CATV Network Frequency Response Measurement via Low-Amplitude Test Signals
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Solution Overview
Problem
Existing methods for measuring frequency response in CATV networks interfere with normal transmission, especially in digital systems, and are not compatible with modern networks that lack blanking intervals, leading to disruptions and inefficiencies in maintaining network quality.
Innovation Solution
A method and system for measuring frequency response by injecting a test signal with a low amplitude and narrow bandwidth during allocated transmission time slots, allowing the signal to be measurable without impairing digital signals, and using a delayed reception time slot to suppress other signals and calculate the frequency response without disrupting normal transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a test signal is injected to measure frequency response, then measurement capability is improved, but interference with normal transmission occurs
Solution Approach 1:
The patent applies periodic action by injecting test signals only during allocated transmission time slots rather than continuously. The test signal is transmitted in periodic bursts synchronized with the TDMA frame structure, allowing frequency response measurement while leaving other time slots available for normal data transmission without interference
Solution Approach 2:
The patent segments the transmission medium by dividing time into distinct slots - some allocated for test signal injection and others for normal data transmission. This temporal segmentation allows the same physical channel to be used for both measurement and communication purposes without mutual interference
2Reliability
If test signal amplitude is increased to improve measurability, then measurement reliability is improved, but impairment of digital signals occurs
Solution Approach 1:
The patent changes the amplitude parameter of the test signal to a low level that is sufficient for reliable measurement at the receiving end but low enough to avoid impairing digital signals. The system achieves measurement reliability through signal processing techniques rather than high amplitude, allowing coexistence with data transmission
3Measurement precision
If frequency sweeping is performed on allocated channels, then measurement accuracy is improved, but channel availability is reduced
Solution Approach 1:
The patent enables continuous frequency sweeping across all allocated channels by injecting test signals during time slots allocated for upstream transmission. This allows comprehensive measurement of frequency response across the entire operational bandwidth without restricting channel availability for data transmission, as measurements occur in the time domain rather than blocking frequency channels
Data Source
AI summary
An apparatus and method for frequency sweeping a CATV network, suitable for an upstream path frequency sweeping, is presented. A narrowband test signal is injected into the network by a generator coupled to a cable modem during a time interval allocated by the head end for the cable modem to transmit a modulated digital signal. The amplitude of the test signal is lower than the amplitude of the modulated digital signal, so as not to impair reception of said digital signal at the head end. The frequency of the test signal is swept, and the amplitude of the received test signal is measured. A telemetry or a digital signal transmission is used to communicated the values of the amplitude of the test signals between the injection and the measurement locations of the network.