Leakage Detection in Digital Cable Systems Using Pilot Signal Correlation
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Solution Overview
Problem
Legacy egress detection equipment is ineffective in digital cable systems, failing to accurately detect and identify leakage once systems convert to fully digital, necessitating new methods that can reliably detect egress without dedicated bandwidth requirements.
Innovation Solution
A method involving the insertion of low-amplitude signals, conversion to intermediate frequency, digitization, and correlation or FFT analysis to detect leakage, allowing for minimal invasive and cost-effective detection within digital cable systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If legacy egress detection equipment is used in digital cable systems, then the equipment structure is simple and cost-effective, but the detection accuracy is insufficient and cannot reliably detect leakage
Solution Approach 1:
The system inserts pilot signals into the digital cable system before leakage detection. These pilot signals are embedded in the digital signal stream at known frequencies and amplitudes, allowing the detection equipment to correlate received signals with expected pilot patterns. This preliminary insertion of reference signals enables accurate leakage detection by providing a baseline for comparison, resolving the contradiction between detection accuracy and equipment complexity.
Solution Approach 2:
The patent uses pilot signals as an intermediary element between the digital cable system and the detection equipment. These pilot signals serve as a mediator that carries leakage information from the cable system to the detector without requiring complex modifications to either the transmission system or the detection equipment. The pilot signals are inserted at the headend and received at customer premises, providing a reliable reference for leakage detection while keeping the overall system architecture simple.
2Reliability
If dedicated bandwidth is allocated for leakage detection, then the detection reliability is improved, but the bandwidth resources are reduced for other uses
Solution Approach 1:
The patent merges the leakage detection function with the existing digital cable signal transmission by embedding pilot signals within the digital signal stream. Instead of allocating separate dedicated bandwidth for detection, the system combines detection references with the data carrier signals. The pilot signals are inserted at specific frequencies within the available spectrum, allowing simultaneous transmission of digital content and leakage detection references without consuming additional bandwidth resources.
Solution Approach 2:
The digital cable signal serves multiple functions: it carries customer data and simultaneously provides the medium for leakage detection through embedded pilot signals. The same signal path and bandwidth resources are used for both data transmission and egress detection, eliminating the need for dedicated detection bandwidth. The pilot signals are integrated into the existing signal structure, making the system universally applicable without requiring separate detection channels.
3Measurement precision
If high-amplitude signals are inserted for detection, then the detection sensitivity is improved, but the signal impairment to digital channels increases
Solution Approach 1:
The system carefully controls the amplitude parameter of inserted pilot signals, setting them at levels multiple tens of dB below the digital channel power. This parameter optimization ensures that the pilot signals are sufficiently strong for correlation-based detection while remaining imperceptible in the presence of digital signals. The detection sensitivity is maintained through correlation processing rather than increasing pilot signal amplitude, thus avoiding digital channel impairment.
Data Source
AI summary
In a method for detecting leakage in a digital cable system, at least one first signal is inserted on the cable system. The at least one first signal has an amplitude multiple tens of dB below the digital channel power of the digital channels carried on the cable system. A second signal containing the first signal is received. The second signal is converted to an intermediate frequency (IF) signal. The IF signal is digitized and samples of the digitized IF signal are obtained. Digitized samples of a third signal at the nominal frequency of the first signal at maximum amplitude converted to the IF are provided. The digitized IF signal and the digitized samples of a third signal at the nominal frequency of the first signal at maximum amplitude converted to the IF are correlated. The presence of the inserted first signal is detected based upon the result of the correlation. In another method, a pair of first signals are inserted on the cable system. The pair of first signals are spaced apart a fixed frequency and with amplitudes multiple tens of dB below the digital channel power of the digital channels carried on the cable system. A second signal containing the first signal is received and converted to an intermediate frequency (IF) signal. The IF signal is digitized, samples of the digitized IF signal are obtained, and a large scale Fast Fourier Transform (FFT) is applied to the samples to generate an FFT output. The FFT output is examined for generally equally sized signals separated from each other by the fixed frequency in the FFT output. If generally equally sized signals separated from each other by the fixed frequency are detected in the FFT output, a decision is made that the second signal represents detected leakage from the digital cable system.