System and method for digital memorized predistortion for wireless communication

• US 8,731,495 B2
• Filed: 09/14/2012
• Issued: 05/20/2014
• Est. Priority Date: 05/01/2002
• Status: Expired due to Term

• Current Assignee: Dali Wireless Inc. (Dali Systems Co., Ltd.)
• Original Assignee: Dali Systems Co., Ltd.
• Inventors: Yang, Dali, Yang, Jia
• Primary Examiner(s): AKINYEMI, AJIBOLA A
• Application Number:
  US13/619,538
• Publication Number:
  US 20130243124A1
• Time in Patent Office: 613 Days
• Field of Search: 455/126
• US Class Current: 455/126
• CPC Class Codes: H03F 1/3247 using feedback acting on predistortion circuits H03F1/3264 takes precedence
• CPC Class Codes: H03F 2200/336 A I/Q, i.e. phase quadrature, modulator or demodulator being used in an amplifying circuit
• CPC Class Codes: H03F 2200/451 the amplifier being a radio frequency amplifier
• CPC Class Codes: H03F 2201/3224 Predistortion being done for compensating memory effects
• CPC Class Codes: H03F 2201/3227 Adaptive predistortion based on amplitude, envelope or power level feedback from the output of the main amplifier
• 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 3/189 High-frequency amplifiers, e.g. radio frequency amplifiers
• CPC Class Codes: H03F 3/19 with semiconductor devices only
• CPC Class Codes: H03F 3/195 in integrated circuits
• CPC Class Codes: H03F 3/20 Power amplifiers, e.g. Class B amplifiers, Class C amplifiers H03F3/26 - H03F3/30 take precedence
• CPC Class Codes: H03F 3/24 of transmitter output stages
• CPC Class Codes: H03F 3/245 with semiconductor devices only
• CPC Class Codes: H04B 1/0475 with means for limiting noise, interference or distortion H04B1/0483 takes precedence
• CPC Class Codes: H04L 1/0043 Realisations of complexity reduction techniques, e.g. use of look-up tables
• CPC Class Codes: H04L 1/0044 specially adapted for power saving
• CPC Class Codes: H04L 27/367 using predistortion
• CPC Class Codes: H04L 27/368 adaptive predistortion
• CPC Class Codes: H04W 52/52 using AGC [Automatic Gain Control] circuits or amplifiers

Abstract

An embodiment of the invention is a system for signal processing in preparation for wireless transmission, the wireless transmission being from a portable wireless communication device and including use of a power amplifier having nonlinear characteristics. The system includes memory for storing digitally-indexed information. The digitally-indexed information models nonlinear characteristics of the power amplifier, and the digitally-indexed information is stored prior to processing of a first signal that reflects information to be communicated. The system further includes first logic, configured to accept the first signal and to retrieve, based on the first signal, a portion of the digitally-indexed information stored in the memory, and second logic, configured to generate a second signal based on the portion of the digitally-accessed information and on the first signal. The second signal pre-compensates for the nonlinear characteristics of the power amplifier, and the second signal is for wireless transmission based on the second signal.

Claims

1. A method of operating a power amplifier, the method comprising:

initializing the power amplifier;

establishing pre-computed distortion contributions by training based on pre-compensation training feedback signals representative of output of the power amplifier;

storing the pre-computed distortion contributions in a lookup table;

maintaining the lookup table;

accepting an original value that reflects information to be communicated;

generating a digital lookup-table key based on the original value;

retrieving from the lookup table, using the digital lookup-table key, a corresponding pre-computed distortion contribution for the original value;

distorting the original value based on the corresponding pre-computed distortion contribution to obtain a distorted value to pre-compensate for the nonlinear characteristics of the power amplifier; and

wirelessly transmitting a pre-distorted signal based on the distorted value;

wherein establishing pre-computed distortion contributions comprises;

establishing reference information by training based on reference training feedback signals via feedback channels, the reference training feedback signals being representative of the output of the power amplifier; and

storing the reference information in a reference table; and

wherein maintaining the lookup table comprises refraining, once the pre-computed distortion contributions are established, for at least one entire telephone conversation, from further training to establish the pre-computed distortion contributions or the reference information.

2. The method of claim 1 wherein the reference information comprises linearity characteristics of the power amplifier and time-delay parameters of the feedback channels.

3. The method of claim 1 wherein establishing each respective pre-computed distortion contribution comprises:

squaring an in-phase component of a respective pre-compensation training feedback signal to produce a squared in-phase output value;

squaring a quadrature component of the respective pre-compensation training feedback signal to produce a squared quadrature output value;

squaring an in-phase component of a corresponding reference signal according to the reference information to produce a squared in-phase reference value;

squaring a quadrature component of the corresponding reference signal according to the reference information to produce a squared quadrature reference value;

determining an in-phase difference between the squared in-phase reference value and the squared in-phase output value;

determining a quadrature difference between the squared quadrature reference value and the squared quadrature output value; and

determining the respective pre-computed distortion contribution based on the in-phase difference and the quadrature difference.

4. The method of claim 3 wherein the reference information and the pre-computed distortion contributions are established within four seconds.

6. The method of claim 1 wherein the reference information and the pre-computed distortion contributions are obtained through adaptive iteration.

7. The method of claim 1 wherein the power amplifier is a component of a mobile device.

5. A method of operating a power amplifier, the method comprising:

initializing the power amplifier;

establishing pre-computed distortion contributions by training based on pre-compensation training feedback signals representative of output of the power amplifier;

storing the pre-computed distortion contributions in a lookup table;

maintaining the lookup table;

accepting an original value that reflects information to be communicated;

generating a digital lookup-table key based on the original value;

retrieving from the lookup table, using the digital lookup-table key, a corresponding pre-computed distortion contribution for the original value;

distorting the original value based on the corresponding pre-computed distortion contribution to obtain a distorted value to pre-compensate for the nonlinear characteristics of the power amplifier; and

wirelessly transmitting a pre-distorted signal based on the distorted value;

wherein establishing pre-computed distortion contributions comprises;

establishing reference information by training based on reference training feedback signals via feedback channels, the reference training feedback signals being representative of the output of the power amplifier; and

storing the reference information in a reference table; and

wherein maintaining the lookup table comprises refraining, once the pre-computed distortions contributions are established, for at least one day, from further training to establish the pre-computed distortion contributions or the reference information.

8. A method of operating a power amplifier for wireless transmission of signals, the method comprising:

maintaining a lookup table that contains pre-computed distortion contributions;

accepting an original value that reflects information to be communicated;

generating a digital lookup-table key based on the original value;

retrieving from the lookup table, using the digital lookup-table key, a corresponding pre-computed distortion contribution for the original value;

distorting the original value based on the corresponding pre-computed distortion contribution to obtain a distorted value to pre-compensate for the nonlinear characteristics of the power amplifier; and

wirelessly transmitting a pre-distorted signal based on the distorted value;

wherein maintaining the lookup table comprises;

establishing pre-computed distortion contributions by training based on pre-compensation training feedback signals, the pre-compensation feedback signals being representative of output of the power amplifier;

storing the pre-computed distortion contributions in a lookup table; and

refraining, once the pre-computed distortion contributions are established, for at least one entire communication session, from further training to establish the pre-computed distortion contributions or the reference information; and

wherein establishing pre-computed distortion contributions comprises;

establishing reference information by training based on reference training feedback signals via feedback channels, the reference training feedback signals being representative of the output of the power amplifier; and

storing the reference information in a reference table.

9. The method of claim 8 wherein the reference information comprises linearity characteristics of the power amplifier and time-delay parameters of the feedback channels.

10. The method of claim 8 wherein the reference information and the pre-computed distortion contributions are obtained through adaptive iteration.

11. The method of claim 8 wherein establishing each respective pre-computed distortion contribution comprises:

squaring an in-phase component of a respective pre-compensation training feedback signal to produce a squared in-phase output value;

squaring a quadrature component of the respective pre-compensation training feedback signal to produce a squared quadrature output value;

squaring an in-phase component of a corresponding reference signal according to the reference information to produce a squared in-phase reference value;

squaring a quadrature component of the corresponding reference signal according to the reference information to produce a squared quadrature reference value;

determining an in-phase difference between the squared in-phase reference value and the squared in-phase output value;

determining a quadrature difference between the squared quadrature reference value and the squared quadrature output value; and

determining the respective pre-computed distortion contribution based on the in-phase difference and the quadrature difference.

12. The method of claim 11 wherein the reference information and the pre-computed distortion contributions are established within four seconds.

13. The method of claim 8 wherein the power amplifier is a component of a mobile device.

14. A method of operating a power amplifier for wireless transmission of signals, the method comprising:

maintaining a lookup table that contains pre-computed distortion contributions;

accepting an original value that reflects information to be communicated;

generating a digital lookup-table key based on the original value;

retrieving from the lookup table, using the digital lookup-table key, a corresponding pre-computed distortion contribution for the original value;

distorting the original value based on the corresponding pre-computed distortion contribution to obtain a distorted value to pre-compensate for the nonlinear characteristics of the power amplifier; and

wirelessly transmitting a pre-distorted signal based on the distorted value;

wherein maintaining the lookup table comprises;

establishing pre-computed distortion contributions by training based on pre-compensation training feedback signals, the pre-compensation feedback signals being representative of output of the power amplifier;

storing the pre-computed distortion contributions in a lookup table; and

refraining, once the pre-computed distortion contributions are established, for at least one day, from further training to establish the pre-computed distortion contributions or the reference information; and

wherein establishing pre-computed distortion contributions comprises;

establishing reference information by training based on reference training feedback signals via feedback channels, the reference training feedback signals being representative of the output of the power amplifier; and

storing the reference information in a reference table.