Browsing by Author "Santos, Pedro Miguel"
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- An Analysis of the Two-Ray Propagation Model to Support Near-Surface Overwater Wireless Sensor Networks DesignPublication . Gutiérrez Gaitán, Miguel; Pinto, Luis; Santos, Pedro Miguel; Almeida, LuísIn this work, a thorough analysis based on the two-ray model in the presence of tides is performed. The study aims to provide a tool to guide the deployment of near-surface overwater wireless sensor networks, and thus improve its overall link quality regardless of the variations of the tides. We consider realistic parameters, such as the distance between the nodes and the tide-levels range taken from the mouth of the Douro river, Porto and the Seixal Bay, Lisbon. In future works, we will complement the theoretical analysis with network level simulations and an extended experimental campaign.
- Assessing short-range Shore-to-Shore (S2S) and Shore-to-Vessel (S2V) wifi communicationsPublication . D'Orey, Pedro; Gutiérrez Gaitán, Miguel; Santos, Pedro Miguel; Ribeiro, Manuel; Sousa, J. Borges de; Almeida, LuísWireless communications increasingly enable ubiquitous connectivity for a large number of nodes, applications and scenarios. One of the less explored scenarios are aquatic ecosystems, specially when enabled by near-shore and short-range communications. Overwater communications are impaired by a number of distinguishing dynamic factors, such as tides, waves or node mobility, that lead to a widely fluctuating and unpredictable channel. In this work, we empirically characterize near-shore, overwater channels at 2.4 GHz under realistic conditions, including tidal variations, and relatively short TX-RX separations. To this end, we conducted experiments in a coastal estuarine region and on a harbor to characterize Shore-to-Shore (S2S) and Shore-to-Vessel (S2V) communication channels, respectively, and to identify major factors impairing communication in such scenarios. The empirical results show that constructive/destructive interference patterns, varying reflecting surface, and node mobility (i.e. travel direction and particular maneuvers) have a relevant and noticeable impact on the received signal strength. Thus, a set of parameters should be simultaneously considered for improving the performance of communication systems supporting S2S and S2V links, namely tidal variations, reflection surface changes, antenna height, TX-RX alignment and TX-RX separation. The results useful provide insights into realistic S2S and S2V link design and operation.
- Cooperative Bicycle Localization System via Ad Hoc Bluetooth NetworksPublication . Santos, Pedro Miguel; Rosa, Vera; Pinto, Luis; Aguiar, AnaBicycles are becoming increasingly more equipped with embedded connected devices, by design or through after market products, to support applications such as fitness monitoring and tracking. Bluetooth (BT) and BT Low Energy (BLE) technology is often embedded in such devices to support connectivity to a personal mobile device or a dock, when parked. BT/BLE transmit periodic beacons for node discovery that can be explored for V2X applications, such as safety and fleet management. We present a distributed system that explores periodic BT beacons sent by a module embedded in a bicycle to opportunistically locate nodes of interest (NOI). We address the particular application of stolen bicycle detection. In a scenario in which a bicycle is stolen and has its communication system tampered with but BLE remains functional, a service provider (e.g., fleet operator, authorities) is informed of this new NOI and shares an updated NOI list with the NOI detection-enabled bicycles. In turn, the bicycles flag contacts with stolen bicycles to the provider backoffice, at the earliest convenience (depending on available communications interfaces: immediately if cellular is available, or opportunistically when passing by a dock). We describe the operation and software architecture of the system, and an actual implementation in COTS equipment. Experimental measurements of the communication range and a demonstration of the system for oroof-of-concept are also reported.
- Cooperative Vehicular Platooning: A Multi- Dimensional Survey Towards Enhanced Safety, Security and ValidationPublication . Vasconcelos Filho, Ênio; Santos, Pedro Miguel; Koubaa, Anis; Tovar, Eduardo; Severino, RicardoCooperative Vehicular Platooning (Co-VP) is a paradigmatic example of a Cooperative Cyber-Physical System (Co-CPS), which holds the potential to vastly improve road safety by partially removing humans from the driving task. However, the challenges are substantial, as the domain involves several topics, such as control theory, communications, vehicle dynamics, security, and traffic engineering, that must be coupled to describe, develop and validate these systems of systems accurately. This work presents a comprehensive survey of significant and recent advances in Co-VP relevant fields. We start by overviewing the work on control strategies and underlying communication infrastructures, focusing on their interplay. We also address a fundamental concern by presenting a cyber-security overview regarding these systems. Furthermore, we present and compare the primary initiatives to test and validate those systems, including simulation tools, hardware-in-the-loop setups, and vehicular testbeds. Finally, we highlight a few open challenges in the Co-VP domain. This work aims to provide a fundamental overview of highly relevant works on Co-VP topics, particularly by exposing their inter-dependencies, facilitating a guide that will support further developments in this challenging field.
- CoWiPS: Cooperative wireless positioning to identify position mis-reports in vehicular scenariosPublication . Lam, Luis; Santos, Pedro MiguelAutonomous driving (AD) is advancing rapidly, but enhancing situational awareness beyond the internal sensors (cameras, radar, and Lidar) requires cooperative perception services enabled by Vehicle-to-Everything (V2X) links. However, some vehicles can inject incorrect information, either intentionally or by hardware malfunction. Wireless positioning offers a set of physical-layer mechanisms, such as Angle-of-Arrival (AoA) and RSS-based ranging, that can verify the correctness of shared data, particularly position data. We introduce Cooperative Wireless Positioning System (CoWiPS), an innovative mechanism in which a set of cooperating vehicles cooperate to estimate the position of a Vehicle-of-Interest. Our positioning solution achieves accurate position estimations, with 70.16% accuracy within a 10m error margin under 0dB amplitude noise variance, and 50.01% accuracy under 5dB variance.
- Energy savings and emissions reduction of BEVs at an isolated complex intersectionPublication . Reddy, Radha; Almeida, Luis; Santos, Pedro Miguel; Kurunathan, Harrison; Tovar, EduardoImproving urban dwellers quality of life requires mitigating traffic congestion, minimizing waiting delays, and reducing fuel wastage and associated toxic air pollutants. Battery-electric vehicles (BEVs) are envisioned as the best option, thanks to zero exhaust emissions and regenerative braking. BEVs can be human-driven or autonomous and will co-exist with internal combustion engine vehicles (ICEVs) for years. BEVs can help at complex intersections where traffic is saturated. However, their benefits can be reduced by poor intersection management (IM) strategies that coordinate mixed traffic configurations inefficiently. This paper studies energy savings and emissions reduction using BEVs mixed with human-driven ICEVs under eight relevant IM approaches. It shows that adding BEVs has impacts on throughput, energy consumption, waiting delays, and tail-pipe emissions that depend on the specific IM approach used. Thus, this study provides the information needed to support an optimal choice of IM approaches considering the emerging trend towards electrical mobility.
- Experimental evaluation of the two-ray model for near-shore WiFi-based network systems designPublication . Gutiérrez Gaitán, Miguel; Santos, Pedro Miguel; Pinto, Luis; Almeida, LuisIn the design of shore-to-shore and shore-to-vessel wireless links, the impact of the ray reflected on the surface is often neglected. It adds that, in some coastal areas, the geometry of the reflection changes over time due to tides. When choosing an antenna height for an inshore node, often the largest possible height is used, but this approach can lead to signal degradation. The two-ray model is the most fundamental path loss model to account for the contribution of the reflected ray. We carried out experimental measurements at the shores of a freshwater body to verify that the two-ray model can predict the major trends of the path loss experienced by a 2.4 GHz over-water wireless link. We focus on short-to-medium distance links, with antennas installed a few meters above surface. We observed considerable consistency between measurements and model estimates, leading us to conclude that the two-ray model may bring benefits when applied to the network design of over-water links affected by tidal variations, which is our end-goal.
- Improving the Performance of Cooperative Platooning with Restricted Message Trigger ThresholdsPublication . Vasconcelos Filho, Ênio; Santos, Pedro Miguel; Severino, Ricardo; Koubaa, Anis; Tovar, EduardoCooperative Vehicular Platooning (Co-VP) is one of the most prominent and challenging applications of Intelligent Traffic Systems. To support such vehicular communications, the ETSI ITS G5 standard specifies event-based communication profiles, triggered by kinematic parameters such as speed. The standard defines a set of threshold values for such triggers but no careful assessment in realistic platooning scenarios has been done to confirm the suitability of such values. In this work, we investigate the safety and performance limitations of such parameters in a realistic platooning co-simulation environment. We then propose more conservative threshold values, that we formalize as a new profile, and evaluate their impact in the longitudinal and lateral behaviour of a vehicular platoon as it carries out complex driving scenarios. Furthermore, we analyze the overhead introduced in the network by applying the new threshold values. We conclude that a pro-active message transmission scheme leads to improved platoon performance for highway scenarios, notably an increase greater than 40% in the longitudinal performance of the platoon, while not incurring in a significant network overhead. The obtained results also demonstrated an improved platoon performance for semi-urban scenarios, including obstacles and curves, where the heading error decreases in 26%, with slight network overhead.
- Improving WiFi communication with surface nodes at near-shore on tidal watersPublication . Gutiérrez Gaitán, Miguel; d'Orey, Pedro; Santos, Pedro Miguel; Ribeiro, Manuel; Pinto, Luis; Almeida, Luís; de Sousa, J. BorgesWireless radio links deployed in aquatic areas (e.g., sea, rivers, lakes, estuaries) are affected by the conductive properties of the water surface, strengthening signal reflections and increasing destructive interference. Recurrent natural phenomena (e.g. tides or waves) cause shifts in water levels further impairing propagation over water surfaces. In this work, we aim to mitigate the detrimental impact of tides on link quality by providing tailored link distance/height-design regions that minimize average path losses. We focus on line-of-sight (LOS) over-water links between onshore stations and different types of surface nodes, namely AUVs, buoys, or USVs, using 2.4 GHz and 5 GHz frequency bands. Analytical results targeting mission data transfer scenarios demonstrate that the proposed method outperforms, in both frequency bands, the common practice of placing (i) onshore antennas at the largest possible height and/or (ii) surface nodes at a short but arbitrary distance from the shore. A longer version of this summary was presented at IEEE/MTS OCEANS 2021.
- Joint Scheduling, Routing and Gateway Designation in Real-Time TSCH NetworksPublication . Gutiérrez Gaitán, Miguel; Almeida, Luis; Watteyne, Thomas; D'Orey, Pedro; Santos, Pedro Miguel; Dujovne, DiegoThis research proposes a co-design framework for scheduling, routing and gateway designation to improve the real-time performance of low-power wireless mesh networks. We target time-synchronized channel hopping (TSCH) networks with centralized network management and a single gateway. The end goal is to exploit existing trade-offs between the three dimensions to enhance traffic schedulability at systems' design time. The framework we propose considers a global Earliest-Deadline-First (EDF) scheduler that operates in conjunction with the minimal-overlap (MO) shortest-path routing, after a centrality-driven gateway designation is concluded. Simulation results over varying settings suggest our approach can lead to optimal or near-optimal real-time network performance, with 3~times more schedulable flows than a naive real-time configuration.