Application of Spread Spectrum Time Domain Reflectometry for ADSL Fault Detection

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Addis Ababa University


The tremendous increase of interest in an increasingly expanding online world, access service providers face many unique challenges. Each and every subscriber are consistently demand more bandwidth to access video, gaming, and other online content at the same time multiple users demanding consistent performance from the fixed access network. To have more efficient ADSL technology, it wants to trace faulty points to avoid or reduce a loss so that a convenient technique has to be implemented. In copper cable communication, Time domain reflectometry or “Megger” technique was commonly used for characterization and fault location of copper cable transmission systems. TDR measures averaging so lacks accuracy in fault detection and a fault characterization will be done by low voltage, low impedance and echo based analysis. In TDR the analysis detection can be only suitable in short distance due to narrow pulse. ADSL line fault can be detected using TDR when the reflected signal generated due to impedance mismatch and electromagnetic discontinuity. Since fault detection using the classical Time Domain Reflectometry for ADSL technology is vulnerable for different noise, which results attenuation to locate the faulty point accurately. To overcome such problem, these study will implement distributed (SSTDR) fault detection means. Previously different researchers were analyzed and used this fault detection method in order to overcome fault location problem and to enhancing accuracy within a minimal power threshold. Distributed SSTDR fault detection means have been implemented as an operative fault detection technology aimed at finding distorted fault points on aircraft wires. The optimization and fault detection for ADSL technology is done using correlation algorithm by analyzing and correlating the incident signal with reflected signal with bigger bandwidth and kasami sequence generator was used in the simulation and modulated with sine wave and spreaded over the transmission line and despreaded before cross correlation is done. Incident signal and reflected signal is analyzed using correlation function and the maximum peak will determine the fault status and its location. Finally, different form of fault sparked and the fault determined based on the reflected signals. Basic verification parameters are power, signal to noise ratio and distance. This research shows a progress in locating a defect point compared to the classic TDR fault detection techniques for ADSL technology.



ADSL, TDR, SSTDR, Reflectometry, Spread, Spectrum