequency;
a further predistorted version of the source signal is generated by modifying the vector of data symbols (representing the predistorted version of the source signal from the preceding stage) based on a correction term, wherein the correction term is proportional to an error vector (representing an estimated predistortion based on a distortion estimate that would result from passing the composite signal through the multicarrier channel);
the further predistorted versions of all of the source signals are fed-back for processing via the next stage.

9. The method according to claim 8 , wherein the modification of the vector of data symbols (representing the predistorted version of the source signal from the preceding stage) based on the correction term comprises:
processing the error vector (representing the estimated predistortion based on the distortion estimate that would result from passing the composite signal through the multicarrier channel) based on a step-size sequence to generate a modified error vector; and
adding the modified error vector to the vector of data symbols (representing the predistorted version of the source signal from the preceding stage) to generate the further predistorted version of the source signal.

10. The method according to claim 9 , wherein the step size sequence is defined to be positive and decreasing to drive the error vector towards zero.

11. The method according to claim 9 , wherein the step-size sequence serves to optimize performance of the predistortion process by maximizing convergence speed (reduction of the number of predistorter stages) while minimizing residual error.

12. A transmitter apparatus comprising:
a receiver interface configured to receive a plurality of source signals, wherein each source signal comprises a sequence of source data symbols;
an encoder and a modulator configured to encode and modulate each source signal for transmission via a multicarrier channel of a wireless communications system;
a processor configured to generate a final predistorted version for each encoded and modulated source signal;
a transmit filter configured to filter to the final predistorted version of each of the source signals;
a signal processor configured to translate each of the filtered signals to a respective carrier frequency; and
a signal combiner configured to combine the translated signals to generate a composite signal for transmission via the multicarrier channel;
wherein the processor is configured to generate the final predistorted version for each encoded and modulated source signal via an iterative process of a number of stages, wherein, for a given stage and for each source signal, the process comprises:
receiving a respective prior predistorted version of each of the source signals from a preceding stage; and
processing the prior predistorted version of the source signal based on the received prior predistorted versions of all of the source signals from the preceding stage, such that, at each stage, the processing of the prior predistorted version of each source signal takes into account the prior predistorted versions of all the encoded and modulated source signals from the preceding stage, wherein the processing of the prior predistorted version of the source signal is performed based on a characterization of one or more characteristics of the multicarrier channel.

13. The apparatus according to claim 12 , wherein the processing of the prior predistorted version of the source signal based on the received prior predistorted versions of all the encoded and modulated source signals from the preceding stage comprises dete

Assignees

• Hughes Network Systems Llc

Inventors

• Beidas Bassel
• Seshadri Rohit Iyer
• Becker Neal

Classifications

• H04L27/368

  adaptive predistortion · CPC title

• H04B2001/0425

  with linearisation using predistortion · CPC title

• H04L25/03343

  Arrangements at the transmitter end · CPC title

• H04B1/0475 Primary

  with means for limiting noise, interference or distortion (H04B1/0483 takes precedence) · CPC title

• H04B7/15

  Active relay systems · CPC title