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Pedro Santos, "Wireless Protocols and Channel Estimation for Data Gathering with Mobile Nodes," PhD Thesis, Faculdade de Engenharia, Universidade do Porto, May 2017. (Advisors: Ana Aguiar and João Barros; Referee: Falko Dressler)


Data collection is a powerful application in scenarios where mobile and static agents work towards a common goal, as it provides the commanding agent with information about the monitored processes and agents. Mobile and vehicular ad hoc networks (M/VANETs) are a steadfast platform over which data collection applications can be built. Static nodes interact with the M/VANET as data sinks, that interface the ad hoc network with cloud-based services, or as sensor nodes deployed throughout the target field, that regard the mobile network as a dependable communication backhaul. The relevance of our target application - data collection applications over ad hoc networks with mobile and static nodes - motivates the development of dedicated network design solutions addressing scenario characterization, infrastructure planning and network operation. Our thesis aims to show that the design of such solutions can be improved by the use of measurements and datasets from the target scenario. The development of wireless applications requires an accurate characterization of the electromagnetic signal propagation. Propagation behaviour may vary considerably between scenarios due to circumstantial factors such as obstacle density, reflections and noise sources. Empirical channel models aim to capture the behaviour of propagation in a given scenario from measurements of received signal strength and distance between wireless terminals. In some cases, measuring the actual distances between terminals may be difficult or impossible, for instance in mobile scenarios. We address the problem of path loss model parameter estimation in presence of erroneous distance measurements, in particular those obtained from the GPS positions. Our main conclusion is that the path loss model can be estimated with a reasonable accuracy from unreliable distances, provided that the measurements are taken at distances beyond a few standard deviations of the GPS positioning error. In case the maximum communication range does not allow such large distances, we provide a method to correct the erroneous channel model. Field experiments were undertaken to collect measurement data in order to validate our approach. In a number of scenarios, static sensor nodes can harness vehicular backhauls for collecting data to a base station. The interface between sensors and backhaul can be provided by dedicated communication hubs, and network designers can use mobility and connectivity datasets from the target scenario to conduct a hub placement that ensures service requirements while utilizing minimum resources. We address the challenge of placing static wireless nodes over large areas (e.g. at city scale) and driven by infrastructure-to-vehicle (I2V) service requirements, alongside other end-system, logistic and communication constraints. We formulated an optimization problem and developed a solution strategy that minimizes the number of necessary static nodes by mapping our problem into an instance of the Set Cover problem. Our solution strategy involves an model of I2V transfers estimation over large areas that builds on an experimental characterization of throughput and data transfers at the target scenario. Our placement strategy attains less 20% hubs than sensor nodes, and estimates of our model of I2V data transfers fall within one order of magnitude of measurements collected on site. In the operation of a base station-centric collection protocol over an ad hoc network of mobile and static nodes, beaconing is a straightforward strategy to indicate the direction to the sink. Protocols that set up static routes (such as spanning trees) from periodic beacons are bound to suffer from routing information degradation at the nodes, which leads to performance impairments as we show for a reference protocol. We study a protocol design based on wireless broadcast and opportunistic routing so that traffic is not restrained to rigid routes. Given that link-level reliability becomes impractical, network coding is introduced to provide end-to-end reliability. The opportunistic forwarding is expected to contribute to the coding strategy by promoting packet mixing and increasing the number of degrees of freedom arriving to the base station. We set up a simulation framework over connectivity traces from a real-world vehicular testbed, and carry out extensive design-space exploration and benchmarking against a reference structured protocol. Our results support a number of recommendations regarding the practical design of network coding protocols for scenarios with mobility, and clarify the conditions in which our solution exhibits better resilience to routing information degradation.

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Pedro Santos

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    author = {Santos, Pedro},
    title = {{Wireless Protocols and Channel Estimation for Data Gathering with Mobile Nodes}},
    advisor = {Aguiar, Ana and Barros, Jo{\~{a}}o},
    institution = {Faculdade de Engenharia},
    location = {Porto, Portugal},
    month = {5},
    referee = {Dressler, Falko},
    school = {Universidade do Porto},
    type = {PhD Thesis},
    year = {2017},

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