Author
Gonzalo Seco
Bio: Gonzalo Seco is an academic researcher from Autonomous University of Barcelona. The author has contributed to research in topics: GNSS applications & Galileo (satellite navigation). The author has an hindex of 4, co-authored 6 publications receiving 283 citations.
Papers
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TL;DR: It is demonstrated that the diversity order of the system is reduced to 1 when CSI is outdated, being this behavior independent of the level of CSI accuracy.
Abstract: In this paper, we analyze the outage probability and diversity order of opportunistic relay selection in a scenario based on decode and forward and where the available channel state information (CSI) is outdated. The study is conducted analytically by obtaining a closed-form expression for the outage probability, which is defined as the probability that the instantaneous capacity is below a target value. We derive high-SNR approximations for the outage probability. By doing so, we demonstrate that the diversity order of the system is reduced to 1 when CSI is outdated, being this behavior independent of the level of CSI accuracy. A physical explanation for this extreme loss of diversity is provided along with numerical results to support the analytical study.
260 citations
19 Sep 2008
TL;DR: This research presents a probabilistic simulation of the response of the Large Hadron Collider to the Sun’s Sun-synchronised radiofrequency signal.
Abstract: J. A. Lopez-Salcedo (UAB) , Y. Capelle (TAS-F), M. Toledo 3 (GMV), G. Seco (UAB), J. Lopez Vicario (UAB), D. Kubrak (TAS-F), M. Monnerat (TAS-F), A. Mark (GMV), D. Jimenez (ESA) Universitat Autonoma de Barcelona, QC-2052, 08193 Bellaterra (Barcelona), Spain Thales Alenia Space, 26 avenue J.F. Champollion, BP 33787, 31037 Toulouse, France GMV, Isaac Newton, 11, PTM Tres Cantos, 28760 Madrid, Spain European Space Agency ESA/ESTEC Keplerlaan 1, 2200 AG Noordwijk, The Netherlands
14 citations
12 May 2008
TL;DR: A method to improve the quality of the time- delay and Doppler estimates obtained with an unstructured spatial model when an estimate of the DOAs is available and approaches the Cramer-Rao lower bound of the structured model even when suboptimal DOA estimates obtained by ESPRIT are introduced.
Abstract: This paper deals with the joint estimation of temporal (time- delay, Doppler frequency) and spatial (direction-of-arrival, DOA) parameters of several replicas of a known signal in an unknown spatially correlated field. Unstructured and structured models have been proposed in the literature. The former suffers from a severe performance degradation in some scenarios, whereas the latter involves huge complexity. It is shown how the extended invariance principle (EXIP) can be applied to obtain estimates with the quality of those of the structured model, but with the complexity of the unstructured one. We present a method to improve the quality of the time- delay and Doppler estimates obtained with an unstructured spatial model when an estimate of the DOAs is available. Exemplarily, simulation results for time-delay estimation for GPS (global positioning system) are included and confirm that our proposal approaches the Cramer-Rao lower bound (CRLB) of the structured model even when suboptimal DOA estimates obtained by ESPRIT are introduced.
7 citations
04 May 2010
TL;DR: The different architectural trade-offs of the final platform are introduced and the first results of its performance and capabilities with real data are presented.
Abstract: The goal of this paper is to present the architecture and first performance results of the DINGPOS platform. The DINGPOS platform (Demonstrator for INdoor GNSS POSitioning) is a project funded by the ESA that covers the design, development and integration of an experimental indoor positioning system based on the fusion of three different technologies: High Sensitivity GNSS (GPS and the future Galileo), MEMS-based Pedestrian Navigation System and WIFI. This paper introduces the different architectural trade-offs of the final platform and presents the first results of its performance and capabilities with real data.
6 citations
21 Mar 2008
TL;DR: It is shown how the extended invariance principle (EXIP) can be applied to obtain estimates with the quality of those of the structured model, but with the complexity of the unstructured one.
Abstract: This paper deals with the joint estimation of time-delay and spatial (direction-of-arrival, DOA) parameters of several replicas of a known signal in an unknown spatially correlated field. Unstructured and structured models have been proposed for maximum likelihood (ML) estimators in the literature. The former suffers from a severe performance degradation in some scenarios, whereas the latter involves huge complexity. It is shown how the extended invariance principle (EXIP) can be applied to obtain estimates with the quality of those of the structured model, but with the complexity of the unstructured one. We present a method to improve the quality of the time-delay estimates obtained with an unstructured spatial model when an estimate of the DOAs is available. Exemplarily, simulation results for time-delay estimation for GPS (Global Positioning System) are included and confirm that our proposal approaches the Cramer-Rao lower bound (CRLB) of the structured model even when suboptimal DOA estimates obtained by ESPRIT are introduced.
4 citations
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20 Jun 2019
TL;DR: This paper provides a tutorial review on mathematical channel modeling for diffusive MC systems and provides the channel models for time-varying MC systems with moving transmitters and receivers, which are relevant for advanced applications such as smart drug delivery with mobile nanomachines.
Abstract: Molecular communication (MC) is a new communication engineering paradigm where molecules are employed as information carriers. MC systems are expected to enable new revolutionary applications, such as sensing of target substances in biotechnology, smart drug delivery in medicine, and monitoring of oil pipelines or chemical reactors in industrial settings. As for any other kind of communication, simple yet sufficiently accurate channel models are needed for the design, analysis, and efficient operation of MC systems. In this paper, we provide a tutorial review on mathematical channel modeling for diffusive MC systems. The considered end-to-end MC channel models incorporate the effects of the release mechanism, the MC environment, and the reception mechanism on the observed information molecules. Thereby, the various existing models for the different components of an MC system are presented under a common framework and the underlying biological, chemical, and physical phenomena are discussed. Deterministic models characterizing the expected number of molecules observed at the receiver and statistical models characterizing the actual number of observed molecules are developed. In addition, we provide the channel models for time-varying MC systems with moving transmitters and receivers, which are relevant for advanced applications such as smart drug delivery with mobile nanomachines. For complex scenarios, where simple MC channel models cannot be obtained from first principles, we investigate the simulation- and experiment-driven channel models. Finally, we provide a detailed discussion of potential challenges, open research problems, and future directions in channel modeling for diffusive MC systems.
251 citations
TL;DR: It is shown that it may be preferable, in terms of outage and symbol error probability, not to include links in the relay selection process that experience a sufficiently high maximum Doppler shift, since in those cases partial relay selection outperforms best relay selection.
Abstract: We study the effect of outdated channel state information on the outage and error rate performance of amplify-and-forward (AF) relay selection, where only one out of the set of available relays is activated. We consider two variations of AF relay selection, namely best relay selection and partial relay selection, when the selection is based upon outdated channel estimates. For both these variations, closed-form expressions for the outage probability are obtained, along with approximate expressions for the symbol error rate in the medium to high signal-to-noise-ratio (SNR) regime. The diversity gain and coding gain of the above schemes are also explicitly derived. Numerical results manifest that the outage performance of AF relay selection is highly dependent on the level of correlation between the actual channel conditions and their corresponding (outdated) estimates. This result has a significant impact on the deployment of relay selection in practical applications, implying that a high feedback rate may be required in practice in order to attain the full benefits of relay selection. It is further shown that it may be preferable, in terms of outage and symbol error probability, not to include links in the relay selection process that experience a sufficiently high maximum Doppler shift, since in those cases partial relay selection outperforms best relay selection.
233 citations
TL;DR: Cooperative positioning, where first responders exchange position and error estimates in conjunction with performing radio based ranging, is deemed a key technology.
Abstract: A robust, accurate positioning system with seamless outdoor and indoor coverage is a highly needed tool for increasing safety in emergency response and military urban operations. It must be lightweight, small, inexpensive, and power efficient, and still provide meter-level accuracy during extended operations. GPS receivers, inertial sensors, and local radio-based ranging are natural choices for a multisensor positioning system. Inertial navigation with foot-mounted sensors is suitable as the core system in GPS denied environments, since it can yield meter-level accuracies for a few minutes. However, there is still a need for additional supporting sensors to keep the accuracy at acceptable levels during the duration of typical soldier and first responder operations. Suitable aiding sensors are three-axis magnetometers, barometers, imaging sensors, Doppler radars, and ultrasonic sensors. Further more, cooperative positioning, where first responders exchange position and error estimates in conjunction with performing radio based ranging, is deemed a key technology. This article provides a survey on technologies and concepts for high accuracy soldier and first responder positioning systems, with an emphasis on indoor positioning.
209 citations
TL;DR: This article analyzes the challenges facing OSA systems globally, which mainly include interactions among multiple users, dynamic spectrum opportunity, tradeoff between sequential sensing cost and expected reward, and tradeoffs between exploitation and exploration in the absence of prior statistical information.
Abstract: Opportunistic spectrum access (OSA) has been regarded as the most promising approach to solve the paradox between spectrum scarcity and waste. Intelligent decision making is key to OSA and differentiates it from previous wireless technologies. In this article, a survey of decision-theoretic solutions for channel selection and access strategies for OSA system is presented. We analyze the challenges facing OSA systems globally, which mainly include interactions among multiple users, dynamic spectrum opportunity, tradeoff between sequential sensing cost and expected reward, and tradeoff between exploitation and exploration in the absence of prior statistical information. We provide comprehensive review and comparison of each kind of existing decision-theoretic solution, i.e., game models, Markovian decision process, optimal stopping problem and multi-armed bandit problem. We analyze their strengths and limitations and outline further research for both technical contents and methodologies. In particular, these solutions are critically analyzed in terms of information, cost and convergence speed, which are key concerns for practical implementation. Moreover, it is noted that each kind of existing decision-theoretic solution mainly addresses one aspect of the challenges, which implies that two or more kinds of decision-theoretic solutions should be incorporated to address more challenges simultaneously.
207 citations
TL;DR: This paper considers three opportunistic relay selection schemes to reduce the overheard information at the eavesdroppers by choosing the relay having the lowest instantaneous signal-to-noise ratio (SNR) to them, and examines the ratio between the SNR of a relay and the maximum among the corresponding SNRs to the eaves droppers.
Abstract: In this paper, we study opportunistic relay selection in cooperative networks with secrecy constraints, where a number of eavesdropper nodes may overhear the source message. To deal with this problem, we consider three opportunistic relay selection schemes. The first scheme tries to reduce the overheard information at the eavesdroppers by choosing the relay having the lowest instantaneous signal-to-noise ratio (SNR) to them. The second scheme is conventional selection relaying that seeks the relay having the highest SNR to the destination. In the third scheme, we consider the ratio between the SNR of a relay and the maximum among the corresponding SNRs to the eavesdroppers, and then select the optimal one to forward the signal to the destination. The system performance in terms of probability of non-zero achievable secrecy rate, secrecy outage probability and achievable secrecy rate of the three schemes are analyzed and confirmed by Monte Carlo simulations.
165 citations