Combined equalization and coding for T1 data rates on carrier serving area subscriber loops

Techniques are presented to provide high-rate digital services on a limited class of subscriber loops known as a carrier serving area (CSA). Specifically considered is the use of vector coding to reach a goal of 1.544 Mb/s, the T1 carrier rate. The subscriber loop and the parameters that are critical in determining the ability of the loop to support the T1 rate are examined. Three techniques are identified for dealing with the characteristically long postcursors. A nonlinear program is presented to calculate a bound on the performance of vector coding and to identify a target for the allocation of power and bits to the subchannels. Then, the performance of a practical system using finite-length filters is considered. The performance of a special combination of a least-squared-error-block decision-feedback equalizer (LSBDFE) and a four-dimensional trellis code is compared with that of a scalar decision-feedback equalizer (DFE) with both a long feedback section (96 taps) and a feedforward section (32 taps), using the same code