Simulation and Design Studies of Digital Subscriber Lines

Vol. 61, No. 6, July-August 1982 Printed in U.S.A. Simulation and Design Studies of Digital Subscriber Lines By S. V. AHAMED (Manuscript received July 14, 1981) To investigate the feasibility of transmitting data bidirectionally between 56 and 144 kb/s, an extensive simulation and experimental study was undertaken. The computational techniques for the study have been developed and coupled to a large data base, which contains the individual loop configurations of a statistically significant population of the Bell System loop plant. Two modes of transmission (the hybrid and the time-compression multiplexing) are investigated thoroughly by computational techniques, and the simulated plots are compared with experimentally generated oscillograms. These results are displayed graphically by eye diagrams for individual loops and by scatter plots for all the loops in the data base. Different varieties of scatter plots display different attributes of eye diagram. Broad spectrums of such results are cross-compared to choose optimal systems and circuit configurations for a particular mode of transmission at a particular bit rate. Effects of varying terminating networks are also studied and the extent of echo cancellation necessary is investigated by studying the amplitude and the shape of near-end reflections. Various codes are investigated even though the primary emphasis has been on the bipolar code. Major conclusions are summarized in the concluding remarks.