1er. congreso estatal de ramas de estudiantes del IEEE

Peer Reviewe

Visita al C.C.S. de Telefónica en "La Granada"

Peer Reviewe

NDA waveform estimation in the low-SNR regime

This correspondence addresses the problem of nondata-aided waveform estimation for digital communications. Based on the unconditional maximum likelihood criterion, the main contribution of this correspondence is the derivation of a closed-form solution to the waveform estimation problem in the low signal-to-noise ratio regime. The proposed estimation method is based on the second-order statistics of the received signal and a clear link is established between maximum likelihood estimation and correlation matching techniques. Compression with the signal-subspace is also proposed to improve the robustness against the noise and to mitigate the impact of abnormals or outliers.Peer Reviewe

Waveform-independent frame-timing acquisition for UWB signals

In this paper, the problem of frame-level symbol timing acquisition for UWB signals is addressed. The main goal is the derivation of a frame-level timing estimator which does not require any prior knowledge of neither the transmitted symbols nor the received template waveform. The independence with respect to the received waveform is of special interest in UWB communication systems, where a fast and accurate estimation of the end-to-end channel response is a challenging and computationally demanding task. The proposed estimator is derived under the unconditional maximum likelihood criterion, and because of the low power of UWB signals, the low-SNR assumption is adopted. As a result, an optimal frame-level timing estimator is derived which outperforms existing acquisition methods in low-SNR scenarios.Peer Reviewe

Asymptotic equivalence between the unconditional maximum likelihood and the square-law nonlinearity symbol timing estimation

This paper provides a systematic approach to the problem of nondata aided symbol-timing estimation for linear modulations. The study is performed under the unconditional maximum likelihood framework where the carrier-frequency error is included as a nuisance parameter in the mathematical derivation. The second-order moments of the received signal are found to be the sufficient statistics for the problem at hand and they allow the provision of a robust performance in the presence of a carrier-frequency error uncertainty. We particularly focus on the exploitation of the cyclostationary property of linear modulations. This enables us to derive simple and closed-form symbol-timing estimators which are found to be based on the well-known square timing recovery method by Oerder and Meyr. Finally, we generalize the OM method to the case of linear modulations with offset formats. In this case, the square-law nonlinearity is found to provide not only the symbol-timing but also the carrier-phase error.Peer Reviewe

Detection of PPM-UWB random signals

This paper focuses on the symbol detection problem of random pulse-position modulation (PPM) ultrawideband (UWB) signals in the absence of interframe interference. Particular attention is devoted to severely time-varying channels where optimal detectors are proposed for both uncorrelated and correlated scattering scenarios. This is done by assuming the received waveforms to be unknown parameters. In UWB communication systems, the assumption of unknown random waveforms is consistent with the fact that the received waveform has very little resemblance with the original transmitted pulse. In order to circumvent this limitation, a conditional approach is presented herein by compressing the likelihood ratio test with the information regarding the second-order moments of the end-to-end channel response. Both full-rank and rank-one detectors are derived. For the reduced complexity rank-one detector, an iterative procedure is presented that maximizes the J-divergence between the hypotheses to be tested. Finally, simulation results are provided to compare the performance of the proposed detectors in different propagation environments.Peer Reviewe

Encuentro de Ramas del IEEE en Estambul

Peer Reviewe

Encuentro de Ramas del IEEE en Estambul

Peer Reviewe

Performance assessment of a low-complexity autoregressive Kalman filter for GNSS carrier tracking using real scintillation time series

Altres ajuts: Acord transformatiu CRUE-CSICIonospheric scintillation is one of the most challenging sources of errors in global navigation satellite systems (GNSS). It is an effect of space weather that introduces rapid amplitude and phase fluctuations to transionospheric signals and, as a result, it severely degrades the tracking performance of receivers, particularly carrier tracking. It can occur anywhere on the earth during intense solar activity, but the problem aggravates in equatorial and high-latitude regions, thus posing serious concerns to the widespread deployment of GNSS in those areas. One of the most promising approaches to address this problem is the use of Kalman filter-based techniques at the carrier tracking level, incorporating some a priori knowledge about the statistics of the scintillation to be dealt with. These techniques aim at dissociating the carrier phase dynamics of interest from phase scintillation by modeling the latter through some correlated Gaussian function, such as the case of autoregressive processes. However, besides the fact that the optimality of these techniques is still to be reached, their applicability for dealing with scintillation in real-world environments also remains to be confirmed. We carry out an extensive analysis and experimentation campaign on the suitability of these techniques by processing real data captures of scintillation at low and high latitudes. We first evaluate how well phase scintillation can be modeled through an autoregressive process. Then, we propose a novel adaptive, low-complexity autoregressive Kalman filter intended to facilitate the implementation of the approach in practice. Last, we provide an analysis of the operational region of the proposed technique and the limits at which a performance gain over conventional tracking architectures is obtained. The results validate the excellence of the proposed approach for GNSS carrier tracking under scintillation conditions

Tècnica per millorar la tecnologia de banda ultra-ampla

En l'àmbit de la comunicació sense fils, la tecnologia de banda ultra-ampla permet d'obtenir comunicacions de molt elevada velocitat i té aplicacions molt diverses, entre elles els radars d'alta precisió o les transmissions multimèdia. D'altra banda, les peculiars característiques dels senyals de banda ultra-ampla fan que la seva recepció i sincronització presenti importants problemes. Investigadors de la UAB i de la UPC han dissenyat una tècnica per solventar-los.En el ámbito de la comunicación sin hilos, la tecnología de banda ultra- ancha permite obtener comunicaciones de muy elevada velocidad y tiene aplicaciones muy diversas, entre ellas los radares de alta precisión o las transmisiones multimedia. Por otra parte, las peculiares características de las señales de banda ultra-ancha hacen que su recepción y sincronización presente problemas importantes. Investigadores de la UAB y de la UPC han diseñado una técnica para solventarlos.In the field of wireless communication, ultra-wideband technology allows obtaining very high data-rates with diverse applications such as high accuracy radars and multimedia transmissions. However, the particular characteristics of ultra-wideband signals make their synchronization and reception very difficult. Researchers at UAB and UPC have designed a technique to solve this problem