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Detector for FSK Signal

IP.com Disclosure Number: IPCOM000099602D
Original Publication Date: 1990-Feb-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 2 page(s) / 47K

Publishing Venue

IBM

Related People

Murray, JT: AUTHOR

Abstract

Ideal fixed tones have constant magnitude and phase-slope in complex space. Since phase-slope depends on tone frequency, quantification of received phase slopes can be used to detect arbitrary tones.

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Detector for FSK Signal

       Ideal fixed tones have constant magnitude and phase-slope
in complex space.  Since phase-slope depends on tone frequency,
quantification of received phase slopes can be used to detect
arbitrary tones.

      Simple FSK systems effect data transmission via binary
modulation of tone sets - a binary selection between phase slopes
assigned to the data states.  Fig. 1 shows such a phase trace.
Smoothing of the phase transition between steady-state slopes is used
for spectral control.  Detection of FSK can be effected by
discriminating between phase slopes over time.

      Slopes are extracted (Fig. 2) by direct conjugate phase
rotation.  Complex sample sequences provided by a suitable complex
bandpass filter (E2-quadrature phase, equal magnitude transfer
function) are rotated by lagged samples (E3) to yield a vector whose
angle represents the phase difference for the lag chosen.  Difference
rotation is achieved by complex conjugate multiplication of the
samples (E5).  The difference angle (E6) can be obtained from a
reduced complex exponential-to-phase table as shown.

      Normalization of the magnitudes can occur within such tables or
via typical AGC functions to minimize the required tables and
optimize dynamic range.  Additionally, one would smooth over multiple
sequential slope measures to mitigate the effects of noise, phase
jitter, etc., prior to threshold or boundary detection of the slope
during an appropriate sig...