Browsing by Author "Dardari, D."
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Item Open Access Cognitive and Cooperative Wireless Networks(Springer-Verlag Italia s.r.l., 2012) Palazzo, S.; Dardari, D.; Dohler, M.; Gezici, Sinan; Giupponi, L.; Luise, M.; Pérez Romero, J.; Shamai, S.; Noguet, D.; Moy, C.; Asheid, G.The traditional approach of dealing with spectrum management in wireless communications has been the definition of a licensed user granted with exclusive exploitation rights for a specific frequency. While it is relatively easy in this case to ensure that excessive interference does not occur, this approach is unlikely to achieve the objective to maximize the value of spectrum, and in fact recent spectrum measurements carried out worldwide have revealed a significant spectrum underutilization, in spite of the fact that spectrum scarcity is claimed when trying to find bands where new systems can be allocated. Just to mention some examples of measurements, different studies can be found in [1-6], revealing that overall occupation in some studies for frequencies up to 7GHz could be in the order of only 18%.Item Open Access Heterogeneous and Opportunistic Wireless Networks(Springer-Verlag Italia s.r.l., 2012) Pérez-Romero, J.; Palazzo, S.; Galluccio, L.; Morabito, G.; Leonardi, A.; Antón-Haro, C.; Arikan, E.; Asheid, G.; Belleville, M.; Dagres, I.; Dardari, D.; Dohler, M.; Eldar, Y.; Gezici, Sinan; Giupponi, L.; Guillemot, C.; Iosifidis, G.; Kieffer, M.; Kountouris, M.; Luise, M.; Masera, G.; Matamoros, J.; Miliou, N.; Morche, D.; Moy, C.; Navarro, C.; Olmo, G.; Palicot, J.; Pedone, R.; Ramakrishnan, V.; Shamai, S.; Tyczka, P.; Vandendorpe, L.; Vanelli-Coralli, A.; Weidmann, C.; Zalonis, A.Recent years have witnessed the evolution of a large plethora of wireless technologies with different characteristics, as a response of the operators' and users' needs in terms of an efficient and ubiquitous delivery of advanced multimedia services. The wireless segment of network infrastructure has penetrated in our lives, and wireless connectivity has now reached a state where it is considered to be an indispensable service as electricity or water supply. Wireless data networks grow increasingly complex as a multiplicity of wireless information terminals with sophisticated capabilities get embedded in the infrastructure.Item Open Access LOS/NLOS detection for UWB signals: A comparative study using experimental data(IEEE, 2010) Decarli, N.; Dardari, D.; Gezici, Sinan; D'Amico, A.A.In this paper the problem of detecting the channel state between LOS and NLOS conditions is addressed using UWB signals. A new distribution-based identification approach is proposed and its performance is compared with that of other classic schemes. To this purpose experimental data collected in realistic environments have been used. © 2010 IEEE.Item Open Access Performance limits on ranging with cognitive radio(IEEE, 2009-06) Dardari, D.; Karisan, Yasir; Gezici, Sinan; D'Amico, A. A.; Mengali, U.Cognitive radio is a promising paradigm for efficient utilization of the radio spectrum due to its capability to sense environmental conditions and adapt its communication and localization features. In this paper, the theoretical limits on time-of-arrival estimation for cognitive radio localization systems are derived in the presence of interference. In addition, an optimal spectrum allocation strategy which provides the best ranging accuracy limits is proposed. The strategy accounts for the constraints from the sensed interference level as well as from the regulatory emission mask. Numerical results are presented to illustrate the improvements that can be achieved by the proposed approach. © 2009 IEEE.Item Open Access Range estimation in multicarrier systems in the presence of interference: performance limits and optimal signal design(IEEE, 2011) Karisan, Y.; Dardari, D.; Gezici, Sinan; D'Amico, A. A.; Mengali, U.Theoretical limits on time-of-arrival (equivalently, range) estimation are derived for multicarrier systems in the presence of interference. Specifically, closed-form expressions are obtained for Cramer-Rao bounds (CRBs) in various scenarios. In addition, based on CRB expressions, an optimal power allocation (or, spectrum shaping) strategy is proposed. This strategy considers the constraints not only from the sensed interference level but also from the regulatory emission mask. Numerical results are presented to illustrate the improvements achievable with the optimal power allocation scheme, and a maximum likelihood time-of-arrival estimation algorithm is studied to assess the effects of the proposed approach in practical estimators.Item Open Access Static positioning using UWB range measurements(IEEE, 2010) Gholami, M.R.; Ström, E.G.; Sottile F.; Dardari, D.; Conti, A.; Gezici, Sinan; Rydström, M.; Spirito, M.A.The performance of several existing and partly new algorithms for positioning of sensor node based on distance estimate is compared when the distance estimates are obtained from a measurement campaign. The distance estimates are based on time-of-arrival measurements done by ultrawideband devices in an indoor office environment. Two different positioning techniques are compared: statistical and geometrical. In statistical category, distributed weighted-multidimensional scaling (dwMDS), least squares, and sum product algorithm are evaluated and in geometrical technique projections approach and outer approximation (OA) method are investigated. No method shows the best performance in all cases, while in many situations, sum product algorithm, dwMDS, nonlinear least square, projection approach, OA, and weighted least square work well. Copyright © The authors.Item Open Access Statistics of the MLE and Approximate Upper and Lower Bounds-Part 1: Application to TOA Estimation(IEEE, 2014-08) Mallat, A.; Gezici, Sinan; Dardari, D.; Craeye, C.; Vandendorpe, L.In nonlinear deterministic parameter estimation, the maximum likelihood estimator (MLE) is unable to attain the Cramer-Rao lower bound at low and medium signal-to-noise ratios (SNR) due the threshold and ambiguity phenomena. In order to evaluate the achieved mean-squared-error (MSE) at those SNR levels, we propose new MSE approximations (MSEA) and an approximate upper bound by using the method of interva l estimation (MIE). The mean and the distribution of the MLE ar e approximated as well. The MIE consists in splitting the a priori domain of the unknown parameter into intervals and computin g the statistics of the estimator in each interval. Also, we derive an approximate lower bound (ALB) based on the Taylor series expansion of noise and an ALB family by employing the binary detection principle. The accurateness of the proposed MSEAs and the tightness of the derived approximate bounds 1 are validated by considering the example of time-of-arrival estimation.Item Open Access Statistics of the MLE and Approximate Upper and Lower Bounds-Part 2: Threshold Computation and Optimal Signal Design(2014) Mallat, A.; Gezici, Sinan; Dardari, D.; Vandendorpe, L.Threshold and ambiguity phenomena are studied in Part I of this paper where approximations for the mean-squared error (MSE) of the maximum-likelihood estimator are proposed using the method of interval estimation (MIE), and where approximate upper and lower bounds are derived. In this part, we consider time-of-arrival estimation and we employ the MIE to derive closed-form expressions of the begin-ambiguity, end-ambiguity and asymptotic signal-to-noise ratio (SNR) thresholds with respect to some features of the transmitted signal. Both baseband and passband pulses are considered. We prove that the begin-ambiguity threshold depends only on the shape of the envelope of the ACR, whereas the end-ambiguity and asymptotic thresholds only on the shape of the ACR. We exploit the results on the begin-ambiguity and asymptotic thresholds to optimize, with respect to the available SNR, the pulse that achieves the minimum attainable MSE. The results of this paper are valid for various estimation problems.Item Open Access Statistics of the MLE and approximate upper and lower bounds-Part I: Application to TOA estimation(Institute of Electrical and Electronics Engineers Inc., 2014) Mallat, A.; Gezici, Sinan; Dardari, D.; Craeye, C.; Vandendorpe, L.In nonlinear deterministic parameter estimation, the maximum likelihood estimator (MLE) is unable to attain the Cramér-Rao lower bound at low and medium signal-to-noise ratios (SNRs) due the threshold and ambiguity phenomena. In order to evaluate the achieved mean-squared error (MSE) at those SNR levels, we propose new MSE approximations (MSEA) and an approximate upper bound by using the method of interval estimation (MIE). The mean and the distribution of the MLE are approximated as well. The MIE consists in splitting the a priori domain of the unknown parameter into intervals and computing the statistics of the estimator in each interval. Also, we derive an approximate lower bound (ALB) based on the Taylor series expansion of noise and an ALB family by employing the binary detection principle. The accuracy of the proposed MSEAs and the tightness of the derived approximate bounds are validated by considering the example of time-of-arrival estimation.Item Open Access Statistics of the MLE and approximate upper and lower bounds-part II: Threshold computation and optimal pulse design for TOA estimation(Institute of Electrical and Electronics Engineers Inc., 2014) Mallat, A.; Gezici, Sinan; Dardari, D.; Vandendorpe, L.Threshold and ambiguity phenomena are studied in Part I of this paper where approximations for the mean-squared error (MSE) of the maximum-likelihood estimator are proposed using the method of interval estimation (MIE), and where approximate upper and lower bounds are derived. In this part, we consider time-of-arrival estimation and we employ the MIE to derive closed-form expressions of the begin-ambiguity, end-ambiguity and asymptotic signal-to-noise ratio (SNR) thresholds with respect to some features of the transmitted signal. Both baseband and passband pulses are considered. We prove that the begin-ambiguity threshold depends only on the shape of the envelope of the ACR, whereas the end-ambiguity and asymptotic thresholds only on the shape of the ACR. We exploit the results on the begin-ambiguity and asymptotic thresholds to optimize, with respect to the available SNR, the pulse that achieves the minimum attainable MSE. The results of this paper are valid for various estimation problems.