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Feedback Signal Delay Estimation in Digital Pre-Distortion Using a Wide Band PN Sequence Modulated Signal

IP.com Disclosure Number: IPCOM000245980D
Publication Date: 2016-Apr-21
Document File: 7 page(s) / 242K

Publishing Venue

The IP.com Prior Art Database

Related People

Alfonso Malaga: INVENTOR [+4]

Abstract

Non-linearity of power amplifiers generate output signal frequencies that do not exist in the original signal, resulting in amplitude and phase distortions. A widely used solution to correct signal distortion caused by the power amplifier is Digital Pre-Distortion. The pre-distorter circuit is modeled as a filter with inverse characteristics of the amplifier, canceling out the distortions by pre-distorting the input signal. However, the accuracy and effectiveness of the above mentioned solution depends on the delay estimation between the feedback signal and the pre-distorted signal. Hence an accurate delay estimation method is required and the paper proposes a technique of using Pseudo Noise sequence modulated signal for the same.

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Feedback Signal Delay Estimation in Digital Pre-Distortion Using a Wide Band PN Sequence Modulated Signal

Alfonso Malaga, Mohandas Amarnathan, Venkata Siripurapu, Maddukuri Sravan

ABSTRACT

Non-linearity of power amplifiers generate output signal frequencies that do not exist in the original signal, resulting in amplitude and phase distortions. A widely used solution to correct signal distortion caused by the power amplifier is Digital Pre-Distortion. The pre-distorter circuit is modeled as a filter with inverse characteristics of the amplifier, canceling out the distortions by pre-distorting the input signal. However, the accuracy and effectiveness of the above mentioned solution depends on the delay estimation between the feedback signal and the pre-distorted signal. Hence an accurate delay estimation method is required and the paper proposes a technique of using Pseudo Noise sequence modulated signal for the same.


1. INTRODUCTION

Radio frequency power amplifiers commonly used in communications cause significant non-linear distortion in the signals they amplify while operating near the peak efficiency or saturation when such signals have non-constant envelope. The distortion results in spectrum re-growth and the signal's emissions into the adjacent channels may no longer be in compliance with the emissions mask imposed by the regulations. One of the most commonly used methods to reduce these distortions and achieve linear amplifier output is to operate the amplifiers at lower outputs, but this solution may reduce efficiency. Amplifiers operating below peak efficiency have lower thermal efficiency and require additional expensive cooling arrangements to prevent overheating.

A widely used method to improve power amplifier (PA) efficiency is by active linearization using Digital Pre-Distortion (DPD). It enables more efficient amplifier operation by minimizing the distortion signal components introduced. DPD deliberately

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modifies the amplifier input signal in such a way that the distortion produced by the amplifier is cancelled out. The pre-distortion circuit is implemented as a non-linear digital filter which has the inverse characteristics of the amplifier. Hence when combined with the amplifier, it produces a combined system that is more linear. The digital filter is designed based on the PA feedback signal and pre-distorter output.

The effective implementation of DPD depends on the accuracy of delay estimation in feedback signal. The feedback signal and the pre-distorted signal have to be time aligned. This paper presents a new method to perform the delay estimation between the feedback signal and the pre-distorted signal.


2. EXISTING SOLUTIONS TO THE PROBLEM

There are several methods in literature to date to estimate the delay between the feedback signal and the pre-distorted signal, specifically for DPD. There are methods which estimate sample delay value between transmission and feedback signals from shifted st...