Digital Communications with Emphasis on Data Modems

20IONOSPHERIC PROPAGATION

20.1 INTRODUCTION

The amplitude variations of a signal propagating through the ionosphere [1] result from the destructive and constructive interaction of the signal phase resulting from the numerous signal paths through the nonhomogeneous medium; this phenomenon is referred to as scintillation. In addition to scintillation, signal propagation through the ionosphere is subjected to anomalies characterized by time delay variations, angular errors caused by refractive bending, frequency shifts, dispersion, polarization rotation, and absorption that must be accounted for in the communication link budget. Refractive bending affects azimuth and elevation measurement accuracies while time delay and frequency variations result in range and velocity estimation errors. Dispersion gives rise to symbol broadening and intersymbol interference (ISI) that degrade the symbol‐error performance while polarization rotation and absorption can significantly degrade the available link margin. These errors also impact antenna, symbol, and carrier tracking loops contributing to degraded communication performance.

Signal propagation through the ionosphere is characterized by the refractive index. The refractive index and its influence on the various aspects of a received signal is the subject of this chapter. The significant parameters that influence the signal propagation through the ionosphere are the electron density with units of electrons per cubic‐centimeter and the ...