Browsing by Author "Pinto, Luis"
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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.
- Characterization and Modeling of the Bicycle-Antenna System for the 2.4GHz ISM BandPublication . Pinto, Luis; M. Santos, Pedro; Almeida, Luis; Aguiar, AnaVehicular communication is rapidly becoming a standard reality, and precise models are necessary for accurate performance estimates. Alongside cars and trucks, smaller vehicles such as scooters and bicycles are also set to participate in V2X networking, but have received considerably less attention. In this work, we present an extensive characterization of the gain pattern of a bicycle and antenna system for the IEEE 802.11g standard. We measure the radiation patterns of the antenna of a commodity 2.4 GHz WiFi module mounted on six distinct positions on the body of six archetypal bicycles in an anechoic chamber. The RSSI sample set per angle and antenna position is characterized statistically and input into an empirical model of the gain pattern of the bicycle-antenna system. We define a bicycle-to-X propagation model that pairs the proposed bicycle-antenna gain and a log-distance shadowing path loss model, and conduct outdoor measurement campaign for evaluation. We observe that the gain model measured in chamber matches the measured RSSI at small distances, whereas at larger distances it provides less accuracy.
- 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.
- 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.
- A Glimpse at Bicycle-to-Bicycle Link Performance in the 2.4GHz ISM BandPublication . Santos, Pedro M.; Pinto, Luis; Aguiar, Ana; Almeida, LuisBicycle-to-bicycle (Bi2Bi) communication can be implemented by well-established technologies in the 2.4GHz ISM band: IEEE 802.11, Bluetooth or IEEE 802.15.4. These technologies have distinct performance due to different physical and data link layers. In this paper, we characterize the mentioned 2.4 GHz-operating technologies over opportunistic links established between bicycles using commodity hardware. We find that, in Bi2Bi links, Blue-tooth, IEEE 802.11 at 24 Mbit/s, and IEEE 802.11 with automatic rate adaptation can communicate only in the immediate surroundings (under 15m of range), to maxima of 1.5 Mbit/s, 17 Mbit/s and 25 Mbit/s, respectively. IEEE 802.15.4 and IEEE 802.11 at 1 Mbit/s sustain connectivity up to 30 and 40 meters and peak transfer rates of 50 kbit/s and 800 kbit/s respectively. In addition, we observed that, in all measurement scenarios, link performance depended strongly on whether bicycles were approaching or moving away, rather than on whether one was at the front or back of the other.
- 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.
- 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.
- On the Two-Ray Model Analysis for Overwater Links with Tidal VariationsPublication . Gutiérrez Gaitán, Miguel; Pinto, Luis; Santos, Pedro Miguel; Almeida, LuísThis work explores the impact of antenna heights and polarization on overwater links during the cycle of tidal variations. We focus our attention on links of short-to-medium-range distances with antenna heights near-to-the-water-surface. The typical use-case for such a scenario is an overwater, water quality monitoring wireless sensor network. The radio propagation is simulated using a featured two-ray model that considers the relative permittivity of the water surface and the antenna polarization. The results show that the performance of overwater links may be better with lower antennas than higher antennas as well as with one polarization or the other, intuitively, during part of the tidal cycle.
- A Robust Approach to TDMA Synchronization in Aerial NetworksPublication . Pinto, Luis; Almeida, LuisUnmanned Aerial Vehicles (UAVs) can be a powerful tool for live (interactive) remote inspection of large-scale structures or areas of interest. Instead of manual, local, and labor-intensive inspections, we envision human operators working together with networks of semi-autonomous UAVs. The current state-of-the-art for low-delay high-throughput inter-vehicle networking relies on Time-Division Multiple Access (TDMA) techniques that require accurate synchronization among all network nodes. In this paper, we propose a delay-tolerant synchronization approach that converges to the correct order of the TDMA slots implemented over COTS WiFi in a fully-distributed way and without resorting to a global clock. This highly flexible solution allows building an ad-hoc aerial network based on a backbone of relaying UAVs. We show several alternatives to achieve this synchronization in a concrete aerial network and compare them in terms of slots’ overlap, throughput, and packet delivery. The results show that these alternatives lead to trade-offs in the referenced metrics. The results also provide insight into the delays caused by buffering in the protocol stack and especially in the WiFi interface.
- 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).