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Institution

Deutsche Telekom

CompanyWelwyn Garden City, United Kingdom
About: Deutsche Telekom is a company organization based out in Welwyn Garden City, United Kingdom. It is known for research contribution in the topics: Telecommunications network & Terminal (electronics). The organization has 3473 authors who have published 5208 publications receiving 65429 citations. The organization is also known as: DTAG & German Telecom.


Papers
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Proceedings ArticleDOI
07 Sep 1997
TL;DR: A new approach to voice-activity detection (VAD) which is based on the wavelet transform (WT), which utilizes the WTs flexibility in the time-frequency resolution to compute robust parameters for VAD decision.
Abstract: This paper describes a new approach to voice-activity detection (VAD) which is based on the wavelet transform (WT). The algorithm utilizes the WTs flexibility in the time-frequency resolution to compute robust parameters for VAD decision. Furthermore, it exhibits a low complexity and can be easily adapted to operate as a pre-processor for many speech-coding algorithms. Two versions of the wavelet-transform-based VAD (WT-VAD) are tested against the VAD of the ITU-T G.729 Annex B (G729) and the VAD of the GSM enhanced full-rate codec (GSM), respectively. For a variety of background-noise types the WT-VAD shows superior noise robustness to signal-to-noise ratios above 10 dB.

41 citations

Proceedings ArticleDOI
05 May 2012
TL;DR: This project videotaped the interactions of four users performing magnetic signatures on a phone, in the presence of HD cameras from four different angles, and found the magnetic gestural signature authentication method to be more secure than PIN-based and 2D signature methods.
Abstract: Secure user authentication on mobile phones is crucial, as they store highly sensitive information. Common approaches to authenticate a user on a mobile phone are based either on entering a PIN, a password, or drawing a pattern. However, these authentication methods are vulnerable to the shoulder surfing attack. The risk of this attack has increased since means for recording high-resolution videos are cheaply and widely accessible. If the attacker can videotape the authentication process, PINs, passwords, and patterns do not even provide the most basic level of security. In this project, we assessed the vulnerability of a magnetic gestural authentication method to the video-based shoulder surfing attack. We chose a scenario that is favourable to the attack-er. In a real world environment, we videotaped the interactions of four users performing magnetic signatures on a phone, in the presence of HD cameras from four different angles. We then recruited 22 participants and asked them to watch the videos and try to forge the signatures. The results revealed that with a certain threshold, i.e, th=1.67, none of the forging attacks was successful, whereas at this level all eligible login attempts were successfully recognized. The qualitative feedback also indicated that users found the magnetic gestural signature authentication method to be more secure than PIN-based and 2D signature methods.

41 citations

Book ChapterDOI
01 Jan 2008
TL;DR: The physical and mathematical background of several methods for multichannel sound field reproduction is presented, which aim at the physically correct synthesis of acoustical wave fields with a large number of loudspeakers.
Abstract: Multichannel sound field reproduction aims at the physically correct synthesis of acoustical wave fields with a large number of loudspeakers. It goes beyond stereophony by extending or eliminating the so-called sweet spot. This chapter presents the physical and mathematical description of various methods for this purpose and presents the physical and mathematical background of several methods for multichannel sound field reproduction.

41 citations

Book ChapterDOI
TL;DR: The paper derives criteria and practical protocols for guaranteeing global snapshot isolation at the federation level and generalizes the well-known ticket method to cope with combinations of isolation levels in a federated system.
Abstract: Federated transaction management (also known as multidatabase transaction management in the literature) is needed to ensure the consistency of data that is distributed across multiple, largely autonomous, and possibly heterogeneous component databases and accessed by both global and local transactions. While the global atomicity of such transactions can be enforced by using a standardized commit protocol like XA or its CORBA counterpart OTS, global serializability is not self-guaranteed as the underlying component systems may use a variety of potentially incompatible local concurrency control protocols. The problem of how to achieve global serializability, by either constraining the component systems or implementing additional global protocols at the federation level, has been intensively studied in the literature, but did not have much impact on the practical side. A major deficiency of the prior work has been that it focused on the idealized correctness criterion of serializability and disregarded the subtle but important variations of SQL isolation levels supported by most commercial database systems. This paper reconsiders the problem of federated transaction management, more specifically its concurrency control issues, with particular focus on isolation levels used in practice, especially the popular snapshot isolation provided by Oracle. As pointed out in a SIGMOD 1995 paper by Berenson et al., a rigorous foundation for reasoning about such concurrency control features of commercial systems is sorely missing. The current paper aims to close this gap by developing a formal framework that allows us to reason about local and global transaction executions where some (or all) transactions are running under snapshot isolation. The paper derives criteria and practical protocols for guaranteeing global snapshot isolation at the federation level. It further generalizes the well-known ticket method to cope with combinations of isolation levels in a federated system.

41 citations

Journal ArticleDOI
TL;DR: This work studies the trade-off between the selfish motive of minimizing video distortion and the global good of minimizing network congestions in a convex optimization formulation, and discusses both centralized and distributed solutions for joint routing and rate allocation for multiple streams.
Abstract: The support for multiple video streams in an ad-hoc wireless network requires appropriate routing and rate allocation measures ascertaining the set of links for transmitting each stream and the encoding rate of the video to be delivered over the chosen links. The routing and rate allocation procedures impact the sustained quality of each video stream measured as the mean squared error (MSE) distortion at the receiver, and the overall network congestion in terms of queuing delay per link. We study the trade-off between these two competing objectives in a convex optimization formulation, and discuss both centralized and dis- tributed solutions for joint routing and rate allocation for multiple streams. For each stream, the optimal allocated rate strikes a balance between the selfish motive of minimizing video distortion and the global good of minimizing network congestions, while the routes are chosen over the least-congested links in the network. In addition to detailed analysis, network simulation results using ns-2 are presented for studying the optimal choice of parameters and to confirm the effectiveness of the proposed measures.

40 citations


Authors

Showing all 3475 results

NameH-indexPapersCitations
Jörg Müller6740715282
Anja Feldmann6734017422
Yuval Elovici6254414451
Lior Rokach5535719989
Pan Hui5246817724
Hartmut G. Roskos504349643
Wolfgang Haase5062411634
Shlomi Dolev4851610435
Jean-Pierre Seifert452987516
Stefan Schmid455619088
Fabian Schneider441647437
Karsten Buse433947774
Tansu Alpcan432937840
Florian Metze423187148
Christian Bauckhage422858313
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Performance
Metrics
No. of papers from the Institution in previous years
YearPapers
20232
20227
202139
202061
201984
201897