The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Aug. 08, 1995
Filed:
Sep. 14, 1994
Hiroki Tsuda, Tokyo, JP;
Motoya Iwasaki, Tokyo, JP;
NEC Corporation, Tokyo, JP;
Abstract
In a demodulator, a delay detection means receives a .pi./4-shift QPSK signal and performs delay detection of a signal at an interval of symbols. An averaging circuit respectively averages two channel quadrature signal components of a signal. A preamble detection means detects a preamble having a specific pattern in which a phase shift of .pi./4 of the phase of a received symbol from the immediately preceding symbol and a phase shift of -3.pi./4 of a phase of a next symbol from the immediately preceding symbol are alternately repeated on a phase plane of the two channel quadrature signal components. A phase angle calculating means calculates the phase angle of an output signal from the averaging circuit. A frequency offset estimating circuit calculates a carrier frequency offset. A voltage-controlled oscillator has an output oscillation frequency variably controlled by an output signal from the frequency offset estimating circuit. A frequency converter performs frequency conversion of the output oscillation frequency of the voltage-controlled oscillator and the input .pi./4-shift QPSK signal. A reproduction circuit reproduces a carrier and a clock from an output .pi./4-shift QPSK signal from the frequency converter, and obtains demodulated data by coherent detection.