Forward Distortion Correction in Time-Domain Beamforming

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Solution Overview

Problem

Time-domain beamforming in wireless communication systems experiences spectral regrowth due to sudden coefficient changes, which fails to meet regulatory emission masks, particularly for narrower carrier bandwidths with high power spectral density.

Innovation Solution

The implementation of a method and system that utilize fast transition band digital filters to isolate and subtract non-linear distortion from signals, thereby meeting emission masks with sufficient margins, even with symbol-based beam switching, and achieving improved link-level performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If time-domain beamforming weights are updated on a symbol or slot basis, then beamforming flexibility and adaptability are improved, but spectral regrowth occurs due to sudden coefficient changes at boundaries

Engineering Contradiction:

Improvebeamforming flexibilityVSAvoidspectral regrowth

Core Design Contradiction:

Adaptability or versatilityVSObject-generated harmful factors

Solution Approach 1:

The patent applies preliminary action by performing forward distortion correction before the harmful spectral regrowth occurs. The FDC filter is positioned upstream of the time-domain beamformer in the signal processing chain, pre-compensating for the distortion that will be introduced by subsequent beamforming operations. This allows the system to maintain symbol-level beamweight updates for flexibility while preventing spectral regrowth from affecting the final transmitted signal.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent converts the harmful effect of beamweight updates into a beneficial process by using the known beamweight transition patterns to design a predictive FDC filter. The filter leverages the predictable nature of beamforming updates to pre-correct the signal, transforming what would be harmful spectral regrowth into an opportunity for optimized signal conditioning that actually improves overall system performance.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Device complexity

If channel filter is placed upstream of time domain beamformer, then processing chain is simplified, but distortion close to carrier cannot be removed

Engineering Contradiction:

Improveprocessing chain complexityVSAvoiddistortion removal precision

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

The patent segments the filtering function into two distinct stages: a channel filter placed upstream for basic signal conditioning, and a forward distortion correction filter positioned downstream specifically for removing distortion close to the carrier. This segmentation allows each filter to be optimized for its specific function while maintaining overall system simplicity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The forward distortion correction filter acts as an intermediary component between the channel filter and the time-domain beamformer. It bridges the gap by taking the output of the channel filter and pre-compensating it for the distortion that will be introduced by the beamforming operation, thereby enabling the upstream channel filter to remain simple while achieving high precision distortion removal overall.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Object-generated harmful factors

If baseband zero insertion is used to improve spectrum, then emission masks are met, but link-level performance deteriorates due to lengthy zero insertion

Engineering Contradiction:

Improveemission mask complianceVSAvoidlink-level performance

Core Design Contradiction:

Object-generated harmful factorsVSReliability

Solution Approach 1:

The patent replaces the mechanical approach of baseband zero insertion with a digital signal processing approach using forward distortion correction filtering. Instead of physically inserting zeros into the signal to reduce spectral density, the FDC filter digitally pre-compensates for distortion, achieving emission mask compliance through signal conditioning rather than signal degradation. This substitution maintains signal integrity and link-level performance while meeting regulatory requirements.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the parameter being controlled from signal amplitude (through zero insertion) to signal spectral characteristics (through FDC filtering). By adjusting the FDC filter coefficients and characteristics rather than inserting zeros, the system achieves the same emission mask compliance with superior signal quality and maintained link-level performance.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS20250132797A1Forward distortion correction for time domain beamforming

Publication Date: 2025.04.24 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

AI summary

A method and network node for forward distortion correction for time domain beam forming are provided. According to one aspect, a method in a network node includes filtering cach signal output by the time domain beamformer by a band stop filter, the band stop filter including a stop band overlapping a pass band of the signal output by the time domain beamformer. The method also includes filtering each signal output by the time domain beamformer by a group delay filter in electrical parallel with a band stop filter, the group delay filter providing a group delay to the signal output by the time domain beamformer. The method also includes subtracting an output of each band stop filter from an output of a corresponding group delay filter.