Time Domain Reflectometer for HFC Network Impairment Detection
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Solution Overview
Problem
Existing methods for detecting and locating micro-reflections in Hybrid Fiber-Coax (HFC) networks, such as Time-Domain Reflectometry (TDR), face challenges due to interference with service signals and limited accuracy, making it difficult to effectively pinpoint impedance mismatches in live HFC networks.
Innovation Solution
A handheld TDR meter that uses low-level, wide-bandwidth probe signals and coherent chirp pulses to minimize interference with service signals, allowing for accurate detection and location of micro-reflections by transmitting probe signals during burst intervals and receiving reflections during intervals free from service signals, with calibration to ensure minimal interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional TDR uses high-powered probe signals for accurate detection, then measurement precision is improved, but service signals are disrupted and reflected probe signals are masked
Solution Approach 1:
The patent changes the power parameter of the probe signal from high-powered to low-level, allowing accurate detection of micro-reflections without disrupting service signals or being masked by strong service signals in the live HFC network
Solution Approach 2:
The patent uses burst-mode transmission where probe signals are transmitted only during intervals when service signals are absent, creating a periodic detection scheme that avoids continuous interference while maintaining detection capability
2Object-generated harmful factors
If PNM technique uses upstream QAM service signals as probe signals, then non-invasive testing is achieved, but detection accuracy is limited by bandwidth and pre-equalization coefficients
Solution Approach 1:
The patent performs calibration by injecting a calibration signal at a known location before actual measurements, establishing a reference that compensates for network variations and improves the accuracy of subsequent micro-reflection location measurements
Solution Approach 2:
The patent replaces the PNM technique's reliance on pre-equalization coefficient analysis with a direct time-domain reflection measurement approach, substituting the indirect electrical parameter analysis with direct temporal measurement of signal reflections
3Measurement precision
If downstream signal autocorrelation is used for mismatch detection, then non-invasive testing with wide bandwidth is achieved, but accumulation time is too long and service signal traffic is impacted
Solution Approach 1:
The patent uses burst-mode transmission where probe signals are transmitted only during intervals when service signals are absent, creating a periodic detection scheme that achieves sufficient signal accumulation without requiring long continuous measurement periods that would impact service traffic
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides non-invasive, low-cost, and low-power TDR meter for detecting micro-reflections with high sensitivity and accuracy, capable of locating impairments within 50 feet, effectively overcoming the limitations of existing methods by maximizing time resolution and minimizing interference.
Implementation Method 1
transmitting a sequence of low-level probe signals to the linear impairment and causing a reflection of the probe signals from the linear impairment
Implementation Method 2
The receiver receives the sequence of reflected probe signals during a plurality of receiving intervals, respectively, and receives the burst signals during the receiving intervals that overlap the burst intervals. The level detector measures a level of the signals received by the receiver during each of the receiving intervals
Implementation Method 3
The accumulator coherently accumulates only those reflected probe signals that are received during receiving intervals substantially free of the burst signals
Implementation Method 4
each probe signal is defined by a band of frequencies within the upstream frequency band and has a bandwidth that extends substantially the width of the upstream frequency band... estimating a time delay between transmission of the probe signals by the probe signal transmitter and reception of the reflected probe signals by the receiver
Data Source
AI summary
A TDR for locating impairments in an HFC network is claimed. The network carries burst signals in an upstream band during burst intervals. The TDR comprises a transmitter, receiver, level detector, controller, accumulator, and probe detector. The transmitter transmits probe signals to the impairment, causing a reflection of the probe signals. Each probe signal is in the upstream band and has a bandwidth extending the width of the upstream band. The receiver receives the reflected probe signals during receiving intervals, and receives the burst signals during receiving intervals that overlap burst intervals. The level detector measures a level of the signals received during each receiving interval. The controller determines which of the receiving intervals are free of burst signals, based on the level measurement. The accumulator accumulates reflected probe signals received during intervals free of burst signals. The probe detector detects the impairment from the accumulated probe signals and estimates a time delay for the impairment. A distance to the impairment is estimated from the time delay.