Multi-user synchronisation in ad-hoc OFDM-based wireless personal area networks

In this paper, a procedure for dealing with the multi-user synchronisation problem in Orthogonal Frequency Division Multiple Access (OFDMA)-based systems for ad hoc environments is proposed and analysed. We show with this novel approach that it is possible to re-use much of the already extent literature for single-user synchronisation in OFDM and apply it to multi-user ad hoc scenarios. Also a distributed version of the procedure is proposed in order to fairly share out the power consumption among all the devices. The proposed procedure makes use of higher layer capabilities in a cross-layer design and it does not incur too much complexity or power. This issue is specially critical in wireless heterogeneous ad hoc networks where devices can be very limited in terms of transmission and/or computational power.Publicad

International migration and universal healthcare access: evidence from Mexico's 'Seguro Popular'

Although 'Seguro Popular' (SP), a healthcare programme for the uninsured, has been in place in Mexico for more than a decade, its consequences for international migration both to and from the country have received little scholarly attention. Using the spatial variation in the programme's coverage generated through the rollout over time, this paper examines the effects of SP on the number of emigrants and return migrants per household. Based on data from Mexico's National Survey on Demographic Dynamics for 1997–2014, the analysis confirms that being affiliated to SP does not reduce the number of emigrants per household, but such affiliation is, however, positively related to the number of returnees per household. These results are valid across different subsamples of the population and time periods and are robust to omitted variable bias. Our findings have important implications for understanding the effects of social protection policies on international migration patterns

Selective area growth and characterization of InGaN nano-disks implemented in GaN nanocolumns with different top morphologies

This work reports on the morphology control of the selective area growth of GaN-based nanostructures on c-plane GaN templates. By decreasing the substrate temperature, the nanostructures morphology changes from pyramidal islands (no vertical m-planes), to GaN nanocolumns with top semipolar r-planes, and further to GaN nanocolumns with top polar c-planes. When growing InGaN nano-disks embedded into the GaN nanocolumns, the different morphologies mentioned lead to different optical properties, due to the semi-polar and polar nature of the r-planes and c-planes involved. These differences are assessed by photoluminescence measurements at low temperature and correlated to the specific nano-disk geometry

Efficient Implementation of Complementary Golay Sequences for PAR Reduction and Forward Error Correction in OFDM-based WLAN systems

In this paper the use of complementary Golay sequences (CGS) for peak-to-average power ratio (PAR) reduction and forward error correction (FEC) in an orthogonal frequency division multiplexing (OFDM)-based wireless local area network (WLAN) system is explored; performance is examined and complexity issues are analyzed. We study their PAR reduction performance depending on sequence lengths and we have found that, for the case that the number of sub-carriers differs from the sequence length, some interesting relationships can still be stated. Regarding their error correction capabilities, these sequences are investigated considering M-PSK constellations applied to the OFDM signal specified in IEEE 802.11a standard. Computational load for both Golay encoding and decoding processes is addressed and we provide an exhaustive analysis of their complexity. In order to overcome memory restrictions and speed up algorithmic operations, a novel algorithm for real-time generation of the Golay Base Sequences is proposed and evaluated giving as a conclusion that these sequences can be real-time generated with actual Digital Signal Processors (DSP). Our proposal lies on an efficient permutation algorithm that obtains the current permutation without the need for generating previous ones. Its complexity is calculated and turns out to be significantly low; the advantages are specially appreciated at the decoding stage. We also introduce a hybrid solution to get a trade-off between complexity and memory requirements. Moreover, the whole system is also implemented in a DSP to validate the proposal in a prototype, where its feasibility has been confirmed.This work has been partly funded by the Spanish government with projects MACAWI (TEC 2005-07477-c02-02) and MAMBO (UC3M-TEC-05-027)

Effects of channel estimation on multiuser virtual MIMO-OFDMA relay-based networks

A practical multiuser cooperative transmission scheme denoted as Virtual Maximum Ratio Transmission (VMRT) for multiple-input multiple-output-orthogonal frequency division multiple access (MIMO-OFDMA) relay-based networks is proposed and evaluated in the presence of a realistic channel estimation algorithm and using low-density parity-check (LDPC) codes. It is shown that this scheme is robust against channel estimation errors. It offers diversity and array gain, keeping the complexity low with a multiuser and multiantenna channel estimation algorithm that is simple and efficient. In addition, the combination with LDPC codes provides improved gains; diversity gains larger than 6 dB can be easily obtained with a reduced number of relays. Thus, this scheme can be used to extend coverage or increase system throughput by using simple cooperative OFDMA-based relays.The authors would like to thank Jae-Yun Ko for his valuable help at the beginning of our work. This work has been partly funded by the projects MULTIADAPTIVE (TEC2008-06327- C03-02), COMONSENS (CSD2008-00010) and CODIV (ICT-2007-215477).Publicad

Design and implementation of synchronization and AGC for OFDM-based WLAN receivers

An efficient implementation of several tasks at the receiver becomes crucial in OFDM-based high-speed WLAN systems, such as automatic gain control, time and frequency synchronization and offset tracking. This paper deals with fixed point constraints and accuracy requirements for implementation of those algorithms. Also, a complete set of thresholds for the practical implementation of time and frequency synchronization sub-blocks is obtained. Moreover, a technique to mitigate the remaining frequency offset after coarse acquisition is proposed, yielding a good trade-off between performance and complexity. Finally, we propose the implementation of a simple and effective automatic gain control procedure.This work has been partially funded by Spanish government with project TIC 2002-03498 (ORISE), Telefonica I+D by the contract nº 25756, and the Chamber of Madrid Community and European Social Fund by a grant to the first author

Expanding the Clinical and Molecular Heterogeneity of Nonsyndromic Inherited Retinal Dystrophies

A cohort of 172 patients diagnosed clinically with nonsyndromic retinal dystrophies, from 110 families underwent full ophthalmologic examination, including retinal imaging, electrophysiology, and optical coherence tomography, when feasible. Molecular analysis was performed using targeted next-generation sequencing (NGS). Variants were filtered and prioritized according to the minimum allele frequency, and finally classified according to the American College of Medical Genetics and Genomics guidelines. Multiplex ligation-dependent probe amplification and array comparative genomic hybridization were performed to validate copy number variations identified by NGS. The diagnostic yield of this study was 62% of studied families. Thirty novel mutations were identified. The study found phenotypic intra- and interfamilial variability in families with mutations in C1QTNF5, CERKL, and PROM1; biallelic mutations in PDE6B in a unilateral retinitis pigmentosa patient; interocular asymmetry RP in 50% of the symptomatic RPGR-mutated females; the first case with possible digenism between CNGA1 and CNGB1; and a ROM1 duplication in two unrelated retinitis pigmentosa families. Ten unrelated cases were reclassified. This study highlights the clinical utility of targeted NGS for nonsyndromic inherited retinal dystrophy cases and the importance of full ophthalmologic examination, which allows new genotypeephenotype associations and expands the knowledge of this group of disorders. Identifying the cause of disease is essential to improve patient management, provide accurate genetic counseling, and take advantage of gene therapyebased treatments. (J Mol Diagn 2020, 22: 532e543; https:// doi.org/10.1016/j.jmoldx.2020.01.003)Supported by grants from the Instituto de Salud Carlos III (ISCIII) of the Spanish Ministry of Health, including the Center for Biomedical Research Network on Rare Diseases (CIBERER), Fondo de Investigacion Sanitaria grant PI16/00539; the Spanish National Organization for the Blind (Fundación ONCE); and Fundación Mutua Madrileña. G.G.-G. is sponsored by the CIBERER, and A.R.-M. is supported by the Río Hortega program from ISCIII.Medicin

Two Neolithic structures at the archaeological site of Casa Garrido Nord II (Moixent, Valencia)

Es presenten les restes de cronologia neolítica documentades a les obres de canalització de gas a la vall de Montesa. Concretament, dues sitges del Neolític II de la seqüència regional, aparegudes al jaciment de Casa Garrido Nord, al terme municipal de Moixent. Encara que els materials són poc significatius, es tracta de les primeres estructures de cronologia neolítica, de les quals tenim constància, en què s’ha realitzat una excavació arqueològica sistemàtica a la comarca de la Costera. Paraules clau: Casa Garrido Nord II. Sitja. Neolític II. La Costera. Assentaments en pla.Es presenten les restes de cronologia neolítica documentades a les obres de canalització de gas a la vall de Montesa. Concretament, dues sitges del Neolític II de la seqüència regional, aparegudes al jaciment de Casa Garrido Nord, al terme municipal de Moixent. Encara que els materials són poc significatius, es tracta de les primeres estructures de cronologia neolítica, de les quals tenim constància, en què s’ha realitzat una excavació arqueològica sistemàtica a la comarca de la Costera. Paraules clau: Casa Garrido Nord II. Sitja. Neolític II. La Costera. Assentaments en pla.Herewith we submit the remains of Neolithic chronology found at the gas piping works performed at the Valley of Montesa (Valencia). They are specifically two Neolithic II underground storage places of a regional sequence, which appeared at the Casa Garrido Nord archaeological site, within the Moixent municipal borough (in the province of Valencia). Although the materials are not very meaningful, they represent the first structures of Neolithic chronology known to us, and therefore we have carried out a systematic archaeological excavation in the area of La Costera (Valencia). Key words: Casa Garrido Nord II. Silo. Neolithic II. La Costera. Settlements on flat lands

El uso de imágenes Ikonos para la cartografía de riesgo de inundación en pequeñas cuencas mediterráneas

La confección de una cartografía efectiva de riesgo de inundación precisa de la elaboración previa de mapas de peligro, que recojan las zonas sometidas a los procesos naturales asociados a la crecida. Para la configuración de estos mapas resulta muy útil el estudio de las áreas afectadas en sucesos concretos. En esta tarea el uso de la teledetección se ha demostrado altamente eficaz para el caso de grandes cuencas, afectadas por procesos de inundación extensivos y llanuras bien definidas. Sin embargo, para el caso de pequeñas cuencas mediterráneas, donde los espacios inundables son de índole muy variada, pequeña dimensión y rápido drenaje, el uso de las imágenes de satélite no siempre ha sido eficaz. La comercialización, en los último años, de imágenes de muy alta resolución (Ikonos, Quickbird) constituye una alternativa viable para la detección de las zonas afectadas en pequeñas cuencas. El presente trabajo constituye un ejemplo de uso de una imagen Ikonos para el análisis de las zonas inundadas durante el suceso de octubre del año 2000 en la Rambla de Poyo - Barranc de Torrent. Esta cuenca tiene una dimensión de 462 km2 , desemboca en la Albufera y presenta varias zonas inundables que afectan al área metropolitana de Valencia. Durante el suceso de octubre del 2000, tuvo lugar una crecida de más de 500 m3/s que dio lugar a diversos problemas de inundación, referenciados, en su día, mediante trabajo de campo y fotografía oblícua. El análisis visual de la imagen IKONOS permite establecer, de una manera rápida y completa, la extensión de la zona inundada, así como inferir los principales procesos de rotura en cauce, derrame y desbordamiento, asociados a la crecida