Method and system for baseband predistortion linearization in multi-channel wideband communication systems

• US 8,149,950 B2
• Filed: 12/20/2007
• Issued: 04/03/2012
• Est. Priority Date: 12/26/2006
• Status: Active Grant

• Current Assignee: Dali Wireless Inc. (Dali Systems Co., Ltd.)
• Original Assignee: Dali Systems Co., Ltd.
• Inventors: Kim, Wan Jong, Cho, Kyoung Joon, Kim, Jong Heon, Stapleton, Shawn Patrick
• Primary Examiner(s): Payne, David C.
• Assistant Examiner(s): Dsouza, Adolf
• Application Number:
  US11/961,969
• Publication Number:
  US 20080152037A1
• Time in Patent Office: 1,566 Days
• Field of Search: None
• US Class Current: 375/296
• 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 2200/57 Separate feedback of real and complex signals being present
• CPC Class Codes: H03F 2201/3224 Predistortion being done for compensating memory effects
• 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 3/24 of transmitter output stages
• CPC Class Codes: H04B 1/0475 with means for limiting noise, interference or distortion H04B1/0483 takes precedence
• CPC Class Codes: H04B 2001/0425 with linearisation using predistortion
• CPC Class Codes: H04B 7/022 Site diversity; Macro-diversity using two or more spaced independent antennas H04B7/04
• CPC Class Codes: H04L 2025/03414 Multicarrier
• CPC Class Codes: H04L 25/03343 Arrangements at the transmitter end
• CPC Class Codes: H04L 27/2618 Reduction thereof using auxiliary subcarriers
• CPC Class Codes: H04L 27/362 Modulation using more than one carrier, e.g. with quadrature carriers, separately amplitude modulated H04L27/366 takes precedence
• CPC Class Codes: H04W 24/02 Arrangements for optimising operational condition
• CPC Class Codes: H04W 24/04 Arrangements for maintaining operational condition
• CPC Class Codes: H04W 40/00 Communication routing or communication path finding
• CPC Class Codes: H04W 40/02 Communication route or path selection, e.g. power-based or shortest path routing
• CPC Class Codes: H04W 72/04 Wireless resource allocation
• CPC Class Codes: H04W 72/0453 Resources in frequency domain, e.g. a carrier in FDMA
• CPC Class Codes: H04W 88/085 Access point devices with remote components

Abstract

An efficient baseband predistortion linearization method for reducing the spectral regrowth and compensating memory effects in wideband communication systems using effective multiplexing modulation technique such as wideband code division multiple access and orthogonal frequency division multiplexing is disclosed. The present invention is based on the method of piecewise pre-equalized lookup table based predistortion, which is a cascade of a lookup table predistortion and piecewise pre-equalizers, to reduce the computational complexity and numerical instability for desired linearity performance with memory effects compensation for wideband transmitter systems.

Claims

1. A method of reducing adjacent channel power ratio and compensating memory effects of multi-channel wideband communication systems using multiplexing modulation techniques comprising the steps of

generating an address from samples of a baseband input signal of a communication system;

retrieving from a memoryless lookup table an entry in accordance with the address;

pre-equalizing the baseband input signal using the following equation;

2. The method of claim 1 wherein the entries in the lookup table are complex coefficients.

3. The method of claim 1 wherein the pre-equalizing step includes piecewise equalization.

4. The method of claim 3 wherein said the piecewise pre-equalizers use a finite impulse response filter rather than an infinite impulse response filter.

5. The method of claim 1 wherein the pre-equalizing step uses finite impulse response filtering.

6. The method of claim 1 further including updating the entries using an indirect learning method.

7. The method of claim 6 wherein the indirect learning method uses a least mean squares algorithm.

8. The method of claim 1 wherein the retrieving step is performed by determining the following equation:

m=round(|u(n)|·

N),

wherein u(n) is the input signal and the round function returns the nearest integer number which is the index (m) and N is the LUT size.

9. The method of claim 1 wherein the multiplying step is performed by the following equation:

x(n)=u(n)·

F_m(|u(n)|),

wherein F_m(|u(n)|) is the complex coefficient of the memoryless LUT.

10. The method of claim 1 further comprising performing a second pre-equalizing step using the following equation:

W^m(|u(n+1)|)=W^m(|u(n)|)+μ

·

(y_FI(n)^T)*·

E(n)

wherein y_FI(n) is the input of the multiple equalizers in the feedback path, E(n) the error signal, p the step size, and * the complex conjugate.

11. A system for reducing adjacent channel power ratio and compensating memory effects of multi-channel wideband communication systems using multiplexing modulation techniques comprising an address generator for generating an address form samples of a baseband input signal of a communication system;

a memoryless lookup table having therein coefficients addressable according to the address;

a multiplier for combining the baseband input signal and the coefficients;

lookup table entry; and

an equalizer for pre-equalizing the multiplier to compensate for memory effects in a power amplifier of the communications system, wherein pre-equalizing comprises using the following equation;