Power series predistorter and control method thereof

• US 20060262880A1
• Filed: 05/16/2006
• Published: 11/23/2006
• Est. Priority Date: 05/18/2005
• Status: Active Grant

• Current Assignee: NTT Docomo Incorporated (Nippon Telegraph and Telephone Corporation)
• Original Assignee: NTT Docomo Incorporated (Nippon Telegraph and Telephone Corporation)
• Inventors: Narahashi, Shoichi, Suzuki, Yasunori, Mizuta, Shinji
• Granted Patent: US 7,907,678 B2
• Time in Patent Office: Days
• US Class Current: 375/297
• CPC Class Codes: H03F 1/3258 based on polynomial terms

Abstract

In a distortion generation path of a power series predistorter, a frequency characteristic compensator that adjusts the frequency characteristic of a distortion component is provided in series with an odd-order distortion generator. The output of a power amplifier is divided to obtain an output signal of the power amplifier, the output signal of the power amplifier is down-converted by a down converter, and a distortion detector detects a distortion component in the down-converted signal of base band. The frequency characteristic of the distortion component is split into windows each having a band width of Δf by a distortion component frequency characteristic splitter, and the power of the distortion component in each window is detected. Based on the detected power, the frequency characteristic compensator adjusts a part of the frequency characteristic of the distortion component associated with each window.

Claims

1. A power series predistorter that generates a predistortion component for compensating for a distortion component produced by a power amplifier, comprising:

a linear transmission path for linearly transmitting an input signal;

a distortion generation path including an odd-order distortion generator for generating an odd-order distortion component for the input signal;

a frequency characteristic compensator inserted in series in the distortion generation path, for adjusting the frequency characteristic of the odd-order distortion component;

a combiner for combining an output of the linear transmission path and an output of the distortion generation path to form an output of the predistorter;

a distortion detector for detecting a distortion component in an output of the power amplifier;

a distortion component frequency characteristic splitter for splitting the frequency band of the distortion component into windows each having a predetermined band width and for detecting a power of the distortion component in each window; and

a frequency characteristic controller for controlling adjustment of coefficients in frequency band of the frequency characteristic corresponding to said window by the frequency characteristic compensator based on the power of the distortion component detected in each window.

2. The power series predistorter according to claim 1, wherein the band width of said window produced by said distortion component frequency characteristic differs inside and outside of the frequency band of said input signal.

3. The power series predistorter according to claim 1, wherein said distortion component frequency characteristic splitter comprises a digital band-pass filter for discretely sweeping a center frequency of the window to detect the distortion component at intervals of said band width.

4. The power series predistorter according to claim 1, wherein said distortion component frequency characteristic splitter comprises a plurality of band-pass filters for detecting distortion components for a plurality of windows concurrently.

5. The power series predistorter according to claim 1, wherein said distortion component frequency characteristic splitter comprises a variable digital filter having a band width equal to said window and a center frequency which is swept, and a power detector for detecting a power in each window from the output of said variable digital filter.

6. The power series predistorter according to claim 1, wherein said distortion component frequency characteristic splitter comprises an FFT processing unit that performs FFT on said detected distortion component to provide a predetermined number of spectrum samples as a plurality of frequency bands of said windows and a power detector for detecting a power of each spectrum sample received from said FFT processing unit as the power of distortion component detected for each window.

7. The power series predistorter according to claim 1, wherein said frequency characteristic compensator comprises an FFT processing unit that converts every predetermined number of samples input to said frequency characteristic compensator into a predetermined number of spectrum samples in the frequency domain, a plurality of coefficients adjusters each for changing amplitude and phase of the spectrum sample associated with each window in the output of said FFT processing unit based on the power of the distortion component detected in the window, and an IFFT processing unit that converts outputs of said plurality of coefficients adjusters into samples in the time domain.

8. The power series predistorter according to claim 7, wherein the distortion component frequency characteristic splitter comprises a representative value determination unit that determines a representative value of the powers of the distortion components detected in every plurality of windows, and wherein said frequency characteristic controller controls every plurality of said coefficients adjusters to perform a common control on a plurality of spectrum samples associated with said plurality of windows based on said representative value.

9. The power series predistorter according to claim 1, wherein said odd-order distortion generator comprises a plurality of odd-order distortion generators that receive said input signal and generate a plurality of distortion components of different odd orders, and said frequency characteristic compensator comprises a plurality of frequency characteristic compensators that adjust the outputs of said plurality of odd-order distortion generators respectively.

10. The power series predistorter according to claim 1, wherein said frequency characteristic compensator is constituted by an FIR filter, and the transfer function of said FIR filter is controlled by said frequency characteristic controller based on said windows.

11. The power series predistorter according to claim 1, further comprising:

a vector adjuster that is provided in said distortion generation path, for adjusting phase and amplitude of the odd-order distortion component generated by said odd-order distortion generator; and

a vector adjustment controller for controlling said vector adjuster based on the distortion component detected by said distortion detector.

12. A control method for a power series predistorter that compensates for a distortion component produced by a power amplifier, comprising steps of:

(a) distributing an input signal to a linear transmission path and a distortion generation path;

(b) generating an odd-order distortion component for the input signal in said distortion generation path;

(c) adjusting the frequency characteristic of the odd-order distortion component on a predetermined-band-width basis;

(d) combining said adjusted odd-order distortion component and the output of said linear transmission path and outputting the result of the combination from said power series predistorter;

(e) detecting a distortion component in the output of the power amplifier;

(f) splitting the frequency characteristic of said detected distortion component into windows each having a predetermined band width and detecting a power of the distortion component in each window; and

(g) controlling adjustment of each frequency band in the frequency characteristic of the odd-order distortion component in said distortion generation path corresponding to said window based on the power of the distortion component detected in said window.

13. The control method according to claim 12, wherein said step (b) is a step of generating a plurality of distortion components of different odd orders for the input signal, said step (c) is a step of adjusting the frequency characteristic of each of said plurality of distortion components of different odd orders on a predetermined-band-width basis, said step (d) is a step of combining said plurality of adjusted distortion components of different odd orders and the output of said linear transmission path, and said step (g) is a step of controlling the band-based adjustment of the frequency characteristic of each of said plurality of distortion components of different odd orders based on the power of the distortion component detected in each window.

14. The control method according to claim 13, wherein said step (g) comprises a step of determining whether said power of the detected distortion component is equal to or less than a target value before the adjustment of each odd-order distortion and a step of omitting the adjustment of the next odd-order distortion if the power is equal to or less than the target value.

15. The control method according to claim 12, further comprising steps of:

(h) determining a power of said detected distortion component; and

(i) adjusting a vector of said odd-order distortion based on the power of said distortion component.

16. The control method according to claim 12, wherein said step (f) includes a step of determining a representative value of the powers of the distortion components detected in a plurality of windows, and said step (g) is a step of performing a common control on a plurality of spectrum samples associated with said plurality of windows based on said representative value.