Link adaptation for Ka band low Earth orbit Earth Observation systems: A realistic performance assessment

In this paper, a proposal is sketched for realizing high data rate downlinks in next‐generation Ka band low Earth orbit (LEO) Earth Observation (EO) systems. The work aims at realistically assessing the throughput advantage stemming from link adaptation strategies—embraced by most wireless and satellite communication standards—compared with non‐adaptive transmission, which is the approach followed in conventional X band EO systems. The transmission strategies examined include constant, (static and dynamic) variable, and adaptive flavors of coding and modulation, each representing a different performance/system complexity trade‐off. Practicality is pursued to the extent possible by incorporating state‐of‐the‐art orbital, ground station, spacecraft, propagation, physical layer, and system implementation characteristics. The results manifest that under particular conditions, link adaptation offers throughput improvements of up to 100% against non‐adaptive transmission schemes in Ka band LEO EO systems. Copyright © 2012 John Wiley & Sons, Ltd.     

Practical MIMO aspects in dual polarization per beam mobile satellite broadcasting

Building upon a number of recent publications promoting the use of multiple‐input multiple‐output (MIMO) over dual polarization per beam mobile satellite broadcasting (MSB), the present paper sets MIMO well on its way for practical implementation in next‐generation MSB by analyzing critical aspects of this novel architecture. Specifically, it carries out a sensitivity analysis of various system parameters including how time interleaving, terminal antenna cross‐polarization discrimination and intrasytem interference impact MIMO performance. Next, the paper proposes a channel estimation approach compatible with the latest digital video broadcasting‐satellite to handheld (DVB‐SH) standard for MIMO land mobile satellite (LMS) channel estimation. Finally, the impact of non‐linear distortion on the most prominent space–time coding alternatives is investigated. Copyright © 2012 John Wiley & Sons, Ltd.     

Design of Circular Switched Parasitic Dipole Arrays Using a Genetic Algorithm

Circular switched parasitic dipole arrays are designed in this letter, using the method of genetic algorithms. Three possible configurations are proposed: a simple circular array with one element driven and the others short-circuited, and two implementations of double-ring array. In the latter case, an inner ring of parasitic elements is added. Electronic steering is achieved through switching of the elements by circular permutation. The aim of the design is to obtain a desired radiation pattern, and to achieve impedance matching of the single active element. The arrays are simulated with the SuperNEC2.4 package and the induced emf method. Double-ring arrays offer better patterns and more accurate impedance matching than simple circular arrays at 1.8 GHz. The designed arrays achieve SWR values below 2.5 from 1.7 to 1.9 GHz. The radiation patterns remain satisfying in an average bandwidth equal to 6.5% of the carrier frequency.     

Dual polarization MIMO in LMS broadcasting systems: Possible benefits and challenges

The benefits of employing dual polarization in wireless multiple‐input multiple‐output (MIMO) communication systems are only recently becoming apparent due to the continuous measurement and modeling efforts by the terrestrial research community. Land mobile satellite (LMS) broadcasting systems exhibit distinct channel, system and geometrical characteristics and are subjected to stringent spatial limitations compared to terrestrial wireless. Therefore, it remains to be investigated which operating conditions favor the joint instead of the independent encoding/decoding over the two polarizations of satellite beams. After outlining the relevant progress made in wireless dual polarization MIMO systems, the present work carries out a thorough comparison between the joint and independent encoding/decoding approaches in typical single‐satellite LMS systems exploiting state‐of‐the‐art building blocks. This comparative analysis investigates both the capacity and error performance under a fair framework between systems occupying the same resources. Since the same analytical tools are used for both terrestrial and satellite dual polarization systems, the present paper may also serve as an analytical bridge between the two. Copyright © 2010 John Wiley & Sons, Ltd.     

Railway satellite channel at Ku band and above: Composite dynamic modeling for the design of fade mitigation techniques

Past studies on the railway satellite channel (RSC) at Ku band and above consider exclusively the attenuation coming from the metal power arches (PAs) along the railway route, producing significant though deterministic periodical fast fading. Nevertheless, limited attention has been given to model tropospheric effects on the RSC. The present paper takes a more comprehensive view of the RSC by introducing a novel stochastic dynamic model of rain fading in mobile satellite systems on top of the diffraction because of PAs. The proposed approach builds upon well‐established research on rain attenuation time series synthesizers employing stochastic differential equations. It is shown that this propagation tool may provide significant aid, in general, in mobile satellite system simulations and in the design of fade mitigation techniques (FMTs), particularly aiming at the railway scenario. The tool enables the generation of fade events, fade duration statistics, rain attenuation power spectrum and predicting the necessary FMT control loop margin. This is particularly useful for the RSC because most of the proposed FMTs focusing on PAs are not appropriate for compensating atmospheric fading. Copyright © 2011 John Wiley & Sons, Ltd.     

Multimodal registration of retinal images using self organizing maps

In this paper, an automatic method for registering multimodal retinal images is presented. The method consists of three steps: the vessel centerline detection and extraction of bifurcation points only in the reference image, the automatic correspondence of bifurcation points in the two images using a novel implementation of the self organizing maps and the extraction of the parameters of the affine transform using the previously obtained correspondences. The proposed registration algorithm was tested on 24 multimodal retinal pairs and the obtained results show an advantageous performance in terms of accuracy with respect to the manual registration.     

Oxidative stress due to anesthesia and surgical trauma: Importance of early enteral nutrition

Anesthesia and surgical trauma are considered major oxidative and nitrosative stress effectors resulting in the development of SIRS. In this study we evaluated the usefulness of early enteral nutrition after surgical trauma. Sixty male Wistar rats were subjected to midline laparotomy and feeding‐gastrostomy. Twenty of these rats served as controls after recovering from the operation stress. The remaining rats received, through gastrostomy, enteral nutrition or placebo‐feeding for 24 h. Oxidative stress markers and CC chemokine production were evaluated in rat serum and liver tissue. The operation itself was found to increase nitric oxide (NO) and malondialdehyde (MDA) and to decrease superoxide dismutase (SOD) and glutathione peroxidase (GSH‐Px), as well as liver tissue energy charge (EC) in relation to controls. The rats receiving enteral feeding exhibited statistically significantly lower levels of NO and MDA, and higher levels of SOD, GSH‐Px, and liver EC, in relation to placebo feeding rats. The operation significantly increased the chemokines monocyte chemoattractant protein (MCP)‐1 and regulated upon activation, normal T‐cell expressed, and secreted (RANTES) in rat serum, while enteral nutrition caused a further significant increase in chemokine levels in serum. mRNA chemokine expression in liver was increased in a similar pattern. These findings indicate that early enteral feeding might play an important role after surgery ameliorating oxidative stress, affecting positively the hepatic EC and regulating, via chemokine production, cell trafficking, and healing process.     

Detecting Collaborations in Text Comparing the Authors' Rhetorical Language Choices in The Federalist Papers

In author attribution studies function words or lexical measures areoften used to differentiate the authors' textual fingerprints. Thesestudies can be thought of as quantifying the texts, representing thetext with measured variables that stand for specific textual features.The resulting quantifications, while proven useful for statisticallydifferentiating among the texts, bear no resemblance to the understanding a human reader – even an astute one – would develop whilereading the texts. In this paper we present an attribution study that,instead, characterizes the texts according to the representationallanguage choices of the authors, similar to a way we believe close humanreaders come to know a text and distinguish its rhetorical purpose. Fromour automated quantification of The Federalist papers, it isclear why human readers find it impossible to distinguish the authorshipof the disputed papers. Our findings suggest that changes occur in theprocesses of rhetorical invention when undertaken in collaborativesituations. This points to a need to re-evaluate the premise ofautonomous authorship that has informed attribution studies of The Federalist case.