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The Lite (Light) satellite for the study of B-mode polarization and Inflation from cosmic background Radiation Detection (LiteBIRD) is a Japan Aerospace Exploration Agency (JAXA)-led Strategic Large-Class mission designed to search for the existence of the primordial gravitational waves produced during the inflationary phase of the early Universe, through the measurement of their imprint onto the polarization of the Cosmic Microwave Background (CMB). It is an international collaboration, with European Union (EU) operations being coordinated by France. A short study on the merits of 2-dimensional versus 3-dimensional elements in the Finite Element Model (FEM) meshing of basic plates and beams was performed as well as the analysis of two different methods of representing threaded connections in FEM models. Both these activities were in service of the creation of a FEM model of the structure of the contribution of the EU to LiteBIRD: the Medium-High-Frequency Telescope (MHFT). All analysis was done using the Siemens NX software and the Simcenter Nastran solver. This model has passed preliminary quality checks and will be used for future structural analysis intended to verify the integrity of the design, its compliance with JAXA requirements, and to perform screw dimensioning. The results of those analyses will inform possible future design changes or will support the current design. Logistical work on the project was also performed, consisting of the groundwork to initiate an Assembly, Integration and Testing (AIT) plan and an Assembly, Integration and Verification (AIV) plan. This primarily involved the creation of a Model Definition Document, which contained clear and complete descriptions of the different MHFT models to be used throughout project development. The document defines the purpose and components of the models, the dependencies between models, as well as the necessary tests to be performed on each as part of the AIT and AIV process. A list of the structure interfaces was also created, which will contribute to the development of an interface control document.

The expectation for ever-present broadband connectivity is growing along with the proliferation of "always-on" mobile devices such as PDAs, laptops and cell phones. The International Telecommunications Union predicts people worldwide will soon live in "ubiquitous network societies," where interconnected appliances and devices provide relevant content and information whatever the location of the user. While some public spaces currently offer wireless internet, broadband subscribers typically lose guaranteed connections each time they leave their access points. One increasingly popular solution, shared broadband signals, relies on a model of peer-to-peer networking. Instead of information passing from "one to many," it may travel from "many to many." This form of viral networking is taking hold at the grassroots level of media activism, as well as within the elite realm of venture capitalism. This study encompasses both semi-structured qualitative interviews and a survey in order to gain a deeper understanding of a complex phenomenon: the potential for peer-to-peer signal sharing to expand digital inclusion in the United States. The research approaches WiFi signal sharing as more than a promising "last mile" technology. Rather, it finds that WiFi sharing communities have the potential to disrupt the current political economy of telecommunications by privileging digital inclusion, innovation and localism over profits and globalization. This research extends knowledge by delving into the demand-side of the peer networking movement as a means of better understanding potential pathways to connectivity. The interview findings reflect the perspectives of people who opt to share their WiFi signals, policymakers, incumbent ISPs, and both non-profit and for-profit entities that facilitate peer-to-peer networking. Local officials stressed the need for wireless community activists to work with residents of disenfranchised neighborhoods, who stand to benefit the most from free broadband access. Federal-level informants suggested that high quality spectrum--so called "white spaces"--could enable peer-to-peer networks to transmit more powerful WiFi signals. Responses to a questionnaire disseminated to mesh network members suggest that these grassroots communities facilitate public participation in technology, as well as encourage civic engagement. The study concludes with recommendations--geared toward federal policymakers, local officials, ISPs and broadband activists--for supporting and sustaining peer-to-peer networking communities. / Mass Media and Communication

This thesis studies multicasting high bandwidth media traffic in wireless mesh networks (WMNs). Traditional multicast methods use a single multicast tree to reach all destinations, and adapt the multicast rate to the destination with the worst path quality. This approach does not fully utilize the network resources nor distinguish the quality of service (QoS) requirements of different users. It also penalizes the users having better path quality and requiring higher QoS. In multi-hop transmissions, the end-to-end transmission rate is limited by the link with the worst transmission conditions. This makes it difficult to multicast high-bandwidth media traffic with good quality. Using multiple description coding (MDC), the source traffic can be split into multiple sub-streams, referred to as descriptions, each of which requires a much lower bandwidth and can be transmitted along separate paths. In this thesis, we study routing and QoS provisioning jointly for multicasting multiple description (MD) encoded media traffic in WMNs. Routing for the multiple descriptions is jointly studied, while considering the channel quality of different links in the network and QoS at individual destinations. The work in this thesis is divided into two parts. The first part (Chapters 3 and 4) considers balanced descriptions, each of which contributes equally to the quality of the recovered media at a destination, and we study the problem of power efficient multicasting for the MD-encoded media traffic in WMNs. In Chapter 3, single-hop transmissions are considered. That is, the access points (APs) that store the source traffic communicate with the destination nodes directly. We study two problems jointly, description assignments and power allocations. The former is to assign a description for each AP to transmit, and the latter is to allocate the transmission power for the APs. Different power efficiency objectives are considered, subject to satisfying the QoS requirements of the destination nodes. For each objective, an optimization problem is formulated and heuristic solutions are proposed. Chapter 4 extends the work to multi-hop transmissions, where relay stations (RSs) are available to forward the traffic from the APs to the destinations. We consider two different routing structures based on whether an RS is allowed to forward more than one description. The objective is to minimize the total transmission power of the APs and the RSs in the network, subject to the QoS requirements of the destinations. An optimum problem is formulated and then translated to an integer and linear programming problem, and a centralized scheme with much lower complexity is proposed. Following that, a distributed scheme, referred to as minimum weight k-path scheme, is proposed, which builds one multicast tree for each description. By permitting only neighboring nodes to exchange related information, the scheme allows each node to find its best parent node based on the additional transmission power needed to establish the link. The second part (Chapter 5) of the thesis considers unbalanced descriptions. Routing for the multiple descriptions is jointly considered with application layer performance, so that the maximum distortion of recovered media at the destinations is minimized. An optimization problem is first formulated, and a centralized scheme with lower complexity is proposed. The centralized scheme first finds a set of candidate paths for each destination based on a predefined set of criteria, then it iteratively expands the multicast trees by only merging the paths that minimize the maximum distortion for all destinations. A distributed scheme is also proposed by modifying the minimum weight k-path scheme. In the modified scheme, each RS makes a local decision to join different multicast trees based on the expected distortion among its connected downstream nodes. The proposed multicasting schemes require much lower implementation complexity, compared to the optimum solutions. The centralized scheme is more suitable for small size networks, and achieves close-to-optimum performance for a wide range of parameter settings. The distributed scheme only requires neighboring nodes to exchange information, and can be implemented to networks with a relatively large number of APs, RSs, and destination nodes. / Thesis / Doctor of Philosophy (PhD)