Iván A. Pérez-Álvarez

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Although most of the research on Cognitive Radio is focused on communication bands above the HF upper limit (30 MHz), Cognitive Radio principles can also be applied to HF communications to make use of the extremely scarce spectrum more efficiently. In this work we consider legacy users as primary users since these users transmit without resorting to any(More)
The authors present full wave simulations and experimental results of propagation of electromagnetic waves in shallow seawaters. Transmitter and receiver antennas are ten-turns loops placed on the seabed. Some propagation frameworks are presented and simulated. Finally, simulation results are compared with experimental ones.
Shallow seawaters are problematic for acoustic and optical communications. Sensor networks based on electromagnetic (EM) communications are evaluated in this environment. In order to characterize the underwater channel, several measurement systems have been designed, built and tested in the sea obtaining very reliable results. Experiments carried out with(More)
We analyze the problem of localization algorithms for underwater sensor networks. We first characterize the underwater channel for radio communications and adjust a linear model with measurements of real transmissions. We propose an algorithm where the sensor nodes collaboratively estimate their unknown positions in the network. In this setting, we assume(More)
We use real measurements of the underwater channel to simulate a whole underwater RF wireless sensor networks, including propagation impairments (e.g., noise, interferences), radio hardware (e.g., modulation scheme, bandwidth, transmit power), hardware limitations (e.g., clock drift, transmission buffer) and complete MAC and routing protocols. The results(More)
The observed signals that usually play the role of error references for adaptive echo cancellers and channel equalizers in data communications are basically composed by data plus a residual error. The goal of such systems is to eliminate those errors to enhance the present data. However, in some systems, depending on the convergence stage, the presence of(More)
Multiple users transmit in the HF band with worldwide coverage but collide with other HF users. New techniques based on cognitive radio principles are discussed to reduce the inefficient use of this band. In this paper, we show the feasibility of the Upper Confidence Bound (UCB) algorithm, based on reinforcement learning, for an opportunistic access to the(More)