Dégradation de la qualité due aux trajets multiples dans un système a transmission numérique a quatre états de phase

A study is made on the effect of propagation on digital transmission based on two series of measurements made with four phase shift keying and differential demodulation equipment at bit rates of 38.8 and 216 Mbit/s. Degradation due to selectivities of attenuation caused by multipath propagation is inferred for both experiments : whereas the degradation is low at 38.8 Mbit/s, it becomes very large at 216 Mbit/s. The results are interpreted and commented upon. By taking a dual beam model, a calculation is made for degradation due to propagation under multipath conditions, as a function of the delay of the reflected beam.