AbstractThe growth of satellite communication industry and the need to offer new and better services, to compete with optical fiber systems, have driven the satellite industry to search for higher bandwidth and improved cost of services. Higher frequency bands, such as Ka and V-band, came into play. These frequency bands have the advantage of efficient use of spectrum, the ability to transfer data at much higher rates, and the use of smaller antennas resulting in lower cost for the user. A major drawback though, is the severity of propagation impairments. Scintillation becomes important for low-fade margin systems operating at high frequencies and with low elevation angles and therefore must be taken into account in the design of satellite communication systems.
The first part of the thesis deals with the analysis of beacon data and presentation of various statistics, namely short and long-term distributions of scintillation amplitudes and intensity. Their correlations with meteorological parameters are also presented. A dynamic model of tropospheric scintillation is developed, which permits the generation of scintillation time series based on known scintillation characteristics, such as spectral shape and probability density function. The model employs readily obtainable input parameters (antenna diameter, path elevation angle, frequency, ground temperature and humidity) and yields statistics that compare extremely well with existing prediction models as well as measured scintillation data (up to the fourth moment). Important applications of the new model are for simulating the performance of scintillation-degraded communication links and predicting required scintillation fade margins.
The second part of the thesis investigates the effects of scintillation on digital satellite communication systems using simulations implemented in COSSAP. Simulation results show that the higher the order of the modulation that is being used, the larger is the effect of scintillation on the bit error rate performance of the link.
In the third part of the thesis, fade mitigation techniques to overcome the effects of scintillation fading are discussed. Analysis of an adaptive modulation system using three modulation techniques is presented and its advantages demonstrated. The adaptive system can be used to mitigate scintillation fading and at the same time increase the capacity of the system, decreasing system outage time through an efficient utilisation of available resources.
In the last part, data transfer scenarios in VSAT systems incorporating adaptive modulation, ARQ and adaptive up-link power control are presented. The implementation of the adaptive system in a COSSAP simulation platform is discussed and individual adaptive components are simulated and presented in detail.
|Date of Award
- Artificial satellites in telecommunication