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- Optimal antenna-height design for improved capacity on over-water radio links affected by tidesPublication . Gutiérrez Gaitán, Miguel; Santos, Pedro M.; Pinto, Luis R.; Almeida, LuisModern observation systems can be composed by heterogeneous entities (e.g., buoys, USVs, UAVs, on-shore sensors, etc.) that rely on dependable communications for coordination and data collection, often provided by over-water radio-frequency (RF) links. In tide-affected water bodies, RF links at a fixed height from the shore can experience the so-called tidal fading, a cyclic time-varying tide-induced interference. To mitigate it, the classical space-diversity reception technique (i.e., the use of two or more receiver antennas positioned at different heights) is often applied, commonly combined with the consideration of having one of the antennas at the largest possible height. Yet, this approach does not always ensure the best performance. In this work, we focus on static over-water links of short-to-medium-range distances that use antennas installed at a few meters above surface. We leverage the geometrical basis of the two-ray propagation model to investigate the optimal single-antenna height design that minimizes overall average path losses over a given tidal range. We then extend this analysis to incorporate a second receiver antenna and identify its optimal antenna height. Analytical results show that our method considerably outperforms the more classical approach, thus enabling superior (average) link capacities.
- Modeling LoRa Communications in Estuaries for IoT Environmental Monitoring SystemsPublication . Gutiérrez Gaitán, Miguel; D'Orey, Pedro; Cecílio, José; Rodrigues, Marta; Santos, Pedro Miguel; Pinto, Luis; Oliveira, Anabela; Casimiro, António; Almeida, LuisLow-power wide-area networks are extending beyond the conventional terrestrial domain. Coastal zones, rivers, wetlands, among others, are nowadays common deployment settings for Internet-of-Things nodes where communication technologies such as LoRa are becoming popular. In this article, we investigate large-scale fading dynamics of LoRa line-of-sight links deployed over an estuary with characteristic intertidal zones, considering both shore-to-shore and shore-to-vessel communications. We propose a novel methodology for path loss prediction which captures i) spatial, ii) temporal and iii) physical features of the RF signal interaction with the environmental dynamics, integrating those features into the two-ray propagation model. To this purpose, we resort to precise hydrodynamic modeling of the estuary, including the specific terrain profile (bathymetry) at the reflection point. These aspects are key to accounting for a reflecting surface of varying altitude and permittivity as a function of the tide. Experimental measurements using LoRa devices operating in the 868~MHz band show major trends on the received signal power in agreement with the methodology's predictions.
- NB-IoT path loss experimental measurements in urban outdoor environmentsPublication . Moreno, Martín; Oxman, Daniela; Sandoval, Jorge; Meza, Cesar A. Azurdia; Gutiérrez Gaitán, Miguel; Játiva, Pablo Palacios; Firoozabad, Ali DehghanThis paper presents a performance analysis of the Narrowband Internet of Things (NB-IoT) network coverage in urban outdoor environments, focusing on experimental measurements toward path loss modeling. Conducted in a major Latin American city, the study explores the deployment of NB-IoT in LTE guardband 28 (700 MHz), offering valuable information on the network characteristics and coverage performance within this narrow spectrum. Four path loss models are considered, including comparisons between alpha-beta-gamma (ABG) and close-in (CI) empirical models. The end goal is to provide practical tools to optimize the deployment of the NB-IoT network in various urban environments. The results obtained offer a fresh perspective on the importance of experimental validation to accurately predict NB-IoT network coverage and signal quality in a real-world setting. Notably, the work has been carried out in collaboration with a Chilean telecom operator.
- Real-Time Communication Support for Over-water Wireless Multi-hop NetworksPublication . Gutiérrez Gaitán, Miguel; Santos, Pedro Miguel; Almeida, LuisThe prospect scenario for wireless communications and networking technologies in aquatic environments is nowadays promising. The growing interest around this subject in the last decades has recently been accelerated due to the more powerful capabilities of a number of sensing, control and communication devices. Moored, fixed, drifting, and vehicular nodes form now a rich ecosystem of autonomous embedded systems potentially connected in a multi-hop (and over-water) fashion, which demand innovative solutions to satisfy the ever-increasing requirements of reliability, bandwidth, latency and cost. The efforts in this direction, mostly as a result of the push from the Internet-of-Thing (IoT) and related communication paradigms, are now at an early stage, and thus still pose significant, technical and research challenges, especially from the perspective of communication and networking for applications involving real-time and/or multimedia networking traffic. In this research, we focus on the communication and networking aspects of over-water multi-hop networks aiming at support real-time and/or multimedia (audio/video) traffic using IEEE 802.11 (WiFi) commodity technologies. Special attention is devoted to the impact of cyclic water-level variations (such as tides and waves) on the overall network performance, and how an integrated approach to (i) network design, (ii) protocol adaptation and (iii) routing can contribute to mitigating such an issue.
- 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.
- Multi-Gateway Designation for Real-Time TSCH Networks using Spectral Clustering and CentralityPublication . Gutiérrez Gaitán, Miguel; Dujovne, Diego; Zuñiga, Julián; Figueroa, Alejandro; Almeida, LuisThis letter proposes a multi-gateway designation framework to design real-time wireless sensor networks (WSNs) improving traffic schedulability, i.e., meeting the traffic time constraints. To this end, we resort to Spectral Clustering un-supervised learning that allows defining arbitrary k disjoint clusters without knowledge of the nodes physical position. In each cluster we use a centrality metric from social sciences to designate one gateway. This novel combination is applied to a time-synchronized channel-hopping (TSCH) WSN under earliest-deadline-first (EDF) scheduling and shortest-path routing. Simulation results under varying configurations show that our framework is able to produce WSN designs that greatly reduce the worst-case network demand. In a situation with 5gateways, 99% schedulability can be achieved with 3.5 times more real-time flows than in a random benchmark.
- Synchronous Framework Extended for Complex IntersectionsPublication . Reddy, Radha; Almeida, Luís; Gutiérrez Gaitán, Miguel; Santos, Pedro Miguel; Tovar, EduardoIntelligent intersection management systems are an integral part of Smart Cities and have a profound impact in urban traffic management. I n a previous work, the authors proposed a specific Intelligent Intersection Management Architecture (IIMA) with the associated Synchronous Intersection Management Protocol (SIMP) for simple single-lane isolated intersections that outperformed other competing protocols in throughput, time loss and polluting emissions. IIMA/SIMP supports both autonomous and human-driven vehicles. This paper extends such work to more complex multi-lane intersections, comparing against traditional and intelligent intersection management approaches. Simulation results achieved with SUMO confirm the advantages of IIMA/SIMP even in complex intersections, improving throughput, average speed, waiting time, trip time loss, and associated fuel consumption.obs: Extended Abstract has been accepted and invited for full-paper submission.
- Wi-Fi-based network systems design over freshwater: Experimental evaluation using COTS devicesPublication . Gutiérrez Gaitán, Miguel; Santos, Pedro Miguel; Pinto, Luis; Almeida, LuísTo experimentally assess the impact of surface reflection on the received signal strength of a set of short-andmedium-range shore-to-shore links (<200 m) that use antennas installed at two heights, at a few meters above surface (<3 m).
- On the path loss performance of underwater visible light communication schemes evaluated in several water environmentsPublication . Almonacid, Lucas; Játiva, Pablo Palacios; Meza, Cesar A. Azurdia; Dujovne, Diego; Soto, Ismael; Firoozabadi, Ali Dehghan; Gutiérrez Gaitán, MiguelThis paper presents an in-depth study into the necessity of efficient communication systems in underwater environments, with a primary focus on Underwater Visible Light Communication (UVLC). A novel path loss model that adapts to different water types is proposed to improve existing UVLC channel models. Validation against various scenarios, including different water types and receiver aperture diameters, is carried out using Monte Carlo simulations. The results demonstrate the efficiency and accuracy of the model by carefully fitting the actual performance of the UVLC systems. The results show a considerable improvement over previous models that only considered Lambert’s path loss and geometric path loss. Despite some variations observed at larger distances between the transmitter and receiver, the proposed model exhibits significant promise in the understanding and application of UVLC in different underwater environments. This study serves as a preliminary step toward developing more sophisticated and efficient models for UVLC systems.
- Two-ray model analysis for overwater communication at 28 GHz with different heightsPublication . Celades-Martínez, Jorge; Rodríguez, Mauricio; Gutiérrez Gaitán, Miguel; Almeida, LuisThis research aims to assess the signal propagation behavior of millimeter waves (mmWaves) over maritime environments. It focuses on the path loss performance of shore-to-vessel and vessel-to-vessel overwater communication at 28 GHz when considering line-of-sight conditions. The study is conducted by means of synthetic simulations at four different receiver antenna heights with respect to the water surface, representing emerging maritime Internet-of-Things application scenarios. Simulation results are shown concerning the path loss and the excess path loss – additional path loss relative to that in free-space – for each particular antenna height, over different TX-RX separations. We also show the cumulative distribution function of the excess path loss. The outcomes reveal variations of up to 10 dB in path loss performance depending on the height-distance setup. The results also reveal an initial distance range for all antenna heights in which the excess path loss is below 3 dB with 90% probability.