Mathematical modeling and simulation of the DS3 transmission system.

摘要

Mathematical modeling and waveform level simulation of the DS3 transmission system is performed in this research. A simulation package written in "C" is developed for modeling the DS3 transmission system. This package provides a user friendly environment for the design study with graphical capabilities. The DS3 signal characteristics are defined at different points of the transmission system. The main purpose of this simulation is designing an adaptive time domain equalizer (ATDE) used for reducing intersymbol interference (ISI) and noise. The ATDE is implemented with a fractionally-spaced equalizer (FSE) and a decision feedback equalizer (DFE). The tap-weights of this ATDE are controlled by the least mean square (LMS) algorithm. The transmission channel is assumed to be a coaxial cable. Due to the limited bandwidth of the cable, the transmitted signal is linearly distorted as it travels through this cable and hence ISI results. In addition to the ISI, Gaussian noise adds to this signal. As a result, the received signal is corrupted with ISI and noise which must be removed by the aid of the ATDE before this signal can be successfully detected. This ATDE will be used for equalizing an arbitrary length of the coaxial cable. The major focus of this research will deal with the problem of obtaining the required number of tap-weights and their spacing in time as well as determining the structure of the ATDE. Extensive computer simulation of the ATDE with different configurations will be carried out to obtain acceptable performance. In particular, eye diagram plots are helpful for evaluating the ATDE performance with the percentage of the vertical eye opening as a design objective. The simulation provides signal time histories at different points of the DS3 transmission system. Also signal autocorrelation function (ACF) and power spectral density (PSD) are calculated and displayed. Finally, a hardware prototype for the ATDE has been built and tested successfully with the results that agree very closely with the simulation.