This dissertation addresses the problem of designing link layer protocolswhich are flexible enough to accommodate the demands offuture wirelesscommunication systems (FWCS).We show that entire link layer protocols withdiverse requirements and responsibilities can be composed out ofreconfigurable and reusable components.We demonstrate this by designing andimplementinga novel concept termed Flexible Link Layer (FLL)architecture.Through extensive simulations and practical experiments, weevaluate a prototype of the suggested architecture in bothfixed-spectrumand dynamic spectrum access (DSA) networks.FWCS are expected to overcome diverse challenges including the continualgrowthin traffic volume and number of connected devices.Furthermore, theyare envisioned to support a widerange of new application requirements andoperating conditions.Technology trends, including smart homes,communicating machines, and vehicularnetworks, will not only grow on ascale that once was unimaginable, they will also become the predominantcommunication paradigm, eventually surpassing today's human-producednetwork traffic.In order for this to become reality, today's systems have to evolve in manyways.They have to exploit allocated resources in a more efficient andenergy-conscious manner.In addition to that, new methods for spectrumaccess and resource sharingneed to be deployed.Having the diversificationof applications and network conditions in mind, flexibility at all layersof a communication system is of paramount importance in order to meet thedesired goals.However, traditional communication systems are often designed with specificand distinct applications in mind. Therefore, system designers can tailorcommunication systems according to fixedrequirements and operatingconditions, often resulting in highly optimized but inflexiblesystems.Among the core problems of such design is the mix of data transferand management aspects.Such a combination of concerns clearly hinders thereuse and extension of existing protocols.To overcome this problem, the key idea explored in this dissertation is acomponent-based design to facilitate the development of more flexible andversatile link layer protocols.Specifically, the FLL architecture,suggested in this dissertation, employs a generic, reconfigurable datatransfer protocol around which one or more complementary protocols, calledlink layer applications, are responsible for management-related aspects ofthe layer.To demonstrate the feasibility of the proposed approach, we have designedandimplemented a prototype of the FLL architecture on the basis ofareconfigurable software defined radio (SDR) testbed.Employing the SDRprototype as well as computer simulations, thisdissertation describesvarious experiments used to examine a range of link layerprotocols for bothfixed-spectrum and DSA networks.This dissertation firstly outlines the challenges faced by FWCSanddescribes DSA as a possible technology component for their construction.Itthen specifies the requirements for future DSA systemsthat provide thebasis for our further considerations.We then review the background on linklayer protocols, surveyrelated work on the construction of flexibleprotocol frameworks,and compare a range of actual link layer protocols andalgorithms.Based on the results of this analysis, we design, implement, andevaluatethe FLL architecture and a selection of actual link layerprotocols.We believe the findings of this dissertation add substantively to theexisting literature on link layer protocol design and are valuable fortheoreticians and experimentalists alike.
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