Loop Start Trunk Impedance Selection via Echo Path Analysis
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The selection of optimal impedance settings for Loop-Start (LS) trunk lines between a Private Branch Exchange (PBX) and Central Office (CO) is currently subjective and time-consuming, often resulting in poor echo cancellation due to impedance mismatches, leading to intrusive echo issues when network delays exceed 36 ms.
Innovation Solution
A method that measures the impulse response of the trans-hybrid echo path and calculates a figure of merit based on the power spectrum of the frequency-domain transfer function to select the best impedance setting, minimizing echo reflections by systematically testing candidate settings and applying the one with the highest merit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If manual trial and error method is used to select impedance settings, then selection process is simple, but it consumes enormous human effort and time
Solution Approach 1:
The system performs self-measurement and self-selection of optimal impedance settings by automatically measuring the impulse response of the trans-hybrid echo path and calculating figures of merit, eliminating the need for manual trial and error methods
Solution Approach 2:
The patent replaces manual mechanical adjustment methods with electronic automation, using digital signal processing to measure impulse responses and algorithmically determine optimal impedance settings based on calculated merit figures
2Adaptability or versatility
If compromise impedance setting is used to match wide range of impedances, then adaptability is improved, but echo return loss performance deteriorates
Solution Approach 1:
The system dynamically changes impedance parameters by measuring the actual line characteristics and selecting from multiple candidate impedance settings the one that optimizes echo return loss for the specific line conditions
Solution Approach 2:
The patent introduces dynamic adaptation where the impedance setting is not fixed but can be adjusted based on measured line characteristics, allowing the system to optimize performance for each specific trunk line rather than using a static compromise setting
3Measurement precision
If objective algorithmic method is implemented for selecting impedance settings, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent uses an intermediary measurement signal (impulse signal) that passes through the hybrid and returns, allowing indirect measurement of the trans-hybrid echo path characteristics without requiring direct access to internal circuit parameters
Solution Approach 2:
The system creates a digital copy or model of the acoustic echo path by measuring and storing the impulse response characteristics, which can then be analyzed algorithmically to determine optimal impedance settings without physically modifying the hardware
Data Source
AI summary
A method of selecting an optimum impedance for a loop start trunk line, comprising successively applying respective ones of a plurality of impedance settings to the loop start trunk line, for each impedance setting measuring the impulse response of the trans-hybrid echo path by applying audio test signals to obtain a time-domain trans-hybrid transfer function and deriving a frequency-domain spectrum representative of trans-hybrid loss, and then calculating figure of merit of the transfer function based on the power spectrum. Once all impedance settings have been tested, the optimum impedance is selected as the impedance setting associated with the highest calculated figure of merit.