U.S. Philips Corporation

Dirk Muilwijk

Frank De Jager

Cornelis B Dekker

In circuits for reproducing carriers for continuous phase modulation having a rational modulation index these signals are multiplied in a multiplier for producing a harmonic, with unique phases occurring due to phase addition irrespective of the information to be conveyed. This harmonic is selected by means of a bandpass filter and supplied to a divider for reproducing the carrier signal. However, as the desired phases only occur at certain instants the effect of jitter in the reproduced carrier signal is undesirably high. Jitter suppression is considerably improved by supplying to the bandpass filter only the instantaneous values of the virtually desired phases occurring at the specific instants.

Circuit for extracting carrier signals

In mobile radio communication it often happens that the received signal disappears owing to, for example, fading. If a receiver is used which is based on the coherent detection principle, acquisition of the carrier must consequently be done repeatedly. In order to avoid the loss of information resulting therefrom, non-coherent detection is used in the receiver for angle-modulated carrier signals in combination with a decision criterion which is based on the possible phase trajectories of the demodulated signal.

Receiver for angle-modulated carrier signals

A system for transmitting n-level data signals by means of an angle-modulated carrier having a constant amplitude and a continuous phase. The constant amplitude enables amplification in non-linear transmitter output stages. Associated with the n-levels are k(k&gt;n) phase variations in accordance with such a rule, depending on preceding phase variations, that the spectrum of the angle-modulated signal becomes narrower. In a symbol interval the phase of the carrier changes by an amount from the sequence extending from -(k-1).pi./n to (k+1).pi./n in increments of 2.pi./n. The receiver is formed by a differential n-phase receiver. The system is used inter alia for radio transmission of digital information.

System for multi-level data transmission by means of an angle-modulated

A system having a transmitter and a receiver for transmitting binary data signals of a given symbol rate, an angle-modulated carrier signal of a substantially constant amplitude and a continuous phase being generated in the modulation stage of the transmitter, and the transmitted modulated signal being orthogonally, coherently demodulated in the receiver. The modulation stage of the transmitter is arranged so that the phase of the modulated signal changes in each symbol interval by an amount from the sequence -.pi./2, -.pi./4, 0, .pi./4, .pi./2 (rad.), which amount is determined for the relevant symbol interval by at least two successive data symbols, and the value of the phase within the relevant symbol interval is determined by a filtered version of at least these two succesive data symbols. These measures result in a system which, without sacrificing the remaining desired communication properties of FFSK-systems, utilizes the available frequency spectrum in a more efficient manner than FFSK-systems, because the modulated signal has both a narrower spectral main lobe and, for frequencies outside this spectral main lobe, considerably less power than the FFSK-signal. Consequently this system is very well suited for efficient data transmission over radio links.

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Hilversum, Netherlands

Dirk Muilwijk