Demodulators – Phase shift keying or quadrature amplitude demodulator – Input signal combined with local oscillator or carrier...
Patent
1988-12-28
1989-09-12
Grimm, Siegfried H.
Demodulators
Phase shift keying or quadrature amplitude demodulator
Input signal combined with local oscillator or carrier...
375 39, 375 81, H04L 2706, H04L 2722
Patent
active
048663956
ABSTRACT:
A universal demodulator programmable for any digitally modulated carrier signal having a known constellation format which can be characterized by a unique constellation pattern of phase-amplitude states. The demodulator also generates phase and gain-error signals for locking onto the phase and amplitude of the digitally modulated carrier. The demodulator splits the received digitally modulated carrier signal into an inphase component, D.sub.x, and a quadrature-phase component, D.sub.y. Using a preprogrammed memory device keyed to the identified modulation format, each D.sub.x signal is mapped into one of a plurality of one-dimensional zones each having R.sub.x center values. Using a second preprogrammed memory device also keyed to the identified modulation format, each D.sub.y signal is similarly mapped into a plurality of orthogonal one-dimensional zones having R.sub.y centers. Each pair of R.sub.x and R.sub.y values represents a point in a two-dimensional signal space corresponding to one of the transmitted phase amplitude states. The data assignment signals, A.sub.x and A.sub.y, are generated and outputted by selecting a predetermined portion of the R.sub.x and R.sub.y center values. Using the digital signals R.sub.x, R.sub.y, D.sub.x and D.sub.y and signal vector relationships, a logic circuit generates for each periodic signal pair a phase-error signal .PHI..sub.e corresponding to the phase difference between the phase angle associated with (D.sub.x and D.sub.y) and the phase angle associated with (R.sub.x and R.sub.y). Also generated is a gain-error signal G.sub.e corresponding to the amplitude differential between the amplitude associated with (D.sub.x and D.sub.y) and the amplitude associated with the signal pair (R.sub.x and R.sub.y). The phase and amplitude of the modulated carrier signal is adjusted in accordance with the phase-error signal .PHI..sub.e and the gain-error signal G.sub.e respectively.
REFERENCES:
patent: 4404532 (1983-09-01), Welti
patent: 4546322 (1985-10-01), Crutcher
"A Generalized `Polarity-Type` Costas Loop for Tracking MPSK Signals", by Holly C. Osborne, IEEE Transactions on Communications, vol. Com-30, No. 10, Oct. 1982, pp. 2289-2296.
"Carrier Recovery Systems for Arbitrarily Mapped APK Signals", by Yoshio Matsuo and Junji Namiki, IEEE Transactions on Communications, vol. COM-30, No. 10, Oct. 1982, pp. 2385-2390.
Gilbert Douglas M.
Grimm Siegfried H.
GTE Government Systems Corporation
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