| Satellite communication systems are specified for a certain and usually relatively high reliability. To achieve the reliability, margins are added to the system design to account for low-probability, high propagation loss conditions. Often the parameters of the system are fixed, e.g., causing the system to operate at the power levels or modulation required to close the link during a fade. This represent a disadvantage during the non-fade times. An alternative approach allows the data rate to increase during the higher probability clear weather events. This type of system adapts to the changing conditions.;This work attempts to quantify the advantages of an adaptive satellite communications system over one that cannot be changed. A theoretical treatment is used to show this advantage.;This work develops a metric named the spectral efficiency improvement factor that relates the average spectral efficiency of the adaptive system to the deterministic spectral efficiency of the fixed system. The spectral efficiency improvement factor is used to examine two cases in depth. First, the value of adaptation as subsystem components such as antennas are considered. As part of this first examination, high and low satellite to ground station look angles are also simulated. Second, regions of the continental United States are determined where adaptive systems are most advantageous.;The Spectral Efficiency Improvement factor shows adaptivity is more advantageous in: 1) climates with a high rain rate, 2) high RF carrier frequency, 3) systems that use antennas with horizontal polarization, and 4) at low elevation angles from the satellite to the groundstation.;This work also discusses an implementation of a SC-FDMA waveform that has correlation properties with a single main peak even though the time domain representation contains multiple repeats of the user symbols.;This work implements a modem in MATLAB and a modulator in VHDL for initial testing of the waveform. |
