The stupendous growth in wireless and mobile devices in the recent years has prompted researchers to look at innovative approaches that enable effective use of the available resources. In this thesis, we propose a medium access control (MAC) protocol, referred to as EM-MAC, that enables wireless devices with multi-channel access capabilities while minimizing energy consumption. EM-MAC relies on iMAC's efficient channel selection mechanism to resolve the medium contention on the common control channel, and to select the best available data channel for data communication. Our protocol saves energy by allowing devices that have not gained access to the medium to switch to doze mode until the channel becomes idle again. The pair of devices that gains access to the data channel reserves and uses the channel until the end of the reservation period. At the end of each reservation period, devices belonging to a given data channel contend again for the medium, and only the pair of devices that wins access to the medium is allowed to communicate on the channel while all other devices switch to doze mode. Using simulations, we show that EM-MAC yields substantial energy savings when compared with iMAC. / Graduation date: 2012

The work presents investigations into the development of a fuel-powered compact SMA actuator system. For the final SMA actuator, the K-alloy SMA strip (0.9 mm x 2.5 mm), actuated by a forced convection heat transfer mechanism, was embedded in a rectangular channel. In this channel, a rectangular piston, with a slot to accommodate the SMA strip, ran along the strip and was utilized to prevent mixing between the hot and the cold fluid in order to increase the energy density of the system. The fuel, such as propane, was utilized as main energy source in order to achieve high energy and power densities of the SMA actuator system. Numerical analysis was carried out to determine optimal channel geometry and to estimate maximum available force, strain and actuation frequency. Multi-channel combustor/heat exchanger and micro-tube heat exchanger were designed and tested to achieve high heat transfer rate and high compactness. The final SMA actuator system was composed of pumps, valves, bellows, multi-channel combustor/heat exchanger, micro-tube heat exchanger and control unit. The experimental tests of the final system resulted in 250 N force with 2 mm displacement and 1.0 Hz actuation frequency in closed-loop operation, in which the hot and the cold fluid were re-circulated by pumps.

Purpose/Aim: The aim of the paper is to find out if there is a correlation between playing MMORPGs and having better skills in using multi-channel communication. Material/Method: A media-skill test was conducted in the internet testing the participants’ ability to respond to targets in three different channels and media at the same time. The results of the study where used for statistical comparisons of the different groups of participants sorted according to their media use. Main results: People who use the internet more and who play computer games, especially MMORPGs, have a better Multi-Media Multi-Channel Communication Literacy. There is fast learning visible for people with a use of the respective medium of up to five hours a week. Playing makes you better, not playing a lot.

The work presents investigations into the development of a fuel-powered compact SMA actuator system. For the final SMA actuator, the K-alloy SMA strip (0.9 mm x 2.5 mm), actuated by a forced convection heat transfer mechanism, was embedded in a rectangular channel. In this channel, a rectangular piston, with a slot to accommodate the SMA strip, ran along the strip and was utilized to prevent mixing between the hot and the cold fluid in order to increase the energy density of the system. The fuel, such as propane, was utilized as main energy source in order to achieve high energy and power densities of the SMA actuator system. Numerical analysis was carried out to determine optimal channel geometry and to estimate maximum available force, strain and actuation frequency. Multi-channel combustor/heat exchanger and micro-tube heat exchanger were designed and tested to achieve high heat transfer rate and high compactness. The final SMA actuator system was composed of pumps, valves, bellows, multi-channel combustor/heat exchanger, micro-tube heat exchanger and control unit. The experimental tests of the final system resulted in 250 N force with 2 mm displacement and 1.0 Hz actuation frequency in closed-loop operation, in which the hot and the cold fluid were re-circulated by pumps.

A wireless channel is shared by all devices, in the vicinity, that are tuned to the channel, and at any given time, only one of the devices can transmit information. One way to overcome this limitation, in throughput capacity, is to use multiple orthogonal channels for different devices, that want to transmit information at the same time. In this work, we consider the use of multiple orthogonal channels in wireless data networks. We explore algorithms and protocols for such multi-channel wireless networks under two broad categories of network-wide and link-level challenges. Towards handling the network-wide issues, we consider the channel assignment and routing issues in multi-channel wireless networks. We study both single radio and multi-radio multi-channel networks. For single radio multi-channel networks, we propose a new granularity for channel assignment, that we refer to as component level channel assignment. The strategy is relatively simple, and is characterized by several impressive practical advantages. For multi-radio multi-channel networks, we propose a joint routing and channel assignment protocol, known as Lattice Routing. The protocol manages channels of the radios, for the different nodes in the network, using information about current channel conditions, and adapts itself to varying traffic patterns, in order to efficiently use the multiple channels. Through ns2 based simulations, we show how both the protocols outperform other existing protocols for multi-channel networks under different network environments. Towards handling the link-level challenges, we identify the practical challenges in achieving a high data-rate wireless link across two devices using multiple off-the-shelf wireless radios. Given that the IEEE 802.11 a/g standards define 3 orthogonal wi-fi channels in the 2.4GHz band and 12 orthogonal wi-fi channels in the 5GHz band, we answer the following question: ``can a pair of devices each equipped with 15 wi-fi radios use all the available orthogonal channels to achieve a high data-rate link operating at 600Mbps?' Surprisingly, we find through experimental evaluation that the actual observed performance when using all fifteen orthogonal channels between two devices is a mere 91Mbps. We identify the reasons behind the low performance and present Glia, a software only solution that effectively exercises all available radios. We prototype Glia and show using experimental evaluations that Glia helps achieve close to 600Mbps data-rate when using all possible wi-fi channels.

It is often required in communication and navigation systems to be able to receive signals from multiple stations simultaneously. A common practice to do this is to use multiple hardware resources; a different set of resources for each station. In this thesis, a Coherent Amplitude Modulated (AM) receiver system was developed based on Software Defined Radio (SDR) technology enabling reception of multiple signals using hardware resources needed only for one station. The receiver system architecture employs Time Division Multiplexing (TDM) to share the single hardware resource among multiple streams of data. The architecture is designed so that it can be minimally modified to support any number of stations. The Verilog Hardware Description Language (HDL) was used to capture the receiver system architecture and design. The design and architecture are initially validated using HDL post-synthesis and post-implementation simulation. In addition, the receiver system architecture and design were implemented to a Xilinx Field Programmable Gate Array (FPGA) technology prototyping board for experimental testing and final validation.

In the thesis, we address the fundamental problem of opportunistic spectrum access in a multi-channel communication system. Specifically, we consider a communication system in which a user has access to multiple channels, but is limited to sensing and transmitting only on one at a given time. We explore how the smart user should exploit past observations and the knowledge of the stochastic properties of these channels to maximize its transmission rate by switching channels opportunistically. Formally, we provide a generic analysis on the opportunistic spectrum access problem by casting the problem into the restless multi-armed bandit (RMAB) problem, one of the most well-known generalizations of the classic multi-armed bandit (MAB) problem, which is of fundamental importance in stochastic decision theory. Despite the significant research efforts in the field, the RMAB problem in its generic form still remains open. Until today, very little result is reported on the structure of the optimal policy. Obtaining the optimal policy for a general RMAB problem is often intractable due to the exponential computation complexity. Hence, a natural alternative is to seek a simple myopic policy maximizing the short-term reward. Therefore, we develop three axioms characterizing a family of functions which we refer to as regular functions, which are generic and practically important. We then establish the optimality of the myopic policy when the reward function can be expressed as a regular function and the discount factor is bounded by a closed-form threshold determined by the reward function. We also illustrate how the derived results, generic in nature, are applied to analyze a class of RMAB problems arising from multi-channel opportunistic access. Next, we further investigate the more challenging problem where the user has to decide the number of channels to sense in each slot in order to maximize its utility (e.g., throughput). After showing the exponential complexity of the problem, we develop a heuristic v-step look-ahead strategy. In the developed strategy, the parameter v allows to achieve a desired tradeoff between social efficiency and computation complexity. We demonstrate the benefits of the proposed strategy via numerical experiments on several typical settings.

The European Union (EU) is the most far-reaching attempt yet undertaken to institutionalize democratic policy-making beyond the nation-state. To what extent, and in what ways, do various channels of representation contribute towards the realization of this aim? This dissertation takes stock of current research on the EU’s system of representation, and seeks to expand its agenda so that this central question can be properly addressed. In contrast to prior empirical work in the field, the dissertation employs research designs that incorporate several forms of representation into a unified evaluative framework. This multi-channel approach to political representation paves the way for a systematic comparison of how different forms of representation (electoral, territorial and corporate) perform in the EU context. It also makes possible an empirical assessment of a key proposition in current representation theory: that elections, in large and heterogeneous political systems, are outperformed by other forms of representation. The three articles in the dissertation draw on existing cross-country data, interviews with policy-makers and a new dataset collected by the author. They scrutinize representation in three principal channels: electoral representation in the European Parliament, government representation in the preparatory bodies of the Council of Ministers, and representation through organized interests that seek to influence EU policy. The first article examines the balance of power that has emerged between these three channels of representation in the EU’s legislative process, and how the current balance is likely to affect the Union’s legitimacy. The second article investigates how different channels of representation perform in terms of providing linkage between Brussels-based representatives and their domestic principals. The third article examines the extent to which different channels of representation contribute to the coordination of EU policy-making domestically, at the European level, and across the two levels of government. Finally, this dissertation makes a methodological contribution by applying social network analysis (SNA) to classic problems of representation within and across different channels of representation. This approach is novel to the field. Researchers should be able to exploit SNA and relational data fruitfully in the future, in the study of representational relationships in the EU and numerous other contexts.

The increasing interest for immersive experiences in areas such as augmented and virtual reality makes high quality 3D sound more important than ever before. A technique for capturing and rendering 3D audio which has received more attention during the last twenty years are Higher Order Ambisonics (HOA). Higher Order Ambisonics is a scene based audio format which has a lot of advantages compared to other standard formats. Hovever, one problem with HOA is that it requires a lot of bandwidth. For example, sending an uncoded high quality HOA signal requires 49 channels to be transmitted at the same time which requires a bandwidth of about 40 Mbps. A lot of effort has been made in the last ten years on coding HOA signals. In this thesis, two different approaches are taken on coding HOA signals. In one approach, called Sound Field Rotation (SFR) in this thesis, the microphone that records the sound field is virtually rotated to see if it is possible to make some of the channels zero. The second approach, called Sound Field Decomposition (SFD) in this thesis, use Principal component analysis to decompose a sound field into a foreground and background component. The Sound Field Decomposition approach is inspired by the emerging MPEG-H 3D Audio standard for coding HOA signals. The result shows that the Sound Field Rotation method only works for very simple sound scenes. It has also been shown that a 49 channels HOA signal can be reduced to as little as 7 channels if the sound scene consists of a point source. The Sound Field Deomposition method worked for more complex sound scenes. It was shown that a MPEG similar system could be improved. Result from MUSHRA (Multiple stimuli with hidden reference and anchor) listening tests showed that an improved MPEG similar system reached a MUSHRA score about 78 while the MPEG similar system reached 55 at a bitrate of 256 kbps. Without coding each monochannels with the 3GPP EVS (Enhanced voice services) codec, the improved MPEG similar system reached the MUSHRA score 85. At 256 kbps, the improved MPEG similar system coded the HOA signal into six channels instead of 49 for the uncoded signal. From objective results, it was shown that the improved MPEG similar system had largest effect at low bitrates.

This portfolio of compositions investigates the adaptation of state-space models, frequently used in engineering control theory, to the electroacoustic composition context. These models are mathematical descriptions of physical systems that provide several variables representing the system’s behaviours. The composer adapts a set of state-space models of either abstract, mechanical or electrical systems to a music creation environment. She uses them in eight compositions: five mixed media multi-channel pieces and three mixed media pieces. In the portfolio, the composer investigates multiple ways of meaningfully mapping these system’s behaviours into music parameters. This is done either by exploring and creating timbre in synthetic sound, or by transforming existing sounds. The research also involves the process of incorporating state-space models as a real-time software tool using Max and SuperCollider. As real-time models offer several variables of continuous evolutions, the composer mapped them to different dimensions of sound simultaneously. The composer represented the model’s evolutions with either short/interrupted, long or indefinitely evolving sounds. The evolution implies changes in timbre, length and dynamic range. The composer creates gestures, textures and spaces based on the model’s behaviours. The composer explores how the model’s nature influences the musical language and the integration of these with other music sources such as recordings or musical instruments. As the models represent physical processes, the composer observes that the resulting sounds evolve in organic ways. Moreover, the composer not only sonifies the real-time models, but actually excites them to cause changes. The composer develops a compositional methodology which involves interacting with the models while observing/designing changes in sound. In that sense, the composer regards real-time state-space models as her own instruments to create music. The models are regarded as additional forces and as sound transforming agents in mixed media pieces. In fixed media pieces, the composer additionally exploits their linearity to create space through sound de-correlation.