Analysis and performance evaluation studies of high bit ratedigital subscriber lines (HDSL) using QAM and PAM schemes with idealdecision feedback equalization (DFE) within a carrier serving area (CSA)

摘要

QAM and PAM technologies are compared for possible HDSLapplication. Analysis and simulation studies with ideal decisionfeedback equalization (DFE) on a sample of loops within a carrierserving area (CSA) are presented. Self near-end crosstalk (NEXT) hasbeen assumed to be the dominant source of external impairment.Simulation studies using a 64-point symbol rectangular constellationwith a transmission rate of 1.6 Mb/s (in the vicinity of DS1 rate of1.544 Mb/s) with a carrier frequency of 153.5 kHz and 10th-orderButterworth transmit and receive filters are presented for a sample ofloops extracted from Bellcore's 1983 loop survey database. It is shownthat a large improvement in SNR is required to make 1.544-Mb/s 64-pointQAM a viable transmission technology for HDSL application in a CSAenvironment. The baseband PAM with 800-kb/s and 4-level code (2B1Q) hasa performance which is, on the average, 5 dB superior to that of thesimulated QAM across the tested loops