Extending MAC-layer QoS from wired to wireless segments, and from single cell to multi-cell overlapping environment
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Internet services today, especially real-time ones, require at least the same level of Quality of Experience (QoE) over radio links, as that provided by the wired parts for which most of the IP-based multimedia applications were originally designed. This leads to a problem of service quality consistency across the radio and wired segments of the network. In order to provide satisfactory QoE, provision of underlying layer Quality of Service, QoS, for multimedia applications over networks has been a long-standing and critical topic, especially within the radio access segment of the next generation wireless/mobile environment. With the assistance of QoE and multimedia adaption at the application layers, QoS components, such as QoS framework and service differentiation mechanisms, are better defined at MAC and IP layers; It is where radio limitation is commonly defined by time slot/division, frequency, code division, sector, and direction gain etc. The problems of the QoS frameworks today vary from insufficient level of control, to scalability and complexity, as well as IP-mobility related problems. In the layer of medium access control (MAC), QoS fairness, especially in a highly loaded and/or overloaded system, is an issue in Contention Schemes for Service Differentiation. The shortcoming of efficiency (overhead and request collision) and complexity of polling schemes for Service Differentiation have also been observed. These two schemes would perform even worst in a multi-cell overlapping environment, rather than a single cell environment, without any central resources management. This thesis investigates QoS supports for wireless network. The primary goal is to design effective QoS mechanisms/framework, in the context of medium access control in WLAN 802.11, to ensure wireless connectivity for multimedia traffic. Firstly, we propose a hybrid architecture following the principles of Differentiated Service (DiffServ) model over the core part of the network, and the principles of Integrated Services (IntServ explicit control) model locally over the wireless access segment. We then present in detail an example solution consistent with the hybrid QoS architecture principles, with an admission control core of Fair Intelligent Congestion Control (FICC). Within the framework, we analysed contention and polling schemes as the candidates of service differentiation in the MAC layer, and based on these results, we found our proposed the Multi-cycle Polling mechanism can actually meet the QoS requirements. We finally draw our attentions on Service Differentiation Scheme in a Multi-cell Overlapping WLAN Environment. Due to widely use of WLAN almost in every smart-handset and notebook today and its shortcoming in spectrum efficiency and interference, the Co-existence/overlapping among WLAN themselves and other systems would become even more challenging. In fact, there is more and more serious interference incidents reported particularly in Metro transport systems in 2013. In this research, the graph colouring technique for grouping assignment is applied and the novel overlapping coordination scheme has been proved to effectively support QoS Service Differentiation in the interference environment. With the admission control core of FICC and the proposed Service Differentiation Schemes under the Hybrid framework, the wireless QoS issues have been well addressed for both single-cell and multi-cell environments.
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