Development of a satellite communications software system and scheduling strategy

Gilmore, John Sebastian (2010-03)

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010.

Thesis

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.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/4152
This item appears in the following collections: