Faculty of Mathematics and Natural Sciences, University of Oslo
Antall sider: 159
The thesis formulates effective strategies for delivery of streaming content for mobile users in resource-limited networks. We consider the entire end-to-end delivery path from the source to the destination. In the work, we take into account 1) the presence of a large number of mobile devices operating inside an area with overlapping coverage of several mobile networks; and 2) the ability of the mobile devices to exploit several network technologies and to be connected to different access points simultaneously. We aim to improve the performance of the whole system by jointly considering users’ requirements and network limitations and by identifying and implementing adaptation mechanisms for different parts of the delivery path. Taking into account the complexity of the whole system, the thesis aims to design mechanisms operating in a decentralized manner with partial knowledge of the system.
For this purpose, we study the ADIMUS architecture which addresses the problem of distributing streaming content for mobile users. The ADIMUS architecture clearly separates the system into two distinct parts: the backbone part of the network and the wireless part. We study resource adaptation mechanisms for both of these parts that include 1) overlay routing for the backbone and 2) multi-access approaches for heterogeneous wireless network. For overlay routing in the backbone, we consider multipath streaming techniques. For the wireless part, we improve the utilization of resources by intelligently redistributing mobile devices among the available wireless connections. To evaluate the adaptation mechanisms for both of these parts, we build mathematical models for the overlay network and for the heterogeneous wireless network. These mathematical models are used as upper bounds for operation of the adaptation solutions. We also define the lower bounds to these solutions based on earlier proposed solutions from the literature.
For the overlay network, we develop and evaluate a distributed rate-allocation algorithm
for delivery of video in a Video-on-Demand (VoD) system built upon multipath delivery. The algorithm’s operation is based on information collected by overlay nodes. The algorithm is evaluated in the OMNet++ simulation environment and analyzed against the aforementioned lower and upper bounds. We show that the algorithm performs close to the optimal solution in terms of proportionally fair bandwidth allocation between receivers of the overlay part of the architecture.
For the heterogeneous wireless network, we consider the network selection to use for multiuser environments with possible multicast configurations that allows the network to perform load balancing, improve the users’ overall QoS, and increase the throughput of the networks. The novelty of the proposed solutions is that the network selection is done in a decentralized manner with only limited information available to decision makers. The solutions are evaluated through multiple simulations. We show that the solutions provide a substantial improvement in performance compared to their lower bounds.
We also investigate a multiple connection approach for multicast groups with mobile terminals connecting to several networks simultaneously and receiving data through multiple paths. We show that the total usage of resources is reduced compared to a single path approach.