Granted Patent B2

US 12,750,013 · App. 18/238,011 · Granted Sep 29, 2026

Inventors: Stephen A. Laraway (Kaysville, UT); Brent J. Berry (Mountain Green, UT)

Assignee: L3Harris Technologies, Inc.

H03F1/3258H03F1/3247H03F3/195H03F3/24H04B1/0475H03F2200/451H03F2201/3224H03F2201/3233H04B2001/0425

Abstract

Claims (77)

1 . A method of digital predistortion initialization, the method comprising:

receiving an original propagated electrical signal resulting from an original multi-tone electrical signal input into a nonlinear channel;

determining a modified input electrical signal that pre-compensates for the nonlinear channel, such that transmitting the modified input electrical signal through the nonlinear channel results in a modified output electrical signal having reduced distortions relative to the nonlinear distortions in the original propagated electrical signal;

using the original multi-tone electrical signal and the modified output electrical signal to determine nonlinear filter coefficients for a nonlinear filter that reduces nonlinear distortions in an output electrical signal from the nonlinear channel when the nonlinear filter is applied to an input electrical signal, input into the nonlinear channel, to perform predistortion prior to the transmission of the input electrical signal through the nonlinear channel;

wherein determining nonlinear coefficients for the nonlinear filter is based on the modified output electrical signal and the original multi-tone electrical signal having multiple simultaneous tones; and

wherein the modified input electrical signal is determined using an iterative process that adapts the modified input electrical signal to reduce levels of intermodulation distortions in the modified output electrical signal, wherein the intermodulation distortions are based on the multiple simultaneous tones, wherein the iterative process comprises, for at least one intermodulation distortion component:

estimating phase and amplitude of the at least one intermodulation distortion component in the modified output electrical signal; and

determining the nonlinear coefficients based on the estimated phase and amplitude of the at least one intermodulation distortion component.

2 . The method of claim 1 , wherein the nonlinear channel has a nonlinear distortion portion, followed in sequence by a second linear distortion portion, an output electrical signal having second linear distortions, below a predetermined threshold, due to the second linear distortion portion, after processing by the nonlinear channel.

3 . The method according to claim 2 , wherein the second linear distortion portion inherently results in the original propagated electrical signal having the second linear distortions below the predetermined threshold.

4 . The method according to claim 2 , further comprising predistorting the original propagated electrical signal into the nonlinear channel, based on the second linear distortion portion to cause the original propagated electrical signal to be a first corrected signal having the second linear distortions below the predetermined threshold.

5 . The method according to claim 4 , further comprising:

determining coefficients for a second linear filter that performs the predistorting of the original propagated electrical signal which reduces the second linear distortions in the output electrical signal; and

applying the second linear filter to the modified input electrical signal.

6 . The method according to claim 5 , wherein applying the second linear filter to the input signal causes coefficients of the nonlinear filter to be linear-in-parameter, and the determining coefficients of the second linear filter is performed by solving for the coefficients of the second filter using a least-squares method.

7 . The method according to claim 5 , further comprising:

initializing the second linear filter by

selecting as the original propagated electrical signal, respective multi-tone signals from a set of multi-tone signals, each multi-tone signal having a respective set of frequencies from a plurality of discrete frequencies, and the plurality of discrete frequencies being selected to span a predefined frequency range,

determining amplitude linear equations based on measured intermodulation distortion components of the output electrical signal, when the nonlinear channel is excited by the respective multi-tone signals from the set of multi-tone signals,

determining phase linear equations based on the measured intermodulation distortion components of the output electrical signal, when the nonlinear channel is excited by the respective multi-tone signals from the set of multi-tone signals, and

determining the second linear filter coefficients based on the amplitude linear equations and the phase linear equations.

8 . The method according to claim 1 , wherein the nonlinear filter is linear-in-parameter, and determining coefficients of the nonlinear filter is performed by solving for the coefficients of the nonlinear filter using a least-squares method using the original input multi-tone electrical signal and the modified output electrical signal.

9 . The method according to claim 1 , wherein the nonlinear channel has a first linear distortion portion preceding a nonlinear distortion portion, and determining nonlinear filter coefficients of the nonlinear filter further comprises selecting coefficients of the nonlinear filter that reduce distortions caused by the first linear distortion portion in addition to reducing the nonlinear distortions.

10 . The method according to claim 1 , wherein

determining the coefficients for the nonlinear filter further includes determining the nonlinear filter coefficients to reduce nonlinear distortions that arise, at least in part, from a power amplifier in the nonlinear channel, such that the nonlinear distortions, which are reduced by the nonlinear filter, include compression and/or saturation of the power amplifier.

11 . The method according to claim 5 , further comprising:

initializing the second linear filter and the nonlinear filter by

generating an input electrical signal to be a set of multi-tone electrical signals comprising a portion having a first frequency component and a second frequency component;

transmitting the input electrical signal through the nonlinear channel to generate the original propagated electrical signal, the original propagated electrical signal including one or more intermodulation distortion components of the first frequency component and the second frequency component that are generated by transmitting the multi-tone electrical signal through the nonlinear channel;

wherein determining coefficients for the nonlinear filter and the second linear filter is performed using a synchronization that time synchronizes the set of multi-tone electrical signals.

12 . The method according to claim 1 , wherein

determining the nonlinear coefficients for the nonlinear filter includes that

the nonlinear channel has a memory,

the nonlinear filter comprises a memory polynomial, and

determining the nonlinear coefficients for the nonlinear filter includes setting coefficients of the memory polynomial to values that reduce the nonlinear distortions with the memory, and

the values of the coefficients of the memory polynomial being determined using a system of linear equations that relates the coefficients of the memory polynomial, the input electrical signal, and a modified input electrical signal, wherein

the modified input electrical signal is an electrical signal that, when input to the nonlinear channel, reduces the nonlinear distortions and/or intermodulation distortion components in the output electrical signal from the nonlinear channel.

13 . The method according to claim 1 , wherein

determining the nonlinear coefficients for the nonlinear filter includes that

the nonlinear filter comprises a memoryless nonlinear filter and another linear filter, and

determining the nonlinear coefficients for the nonlinear filter includes setting coefficients of the memoryless nonlinear filter and the another linear filter to values that reduce the nonlinear distortions.

14 . A method of reducing distortion in an electrical signal for wireless transmission, the method comprising:

generating a multi-tone electrical signal comprising a first portion and a second portion, the first portion having at least a first frequency component and a second frequency component, and the second portion having a synchronization signal;

transmitting the multi-tone electrical signal through a nonlinear channel to generate an output electrical signal at an output of the nonlinear channel, the nonlinear channel causing linear distortions and nonlinear distortions in the output electrical signal;

detecting, in the output electrical signal, intermodulation distortion components, the first frequency component, and the second frequency component;

using the synchronization signal to measure, in the output electrical signal, phases of the intermodulation distortion components, the first frequency component, and the second frequency component; and

determining coefficients of a digital predistortion processor based on

the intermodulation distortion components,

the first frequency component,

the second frequency component, and

the phases of the intermodulation distortion components, the first frequency component, and the second frequency component, wherein

the digital predistortion processor reduces the intermodulation distortion components in the output electrical signal, wherein the intermodulation distortions are based on the first frequency component and the second frequency component.

15 . The method according to claim 14 , wherein

the synchronization signal comprises a pseudo-random noise sequence, and

the measuring of the phases in the output electrical signal includes using the synchronization signal to time align the intermodulation distortion components, the first frequency component, and the second frequency component.

16 . The method according to claim 14 , wherein the generating of the multi-tone electrical signal is repeated using respective frequency pairs for the first frequency component and the second frequency component, the respective frequency pairs having different center frequencies and having different frequency spacings between the first frequency component and the second frequency component.

17 . The method according to claim 14 , wherein the generating of the multi-tone electrical signal is repeated using respective frequency pairs for the first frequency component and the second frequency component, the respective frequency pairs having frequencies that are spaced apart by integer multiples of a predefined frequency period wo.

18 . The method according to claim 14 , wherein

the generating of the multi-tone electrical signal is repeated using respective frequency pairs for the first frequency component and the second frequency component, wherein

frequencies of the respective frequency pairs span a predefined frequency range, and

bandwidths of the respective frequency pairs span another predefined frequency range.

19 . A transmitter, comprising:

a waveform generator configured to generate an input electrical signal;

a digital predistortion processor configured to receive the input electrical signal and apply thereto a nonlinear filter;

a digital to analog converter configured to convert an output of the digital predistortion processor to an analog signal;

a nonlinear channel comprising an amplifier that is configured to amplify the analog signal, the nonlinear channel causing nonlinear distortions and linear distortions to the analog signal;

an analog to digital converter configured to convert a part of the analog signal to an output electrical signal; and

processing circuitry configured to initialize values of coefficients of the nonlinear filter of the digital predistortion processor to pre-compensate for and thereby reduce the nonlinear distortions to the analog signal, the processing circuitry being configured to initialize the values of the coefficients of the first filter and the second filter by:

receiving an original propagated electrical signal resulting from a multi-tone electrical signal input into the nonlinear channel, the original propagated electrical signal having second linear distortions, below a predetermined threshold, after processing by the nonlinear channel, the original propagated electrical signal further having nonlinear distortions caused by the nonlinear channel,

determining a modified input electrical signal that pre-compensates for the nonlinear distortions, such that transmitting the modified input electrical signal through the nonlinear channel results in a modified output electrical signal having reduced nonlinear distortions relative to the nonlinear distortions in the original propagated electrical signal,

using the original input electrical signal and the modified input-output electrical signal to determine nonlinear filter coefficients for the nonlinear filter, that reduces nonlinear distortions in an output electrical signal from the nonlinear channel when the nonlinear filter is applied to an input electrical signal, input into the nonlinear channel, to perform predistortion prior to the transmission of the input electrical signal through the nonlinear channel,

wherein determining nonlinear coefficients for the nonlinear filter is based on the modified output electrical signal and the original propagated electrical signal having multiple simultaneous tones; and

wherein the modified input electrical signal is determined using an iterative process that adapts the modified input electrical signal to reduce levels of intermodulation distortions in the modified output electrical signal, wherein the intermodulation distortions are based on the multiple simultaneous tones, wherein the iterative process comprises, for at least one intermodulation distortion component:

estimating phase and amplitude of the at least one intermodulation distortion component in the modified output electrical signal; and

determining the nonlinear coefficients based on the estimated phase and amplitude of the at least one intermodulation distortion component.

20 . The transmitter of claim 19 , wherein the processing circuitry is further configured to:

predistort an input signal input into the nonlinear channel, based on the linear distortions to cause the original propagated electrical signal to be a first corrected signal having the second linear distortions, below the predetermined threshold.

Assignments (1)

Continuity (1)

References Cited (24)