Quelques résultats théoriques et expérimentaux sur la modulation par déplacement de fréquence à deux états et à phase continue d’indice 0,5 (MSK)

Minimumshift keying modulation seems to be very attractive for digital transmission systems in particular because an only small degradation can be expected on non linear channels. In the first part of this paper, some general features of the signal are recalled. After a theoretical method for the calculation of the bit error rate in presence of inter symbol interference is described; the results are compared with experimental values, obtained with a modulator demodulator build incnet laboratories in Lannion.     

Étude théorique et expérimentale d’une modulation simplifiée par déplacement de fréquence d’indice 1/2 à phase continue

The minimum shift keying modulation (MSK)to which a lot of recent publications have been done,presents some advantage about linear and non-linear distortions towards common 2 or 4 Phase Shift Keying (PSK)modulations. The simplified MSK modulation described in this paper is obtained by linear filtering of a coherent 2 phase shift keying modulation. Then the demodulator can be implemented with a matched filter followed by a coherent demodulator using only one carrier recovery circuit. In the first part of this paper, the modulator and the demodulator are described. After, some theorical results in the presence of noise and other impairments are given. In CCETT laboratories at Rennes, a modem has been realized at a data rate of 2,048 Mbit/s and performs at 0,8 dB of the theoretical results.     

Étude du couplage d’une onde électromagnétique externe et d’une ligne de transmission aérienne non uniforme

In this paper, a flexible and efficient method for analyzing the electromagnetic field to nonuniform multiwire aerial lines coupling is proposed. This analysis in based upon the finite- difference time- domain (fdtd) algorithm. The transient responses of nonuniform lines excited by different waves obtained by this method are compared with those of Spice and literature. The good agreement between all the simulation results validates the proposed approach.     

Amélioration de la sensibilité de détection et de la qualité du radargramme d’un radar pénétrant GPR par une modulation micro-onde

The primary effect of the field continuously capted by aGpr is the production of a class which limits the contrast of the reflections on the targets. The target response becomes illegible sight the influence of certain disturbances which are due to the reflections caused by certain parasitic elements which are randomly distributed in the soil and the dispersion phenomenon. We present in this paper an approach based on a μ-wave modulation which allowed stage this problem. The technique suggested makes it possible to do a classification of capted signals. It will be shown that the frequency of modulation f_m must be higher than a cut-off frequency f_c which depends on the electric parameters of the ground. In a second part of this paper, we show how to improve quality of the radargram of a systemGpr by a simple convolution between the collected signal and a wavelet with a defined parameters.