Modeling and Simulation of Media Access Protocols in Mobile Satellite Systems

Abstract

For the need of the mobile satellite system, this thesis studies how satellites are used for mobile communication, how satellite network constellation is designed to cover the globe and shows the advantages of Low Earth Orbits (LEOs) satellite systems above Medium Earth Orbits (MEOs) and Geostationary Earth Orbit (GEO) satellite systems especially for their good performance and well global coverage. Then the media access protocols objectives are discussed and the spread slotted Aloha access scheme is chosen to be simulated because it is the suitable access technique for the mobile satellite systems, because it suit for systems with large number of users and personal communication. The thesis comprises a Borland C++ simulation programs to study the performance of the spread slotted Aloha access scheme. The first simulation programs simulate the capacity of the uplink channel for a mobile satellite system model which uses the spread slotted Aloha access scheme, and another simulation programs to simulate the throughput of the spread slotted Aloha multiple access scheme for the same system model. The outcome of the simulation shows that the uplink channel capacity is a soft capacity because it depends on the interference level, as the interference level increases the capacity of the channel is decreases and vise versa. The interference level depends on the number of the users on the system and also depends on the user bit rate, as the bit rate increases the channel load factor increases then the channel soft capacity increases. The throughput of the spread slotted Aloha scheme increases as the number of the users on the system increases but also the interference level is increasing, and if the interference level reaches a threshold (which depends on the system multiple access capability) the throughput of the system begins to decrease. The performance of the spread slotted Aloha access scheme depends on the channel interference level and the parameters which affects the interference level.