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Received Line Signal Quality Analysis

IP.com Disclosure Number: IPCOM000052195D
Original Publication Date: 1981-May-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 2 page(s) / 13K

Publishing Venue

IBM

Related People

Haas, LC: AUTHOR [+2]

Abstract

This article describes a received-line-signal quality measurement technique In which the modem provides summary results of the effects of line impairments. The technique uses quadratic error and hit count parameters to characterize the impact of line impairments.

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Received Line Signal Quality Analysis

This article describes a received-line-signal quality measurement technique In which the modem provides summary results of the effects of line impairments. The technique uses quadratic error and hit count parameters to characterize the impact of line impairments.

The technique is based upon the effects of line impairments on the so-called "eye pattern" (also referred to as "signal constellation" or "signal space"), which is a representation of the actual received signal versus the theoretical target points. During the demodulation process the modem determines the position of the received signal at each baud time. It then determines the closest theoretical target point to be the signal transmitted. If there are no line impairments that affect the demodulation process, the received signal will fall close to the theoretical target point, and there will be no error. However, if line impairments affect the demodulation process, the received signal can be moved closer to an incorrect target point and an error can occur.

The eye-pattern analysis is performed at the end of the demodulation process. This is after the digital signal processing has adjusted the receive level, any frequency shift has been cancelled, and the equalizer has compensated for group delay and attenuation distortion. Until these impairments exceed the range of compensation, the eye pattern is unaffected and so is the reliability of data transmission. Once these impairments exceed the range of compensation, they begin affecting the eye pattern and, depending on their magnitude, they may affect the reliability of data transmission. Thus, the operator does not have to react to line impairments that do not affect data transmission.

The eye-pattern analysis consi...