Eliminating Aliasing Noise in Multi-Carrier Modulation Systems

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Solution Overview

Problem

In multi-carrier modulation systems, aliasing noise from crosstalk between different DSL signals, such as ADSL and VDSL, affects the performance and stability of in-band signals due to poor anti-aliasing filtering capabilities in most modems, leading to service disruptions.

Innovation Solution

The method involves dividing the frequency range into non-overlapping bands, acquiring power spectrum density templates, calculating the difference between aliasing noise and background noise, and adjusting the transmitting power of out-band subcarriers to eliminate aliasing noise, thereby improving the stability of in-band services without requiring upgrades to Customer Premises Equipment.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If Downstream Power Back Off (DPBO) is performed to reduce the power of signals sent by the roadside cabinet, then crosstalk noise is reduced, but aliasing noise still affects in-band signals due to poor anti-aliasing filtering capabilities

Engineering Contradiction:

Improvecrosstalk noiseVSAvoidsignal stability

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The frequency spectrum is divided into multiple non-overlapping bands (first band, second band, third band, etc.), with in-band subcarriers and out-band subcarriers separated into different frequency ranges. This segmentation allows independent power control and aliasing management for different bands, enabling precise elimination of aliasing noise from out-band subcarriers that would otherwise contaminate in-band signals through poor anti-aliasing filtering

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The transmitting power of out-band subcarriers is dynamically adjusted based on calculated aliasing noise levels. By changing the power parameter of out-band subcarriers according to the measured difference between aliasing noise and background noise, the system optimizes the balance between maintaining signal quality and minimizing aliasing interference in in-band services

Inventive Principle:

Principle #35Parameter changes

2Productivity

If the amplitude of VDSL signal exceeds a specific value, then transmission rate is improved, but aliasing noise is generated that affects ADSL signal performance

Engineering Contradiction:

Improvetransmission rateVSAvoidaliasing noise

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The system measures the actual aliasing noise level in in-band subcarriers by comparing received signal quality against expected background noise levels. This feedback information is used to calculate the appropriate power reduction for out-band subcarriers, creating a closed-loop control system that dynamically adjusts transmitting power to maintain optimal performance while minimizing aliasing interference

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If most modems with poor anti-aliasing filtering capabilities are used, then device complexity is reduced, but aliasing noise from out-band subcarriers contaminates in-band signals

Engineering Contradiction:

Improvefiltering capabilityVSAvoidsignal quality

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent introduces an intermediary control mechanism at the network side (roadside cabinet) that manages aliasing noise before it reaches the customer premises equipment. By controlling the transmitting power of out-band subcarriers and coordinating frequency band allocation, the system compensates for the poor anti-aliasing filtering capabilities of simple modems, maintaining signal quality without requiring complex filtering hardware at the customer end

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS8923454B2Method, apparatus and system for eliminating aliasing noise in multi-carrier modulation system

Publication Date: 2014.12.30 HUAWEI TECH CO LTD

AI summary

A method, an apparatus and a system for eliminating aliasing noise in a multi-carrier modulation system are disclosed. The method includes: acquiring a first power spectrum density template; acquiring information of in-band subcarriers whose aliasing noise is greater than background noise, and acquiring a difference between the aliasing noise and the background noise of the in-band subcarriers; adjusting the first power spectrum density template according to the information of the in-band subcarriers and the corresponding difference to obtain a second power spectrum density template; and sending signals according to the second power spectrum density template. The method, the apparatus, and the system disclosed herein eliminate the aliasing crosstalk noise, improve the performance and stability of in-band services without involving upgrade or modification of the Customer Premises Equipment (CPE), and are easy to implement.