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

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