Adaptation, optimisation and simulation of the CSMA/CA protocol for a low earth orbit satellite UHF link

[摘要] A low earth orbit satellite is to provide the telecommunications link to facilitate emailservices to rural areas, where the infrastructure necessary for e-mail is lacking(e.g. no telephone lines). Communication time with this satellite from any particularpoint on the ground is less than one hour per day. It is thus of utmost importanceto maximise the data throughput rate for the system.The contribution of this thesis is to improve the performance of CSMA/CA byadapting and optimising it for the above application. This improved protocol isused to regulate data flow through the system. Specific attention is given to thecomparison of various random variable distributions for use as the back-off randomvariable.Two pieces of software are further contributed. First, a set of MATLAB scriptswhich are used for comparing various back-off random variable distributions andoptimising each of these distributions. Secondly, an extensive (more than 2500 linesof code) OMNeT++ simulation of the improved CSMA/CA protocol, complete withMATLAB scripts for setting up multiple simulation runs and plotting the results.Both pieces of software accept the system constraints as parameters, and are thuseasily adaptable for a similar system which may use the same protocol, but hasdifferent parameters.It is concluded that the set of MATLAB scripts are a fairly accurate tool foroptimising throughput, as is confirmed by the OMNeT++ simulations, and thatOMNeT++ has merit for simulating the given type of system and protocol.

[发布机构] Stellenbosch University