A Radio Link Quality Model and Simulation Framework for Improving the Design of Embedded Wireless Systems

Despite the increasing application of embedded wireless systems, developers face numerous challenges during the design phase of the application life cycle. One of the critical challenges is ensuring performance reliability with respect to radio link quality. Specifically, embedded links experience exaggerated link quality variation, which results in undesirable wireless performance characteristics. Unfortunately, the resulting post-deployment behaviors often necessitate network redeployment. Another challenge is recovering from faults that commonly occur in embedded wireless systems, including node failure and state corruption. Self-stabilizing algorithms can provide recovery in the presence of such faults. These algorithms guarantee the eventual satisfaction of a given state legitimacy predicate regardless of the initial state of the network. Their practical behavior is often different from theoretical analyses. Unfortunately, there is little tool support for facilitating the experimental analysis of self-stabilizing systems. We present two contributions to support the design phase of embedded wireless system development. First, we provide two empirical models that predict radio-link quality within specific deployment environments. These models predict link performance as a function of inter-node distance and radio power level. The models are culled from extensive experimentation in open grass field and dense forest environments using all radio power levels and covering up to the maximum distances reachable by the radio. Second, we provide a simulation framework for simulating self-stabilizing algorithms. The framework provides three feature extensions: (i) fault injection to study algorithm behavior under various fault scenarios, (ii) automated detection of non-stabilizing behavior; and (iii) integration of the link quality models described above. Our contributions aim at avoiding problems that could result in the need for network redeployment

A PROTOCOL SUITE FOR WIRELESS PERSONAL AREA NETWORKS

A Wireless Personal Area Network (WPAN) is an ad hoc network that consists of devices that surround an individual or an object. Bluetooth® technology is especially suitable for formation of WPANs due to the pervasiveness of devices with Bluetooth® chipsets, its operation in the unlicensed Industrial, Scientific, Medical (ISM) frequency band, and its interference resilience. Bluetooth® technology has great potential to become the de facto standard for communication between heterogeneous devices in WPANs. The piconet, which is the basic Bluetooth® networking unit, utilizes a Master/Slave (MS) configuration that permits only a single master and up to seven active slave devices. This structure limitation prevents Bluetooth® devices from directly participating in larger Mobile Ad Hoc Networks (MANETs) and Wireless Personal Area Networks (WPANs). In order to build larger Bluetooth® topologies, called scatternets, individual piconets must be interconnected. Since each piconet has a unique frequency hopping sequence, piconet interconnections are done by allowing some nodes, called bridges, to participate in more than one piconet. These bridge nodes divide their time between piconets by switching between Frequency Hopping (FH) channels and synchronizing to the piconet\u27s master. In this dissertation we address scatternet formation, routing, and security to make Bluetooth® scatternet communication feasible. We define criteria for efficient scatternet topologies, describe characteristics of different scatternet topology models as well as compare and contrast their properties, classify existing scatternet formation approaches based on the aforementioned models, and propose a distributed scatternet formation algorithm that efficiently forms a scatternet topology and is resilient to node failures. We propose a hybrid routing algorithm, using a bridge link agnostic approach, that provides on-demand discovery of destination devices by their address or by the services that devices provide to their peers, by extending the Service Discovery Protocol (SDP) to scatternets. We also propose a link level security scheme that provides secure communication between adjacent piconet masters, within what we call an Extended Scatternet Neighborhood (ESN)

Reducing Communication Delay Variability for a Group of Robots

A novel architecture is presented for reducing communication delay variability for a group of robots. This architecture relies on using three components: a microprocessor architecture that allows deterministic real-time tasks; an event-based communication protocol in which nodes transmit in a TDMA fashion, without the need of global clock synchronization techniques; and a novel communication scheme that enables deterministic communications by allowing senders to transmit without regard for the state of the medium or coordination with other senders, and receivers can tease apart messages sent simultaneously with a high probability of success. This approach compared to others, allows simultaneous communications without regard for the state of the transmission medium, it allows deterministic communications, and it enables ordered communications that can be a applied in a team of robots. Simulations and experimental results are also included

First, the Bad News: Opposition Media in Authoritarian Regimes

Why do dictatorships sometimes allow opposition groups to publish media, but at other times forbid opposition media? I propose a theory that dictators tolerate opposition media selectively in order to limit protests. I formalize the theory in a signaling model, from which I derive several testable empirical implications. I illustrate the logic of the theory with a case study of the Ben Ali dictatorship in Tunisia during its first five years (1987-1992), based in part on interviews I carried out in Tunisia. I show how the theory explains variation in Ben Ali's willingness to allow opposition media, across both time and opposition groups. To test the implications of the model quantitatively, I construct a panel dataset on ten Arab countries with authoritarian regimes during 1992-2017. The data measure which regimes allowed opposition groups to produce media in which years and are based on my research on a wide range of opposition groups (of various ideologies and legal statuses) and of media (including newspapers, websites, and TV channels).I find that dictators allow opposition media when their regimes are most likely to survive an uprising, in order to signal their strength to citizens and discourage them from protesting. In particular, in years when authoritarian regimes experience strong economic performance – including low unemployment, high economic growth, and plentiful revenue from oil and natural gas – they are far more likely to permit opposition media. After the "Arab Spring" uprisings of 2011 revealed that the region's authoritarian regimes were more vulnerable to mass unrest than they previously appeared, those regimes became much less likely to tolerate opposition media. By advancing a new theory and analyzing original empirical evidence, this study contributes to our understanding of why media freedom varies in authoritarian regimes

Design and evaluation of safety-critical applications based on inter-vehicle communication

Inter-vehicle communication has a potential to improve road traffic safety and efficiency. Technical feasibility of communication between vehicles has been extensively studied, but due to the scarcity of application-level research, communication\u27s impact on the road traffic is still unclear. This thesis addresses this uncertainty by designing and evaluating two fail-safe applications, namely, Rear-End Collision Avoidance and Virtual Traffic Lights

Who trusts Berlusconi? An econometric analysis of the role of television in the political arena

This paper contributes to the literature by carrying out the first econometric investigation into the role of television in the formation of political consensus in Italy. Based on probit and instrumental variables estimates, we find trust in television to be the most significant predictor of trust in the Italian prime minister. The latter is also strongly and negatively correlated with trust in the judicial system and tolerance towards immigrants.

Evaluation and Analysis of Node Localization Power Cost in Ad-Hoc Wireless Sensor Networks with Mobility

One of the key concerns with location-aware Ad-hoc Wireless Sensor Networks (AWSNs) is how sensor nodes determine their position. The inherent power limitations of an AWSN along with the requirement for long network lifetimes makes achieving fast and power-efficient localization vital. This research examines the cost (in terms of power) of network irregularities on communications and localization in an AWSN. The number of data bits transmitted and received are significantly affected by varying levels of mobility, node degree, and network shape. The concurrent localization approach, used by the APS-Euclidean algorithm, has significantly more accurate position estimates with a higher percentage of nodes localized, while requiring 50% less data communications overhead, than the Map-Growing algorithm. Analytical power models capable of estimating the power required to localize are derived. The average amount of data communications required by either of these algorithms in a highly mobile network with a relatively high degree consumes less than 2.0% of the power capacity of an average 560mA-hr battery. This is less than expected and contrary to the common perception that localization algorithms consume a significant amount of a node\u27s power

Policy or person?:What voters want from their representatives on Twitter

Social media have the potential to transform democracies as they allow for direct contact between representatives and represented. Politicians can use social media to show their policy positions but they can also give insight into their private lives. Based on survey experiments in Germany and Switzerland we show that social media messages about politicians’ private lives rather deter voters. Instead, we find that voters prefer candidates that communicate policy positions. The effect of a policy-oriented communication style on Twitter can even lead to appreciating a politician from a different party in Switzerland, which has an electoral system that gives a strong incentive to cultivate a personal vote