Overhearing the Wireless Interface for 802.11-based Positioning Systems

Not only the proliferation of 802.11, but also the capability to determine the position of mobile devices make 802.11 highly appealing for many application areas. Typically, a mobile device that wants to know its position regularly performs active or passive scans to obtain the signal strength measurements of neighboring access points. Active and passive scanning are survey techniques originally intended to be performed once in a while to learn about the presence and signal reception quality of access points within communication range. Based on this survey the best suitable access point is selected as the gateway to the wired network. However, so far, no investigations are known to have been launched into how regular scanning affects concurrent data transmissions from an end-user point of view. In this paper, we explore how common data communication is affected while actively or passively scanning at the same time. We found that with an active scanning interval of less than 2 seconds the network conditions such as throughput and round trip delay are insufficient for interactive applications. The same is true for passive scanning if a scanning interval of less than 7 seconds is chosen. Furthermore, we present a novel scan scheme called Monitor Sniffing to reduce client service disruptions. Monitor Sniffing exploits the fact that 802.11 operates on overlapping channels by overhearing the wireless interface. We have implemented our Monitor Sniffing algorithm using commodity 802.11g hardware, and we demonstrate that it is faster than active and passive scanning and does not disturb concurrent data communication. Finally, our approach only requires software modifications on the client side, making the adoption process quite easy

Positionierung mit Wireless-LAN und Bluetooth

In diesem Artikel wird ein Überblick über bestehende Wireless-LAN- und Bluetooth-basierte Positionierungssysteme gegeben. Eine detaillierte identifikation der Merkmale und Eigenschaften der unterschiedlichen Systeme soll helfen, Positionierungsverfahren anhand ihrer Eigenschaften einzuordnen

Enhancing curvature scale space features for robust shape classification

The curvature scale space (CSS) technique, which is also part of the MPEG-7 standard, is a robust method to describe complex shapes. The central idea is to analyze the curvature of a shape and derive features from inflection points. A major drawback of the CSS method is its poor representation of convex segments: Convex objects cannot be represented at all due to missing inflection points. We have extended the CSS approach to generate feature points for concave and convex segments of a shape. This generic approach is applicable to arbitrary objects. In the experimental results, we evaluate as a comprehensive example the automatic recognition of characters in images and videos

Robust Character Recognition in Low-Resolution Images and Videos

Although OCR techniques work very reliably for high-resolution documents, the recognition of superimposed text in low-resolution images or videos with a complex background is still a challenge. Three major parts characterize our system for recognition of superimposed text in images and videos: localization of text regions, segmentation (binarization) of characters, and recognition. We use standard approaches to locate text regions and focus in this paper on the last two steps. Many approaches (e.g., projection profiles, k-mean clustering) do not work very well for separating characters with very small font sizes. We apply in a vertical direction a shortest-path algorithm to separate the characters in a text line. The recognition of characters is based on the curvature scale space (CSS) approach which smoothes the contour of a character with a Gaussian kernel and tracks its inflection points. A major drawback of the CSS method is its poor representation of convex segments: Convex objects cannot be represented at all due to missing inflection points. We have extended the CSS approach to generate feature points for concave and convex segments of a contour. This generic approach is not only applicable to text characters but to arbitrary objects as well. In the experimental results, we compare our approach against a pattern matching algorithm, two classification algorithms based on contour analysis, and a commercial OCR system. The overall recognition results are good enough even for the indexing of low resolution images and videos

Automatic Generation of Video Summaries for Historical Films

A video summary is a sequence of video clips extracted from a longer video. Much shorter than the original, the summary preserves its essential messages. In the project ECHO (European Chronicles On-line) a system was developed to store and manage large collections of historical films for the preservation of cultural heritage. At the University of Mannheim we have developed the video summarization component of the ECHO system. In this paper we discuss the particular challenges the historical film material poses, and how we have designed new video processing algorithms and modified existing ones to cope with noisy black-and-white films. We also report empirical results from the use of our summarization tool at the four major European national video archives

COMPASS: A Probabilistic Indoor Positioning System Based on 802.11 and Digital Compasses

Positioning systems are one of the key elements required by context-aware application and location-based services. This paper presents the design, implementation and anaylsis of a positioning system called COMPASS which is based on 802.11 compliant network infrastructure and digital compasses. On the mobile device, COMPASS samples the signal strength values of different access points in communication range and utilizes the orientation of the user to preselect a subset of the training data. The remaining training data is used by a probabilistic position determination algorithm to determine the position of the user. While prior systems show only limited accuracy due to blocking effects caused by human bodies, we apply digital compasses to detect the orientations of the users so that we can handle these blocking effects. After a short period of training our approach achieves an average error distance of less than 1.65~meters in our experimental environment of 312 square meters

Prevalence of metabolic syndrome in patients with schizophrenia, and metabolic changes after 3 months of treatment with antipsychotics - results from a German observational study

<p>Abstract</p> <p>Background</p> <p>This observational study explored the prevalence of metabolic syndrome (MetS) in adult in- and outpatients with untreated or treated schizophrenia at baseline, and month-3 after initiation or switch of antipsychotic treatment.</p> <p>Methods</p> <p>MetS-prevalence (AHA/NHLB-definition) was assessed and Clopper-Pearson 95% confidence intervals (CIs) were calculated. Factors associated with MetS were explored through univariate and multivariate logistic regressions (both visits).</p> <p>Results</p> <p>MetS-prevalence was 44.3% (CI 39.8;48.9) at baseline and 49.6% (CI 45.0;54.2) at month-3. Previously unmedicated patients showed the lowest baseline MetS-prevalence (24.7%, CI 18.3;32.1). MetS-prevalence was not significantly different, regardless if patients previously received typical or atypical antipsychotics. Increased MetS-risk was associated with somatic comorbidity and non-smoking at both visits, and with non-psychiatric co-medication, male sex, and increased C-reactive protein at month-3.</p> <p>Conclusions</p> <p>At baseline, MetS was most prevalent in patients with previous antipsychotic medication. Limited metabolic changes were observed 3 months after switch/initiation of antipsychotic therapy.</p> <p>Trial Registration Number</p> <p>ClinicalTrials.gov Identifier: n.a.</p

Comparative Genomic Analysis of the Human Pathogen Wohlfahrtiimonas Chitiniclastica Provides Insight Into the Identification of Antimicrobial Resistance Genotypes and Potential Virulence Traits

Recent studies suggest that Wohlfahrtiimonas chitiniclastica may be the cause of several diseases in humans including sepsis and bacteremia making the bacterium as a previously underappreciated human pathogen. However, very little is known about the pathogenicity and genetic potential of W. chitiniclastica ; therefore, it is necessary to conduct systematic studies to gain a deeper understanding of its virulence characteristics and treatment options. In this study, the entire genetic repertoire of all publicly available W. chitiniclastica genomes was examined including in silico characterization of bacteriophage content, antibiotic resistome, and putative virulence profile. The pan-genome of W. chitiniclastica comprises 3819 genes with 1622 core genes (43%) indicating a putative metabolic conserved species. Furthermore, in silico analysis indicated presumed resistome expansion as defined by the presence of genome-encoded transposons and bacteriophages. While macrolide resistance genes macA and macB are located within the core genome, additional antimicrobial resistance genotypes for tetracycline ( tetH, tetB , and tetD ), aminoglycosides ( ant(2’’)-Ia, aac(6’)-Ia , aph(3’’)-Ib , aph(3’)-Ia , and aph(6)-Id )), sulfonamide ( sul2 ), streptomycin ( strA ), chloramphenicol ( cat3 ), and beta-lactamase ( blaVEB ) are distributed among the accessory genome. Notably, our data indicate that the type strain DSM 18708 T does not encode any additional clinically relevant antibiotic resistance genes, whereas drug resistance is increasing within the W. chitiniclastica clade. This trend should be monitored with caution. To the best of our knowledge, this is the first comprehensive genome analysis of this species, providing new insights into the genome of this opportunistic human pathogen