Quality-of-Service provision for satellite systems implementing adaptive physical layer

Abstract

Wireless communications have always been characterised by the challenge of fully exploiting the channel capacity limits. In the past, it was usually necessary to reach a compromise between spectral efficiency and service availability. New developments in wireless technology provide a breakthrough performance since complexity is introduced as a new degree of freedom in the classical spectral efficiency versus service availability compromise. New wireless communication systems provide Fade Mitigation Techniques (FMT) that allow for the transmission to constantly adapt itself to the channel conditions. DVB-S2 is the standard for second-generation specification for satellite broadcasting and it makes normative the use of Adaptive Coding and Modulation (ACM) as a FMT for interactive applications, hence implementing an Adaptive Physical Layer. The channel conditions must be reported by interactive terminals in order to implement the adaptability to the channel conditions. The introduction of an Adaptive Physical Layer creates an impact in the entire system design due to the fact that capacity is no longer constant, but rather time-and-location dependent. The basic assumption of having a constant capacity was a fundamental postulation in the classical communications systems design, based on a communications stack with a set of layers. Hence, the complexity of an Adaptive Physical Layer system is not limited to the physical layer but it affects other layers and the entire system in general. The work towards the PhD was focused on one broad subject and in the development of a unified framework in order to study and address this subject. The subject was QoS provision for Adaptive Physical Layer systems, with special focus on broadband satellite systems. The subject of QoS provision is considered a multi-layer problem and current approaches for fixed capacity systems already provide solutions based on this perspective. The unified framework, which was developed to address the QoS provision subject, integrates two apparently disjoint fields. The first is cross-layer design, which is a new approach for addressing layer inter-dependency without breaking the communications stack structure. This approach allows for the development of techniques and methodologies for optimising the inter-dependent layers, which is especially important for addressing the challenges introduced by the inherent variability of Adaptive Physical Layer systems. The second is game theory, which is a branch of applied mathematics with roots in economics although with applications in many other areas including communication systems and networks. More than a set of tools, game theory provides a mindset for optimising multi-objective problems by translating them into multi-player games. Afterwards, these can easily be solved within game theory and the solution set can be translated back into algorithms and techniques to be applied in the communications system. This final step brings together both different fields, since addressing an Adaptive Physical Layer problem with game theory results in a solution that requires cross-layer design in its system implementation. The work towards the PhD was developed within the scope of different projects, some of which were quite relevant in terms of dimensions and available resources. This allowed for an in-depth testing and validation of techniques, methodologies and architectures that were developed to address the challenge of providing QoS over broadband satellite systems implementing an Adaptive Physical Layer. Furthermore, cross-validation was applied at every level, which means that the tools developed within the unified framework were validated in terms of theoretical, event-driven simulation and real-time emulation.