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Figueiras J.,Telecommunications Research Center Vienna Ftw | Gronbaek J.,Telecommunications Research Center Vienna Ftw | Ceccarelli A.,University of Florence | Schwefel H.-P.,Telecommunications Research Center Vienna Ftw | Schwefel H.-P.,University of Aalborg
Proceedings of IEEE International Symposium on High Assurance Systems Engineering | Year: 2012

Context-dependent decisions in safety-critical applications require careful consideration of accuracy and timeliness of the underlying context information. Relevant examples include location-dependent actions in mobile distributed systems. This paper considers localization functions for personalized warning systems for railway workers, where the safety aspects require timely and precise identification whether a worker is located in a dangerous (red) or safe (green) zone within the worksite. The paper proposes and analyzes a data fusion approach based on low-cost GPS receivers integrated on mobile devices, combined with electronic fences strategically placed in the adjacent boundaries between safe and unsafe geographic zones. An approach based on the combination of a Kalman Filter for GPS-based trajectory estimation and a Hidden Markov Model for inclusion of mobility constraints and fusion with information from the electronic fences is developed and analyzed. Different accuracy metrics are proposed and the benefit obtained from the fusion with electronic fences is quantitatively analyzed in the scenarios of a single mobile entity: By having fence information, the correct zone estimation can increase by 30%, while false alarms can be reduced one order of magnitude in the tested scenario. © 2012 IEEE.

Laner M.,Vienna University of Technology | Svoboda P.,Vienna University of Technology | Hasenleithner E.,Telecommunications Research Center Vienna ftw | Rupp M.,Vienna University of Technology
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2011

Users expect mobile Internet access via 3G technologies to be comparable to wired access in terms of throughput and latency. HSPA achieves this for throughput, whereas delay is significantly higher. In this paper we measure the overall latency introduced by HSUPA and accurately dissect it into contributions of USB-modem (UE), base station (NodeB) and network controller (RNC). We achieve this by combining traces recorded at each interface along the data-path of a public operational UMTS network. The actively generated sample traffic covers real-time applications. Results show the delay to be strongly dependent on the packet size, with random components depending on synchronization issues. We provide models for latency of single network entities as well as accumulated delay. These findings allow to identify optimum settings in terms of low latency, both for application and network parameters. © 2011 Springer-Verlag.

Egger S.,Telecommunications Research Center Vienna Ftw | Hossfeld T.,University of Würzburg | Schatz R.,Telecommunications Research Center Vienna Ftw | Fiedler M.,Blekinge Institute of Technology
2012 4th International Workshop on Quality of Multimedia Experience, QoMEX 2012 | Year: 2012

A considerable share of applications such as web or e-mail browsing, online picture viewing and file downloads imply waiting times for their users, which is due to the turn-taking of information requests by the user and correspoding response times until each request is fulfilled. Thus, end-user quality perception in the context of interactive data services is dominated by waiting times; the longer the latter, the less satisfied the user becomes. As opposed to heavily researched multimedia experience, perception of waiting times is still not strongly explored in the context of Quality of Experience (QoE). This tutorial will contribute to closing this gap. In its first part, it addresses perception principles and discusses their applicability towards fundamental relationships between waiting times and resulting QoE. It then investigates to which extent the same relationships can also be used to describe QoE for more complex services such as web browsing. Finally, it discusses applications where waiting times determine QoE, amongst other factors. For example, the past shift from UDP media streaming to TCP media streaming (e.g. youtube.com) has extended the relevance of waiting times also to the domain of online video services. In particular, user-perceived quality suffers from initial delays when applications are launched, as well as from freezes during the delivery of the stream. These aspects, which have to be traded against each other to some extent, will be discussed mainly for HTTP video streaming in the last part of this tutorial. © 2012 IEEE.

Berger A.,Telecommunications Research Center Vienna ftw | Gojmerac I.,Telecommunications Research Center Vienna ftw | Jung O.,Telecommunications Research Center Vienna ftw
Security and Communication Networks | Year: 2010

In this paper, we discuss the security threats of next-generation telecommunication core networks induced by the adoption of Internet technology. The 3GPP IP multimedia subsystem (IMS) is based on the Internet protocol (IP) and hence inherits many security problems from the Internet world. We provide a review of the most prominent vulnerabilities, covering both fundamental functions like routing and name resolution as well as message tampering and implementation attacks, and we show their impact on the IMS. Further, we address the topics of denial of service (DoS) attacks and unsolicited communication (UC). Despite the large number of security threats, the IMS standardization foresees no security monitoring and fully relies on standard countermeasures as known from the Internet. This paper provides a survey of these threats and relates them to the available solutions. We motivate the need for a powerful and modular monitoring platform for the IMS and provide an overview of the existing work in this research field. © 2009 John Wiley & Sons, Ltd.

Pucher M.,Telecommunications Research Center Vienna ftw | Schabus D.,Telecommunications Research Center Vienna ftw | Yamagishi J.,University of Edinburgh | Neubarth F.,Austrian Research Institute for Artificial Intelligence OFAI | Strom V.,University of Edinburgh
Speech Communication | Year: 2010

An HMM-based speech synthesis framework is applied to both standard Austrian German and a Viennese dialectal variety and several training strategies for multi-dialect modeling such as dialect clustering and dialect-adaptive training are investigated. For bridging the gap between processing on the level of HMMs and on the linguistic level, we add phonological transformations to the HMM interpolation and apply them to dialect interpolation. The crucial steps are to employ several formalized phonological rules between Austrian German and Viennese dialect as constraints for the HMM interpolation. We verify the effectiveness of this strategy in a number of perceptual evaluations. Since the HMM space used is not articulatory but acoustic space, there are some variations in evaluation results between the phonological rules. However, in general we obtained good evaluation results which show that listeners can perceive both continuous and categorical changes of dialect varieties by using phonological transformations employed as switching rules in the HMM interpolation. © 2009 Elsevier B.V.

Hyytia E.,Telecommunications Research Center Vienna Ftw
2009 Proceedings of the 1st International Workshop on Security and Communication Networks, IWSCN 2009 | Year: 2010

Many of the cryptographic primitives can be used in several ways. One interesting application of the Shamir's secret sharing scheme in the context of privacy aware traffic monitoring is to escrow a secret key after m suspicious events have been observed [1]. In the proposed system, a so-called front-end component encrypts the monitored data traffic, which is then stored at the back-end. At the same time, the front-end analyzes the traffic, and if suspicious packets are observed, this is indicated to the back-end by revealing one share of the corresponding encryption key. Once m suspicious events have been detected, the backend can disclose the secret key, decrypt the particular traffic flow, and carry out further investigations. In this paper we study the secret sharing scheme as a counter at the limit when the threshold m is relatively large. We first analyze how the scheme behaves as m approaches the maximum possible value of p - 1, where p is a prime number (design parameter). Then, we also analyze a probabilistic version developed to overcome the limited counting range, or excessive reporting overhead, by revealing shares only with a certain probability after each event, and provide expressions describing the resulting inaccuracy from the introduced randomness. Finally, we also propose a hybrid solution to mitigate the otherwise detoriating performance by using a forward error correction scheme similar to LT codes to encode the shared secret revealing process.

Statovci D.,Telecommunications Research Center Vienna Ftw | Nordstrom T.,Telecommunications Research Center Vienna Ftw
European Signal Processing Conference | Year: 2015

The performance of multiuser digital subscriber line (DSL) systems is constrained by crosstalk noise. This becomes especially noticeable in DSL systems that use high frequencies as in very high speed DSL (VDSL), since the crosstalk increases with frequency. To minimize the performance losses due to the crosstalk the users should coordinate and optimize their spectra with the aim of jointly maximizing the bit rates of all users. However, the multiuser DSL environment is modelled as a Gaussian interference channel and the rate region for this channel model is still an unsolved problem in information theory. This problem, for multiuser frequency division duplex discrete multi-tone (FDD-DMT) systems, is solved in a suboptimal way by our proposed Normalized-Rate Iterative Algorithm (NRIA). The NRIA determines optimized down- and upstream subcarrier allocations for the bundle and implicitly performs power control and power allocation for all users. In this paper we show, by simulation, that this algorithm achieves a significant performance improvement over existing standardized upstream power back-off (UPBO) and spectra plans in VDSL. © 2004 EUSIPCO.

Belanovic P.,Technical University of Madrid | Valerio D.,Telecommunications Research Center Vienna Ftw | Paier A.,Vienna University of Technology | Zemen T.,Telecommunications Research Center Vienna Ftw | And 3 more authors.
IEEE Transactions on Vehicular Technology | Year: 2010

Future intelligent transportation systems (ITS) will necessitate wireless vehicle-to-infrastructure (V2I) communications. This wireless link can be implemented by several technologies, such as digital broadcasting, cellular communication, or dedicated short-range communication (DSRC) systems. Analyses of the coverage and capacity requirements are presented when each of the three systems is used to implement the V2I link. We show that digital broadcasting systems are inherently capacity limited and do not appropriately scale. Furthermore, we show that the Universal Mobile Telecommunications System (UMTS) can implement the V2I link using either a dedicated channel (DCH) or a multimedia broadcast/multicast service (MBMS), as well as a hybrid approach. In every case, such V2I systems scale well and are capacity limited. We also show that wireless access in vehicular environment (WAVE) systems scale well, provide ample capacity, and are coverage limited. Finally, a direct quantitative comparison of the presented systems is given to show their scaling behavior with the number of users and the geographical coverage. © 2009 IEEE.

Hossfeld T.,University of Würzburg | Egger S.,Telecommunications Research Center Vienna Ftw | Schatz R.,Telecommunications Research Center Vienna Ftw | Fiedler M.,Blekinge Institute of Technology | And 2 more authors.
2012 4th International Workshop on Quality of Multimedia Experience, QoMEX 2012 | Year: 2012

End user quality perception in the context of Internet applications is often characterized by waiting times before service consumption as well as interruptions during service consumption. In particular in case of bad network conditions, network and service providers have to trade off between these two impairment types, i.e. between the devil and the deep blue sea. In this paper we investigate this tradeoff in order to guide the design and development of Internet applications and network management approaches. The contribution of this paper is twofold. Firstly, we quantify the impact of initial delays on the user perceived Quality of Experience (QoE) for different application scenarios by means of subjective laboratory and crowdsourcing studies. We show that QoE for a given waiting time strongly depends on the concrete application at hand but that rating diversity remains fairly application-invariant. Secondly, using the example of YouTube video streaming we compare the influence of initial delays and interruptions (stallings) during watching. Our results demonstrate that users are extremely sensitive to interruptions and that services should be designed accordingly e.g. by increasing initial delay for prebuffering to overcome lack of resources. © 2012 IEEE.

Reichl P.,Telecommunications Research Center Vienna ftw
Annales des Telecommunications/Annals of Telecommunications | Year: 2010

Providing Quality of Service (QoS) differentiation in future IP-based networks is closely linked to the concurrent implementation of appropriate pricing and charging mechanisms. Thus, in recent years, a broad range of QoS-based charging mechanisms have been proposed, ranging from Paris Metro Pricing and effective bandwidth pricing to the Cumulus Pricing Scheme or the Contract and Balancing Mechanism. However, the strongly increasing interest in Quality of Experience (QoE/QoX) so far has not led to a comparable burst of research activity in the Internet Economics community. Therefore, in order to highlight this important paradigm shift froma charging perspective, we first will review the most prominent QoS-based charging schemes and provide some discussion on lessons learned. In the next step, we describe the imminent transition from QoS to QoX from an economic point of view and discuss recent proposals for pricing of QoX. The paper ends with an outlook on current and future work in this highly interesting research field.© Institut TELECOM and Springer-Verlag 2009.

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