timization of Discrete Multitone to aintain Spectrum Compatibility with Other nsmission Systems on Twisted Copper

The growing demand to transmit high-speed digital data in many local area networks (LAN ’s ) and digital subscriber lines (DSL’s) has resulted in a wide variety of transmission systems that have to co-exist on twisted wire copper pairs. In this paper, we address the problem of maintaining speehvnz compatibility between various services that may use Merent transmission technologies, by shaping in an optimal manner, the power spectral density (PSD) of the transmit signal. A multitone modulation scheme such as discrete multitone @MT) has the flexibility of optimizing the power spectrum over more than one (disjoint) frequency band, and is suitable for trvisted pair subscriber loops, and other transmission media, where the optimized transmit spectrum is likely to occnpy more than one frequency bands. DMT has been selected by the American National Standards Institute (ANSI) TlE1.4 Standards Committee as the standard modulation scheme for asymmetric DSL (ADSL). The results presented in this paper are for the specific application of DMT to transport ADSL payloads of over 6 Mb/s from the network to the customer. We consider speccompatibility between ADSL, the T1 repeater system, high bit-rate DSL O S L ) , and integrated services digital networks (ISDN) basic rate access (BRA) systems. The simulation results show that: 1) One can customize the transmit PSD to achieve optimum ADSL performance in a specified noise environment; 2) this optimum performance can result in as much as approximately 6 dB improvement in signalto-noise ratio (SNR) when compared to the nonopthized PSD chosen by the T1E1.4 committee; 3) in achieving the above hprovements, the total maximum transmit power is s@ consistent with the limit set by the TlE1.4 committee. Further work is required to support the simulation results with measured data The mathematical analysis is based on the use of Lagrange multipliers to solve the constrained optimization problem, and is easily extended to other asymmetric and full-duplex wirehe transmission systems operating at much higher data rates. The practicality of implementing the proposed optimization romtke requires further investigation.