Capacity Analysis in Downlink WCDMA Systems Using Soft Handover Techniques With SIR-Based Power Control and Site Selection Diversity Transmission

This work analyzes the downlink performance of a WCDMA system with site selection diversity transmission power control (SSDT) during soft handover mode. Signal to interference ratio (SIR) power control techniques are modeled and used in the simulations of this analysis. The study is focused on finding the optimum soft handover margin in terms of maximum system capacity under energy-per-bit to noise spectral density ratio (Eb/N0) quality requirements. The results of this analysis show an increase in user capacity of about 15 -20 % for optimum soft handover margins of 5 – 5.5 dB. Nevertheless, the resources required (number of scrambling codes) by base station increase faster than the number of active users in terms of soft handover margin up to soft handover margin values of approximately 9.5 dB.Reig, J. (2006). Capacity Analysis in Downlink WCDMA Systems Using Soft Handover Techniques With SIR-Based Power Control and Site Selection Diversity Transmission. IEEE Transactions on Vehicular Technology. 55(4):1362-1372. doi:10.1109/TVT.2006.877705S1362137255

Performance of Maximal Ratio Combiners over Correlated Nakagami-m Fading Channels with Arbitrary Fading Parameters

In this letter, performance metrics of maximal ratio combiners (MRC) over correlated Nakagami-m fading are calculated with both arbitrary fading parameters and average powers. We derive the moment generating function (MGF) of the sum of correlated gamma variables with arbitrary fading parameters. Using the MGF-based approach, we obtain the variance of the signal-to-noise ratio (SNR) at the output of the combiner, the outage probability, the average symbol error rate for coherent multichannel reception, and the diversity gain. The results for an exponentially decaying model of the fading parameter are presented and discussed.Reig, J. (2008). Performance of Maximal Ratio Combiners over Correlated Nakagami-m Fading Channels with Arbitrary Fading Parameters. IEEE Transactions on Wireless Communications. 7(5):1441-1445. doi:10.1109/TWC.2008.060129S144114457

Non-radial pulsations in the Be/X binaries 4U0115+63 and SAXJ2103.5+4545

The discovery of non-radial pulsations (NRP) in the Be/X binaries of the Magellanic Clouds (MC, eg. Fabrycky 2005, Coe et al. 2005, Schmidtke & Cowley 2005) provided a new approach to understand these complex systems, and, at the same time, favoured the synergy between two different fields: stellar pulsations and X-ray binaries. This breakthrough was possible thanks to the MACHO and OGLE surveys. However, in our Galaxy, only two Be/X have been reported to show NRP: GROJ2058+42 (Kiziloglu et al. 2007) and LSI+61 235 (Sarty et al. 2009). Our objective is to study the short-term variability of Galactic Be/X binaries, compare them to the Be/X of the MC and to the isolated Galactic Be observed with CoRoT and Kepler. We present preliminary results of two Be/X stars, namely 4U0115+63 and SAXJ2103.5+4545 showing multiperiodicity and periodicity respectively, most probably produced by non-radial pulsations.Comment: 2 pages, 2 figures, IAUS 272 "Active OB stars: structure, evolution, mass loss and critical limits" conference, Paris, July 2010, submitte

Sobre el ornitónimo "Zaida" y la presencia de la Grulla Damisela (Anthropoides Virgo) en España

Una de las aves del solar hispano más antiguas y más desconocidas es la grulla damisela (Anthropoides virgo). Extinguida de la península ibérica desde la década de los años veinte del siglo pasado, este ave ha recibido diversos vernáculos, desde el más primitivo y genuino de origen arábigo “çaida” (escrito, a veces, como caida, çayda, zaida, zayda, etc.), hasta otros más recientes como “señorita”, “garza de Mallorca”, “grulla de Numidia”, “grulla mora”, “grulla moruna”, o “rugidera”. Nos proponemos pergeñar una somera evolución de aquel olvidado ornitónimo, tan prístino y elegante, recuperando textos literarios e imágenes de interés. Al mismo tiempo, se intenta constatar la presencia de la grulla damisela como ave nativa española

On Simple Estimators of the alpha-mu Fading Distribution

In this letter, new estimators of the alpha-mu distribution are derived based on the skewness of the logarithmic alpha-mu distribution using the moments method. This distribution has been recently proposed to model the received field strength in nonlinear propagation mediums. Therefore, simple and computationally efficient estimators are required to infer the parameters of the received signal amplitude distribution in nonlinear wireless communication propagation channels. The performance of these new estimators is compared to that obtained with the estimators calculated with the moments method of the alpha-mu distribution by solving numerically transcendental equations. These estimators are easily evaluated with simple expressions.Reig, J.; Rubio Arjona, L. (2011). On Simple Estimators of the alpha-mu Fading Distribution. IEEE Transactions on Communications. 59(12):3254-3258. doi:10.1109/TCOMM.2011.080111.090223S32543258591

Estimation of the composite fast fading and shadowing distribution using the log-moments in wireless communications

In this work, we propose a framework to obtain estimators from a variety of distributions used in composite fast fading and shadowing modeling with applications in wireless communications: the Suzuki (Rayleigh-lognormal), Nakagami-lognormal, K (Rayleigh-gamma), generalized-K (Nakagami-gamma) and alpha-mu; (generalized gamma) distributions. These estimators are derived from the method of moments of these distributions in logarithmic units, usually known as log-moments. The goodness-of-fit of these estimators to experimental distributions has been checked from a measurement campaign carried out in an urban environment. Moreover a new method to separate fast fading and shadowing based on the Rathgeber procedure is proposed. The results conclude that the best-fitting distribution to the measurements is the Nakagami-lognormal. Also, the alpha-mu; distribution provides an acceptable matching with the advantage of its simplicity.The authors would like to thank the editor and reviewers their valuable comments which have enriched the quality of this paper. We would also express our gratitude to Dr. C. S. Withers, retired research statistician from the Applied Maths Group at Industrial Research Ltd, Lower Hutt, New Zealand, for his revision of the paper and his estimable remarks. This work has been funded in part by the Spanish Ministerio de Ciencia e Innovacion (TEC-2010-20841-C04-1).Reig, J.; Rubio Arjona, L. (2013). Estimation of the composite fast fading and shadowing distribution using the log-moments in wireless communications. IEEE Transactions on Wireless Communications. 12(8):3672-3681. https://doi.org/10.1109/TWC.2013.050713.120054S3672368112

Tocando de oído: la intrigante y misteriosa Grulla balear

La presente contribución expone la curiosa historia por la cual dos especies etiópicas de la familia de las grullas reciben un nombre genérico insular (Balearica), pese a que nunca han formado parte de la fauna del archipiélago. Las raíces de esta curiosa historia tienen dos mil años de antigüedad, y se analizan aquí los errores y casualidades que han dado lugar a esta situación nomenclatural. Así mismo, se presentan y discuten citas de otras grullas en nuestro entorno geográfico

Efectos de la crisis en el crédito comercial concedido y relevancia de la diversificación de la actividad

ResumenEl objetivo de este trabajo es estudiar las razones por las que las empresas manufactureras españolas conceden crédito comercial a sus clientes. Hemos analizado teórica y empíricamente 2 aspectos: el efecto producido por la crisis financiero-económica y la importancia que tiene la diversificación de la actividad y el tipo de cliente al que se le concede el crédito comercial. Las principales conclusiones que obtenemos son, por una parte, que el incremento del crédito comercial concedido en periodo de crisis provoca que las empresas sean menos competitivas, y en segundo lugar aportamos evidencia de que la diversificación de la actividad y el hecho de que los clientes sean más o menos homogéneos son determinantes en la concesión de crédito comercial.AbstractThis paper contributes to demonstrate the relevance of trade credit in the finances of the Spanish manufacturing companies. A theoretical and empirical analysis is made of the aspects of trade credit: its role within financial and economic crisis, and the relevance of diversification of activity, as well as the type of customer that receives trade credit. The main conclusions are, first, that the increase in trade credit granted in times of crisis causes companies to be less competitive and, secondly, evidence is provided that shows that diversification of activity and the fact that customers are more or less homogeneous are crucial to the trade credit policies

Vertical Integration and Profitability of the Agrifood Industry in an Economic Crisis Context

In a setting of economic and financial crisis, most companies experienced a reduction in their profitability. Thus, our study allows us to identify vertical integration strategies developed by companies to overcome the crisis. This paper is aimed at unveiling the determining factors of the profitability of Spanish agrifood firms, depending on whether they are backwards vertically integrated or not. In order to attain our objective, we implemented a first difference regression model. The main contributions of the article lie in the incorporation of a variable that distinguishes integrated firms from the rest and the separate analysis of the two groups of firms. The results suggest that firms that seek to differentiate themselves, either through offering a specific product or through providing higher quality with a view to maintaining their reputation, are more likely to adopt vertical integration due to the higher transaction costs of relations with suppliers. The grouping carried out in this study is shown to be highly relevant as asset structure implies different strategies for actions aimed at increasing profitability