Browse Prior Art Database

Equalization of Second Harmonic Distortion In A Data Transmission System

IP.com Disclosure Number: IPCOM000048803D
Original Publication Date: 1982-Mar-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 3 page(s) / 47K

Publishing Venue

IBM

Related People

Godard, D: AUTHOR [+2]

Abstract

This article describes an equalization system which cancels non-linear distortions in data transmission systems. The equalization system comprises two filter arrangements which are located on both sides of the conventional equalizer.

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Equalization of Second Harmonic Distortion In A Data Transmission System

This article describes an equalization system which cancels non-linear distortions in data transmission systems. The equalization system comprises two filter arrangements which are located on both sides of the conventional equalizer.

A model of a transmission medium including second harmonic distortion is shown in Fig. 1, where x(t) is the transmitted signal, y(t) the receiver input signal, and BPF1 and BPF2 are linear bandpass filters representing the channel linear distortion, and whose complex impulse response will be noted d(1)(t) and d(2)(t), respectively.

In Quadrature Amplitude Modulation (QAM) data transmission systems, x(t) may be written as: (1) (see original) where (a(n)) are the data symbols taken from a 2-dimensional constellation, g(t) is the transmitting filter impulse response, f(o) is the carrier frequency, and T is the signaling period.

In conventional digital receivers, y(t) is first filtered by a bandpass filter to eliminate signal components above half the receiver sampling frequency, l/Zeta equals M/T, and converted then by an analog to digital (A/D). In-phase and quadrature components are then obtained by passing the sampled signal through a Hilbert transformer. The Hilbert transformer output signal is demodulated, equalized, rotated by an estimated carrier phase Phi(n). A decision circuit generates detected symbols a(n) and an error signal e(n) used for equalizer adaptation and carrier phase tracking.

A QAM receiver including the proposed equalization system is shown in Fig.


2.

When the distortion d(2)(t) is negligible, the se...