Wholly-digital demodulation system for QAM signalling in low capacity links
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United States of America Patent
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May 2, 1995
Grant Date -
N/A
app pub date -
Jul 27, 1993
filing date -
Jul 27, 1992
priority date (Note) -
Expired
status (Latency Note)
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Abstract
The present invention relates to a QAM signal demodulation system able to recover phase and frequency of the carrier and convert the signal to baseband, and to perform these functions when frequency errors are remarkable with respect to the symbol frequency (low capacity links); to reconstruct the synchronism of symbol in order to correctly sampling the analog signal to be processed; to complete the shaping of the signal through a digital filter and to equalize the baseband converted signal (in order to compensate the selective fading effects due to propagation and the linear distortions due to imperfections in the realization of the apparatus). Therefore the system comprises several subsystems devoted to performing the various functions and, in particular, at least a carrier frequency and phase recovery subsystem, a subsystem for reconstructing the synchronism frequency capable of driving the signal sampling circuit, and a subsystem of filters. The present invention is directed to the choice of the particular subsystems used as well as their implementation and interconnections.
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