Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Stellenbosch University and the Katholieke Universiteit Leuven has a joint undertaking
to develop a satellite communications payload. The goals of the project are:
to undertake research and expand knowledge in the area of dynamically configurable
antenna beam forming, to prove the viability of this research for space purposes and
to demonstrate the feasibility of the development in a practical application.
The practical application is low Earth orbit satellite communication system for
applications in remote monitoring. Sensor data will be uploaded to the satellite,
stored and forwarded to a central processing ground station as the satellite passes
over these ground stations. The system will utilise many low-cost ground sensor
stations to collect data and distribute it to high-end ground stations for processing.
Applications of remote monitoring systems are maritime- and climate change
monitoring- and tracking. Climate change monitoring allows inter alia, for the monitoring
of the effects and causes of global warming.
The Katholieke Universiteit Leuven is developing a steerable antenna to be
mounted on the satellite. Stellenbosch University is developing the communications
payload to steer and use the antenna. The development of the communications
protocol stack is part of the project. The focus of this work is to implement the
application layer protocol, which handles all file level communications and also implements
the communications strategy.
The application layer protocol is called the Satellite Communications Software
System (SCSS). It handles all high level requests from ground stations, including
requests to store data, download data, download log files and upload configuration
information. The design is based on a client-server model, with a Station Server
and Station Handler. The Station Server schedules ground stations for communication
and creates a Station Handler for each ground station to handle all ground
station requests. During the design, all file formats were defined for efficient ground
station-satellite communications and system administration. All valid ground station
requests and handler responses were also defined.
It was also found that the system may be made more efficient by scheduling
ground stations for communications, rather than polling each ground station until
one responds. To be able to schedule ground station communications, the times
when ground stations will come into view of the satellite have to be predicted. This
is done by calculating the positions of the Satellite and ground stations as functions
of time. A simple orbit propagator was developed to predict the satellite distance
and to ease testing and integration with the communications system. The times
when a ground station will be within range of the satellite were then predicted and a
scheduling algorithm developed to minimise the number of ground stations not able to communicate.
All systems were implemented and tested. The SCSS executing on the Satellite
was developed and tested on the satellite on-board computer. Embedded implementations
possess strict resource limitations, which were taken into account during the
development process. The SCSS is a multi-threaded system that makes use of thread
cancellation to improve responsiveness. / AFRIKAANSE OPSOMMING: Die Universiteit van Stellenbosch ontwerp tans ’n satelliet kommunikasieloonvrag in
samewerking met die Katolieke Universiteit van Leuven. Die doel van die projek is
om navorsing te doen oor die lewensvatbaarheid van dinamies verstelbare antenna
bundelvorming vir ruimte toepassings, asook om die haalbaarheid van hierdie navorsing
in die praktyk te demonstreer.
Die praktiese toepassing is ’n satellietkommunikasiestelsel vir afstandsmonitering,
wat in ’n Lae-Aarde wentelbaan verkeer. Soos die satelliet in sy wentelbaan beweeg,
sal sensor data na die satelliet toe gestuur, gestoor en weer aangestuur word. Die
stelsel gebruik goedkoop sensorgrondstasies om data te versamel en aan te stuur na
kragtiger grondstasies vir verwerking.
Afstandsmoniteringstelsels kan gebruik word om klimaatsverandering, sowel as
die posisie van skepe en voertuie, te monitor. Deur oa. klimaatsveranderinge te
dokumenteer, kan gevolge en oorsake van globale verhitting gemonitor word.
Die Katholieke Universiteit van Leuven is verantwoordelik vir die ontwerp en
vervaardiging van die satelliet antenna, terwyl die Universiteit van Stellenbosch verantwoordelik
is vir die ontwerp en bou van die kommunikasie loonvrag. ’n Gedeelte
van hierdie ontwikkeling sluit die ontwerp en implementasie van al die protokolle van
die kommunikasieprotokolstapel in. Dit fokus op die toepassingsvlak protokol van die
protokolstapel, wat alle leêrvlak kommunikasie hanteer en die kommunikasiestrategie
implementeer.
Die toepassingsvlaksagteware word die Satellietkommunikasie sagtewarestelsel
(SKSS) genoem. Die SKSS is daarvoor verantwoordelik om alle navrae vanaf grondstasies
te hanteer. Hierdie navrae sluit die oplaai en stoor van data, die aflaai van
data, die aflaai van logs en die oplaai van konfigurasie inligting in. Die ontwerp
is op die standaard kliënt-bediener model gebasseer, met ’n stasiebediener en ’n
stasiehanteerder. Die stasiebediener skeduleer die tye wanneer grondstasies toegelaat
sal word om te kommunikeer en skep stasiehanteerders om alle navrae vanaf die
stasies te hanteer. Gedurende die ontwerp is alle leêrformate gedefinieer om doeltreffende
adminstrasie van die stelsel, asook kommunikasie tussen grondstasies en die
satelliet te ondersteun. Alle geldige boodskappe tussen die satelliet en grondstasies
is ook gedefnieer.
Daar is gevind dat die doeltreffendheid van die stelsel verhoog kan word deur die
grondstasies wat wil kommunikeer te skeduleer, eerder as om alle stasies te pols totdat
een reageer. Om so ’n skedule op te stel, moet die tye wanneer grondstasies binne
bereik van die satelliet gaan wees voorspel word. Hierdie voorspelling is gedoen deur
die posisies van die satelliet en die grondstasies as funksies van tyd te voorspel. ’n
Eenvoudige satelliet posisievoorspeller is ontwikkel om toetsing en integrasie met die SKSS te vergemaklik. ’n Skeduleringsalgoritme is toe ontwikkel om die hoeveelheid
grondstasies wat nie toegelaat word om te kommunikeer nie, te minimeer.
Alle stelsels is geimplementeer en getoets. Die SKSS, wat op die satelliet loop,
is ontwikkel en getoets op die satelliet se aanboord rekenaar. Die feit dat ingebedde
stelsels oor baie min hulpbronne beskik, is in aanmerking geneem gedurende die
ontwikkeling en implementasie van die SKSS. Angesien die SKSS ’n multidraadverwerkingsstelsel
is, word daar van draadkansellasie gebruik gemaak om die stelsel se
reaksietyd te verbeter.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/4152 |
| Date | 03 1900 |
| Creators | Gilmore, John Sebastian |
| Contributors | Wolhuter, R., University of Stellenbosch. Faculty of Engineering. Dept. of Electrical and Electronic Engineering. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 109 p. : ill. |
| Rights | University of Stellenbosch |
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