Abstract: The present invention relates to a method of fractionally spaced adaptive equalization which allows the achievement of the performances of the optimal linear receiver with a high degree of stability of the control algorithms. The technique is applicable to a generic communication system. The present method provides a fractionally spaced equalizer which is perfectly stable and has a good convergence rate without introducing any deterioration of the performances with respect to the optimal receiver and with an extremely low increase in the complexity of realization as compared to the prior art techniques. The invention is based upon the introduction of a whitening filter of the input signal to a fractionally spaced equalizer stabilized with the tap-leakage technique, where the whitening filter is a device able to make the power spectrum density of the signal--repeated with a period equal to the reciprocal of the signalling interval--constant.

Abstract: Efficiency of a digital link, e.g., a microwave link, is improved by coding numeric signals for transmission so as to transmit selected sequences, in terms of peak power of a filtered signal, for transmission through the link. The most favorable numeric sequences may be encoded by baseband numeric coding.

Abstract: The invention relates to a baseband signal combiner and to a sampler typically used in radio relay systems and also in generic communication systems. In order to avoid temporary failures in the free space links, space and/or frequency diversity techniques are used, which consist in the use of two suitably spaced receive antennas or of two transmission frequencies. By suitably combining the signals thus received, the failures in radio links can be redued. The invention provides the use of a particular algorithm of the type CMA (Constant Modulus Algorithm) which, being independent of the combined signal phase, does not interact with the carrier recovery circuits. Moreover, by also applying the same algorithm to the sampler, the cooperation of the two circuits for the optimization of the output signal is obtained.

Abstract: The present invention concerns a system for estimating the carrier frequency of a PSK numeric signal, in which symbols are transmitted at frequency fs. The invention is characterized by the use of an estimate, at each symbol interval, of the angular difference between two successive data. Such estimate, suitably processed, provides the control signal for a circuit that compensates the frequency error between the carrier of the received signal and the local oscillator. In a not limiting embodiment, the invention can be implemented through digital circuitry.

Abstract: The present invention relates to a QAM signal demodulation system able to recover phase and frequency of the carrier and convert the signal to baseband, and to perform these functions when frequency errors are remarkable with respect to the symbol frequency (low capacity links); to reconstruct the synchronism of symbol in order to correctly sampling the analog signal to be processed; to complete the shaping of the signal through a digital filter and to equalize the baseband converted signal (in order to compensate the selective fading effects due to propagation and the linear distortions due to imperfections in the realization of the apparatus). Therefore the system comprises several subsystems devoted to performing the various functions and, in particular, at least a carrier frequency and phase recovery subsystem, a subsystem for reconstructing the synchronism frequency capable of driving the signal sampling circuit, and a subsystem of filters.

Abstract: A method of estimating the carrier frequency of a numeric signal, in which two estimates of the carrier phase are carried out in successive instants of time and the estimated carrier frequency is obtained from the comparison of the above two estimates. The invention also concerns a device for implementing the method, the device including a circuit for estimating the phase of the signal at successive instants in time, a circuit for storing the estimates, and a circuit for comparing the estimates. In a preferred embodiment, both the phase estimator and the comparison circuit are implemented by multipliers and adders.