Characterization of wireless millimeter wave systems considering the impact of reflections and imperfect beam patterns

Communication on millimeter Wave (mm-Wave) frequencies is a key technology for next generation wireless networks. It allows multi-gigabit link speeds in highly crowded network scenarios, by leveraging directional communication. Due to quasi-optical propagation characteristics at mm- Wave frequencies, most works in scientific literature simplify directional links in that band to sharp-edged line of sight beams. However, measurements have identified certain objects to pose strong reflectors, rendering the former assumption unrealistic. This thesis, analyses the impact of reflections and beam side-lobes on mm-Wave networks and studies the resulting impact on interference and coverage. To this aim, reflections and side lobes of off-the-shelf 60 GHz systems are analyzed in an extensive measurement campaign to then verify the established assumptions on mm-Wave propagation. Further, this work analyzes the frame flow of the used protocols to extract the general communication behaviour of the off-the-shelf 60 GHz system.Ingeniería de Sistemas de Comunicacione

Measurement-Based Modeling of Wireless Propagation Channels - MIMO and UWB

Future wireless systems envision higher speeds and more reliable services but at the same time face challenges in terms of bandwidth being a limited resource. Two promising techniques that can provide an increased throughput without requiring additional bandwidth allocation are multiple-input multiple-output (MIMO) systems and ultra-wideband (UWB) systems. However, the performance of such systems is highly dependent on the properties of the wireless propagation channel, and an understanding of the channel is therefore crucial in the design of future wireless systems. Examples of such systems covered by this thesis are wireless personal area networks (papers I and II), vehicle-to-vehicle communications (paper III), board-to-board communications inside computers (paper IV) and sensor networks for industrial applications (paper V). Typically, channel models are used to evaluate the performance of different transmission and reception schemes. Channel modeling is the focus of this thesis, which contains a collection of papers that analyze and model the behavior of MIMO and UWB propagation channels. Paper I investigates the fading characteristics of wireless personal area networks (PANs), networks that typically involve human influence close to the antenna terminals. Based on extensive channel measurements using irregular antenna arrays, typical properties of PAN propagation channels are discussed and a model for the complete fading of a single link is presented. Paper II extends the model from paper I to a complete MIMO channel model. The paper combines the classical LOS model for MIMO with results from paper I by prescribing different fading statistics and mean power at the different antenna elements. The model is verified against measurement data and the paper also provides a parameterization for an example of a PAN scenario. Paper III presents a geometry-based stochastic MIMO model for vehicle-to-vehicle communications. The most important propagation effects are discussed based on the results from extensive channel measurements, and the modeling approach is motivated by the non-stationary behavior of such channels. The model distinguishes between diffuse contributions and those stemming from interaction with significant objects in the propagation channel, and the observed fading characteristics of the latter are stochastically accounted for in the model. Paper IV gives a characterization of UWB propagation channels inside desktop computer chassis. By studying measurement results from two different computers, it is concluded that the propagation channel only shows minor differences for different computers and positions within the chassis. It is also found out that the interference power produced by the computer is limited to certain subbands, suggesting that multiband UWB systems are more suitable for this type of applications. Paper V describes a UWB channel model based on the first UWB measurements in an industrial environment. Analyzing results from two different factory halls, it is concluded that energy arrives at the receiver in clusters, which motivates the use of a classical multi-cluster model to describe the channel impulse response. Parts of the results from this paper were also used as input to the channel model in the IEEE 802.15.4a UWB standardization work. In summary, the work within this thesis leads to an increased understanding of the behavior of wireless propagation channels for MIMO and UWB systems. By providing three detailed simulation models, two for MIMO and one for UWB, it can thus contribute to a more efficient design of the wireless communications systems of tomorrow

Information society and the state: the Greek version of the information society paradigm

The concept of the 'information society' has been systematically deployed to denote a new techno-socio-economic paradigm with information and communication technologies (ICTs) at the centre, which entails significant economic and social transformations and bears implications for governance and potential for development and quality of life. Departing from the deterministic view of information society as a set of uniform societal arrangements, the thesis examines its national variations, as they emerge from the interaction between ICTs and relevant policies with pre-existing social, political and economic realities. Drawing on a conceptual framework based on political economy and historical sociology, it proposes that the unfolding of any national information society is a contested process feeding on the historically formed relationship between the state and the national economy and society. This relationship is expected to inflect international policies and processes in quite idiosyncratic ways, leading to differentiated national information society trajectories, while the state is instrumental in articulating international policy directions with national societal arrangements. Identifying an empirical gap in the examination and analysis in semi-peripheral and middle-income countries, the thesis seeks to address evolving characteristics and dimensions of the 'Greek case' of information society, stressing the dialectic between European policy and the national socio-cultural, political and economic idiosyncrasies, the role of the Greek state, as well as the weaknesses encountered in the process. The emphasis is on the period 1998-2008, which includes the first comprehensive strategy and provides the opportunity to analyse preliminary results of the policies adopted. The empirical material includes relevant policy documents, quantitative indicators, personal observations, as well as a set of elite interviews with policymakers, ICT industry representatives and other actors involved in information society policies and processes

Towards Scalable Synchronization on Multi-Cores

The shift of commodity hardware from single- to multi-core processors in the early 2000s compelled software developers to take advantage of the available parallelism of multi-cores. Unfortunately, only few---so-called embarrassingly parallel---applications can leverage this available parallelism in a straightforward manner. The remaining---non-embarrassingly parallel---applications require that their processes coordinate their possibly interleaved executions to ensure overall correctness---they require synchronization. Synchronization is achieved by constraining or even prohibiting parallel execution. Thus, per Amdahl's law, synchronization limits software scalability. In this dissertation, we explore how to minimize the effects of synchronization on software scalability. We show that scalability of synchronization is mainly a property of the underlying hardware. This means that synchronization directly hampers the cross-platform performance portability of concurrent software. Nevertheless, we can achieve portability without sacrificing performance, by creating design patterns and abstractions, which implicitly leverage hardware details without exposing them to software developers. We first perform an exhaustive analysis of the performance behavior of synchronization on several modern platforms. This analysis clearly shows that the performance and scalability of synchronization are highly dependent on the characteristics of the underlying platform. We then focus on lock-based synchronization and analyze the energy/performance trade-offs of various waiting techniques. We show that the performance and the energy efficiency of locks go hand in hand on modern x86 multi-cores. This correlation is again due to the characteristics of the hardware that does not provide practical tools for reducing the power consumption of locks without sacrificing throughput. We then propose two approaches for developing portable and scalable concurrent software, hence hiding the limitations that the underlying multi-cores impose. First, we introduce OPTIK, a new practical design pattern for designing and implementing fast and scalable concurrent data structures. We illustrate the power of our OPTIK pattern by devising five new algorithms and by optimizing four state-of-the-art algorithms for linked lists, skip lists, hash tables, and queues. Second, we introduce MCTOP, a multi-core topology abstraction which includes low-level information, such as memory bandwidths. MCTOP enables developers to accurately and portably define high-level optimization policies. We illustrate several such policies through four examples, including automated backoff schemes for locks, and illustrate the performance and portability of these policies on five platforms