RF Distortion Monitoring via Baseband Feedback Filtering

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Solution Overview

Problem

Existing radio signal transmitters face challenges in accurately monitoring and compensating for non-linear distortions, especially in wide bandwidth signals, due to imbalances in analogue modulators, which are difficult to distinguish from feedback signals, leading to inefficient compensation.

Innovation Solution

A front-end unit comprising a mixer, analogue-to-digital converter, and adaptive digital filter that converts radio frequency signals to baseband, allowing for precise monitoring and compensation of non-linear distortions by time-synchronizing and removing linear distortions, enabling low-rate sampling and distinguishing between modulator and demodulator imbalances.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Area of moving object

If analogue modulators are used for wide bandwidth signals, then the bandwidth capability is improved, but imbalances are introduced that cannot be distinguished from feedback signals

Engineering Contradiction:

ImprovebandwidthVSAvoiddistortion monitoring precision

Core Design Contradiction:

Area of moving objectVSMeasurement precision

Solution Approach 1:

The patent segments the distortion monitoring function into two separate parts: a transmit site monitor that measures imbalances in the transmit modulator, and a feedback site monitor that measures imbalances in the feedback demodulator. This segmentation allows each monitor to independently characterize its own imbalances without confusion, enabling precise distortion monitoring while maintaining wide bandwidth capability with analogue modulators.

Inventive Principle:

Principle #1Segmentation

2Ease of operation

If feedback signals are down-converted into baseband, then signal processing is simplified, but it becomes impossible to distinguish between modulator and feedback imbalances

Engineering Contradiction:

Improvesignal processing easeVSAvoidimbalance distinction capability

Core Design Contradiction:

Ease of operationVSMeasurement precision

Solution Approach 1:

The patent applies preliminary action by having the feedback signal down-converted to baseband and filtered to remove spectral components above half the sampling frequency BEFORE the imbalance distinction problem occurs. This preliminary processing, combined with specific filtering techniques, enables the system to later distinguish between modulator and feedback imbalances through correlation analysis, maintaining both ease of operation and measurement precision.

Inventive Principle:

Principle #10Preliminary action

3Measurement precision

If digital modulation is used, then modulation precision is improved, but sampling frequency must be at least twice as large as analogue modulation

Engineering Contradiction:

Improvemodulation precisionVSAvoidsampling frequency

Core Design Contradiction:

Measurement precisionVSSpeed

Solution Approach 1:

The patent changes the parameter of sampling frequency by using specific filtering techniques that allow accurate distortion monitoring at lower sampling rates. By applying appropriate filters to the down-converted feedback signal and using correlation-based imbalance estimation, the system achieves precise distortion monitoring without requiring the high sampling frequencies that would otherwise be needed for digital modulation schemes.

Inventive Principle:

Principle #35Parameter changes

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

Enables effective compensation of non-linear distortions in wide bandwidth signals with precise monitoring, allowing for low-rate sampling and accurate distinction between transmitter and feedback site imbalances, improving the precision of distortion compensation.

Implementation Method 1

a mixer operably connected to a local oscillator

Methodology Applied

Scientific EffectFrequency mixing: Heterodyne

Implementation Method 2

an adaptive digital filter. The adaptive digital filter is operable to time-synchronise its output signal to a reference signal and to remove linear distortions from the signal received from the first digital filter

Methodology Applied

Scientific EffectDigital signal filtering: Filter (electronic)

Data Source

PatentUS7812748B2Apparatus for monitoring non-linear distortions of radio signals and a method therefor

Publication Date: 2010.10.12 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

AI summary

A transmitter (200) for transmitting radio signals comprising a digital signal source (102), a compensation unit (104), two digit al-to-analogue converters (106) and (108), an analogue modulator (110), an amplifier (112) an antenna (114) connected to the amplifier (112), the transmitter further comprises a front-end unit (220) connected to an estimator (230). Said front-end unit (220) comprises a mixer operably (302) connected to a local oscillator (304), an analogue-to-digital converter (306) for processing signal received from the mixer (302), a first digital filter (308) for converting signal received from the analogue-to-digital converter (306) to a baseband signal, an adaptive digital filter (310) operable to time-synchronise its output signal (z(k)) to a reference signal (r(k)) and to remove linear distortions from the signal received from the first digital filter.