For the single-pair HDSL (HDSL2), the concept of having different upstream and downstream power spectral densities is highlighted. The signal-to-noise ratio (SNR) at the input of the central office HDSL terminal unit (HTU-C) can be enhanced by boosting the power output of the remote user HDSL terminal unit (HTU-R). Further improvement in performance can be achieved by reducing the HTU-C NEXT interference. Two techniques are proposed to reach this goal. The first approach is to reduce the HTU-C transmitter power in the downstream direction for shorter reach cables. The second approach is borrowed from the analog frequency-modulation preemphasis/deemphasis frequency tilting in the upstream direction. Combining the three techniques leads to at least 6-dB SNR margin improvement for the full reach carrier serving area loops.

A new line equalizer system for time compression burstmode digital suhscriber loop transmission that can equalize a line with multiple bridged taps (BT's) is developed. Using the developed equalizer, up to 5 km (0.4 mmφ) line length and four BT connections can be equalized at a data rate of 80 kbits/s in each direction. The equalizer is composed of a variable gain\surd{f}step equilizer, a decision feedback automatic equalizer, and a newly developed wave difference method (WDM) timing extraction PLL. In order to fabricate the whole circuit on a single-chip LSI, most of the analog portion is organized using; switched capacitor technology. In this paper, the system design concept, circuit configuration, and results of simulations and experiiments are described.