Demodulators – Amplitude modulation demodulator – Having specific distortion – noise or other interference...
Patent
1985-02-26
1986-04-15
LaRoche, Eugene R.
Demodulators
Amplitude modulation demodulator
Having specific distortion, noise or other interference...
329 50, 375 90, 375 96, H03D 300
Patent
active
045830487
ABSTRACT:
A receiver for burst transmission of MSK-modulated binary signals includes in-phase (I) and quadrature (Q) demodulation under the control of reference sine and cosine signals. Initially, the reference signals are near the nominal carrier frequency of the received signal, but at arbitrary phase, so that noncoherent detection takes place. A control circuit is provided to slew the reference signals to the same phase as the MSK carrier for low-noise coherent detection. Because of the burst nature of the communications, data throughput is significantly reduced if reference phase acquisition time is large. In order to reduce the phase acquisition slew time, each burst of data is preceded by a predetermined preamble. In the receiver, the noncoherently detected preamble is applied to a set of four preamble-matched correlators which respond to the I and Q portions of the preamble, and to the cross-coupled Q and I portions contaminating the I and Q portions respectively. At the moment that the preamble completely fills the correlators, each correlator produces a correlation peak having a magnitude and polarity. The relative magnitudes and polarities of the four correlation outputs at the instant of receipt of the preamble uniquely determines the relative phase difference (.theta.) between the sine reference signal and the MSK carrier. The phase difference signal .theta. slews the reference signal phase to near the desired phase at the beginning of the data portion of the burst transmission. In order to keep the reference signals in-phase with the MSK carrier during the data portion of the transmission, the received data is used as a predetermined signal once the bit decisions have been made. The bit-decided data is applied to set of four correlators the taps of which are adaptively controlled in response to the bit decisions to continuously generate .theta. for control of the reference phase.
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Title: Minimum Shift Keying: A Spectrally Efficient Modulation; Author: Subbarayan Pasupathy/IEEE Communications Magazine; Date: Jul. 1979, pp. 14-22.
U.S. Patent Application entitled: Digital Modulation System; Inventor: Edward Joachim Nossen; filed: 12/28/84; Ser. No. 687,546.
Gumacos Constantine
Macina Nicola A.
LaRoche Eugene R.
Meise William H.
Pascal Robert J.
RCA Corporation
Tripoli Joseph S.
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