CMTS Interference Group Discovery for Full-Duplex OFDM Cable Modems

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Solution Overview

Problem

Cable modems operating on shared hybrid fibre coax (HFC) and radio frequency over glass (RFoG) networks face interference issues due to multiple devices using the same channels, which degrades broadband internet access by causing upstream to downstream interference.

Innovation Solution

A method involving a cable modem termination system (CMTS) that generates and manages test signals to identify interference groups (IGs) among cable modems, allowing for the scheduling of full-duplex communication by assigning channels to prevent interference, using orthogonal frequency division multiplexing (OFDM) and echo cancellation techniques.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If multiple cable modems share the same channel(s) on HFC/RFoG infrastructure, then broadband internet access is provided at relatively high speeds, but interference occurs between upstream and downstream signals degrading service quality

Engineering Contradiction:

Improvebroadband internet access speedVSAvoidupstream to downstream interference

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent segments cable modems into different interference groups based on their interference characteristics. By dividing the network into groups where modems within each group have similar interference patterns, the system can apply targeted echo cancellation techniques to specific groups, effectively reducing upstream-to-downstream interference while maintaining high-speed broadband access.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent implements a feedback mechanism where cable modems transmit test signals and receive measurements of upstream-to-downstream interference. The CMTS collects these measurements, determines interference groups, and uses this feedback information to schedule transmissions and apply echo cancellation, continuously optimizing interference mitigation based on actual network conditions.

Inventive Principle:

Principle #23Feedback

2Reliability

If cable modems transmit test signals for interference measurement, then interference groups can be discovered and scheduled, but additional signaling overhead is introduced on the network

Engineering Contradiction:

Improveinterference group discovery accuracyVSAvoidsignaling overhead

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The patent makes existing OFDM pilot signals serve dual purposes: their primary function for channel estimation and their secondary function for interference measurement. By utilizing the same pilot signals already present in the downstream transmission for both channel equalization and interference group discovery, the system achieves reliable interference measurement without introducing additional dedicated test signals, thus avoiding extra signaling overhead.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The system uses the cable modems' own transmitted signals and the existing downstream pilot structure to perform interference measurements. The test signals are embedded within the normal OFDM framework, allowing the network to self-diagnose interference conditions using resources already allocated for data transmission, eliminating the need for separate measurement infrastructure.

Inventive Principle:

Principle #25Self-service

3Productivity

If full-duplex communication is enabled on the same channel, then simultaneous upstream and downstream communications are achieved, but interference mitigation complexity increases

Engineering Contradiction:

Improvesimultaneous upstream and downstream communication efficiencyVSAvoidinterference mitigation complexity

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent divides the network into interference groups where modems with similar interference characteristics are clustered together. This segmentation allows the CMTS to apply simplified echo cancellation strategies tailored to each group's characteristics, reducing the overall complexity compared to attempting to mitigate interference from every individual modem independently across the entire network.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent changes the scheduling parameters and transmission timing based on the discovered interference groups. By adjusting when and how different groups transmit upstream signals, the system optimizes the interference profile to make echo cancellation more effective and simpler to implement, rather than trying to handle all interference scenarios with a single complex algorithm.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS11463126B2Signaling method for interference group discovery in cable modems

Publication Date: 2022.10.04 INTEL CORP

AI summary

A cable modem system for discovering interference groups (IGs) includes an infrastructure and a cable modem termination system (CMTS). The infrastructure is for transferring data. The CMTS is configured to initiate generation of test signals by a set of cable modems (CMs), obtain a set of test measurements for the set of CMs, discover interference groups (IGs) of the set of CMs based on the obtained set of test measurements and assign a plurality of upstream and downstream channels for the set of CMs that use orthogonal frequency division multiplexing (OFDM) based on the discovered IGs.