Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Nano-satellites are mostly used in lower earth orbit applications, where communication
intervals are limited, often to a combined total of less than one hour per day. With these type
of inherent limitations of lower earth orbits, there are also the physical size and equipment
restriction of nano-satellites to consider, especially those of the CubeSat specification. It is
of critical importance to use the limited time and communication resources as effectively as
possible.
The network protocol has a huge influence on reliability and throughput of a satellite network.
An important requisite for designing, comparing and improving network protocols is
a network protocol simulator, that is able to envisage the design results. Simulation can
facilitate rapid development and unforeseen discoveries. Very little information is currently
available regarding communication protocols used in nano-satellites. This thesis aims to
explore and improve the current status of nano-satellite network simulation, as well as to
demonstrate the development of an improved communication protocol strategy.
It was found that there is a lack of proper simulation tools for satellite networks, which led
to the development of SatSim. SatSim is a discrete event network simulation tool, developed
in Python, which can be used to develop and analyse network protocols. SatSim was verified
by comparing simulation results with other published results, which made use of different
software tools and theoretical throughput calculations.
AX.25 is one of the most commonly used network protocols in the nano-satellite industry.
It was implemented in SatSim and verified with theoretical throughput calculations, as
no other simulation data on AX.25 was available. AX.25 was used as a baseline protocol
to improve upon. FX.25 was developed by the Stensat Group in an attempt to improve
AX.25. FX.25 adds forward error correction to AX.25, by wrapping additional data around
the AX.25 frames. This method maintains backward compatibility with AX.25. FX.25 was
implemented in SatSim and the simulation results proved that FX.25 was a more reliable
protocol than AX.25, as it can communicate at lower elevations and over noisier communication
channels. However, the drawback of the additional forward error correction is the
increased overhead, which reduces the overall payload data throughput.
A modular AX/FX.25 protocol was then implemented in SatSim, to exploit the strengths of
both protocols. This hybrid protocol yielded significant improvements to data throughput
and can enable future software defined radio or hardware developments. / AFRIKAANSE OPSOMMING: Nano-satelliete word hoofsaaklik gebruik in lae-aard wentelbaan toepassings waar kommunikasietyd
beperk is, soms tot minder as een uur per dag. Gepaardgaande met hierdie inherente
beperking van lae-aard wentelbane, is daar ook die verminderde omvang en kapasiteit
van nano-satelliete, veral ten opsigte van die CubeSat spesifikasie. Effektiewe aanwending
van die beperkte tyd en kommunikasie-hulpbronne is dus noodsaaklik.
Die keuse van netwerk protokol het ’n beduidende invloed op die betroubaarheid en data
deurset van ’n satelliet netwerk. ’n Belangrike voorvereiste vir die ontwerp, vergelyking
en verbetering van netwerk-protokolle, is ’n netwerk simulator. Beperkte inligting is tans
beskikbaar oor kommunikasie protokolle in nano-satelliet toepassings. Hierdie tesis fokus
op die verbetering van nano-satelliet netwerk-simulasie, asook die ontwikkelling van ’n verbeterde
netwerk-protokol strategie vir nano-satelliet toepassings.
Dit het na vore gekom dat daar ’n leemte is in die beskikbaarheid van simulasie sagteware
wat gerig is op die ondersoek van satelliet netwerke. Hierdie waarneming het die ontwikkeling
van SatSim genoop. SatSim is ’n diskrete-gebeurtenis netwerk-simulasie sagtewarepakket
wat in die Python programmeertaal ontwikkel is om netwerk protokolle te ontwikkel en te
analiseer. SatSim was geverifieer deur simulasies te vergelyk met die resultate van ander
navorsingspublikasies, wat van verskillende sagtewarepakkette gebruik gemaak het, sowel as
teoretiese deursetberekeninge.
AX.25 is een van die netwerk protokolle wat mees algemeen in die nano-satelliet bedryf
voorkom. AX.25 was geïmplementeer in SatSim en geverifieer met teoretiese deursetberekeninge.
AX.25 was gebruik as ’n grondslag om op te verbeter. FX.25 was ontwikkel
deur die Stensat Group in ’n poging om op AX.25 te verbeter. FX.25 voeg vorentoefoutkorreksie
by tot AX.25, deur addisionele data tot die AX.25 netwerk pakkies te voeg.
Hierdie benadering bewerkstellig agteruit-verenigbaarheid met AX.25. FX.25 was geïmplementeer
in SatSim en simulasieresultate dui daarop dat FX.25 ’n meer betroubare protokol
is as AX.25, omdat dit teen laer elevasiehoeke en oor swakker kommunikasiekanale kan
kommunikeer. Die verbeterde betroubaarheid is ten koste van datadeurset, as gevolg van
die toevoeging van die vorentoe-foutkorreksiedata.
’n Modulêre AX/FX.25 protokol was geïmplemeteer om te kapitaliseer op die sterk eienskappe
van beide protokolle. Hierdie hibriede protokol het ’n beduidende verbetering gelewer
ten opsigte van data deurset en kan toekomstige sagteware-gedefinieerde radio en hardewaretoepassings
stimuleer.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/96114 |
| Date | 12 1900 |
| Creators | Le Roux, Jan-Hielke |
| Contributors | Barnard, Arno, Wolhuter, R., Stellenbosch University. Faculty of Engineering. Department of Electrical and Electronic Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | xv, 103 p. : ill. |
| Rights | Stellenbosch University |
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