System and method for digital memorized predistortion for wireless communication

• US 6,985,704 B2
• Filed: 05/01/2002
• Issued: 01/10/2006
• 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): LE, LANA N
• Application Number:
  US10/137,556
• Publication Number:
  US 20030207680A1
• Time in Patent Office: 1,350 Days
• Field of Search: 455/127.1, 4551272-1275, 455/114.3, 455/114.2, 455/341, 455/239.1, 455/126, 455/1, 375/296, 375/297, 330/149
• 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 system for signal processing in preparation for wireless transmission, the wireless transmission being from a portable wireless communication device, wherein the wireless transmission includes use of a power amplifier having nonlinear characteristics, the system comprising:

memory for storing digitally-indexed information, wherein 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;

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;

second logic, configured to generate a second signal based on the portion of the digitally-accessed information and on the first signal, wherein the second signal pre-compensates for the nonlinear characteristics of the power amplifier, and the second signal is for wireless transmission of a signal based on the second signal.

2. The system according to claim 1, wherein:

the digitally-indexed information includes a lookup table,

the digitally-indexed information includes pre-computed pre-compensation contributions for a plurality of possible values;

the first logic is configured to retrieve a pre-computed pre-compensation contribution based on generating a lookup-table index from value of a portion of the first signal; and

the second logic is configured to generate the second signal based on the retrieved pre-computed pre-compensation contribution.

3. The system according to claim 2, wherein:

the first signal includes an I-channel component and a Q-channel component; and

the lookup table includes an I-channel lookup table and a Q-channel lookup table, wherein the pre-computed pre-compensation contribution includes an I-channel component and a Q-channel component.

4. The system according to claim 2, wherein:

size of the lookup-table index is N bits, wherein N is greater than one and corresponds to more than one symbol; and

the lookup-table index is generated directly from the portion of the first signal, the portion of the first signal being of N bits, wherein the second signal pre-compensates for memoryful nonlinear characteristics of the power amplifier.

5. The system according to claim 2, wherein:

the first signal is an output of a coder;

the system further comprises a symbol wave shaping filter having the first signal as an input and generating an output based on the first signal;

the second logic is configured to generate the second signal by combining the output of the symbol wave shaping filter and the retrieved pre-computed pre-compensation contribution for the first signal.

6. The system according to claim 2, wherein:

the digitally-indexed information is a memorized pre-compensation function that stores representations of possible input values and pre-computed pre-compensation contributions for the possible input values;

the first logic is configured to;

look, given the portion of the first signal as input, in the lookup table;

find an entry corresponding to the portion of the first signal and return a pre-computed pre-compensation, stored in the entry, for the input.

7. The system according to claim 1, wherein the power amplifier is hereinafter referred to as first power amplifier, and the system does not include any auxiliary power amplifier that is for matching the first power amplifier.

8. The system according to claim 1, wherein the power amplifier has a saturation range, and, during operation for wireless transmission, the power amplifier is operated within fewer than three decibels of its saturation range.

9. The system according to claim 1, wherein the power amplifier has a saturation range, and, during operation for wireless transmission, the power amplifier is operated within one decibel of its saturation range.

10. The system according to claim 1, wherein:

the digitally-indexed information is hereinafter referred to as pre-compensation information; and

the system further comprising logic, hereinafter referred to as third logic, configured to compute the pre-compensation information by training based on errors observed from feedback from beyond the power amplifier.

11. The system according to claim 10, wherein:

the feedback is hereinafter referred to as pre-compensation training feedback;

the memory is further for storing information, hereinafter referred to as reference information, that models characteristics, hereinafter referred to as reference characteristics, that are more linear than the nonlinear characteristics;

the third logic is configured to compute the reference information by training based on errors observed from a reference training feedback, from beyond the power amplifier; and

the errors observed from the pre-compensation training feedback comprise an error between the pre-compensation training feedback and the reference information.

12. The system according to claim 11, wherein:

the power amplifier operates in a first range during operational wireless transmission, and the third logic is configured to set the power amplifier to operate in a second range for training to compute the reference information, wherein the power amplifier has more linear characteristics when operating in the second range as compared to when operating in the first range.

13. The system according to claim 11, wherein the third logic is configured to compute both the reference information and the pre-compensation information within one second.

14. The system according to claim 11, wherein the third logic is configured to compute both the reference information and the pre-compensation information in no more than four seconds.

15. The system according to claim 11, wherein the third logic is configured to refrain, once the pre-compensation information is computed, for at least one entire telephone conversation, from further training to compute the pre-compensation information or the reference information, wherein the system remains ready for operational wireless transmission without needing further training to compute the pre-compensation information or the reference information.

16. The system according to claim 15, wherein the third logic refrains, once the pre-compensation information is computed, for at least one day, from further training to compute the pre-compensation information or the reference information, wherein the system remains ready for operational wireless transmission without needing further training to compute the pre-compensation information or the reference information.

17. The system according to claim 10, wherein the third logic is configured to conduct the training, given the feedback, using arithmetic operations selected only from the group consisting of vector addition, vector multiplication, and vector squaring.

18. The system according to claim 1, wherein the wireless transmission is according to any wireless communication scheme selected from the group consisting of CDMA, TDMA, GSM, GPRS, CDMA2000, UMTS, WCDMA, 3PPP, 802.11a, 802.11b, other versions of 3G, and extensions thereof.

19. The system according to claim 1, wherein the portable wireless communication device is a mobile telephone, and the system is within the mobile telephone.

20. A portable electronic device having wireless communication capabilities, the portable electronic device comprising:

a processor for executing commands that direct operations of the portable electronic device;

a wireless transmission stage that includes a power amplifier having nonlinear characteristics;

memory for storing digitally-indexed data including digitally-indexed information that reflects nonlinear characteristics of the power amplifier; and

code stored in the memory that directs the processor to;

determine, given a first signal that includes information to be communicated wirelessly, a correction contribution based on the first signal and on the digitally-indexed information that reflects the nonlinear characteristics of the power amplifier; and

pre-compensate for the nonlinear characteristics of the power amplifier, based on the correction contribution, to obtain a second signal, wherein the wireless transmission stage will transmit wirelessly a signal based on the second signal.

21. The portable electronic device according to claim 20, wherein the processor is a Digital Signal Processor that direct operations other than pre-compensating for the nonlinear characteristics of the power amplifier, whereby adding the code stored in the memory to the portable electronic device, to thereby eliminate a need for dedicated analog pre-compensation circuitry, did not include adding a processor.

22. In a portable mobile device, a method for processing signals in preparation for wireless transmission, wherein the wireless transmission includes use of a power amplifier, the method comprising:

maintaining a lookup table that contains pre-computed distortion contributions, the distortion contributions being for distorting of signals to thereby pre-compensate the signals for nonlinear characteristics of the power amplifier;

accepting a value that reflects information to be communicated, the value hereinafter referred to as an original value;

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

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

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

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

establishing the pre-computed distortion contributions by training based on errors observed from feedback based on output of the power amplifier wherein the feedback is hereinafter referred to as pre-compensation training feedback, the establishing step comprising;

storing information, hereinafter referred to as reference information, that models characteristics, hereinafter referred to as reference characteristics, that are more linear than the nonlinear characteristics, and

establishing the reference information by training based on errors observed from feedback, hereinafter referred to as reference training feedback, based on output of the power amplifier;

wherein the errors observed from the pre-compensation training feedback comprise an error between the pre-compensation training feedback and the reference information.

23. The method according to claim 22, wherein the power amplifier operates in a first range during operational wireless transmission;

and the step of establishing the reference information further comprises setting the power amplifier to operate in a second range for training to establish the reference information, wherein the power amplifier has more linear characteristics when operating in the second range as compared to when operating in the first range.

24. The method according to claim 22, wherein both the reference information and the pre-computed distortion contributions are established within four seconds.

25. The method according to claim 22, further comprising 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.