System and method for digital memorized predistortion for wireless communication
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.
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.
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.
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.
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.