Advanced and novel random medium access techniques for satellite communications

This thesis addresses the development and usage of novel and advanced techniques for wireless Random Access (RA) to the medium in order to enable new types of applications going beyond the current use of Random Access channels for signalling purposes only. A prerequisite for allowing applications other than signalling to be transmitted over Random Access channels are Random Access schemes which can achieve a high bandwidth efficiency in terms of high throughput and very low packet loss ratios. In this thesis a new Random Access scheme, called Contention Resolution Diversity Aloha, based on Successive Interference Cancellation techniques, packet replication and asynchronous transmission is proposed which achieves these goals. Moreover, new access scheme extensions to existing Random Access schemes with Successive Interference Cancellation are proposed, which allow an increase of throughput and reduction of delay by applying the schemes in a different but more efficient way. Following this, the focus is put on the efficient use of Random Access with traditional Demand Assigned Multiple Access (DAMA) techniques. New DAMA Resource Allocation algorithms are presented in this thesis, which ensure an efficient and fair assignment of resources also in case of conflicting requests. With the definition of the DAMA and Random Access schemes, an architecture based on a set of new delay estimation algorithms and QoS data classification is defined, which integrates both DAMA and RA channels. It is shown that with the proposed architecture the overall throughput can be increased as well as the delay can be decreased. For ensuring reliable traffic delivery over the Random Access channels, the use of retransmission mechanisms is crucial. But since retransmission mechanisms also impact the stability of the RA channel, the impact on the stability needs to be analyzed for the new SIC based Random access schemes. In this thesis a mathematical framework based on Markov Chains is presented which allows the design, analysis and optimization of RA channels for stable operation, and the prediction of the average time before failure for unstable parameter settings. Finally all the aforementioned aspects of user data transmission over Random Access channels are combined in a real life use case, namely for the design of a communication system based on RA communication for safety critical aeronautical data exchange, which reduces transmission delay and increases the system efficiency.