CATV Return Band Linearity Measurement Using DOCSIS Carriers

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Solution Overview

Problem

The increasing occupancy of the active upstream bandwidth in CATV systems with content poses a challenge for determining linearity, as traditional methods of using swept carriers to assess linearity often interfere with upstream-bound signals, making it difficult to maintain interference-free and flat frequency responses.

Innovation Solution

A method that utilizes existing DOCSIS carriers to determine linearity by logging into a Cable Modem Termination System (CMTS), calculating transmit carrier ranging errors, pre-equalizer filter coefficients, and adjusting carrier levels, and generating a frequency response plot, thereby avoiding interference with active upstream channels.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If traditional swept carriers are used to determine linearity in the upstream band, then linearity measurement can be performed, but interference with active upstream channels occurs and frequency response flatness deteriorates

Engineering Contradiction:

Improvelinearity measurement accuracyVSAvoidinterference with upstream signals

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent extracts the linearity measurement function from the traditional swept carrier approach and relocates it to the downstream band. By measuring linearity in the downstream frequency range instead of the upstream band, the harmful interference with active upstream channels is eliminated while maintaining measurement capability through alternative measurement locations

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent introduces a downstream carrier as an intermediary measurement tool. Instead of directly measuring upstream linearity with swept carriers that interfere with active channels, a downstream carrier is used as a mediator to indirectly assess system linearity by measuring its response and comparing it against expected characteristics

Inventive Principle:

Principle #24Intermediary (Mediator)

2Quantity of substance

If upstream bandwidth is filled with active channels for data transmission, then data capacity increases, but available bandwidth for linearity testing decreases

Engineering Contradiction:

Improveupstream data capacityVSAvoidlinearity testing capability

Core Design Contradiction:

Quantity of substanceVSAdaptability or versatility

Solution Approach 1:

The patent transitions the linearity measurement from the one-dimensional upstream frequency space to the downstream frequency dimension. By moving the measurement to a different frequency domain (downstream instead of upstream), the system maintains linearity testing capability even when upstream bandwidth is fully utilized for data transmission

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

The downstream carrier serves multiple functions: it acts as both a data transmission carrier and a linearity measurement probe. This multi-functionality allows the system to maintain both high upstream data capacity and linearity testing capability simultaneously, as the same downstream infrastructure serves dual purposes

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS11509954B2CATV return band sweeping using data over cable service interface specification carriers

Publication Date: 2022.11.22 VIAVI SOLUTIONS INC(US)

AI summary

The existing Data Over Cable Service Interface Specification (DOCSIS) carriers generated by field test equipment or by the CATV subscriber modems are used to determine the amplitude response of the return band in a CATV system.