Optimisation des systems of transmission numerique transauroraux en ondes decametriques optimization of H.F. digital radio systems at high latitudes

High latitudes are inevitably encountered in telecommunications, especially in long distance transmissions. At high latitudes the following phenomena appear: auroral and polar absorptions, spread F, perturbations aligned with the magnetic field, sporadic E... which make long distance transmission characteristics special. Researchers were able to establish a channel model from experimental observations of transmissions travelling through high latitudinal regions. The parameters of the model must include the perturbations found at high latitudes, the length of the transmission, and its position relative to the magnetic pole and the auroral zone. From these models, which point out the spectral modifications of the signal, the fading, the duration of coherence, researchers determined the classes of signals which can be needed for H.F. digital telecommunications with the aim of diverse techniques: serial or parallel transmissions, autoadaptative systems, coded transmission systems.