A quaternary partial-response class-IV system for 125 Mbit/s data transmission over unshielded twisted-pair cables

A 125-Mb/s quaternary partial-response class-IV (QPRIV) data transmission system is described for the physical connection between stations and concentrators in a fiber distributed data interface (FDDI) network over unshielded voice-grade twisted-pair cables with a maximum length of 100 m. It is shown that near-end crosstalk (NEXT) cancellation at the receiver is necessary to achieve satisfactory error rates. The problem posed by the drifting phase between the NEXT signal and the signal from the remote transsitter is solved by synchronous digital-to-analog and analog-to-digital conversion and adaptive NEXT cancellation, followed by self-training adaptive interpolation/equalization performed at a rate that is controlled so that the elastic buffer storing input signals for the digital equalizer is kept half full, on average. Numerical results on the convergence of the adaptive filters are given