Transmission capacity and design of a VHDSL-system

In a hybrid fiber/twisted-pair architecture the transmission of data rates much higher than the 1.5 or 2 Mbit/s of the high bit-rate digital subscriber line (HDSL) service can be achieved by reducing the loop length of twisted pair cables in the access network. In this paper we present a channel model for twisted-pair cables for frequencies up to 40 MHz, which is derived from measurements and theoretical analyses. Based on the new channel model the transmission capacity for a symmetrical pulse amplitude modulation (PAM) system with adaptive echo cancellation (EC) and for a carrierless AM/PM (CAP) system based on frequency division multiplexing (FDM) is calculated, Up to a table length of 200 m the PAM system achieves higher data rates, whereas for longer distances CAP systems are advantageous, Over 200 m a data rate of about 30 Mbit/s can be transmitted by both systems with 24 identical self-crosstalk disturbers in the 50-pair distribution cable. Whereas the reach of a 25 Mbit/s echo cancellation system can be increased to 360 m by NEXT cancellation, the range of the FDM system can even be improved from 300 m to 610 m for the same data rate. Crosstalk cancellation results in a high hardware complexity but could be realized with gate arrays in 0.5 or 0.35 μm technology