Differential encoding arrangement for a discrete multi-tone transmission system

Abstract

A random-access local network having multiple nodes provides data communication across residential wiring such as telephone line as a network medium, where each node accesses the network medium using discrete multi-tone (DMT) modulated symbols. The effects of amplitude and phase distortion of transmitted DMT symbols are overcome, without the necessity of complex equalizers, by differentially encoding data prior to transmission, and recovering the transmitted data by comparing phase differentials between consecutive symbol tones. Each transmitted symbol is composed of a plurality of tone signals, each tone signal modulated according to a constellation point in a complex domain. A transmitter modulates data, such as a bit-pair, to a new constellation point based on the value of the bit-pair and a prior position of a consecutively-preceding constellation point, such that the data is represented by the difference in positions between the consecutively-preceding constellation point and the new constellation point. The constellation points are then used to modulate a selected one of the tone signals. Although a receiver detecting the modulated tone signal may recover the transmitted constellation points at different absolute positions due to distortion on he network medium, the relative difference between the consecutively-preceding constellation point and the new constellation point is preserved, enabling the receiver to recover the transmitted data based on the relative difference in positions of the consecutive constellation points. Hence, entire bit stream can reliably transmitted using position changes between consecutive constellation points.