HFC Cable Upstream Signal Attenuation for Ingress Noise Mitigation
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Solution Overview
Problem
Conventional cable communication systems face challenges in effectively mitigating ingress noise, particularly in the lower frequency range of the upstream path bandwidth, which limits the usable spectrum and affects the reliability of upstream information transmission.
Innovation Solution
The implementation of advanced ingress mitigation techniques, including the use of passive filters, active monitoring systems, and selective attenuation methods, aims to identify and reduce ingress sources, particularly focusing on subscriber premises as the primary source of interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If passive filters and selective attenuation methods are used to mitigate ingress noise, then the signal-to-noise ratio and carrier-to-noise ratio in the upstream path bandwidth are improved, but the challenges persist below 20 MHz due to the limitations of these mitigation techniques in the lower frequency range
Solution Approach 1:
The patent introduces an optical intermediary (optical carrier) to convert RF signals to optical signals for transmission through fiber optic cable. This intermediary transformation allows upstream signals to bypass the problematic coaxial cable section where ingress noise occurs, particularly below 20 MHz, thereby maintaining signal integrity and improving transmission reliability in the presence of ingress noise
Solution Approach 2:
The patent replaces the traditional electrical RF transmission system with an optical transmission system. By substituting electrical signals with optical signals and coaxial cable with fiber optic cable, the system eliminates the mechanical/electrical vulnerabilities to ingress noise that plague conventional systems, particularly in the lower frequency range below 20 MHz
2Productivity
If the upstream path bandwidth is used for high aggregate data capacity channel plans, then the data transmission capacity is improved, but the presence of ingress noise particularly below 20 MHz limits the usable spectrum and affects transmission reliability
Solution Approach 1:
The patent transitions from a single-dimensional electrical signal transmission to a two-dimensional hybrid system combining electrical RF signals for downstream and optical signals for upstream transmission. This dimensional change allows the system to achieve high aggregate data capacity while bypassing the ingress noise problem in the electrical domain, thereby maintaining both productivity and reliability
Data Source
AI summary
An HFC cable communication system comprising: a CMTS having a first attenuator to attenuate one or more upstream signals applied to the CMTS; an optical link having a dynamic range and comprising an optical receiver having a second attenuator to attenuate the upstream signal(s) and an optical transmitter having a third attenuator to attenuate the upstream signal(s); a coaxial RF link comprising one or more RF amplifiers having a fourth attenuator to attenuate the upstream signal(s); and one or more subscriber modems to generate the upstream signal(s) at respective transmit RF signal levels. The CMTS implements a long loop ALC to set the transmit RF signal level(s) based on received RF signal levels of the upstream signal(s) at the CMTS. Respective values for the first, second, third and fourth attenuators are selected based on the dynamic range of the optical link so as to facilitate implementation of the long loop ALC and effective transmission of upstream information carried by the upstream signal(s).