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Effects of bridged taps on the channel capacity of very high-bit-rate digital subscriber lines Wang, Amanda

Abstract

The Digital Subscriber Line (DSL) technologies have been developed to meet the growing demand for high speed data transmissions to home. These technologies offer data rates that are of several order of magnitudes compared to today's analog modems operating over the same existing copper twisted pairs. Very-high-bit-rate DSL (VDSL) is the latest member of the DSL family. To date, most of the analysis on channel performance for VDSL systems are based on the model of transmission lines without considering the adverse effects caused by the presence of bridged taps. In practical situations; however, multiple bridged taps can introduce severe propagation loss. This is especially pronounced in VDSL systems because the operating frequency range is higher and the bridged taps are shorter as compared to other DSL systems. Motivated by the above, the objective of this thesis is to study the effects of bridged taps on the channel capacity of VDSL services over the Unshielded Twisted Pair (UTP) under various noise impairment conditions. First, we develop channel models of VDSL loops with the presence of bridged taps. Then, we employ these models to obtain the mathematical expressions for the channel capacity by taking the additive white Gaussian noise (AWGN) and the far-end crosstalk (FEXT) noise into account: Using the proposed analytical models, we have discovered that the channel capacity is only affected by the lengths of the bridged taps but not their physical locations for homogeneous loops in AWGN environment. On the other hand, in a FEXT dominated environment, we have proved that the channel capacity increases when the bridging locations are moved away from the transmitter. In addition, we have determined that FEXT is the dominant impairment for short VDSL loops, while AWGN is the dominating impairment for long loops.

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