This thesis describes the in-orbit measurements, design and simulation of error-control strategies and channel modelling for low-Earth orbiting satellites, specifically in a restrictive small satellite platform. The motivation to pursue such a direction is the quest to optimise the low-Earth orbit (LEO) satellite communication link. Until a few years ago, advanced designs for satellite communications systems had focused on conventional geostationary Earth orbit (GEO) communication technologies which are not necessarily tailored to the LEO environment. Such sub-optimal designs were accommodated by the typical application of LEO satellites - remote sensing satellites - normally being large satellites equipped with huge parabolic dishes. With the recent rapid development in numerous LEO satellite constellations and trend in the satellite industry towards smaller and affordable satelhtes, the prominence of satellites in LEO cannot be ignored and it has become crucial to efficiently utilise the communications link. Until now, a suitable channel model for low-Earth orbit satellites has not existed. In order to provide a viable satellite network, a proper knowledge of the dynamic characteristics of the link is essential. A UHF measurement campaign from the UoSAT -3 microsatellite in LEO was therefore undertaken and analysis of the error statistics provides unique information on the channel behaviour for a broad range of elevation angles. The thesis has investigated generative Markov models as a means of representing the observed error statistics and established that the LEO satellite channel can be accurately described by a multiple-good-state, one-error state Fritchman model, or a four-state Markov model under special circumstances which are outlined. Various error control strategies have been evaluated based on the in-orbit measured data and proposed channel models, therefore verifying the precision of the Fritchman and four-state Markov models. During the course of this work, two schemes comprising type-II hybrid-ARQ based on punctured Reed Solomon codes and byte interleaving were investigated and the tradeoffs were identified. A novel type-II + delay hybrid protocol has been proposed and has been demonstrated to provide further increases in throughput performance. The principal conclusion from this thesis is that, using the results of the measurement campaign with an in-orbit satellite, it has been possible to generate a realistic fading model for use in future planning for LEO satellite systems. Furthermore, the type-II, type-II+delay hybrid and byte interleaving techniques are shown to provide an improvement in throughput performance of the existing store-andforward communications protocol with varying tradeoffs between the techniques.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:484228 |
| Date | January 2000 |
| Creators | Chu, Valerie Yee Yong |
| Publisher | University of Surrey |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://epubs.surrey.ac.uk/774242/ |
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