Prediction and Compensation of Sun Transit in LEO Satellite Systems

The rapid growth of low earth orbit (LEO) satellite communication systems using higher frequency bands such as Ka-band have highlighted effects of different propagation impairments. Sun transit outage is one of the dominant sources of link outages. In order to provide high quality continuous communication, it is necessary to identify, predict and compensate sun outage along earth-satellites paths. In this paper, first of all, a model for predicting impacts of sun transit outage in LEO satellite communication systems is presented. Combined with ground communication terminals, the system carrier-to-noise ratio during sun transit period is analyzed. Furthermore, an adaptive modulation scheme based on CNR is discussed in order to improve throughput and bit-error-rate in satellite communication. Finally, a satellite communication system of Iridium constellation has been simulated, which veritably simulates the application of adaptive modulation under the environment of sun transit. A large number of simulation results of CNR and throughput are conformed to the theoretical analysis. It shows that the prediction of sun transit outage in this paper is reliable and adaptive modulation scheme for compensation is very valid.