Abstract
As we joyfully welcome the advent of a new millennium, the world is undergoing a revolution of networks. Since the networks have entered into the world extensively, the life is getting more convenient and splendid. To satisfy the demand for high-speed and high-performance transmission, various new techniques have been proposed to meet the tide. Among these techniques, asymmetric digital subscriber lines (ADSL) technology is considered to be a viable transmission scheme over the twisted-pair lines, where the discrete multitone (DMT) modulation has been chosen as the standard line code to support high data rate transmission. In this thesis, we propose some approaches to promote the transmission performance based on the basic DMT structure. In the DMT-based ADSL transmission system, a time-domain equalizer (TEQ) is involved to partially equalize the overall effective channel response of the transmission system to a predefined length. Several algorithms based on different criterions have been proposed for designing a time-domain equalizer. In this thesis, a decision feedback equalizer (DFE) is applied in the DMT architecture to shorten the channel and an on-line training algorithm is presented for it. As compared to time-domain equalizers with on-line training, the proposed approach of equalization achieves better performance with comparable computational complexity. This supports that the proposed time-domain equalizer is well suited to DMT-based ADSL systems. There have been several optimal or suboptimal discrete loading algorithms available for DMT modulation. These algorithms are either trying to maximize the data rate or the system performance margin subject to a given constraint. In this thesis, we present a new way of discrete loading to optimize the DMT transmission bandwidth based on the same criteria. As compared to previously described optimal DMT discrete loading algorithms, the proposed approach requires less computational complexity and is more attractive for use in practical applications. Computer simulation results are given to demonstrate its effectiveness for ADSL applications.