OTDR Fault Analysis in PON Sub-Splitter Networks
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In Passive Optical Networks (PONs), fault analysis is challenging due to low backscattered light levels and the complexity introduced by sub-splitters, which makes it difficult to accurately locate and quantify faults, leading to potential misinterpretations in OTDR signal analysis.
Innovation Solution
A method and arrangement that uses Optical Time-Domain Reflectometry (OTDR) measurements, comparing new measurements to a reference state, and inserting the OTDR signal into a multistage splitter before the last splitter stage, allowing for analysis of sub-splitters in a predefined sequence to determine fault locations and magnitudes by accounting for the number of drop links and sub-splitters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If sub-splitters are added to customize and adapt the PON layout to end-users' needs, then the network flexibility and drop link capacity are improved, but the difficulty of obtaining fault location and magnitude increases
Solution Approach 1:
The patent segments the PON network into distinct analytical zones by introducing virtual reference points at each sub-splitter location. The OTDR trace is divided into multiple segments, each corresponding to a specific sub-splitter section. By analyzing each segment independently and comparing it to reference traces, the system can locate faults precisely within specific sub-splitter sections rather than treating the entire network as a single unit.
Solution Approach 2:
The patent performs preliminary actions by establishing reference OTDR traces during network installation or activation, before faults occur. These reference traces are stored and later used for comparison with current measurement traces. This preliminary characterization of the network state enables rapid fault detection and localization by highlighting deviations from the known good state.
2Quantity of substance
If sub-splitters are added to increase drop links, then the network capacity is improved, but the complexity of analyzing the backscattered OTDR signal increases
Solution Approach 1:
The patent divides the complex backscattered signal analysis into manageable segments corresponding to each sub-splitter section. Instead of attempting to analyze the entire superimposed signal from all drop links simultaneously, the system segments the trace and analyzes each segment separately, comparing against corresponding reference segments. This segmentation reduces the computational complexity and makes the analysis tractable.
Solution Approach 2:
The patent applies partial action by focusing the analysis on specific segments of the OTDR trace that are most likely to contain faults, rather than uniformly analyzing the entire trace. The system identifies and prioritizes segments with significant deviations from reference traces, performing detailed analysis only where needed, thus reducing overall computational complexity.
3Measurement precision
If the OTDR receiver circuit is made very sensitive to detect the small backscattered light, then the detection capability is improved, but the receiver becomes saturated by big reflections
Solution Approach 1:
The patent performs preliminary characterization of the network by storing reference OTDR traces that capture the normal reflection patterns. By comparing current traces against these references, the system can identify and compensate for expected large reflections, preventing them from causing false saturation indicators. The reference data enables the receiver to distinguish between normal high-reflection events and actual fault conditions.
Solution Approach 2:
The patent implements feedback by continuously comparing current OTDR measurements with stored reference measurements. When large reflections are detected, the system uses the reference data to determine whether these represent normal network characteristics or actual faults. This feedback mechanism prevents false saturation alarms and enables the receiver to maintain high sensitivity without being overwhelmed by expected reflection events.
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
This approach enhances the accuracy and sensitivity of fault detection and localization in PONs with sub-splitters, providing a cost-efficient solution for identifying fault positions and severities, even in complex architectures.
Implementation Method 1
Optical Time-Domain Reflectometry, OTDR, may be used. The supervision and monitoring of PONs using OTDR is further described in the recommendations L-25, L-40, L-42 and L-53 from the Telecommunication Standardization Sector of International Telecommunication Union (ITU-T). Briefly described, an OTDR device injects a series of optical pulses into the fiber.
Implementation Method 2
Parts of the OTDR signals are reflected back towards the OTDR device. The back reflected, or backscattered, OTDR signal may be used for estimating the fiber's length and overall attenuation, including losses such as splitter losses.
Data Source
Figure 1a~1b
Figure 2
Figure 3~5
AI summary
A method and apparatus is provided for performing fault analysis a Passive Optical Network comprising Optical Network Terminal(s) by using Optical Time Domain Reflectometry, OTDR. An OTDR measurement signal into a multistage splitter which is of ratio 2:Nroot. At least one drop link which is connected to the multistage splitter comprises one or more sub-splitter which is of a ratio 1: Nbranch. a new event location is determined based on the OTDR measurement signal by analyzing OTDR measurement data relating to the sub-splitter based on distance from the multistage splitter and to the sub-splitter. A fault magnitude is calculated for a given location by subtracting an event magnitude obtained from the new OTDR measurement from a reference OTDR measurement and taking into account the number of drop links connected to the last splitter stage and to sub- splitter in the reference measurement and the new measurement, thereby enabling determination of position and severity of the fault locations.