Browsing by Author "Ribeiro, Manuel"
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- 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.
- Empirical Evaluation of Short-Range WiFi Vessel-to-Shore Overwater CommunicationsPublication . d'Orey, Pedro; Gutiérrez Gaitán, Miguel; Santos, Pedro M.; Ribeiro, Manuel; Sousa, J. Borges de; Almeida, LuísUnmanned vehicles used in ocean science, defense operations and commercial activities collect large amounts of data that is further processed onshore. For real-time information exchange, the wireless link between the unmanned vehicle and onshore devices must be reliable. In this work, we empirically evaluate a WiFi link between an autonomous underwater vehicle on the surface and an onshore device under real-world conditions. This work allowed i) collecting a large-scale realistic dataset and ii) identifying major factors impairing communication in such scenarios. The TX-RX antenna alignment, the operation mode (manual vs automatic) and varying reflecting surface induced by AUV mobility lead to sudden changes (e.g. nulls) in the received signal strength that can be larger than 20 dB. This study provides useful insights to the design of robust vessel-to-shore short-range communications.
- 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.
- Wireless radio link design to improve nearshore communication with surface nodes on tidal watersPublication . Gutiérrez Gaitán, Miguel; d'Orey, Pedro; Santos, Pedro Miguel; Ribeiro, Manuel; Pinto, Luís; Almeida, Luís; Sousa, J. Borges deWireless radio links deployed over aquatic areas (e.g., sea, estuaries or harbors) are affected by the conductive properties of the water surface, strengthening signal reflections and increasing interference effects. Recurrent natural phenomena such as tides or waves cause shifts in the water level that, in turn, change the interference patterns and cause varying impairments to propagation over water surfaces. In this work, we aim at mitigating the detrimental impact of tides on the quality of a line-of-sight over-water link between an onshore station and a surface node, targeting mission data transfer scenarios. We consider different types of surface nodes, namely, autonomous underwater vehicles, unmanned surface vehicles and buoys, and we use WiFi technology in both 2.4 GHz and 5 GHz frequency bands. We propose two methods for link distance/height design: (i) identifying a proper Tx-Rx distance for improved link quality at each point of the tidal cycle; (ii) defining the height/distance that minimizes the path loss averaged during the whole tidal cycle.Experimental results clearly show the validity of our link quality model and the interest of method (i). Analytical results confirm method (ii) and show that it outperforms, in both frequency bands, the common practice of placing onshore antennas at the largest possible height and/or surface nodes at a short but arbitrary distance.