Performance Analysis of Digital Subscriber Lines

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Addis Ababa University


In recent years, lots of emerging high-speed applications and networking requirements are calling for cost effective access network solutions. These applications are well driven in the high bandwidth transmission media of the backbone network. However, the last mile transmission media that uses the existing modems of maximum speed 64 kb/s, are failing under these high-speed requirements. Firstly, this problem was approached using the very high bandwidth fiber network but it was seen that present time and foreseeable future end user requirements are only within reach to a speed of 2 Mb/s unjustifying the involved high cost. The practical means followed is to use the widely installed copper based access network. It is the aim of this thesis to use standard techniques to investigate Asymmetric Digital subscriber Line, (ADSL). ADSL is a relatively new modem technology that provides high-speed data rates on the Plain Old Telephone Service (POTS) line. Efficient error control coding schemes and Discrete Multitone (DMT) modulation are the key mechanisms in ADSL. The objective of this work is to develop the software simulation modules for ADSL modem. In this thesis, DMT modulation is realized in an effort to demonstrate the end-to -end transmission of random generated bit streams through the twisted pair channel situated between the transmitter and receiver This simulation in done using a script code with MATLAB® Also largely described in this work are the physical properties of twisted pair channels and their frequency selective distortion. Moreover the high frequency behaviors of copper networks are highly varying among manufacturers. Accordingly twisted pair channel models are used using empirical or measured data. and Bit Error Rate (BER) is used as a measure of performance. The results of this work are performance measurement curves obtained from this end-to-end system simulation. These curves demonstrate the decreasing BER values against SNR agreeing with similar works of digital communications system simulation.



Electrical Engineering