77 research outputs found
Extending DIRAC File Management with Erasure-Coding for efficient storage
The state of the art in Grid style data management is to achieve increased
resilience of data via multiple complete replicas of data files across multiple
storage endpoints. While this is effective, it is not the most space-efficient
approach to resilience, especially when the reliability of individual storage
endpoints is sufficiently high that only a few will be inactive at any point in
time. We report on work performed as part of GridPP\cite{GridPP}, extending the
Dirac File Catalogue and file management interface to allow the placement of
erasure-coded files: each file distributed as N identically-sized chunks of
data striped across a vector of storage endpoints, encoded such that any M
chunks can be lost and the original file can be reconstructed. The tools
developed are transparent to the user, and, as well as allowing up and
downloading of data to Grid storage, also provide the possibility of
parallelising access across all of the distributed chunks at once, improving
data transfer and IO performance. We expect this approach to be of most
interest to smaller VOs, who have tighter bounds on the storage available to
them, but larger (WLCG) VOs may be interested as their total data increases
during Run 2. We provide an analysis of the costs and benefits of the approach,
along with future development and implementation plans in this area. In
general, overheads for multiple file transfers provide the largest issue for
competitiveness of this approach at present.Comment: 21st International Conference on Computing for High Energy and
Nuclear Physics (CHEP2015
Protocole de routage à chemins multiples pour des réseaux ad hoc
Ad hoc networks consist of a collection of wireless mobile nodes which dynamically exchange data without reliance on any fixed based station or a wired backbone network. They are by definition self-organized. The frequent topological changes make multi-hops routing a crucial issue for these networks. In this PhD thesis, we propose a multipath routing protocol named Multipath Optimized Link State Routing (MP-OLSR). It is a multipath extension of OLSR, and can be regarded as a hybrid routing scheme because it combines the proactive nature of topology sensing and reactive nature of multipath computation. The auxiliary functions as route recovery and loop detection are introduced to improve the performance of the network. The usage of queue length metric for link quality criteria is studied and the compatibility between single path and multipath routing is discussed to facilitate the deployment of the protocol. The simulations based on NS2 and Qualnet softwares are performed in different scenarios. A testbed is also set up in the campus of PolytechâNantes. The results from the simulator and testbed reveal that MP-OLSR is particularly suitable for mobile, large and dense networks with heavy network load thanks to its ability to distribute the traffic into different paths and effective auxiliary functions. The H.264/SVC video service is applied to ad hoc networks with MP-OLSR. By exploiting the scalable characteristic of H.264/SVC, we propose to use Priority Forward Error Correction coding based on Finite Radon Transform (FRT) to improve the received video quality. An evaluation framework called SVCEval is built to simulate the SVC video transmission over different kinds of networks in Qualnet. This second study highlights the interest of multiple path routing to improve quality of experience over self-organized networks.Les rĂ©seaux ad hoc sont constituĂ©s dâun ensemble de nĆuds mobiles qui Ă©changent des donnĂ©es sans infrastructure de type point dâaccĂšs ou artĂšre filaire. Ils sont par dĂ©finition auto-organisĂ©s. Les changements frĂ©quents de topologie des rĂ©seaux ad hoc rendent le routage multi-sauts trĂšs problĂ©matique. Dans cette thĂšse, nous proposons un protocole de routage Ă chemins multiples appelĂ© Multipath Optimized Link State Routing (MP-OLSR). Câest une extension dâOLSR Ă chemins multiples qui peut ĂȘtre considĂ©rĂ©e comme une mĂ©thode de routage hybride. En effet, MP-OLSR combine la caractĂ©ristique proactive de la dĂ©tection de topologie et la caractĂ©ristique rĂ©active du calcul de chemins multiples qui est effectuĂ© Ă la demande. Les fonctions auxiliaires comme la rĂ©cupĂ©ration de routes ou la dĂ©tection de boucles sont introduites pour amĂ©liorer la performance du rĂ©seau. Lâutilisation de la longueur des files dâattente des nĆuds intermĂ©diaires comme critĂšre de qualitĂ© de lien est Ă©tudiĂ©e et la compatibilitĂ© entre routage Ă chemins multiples et chemin unique est discutĂ©e pour faciliter le dĂ©ploiement du protocole. Les simulations basĂ©es sur les logiciels NS2 et Qualnet sont effectuĂ©es pour tester le routage MP-OLSR dans des scĂ©narios variĂ©s. Une mise en Ćuvre a Ă©galement Ă©tĂ© rĂ©alisĂ©e au cours de cette thĂšse avec une expĂ©rimentation sur le campus de PolytechâNantes. Les rĂ©sultats de la simulation et de lâexpĂ©rimentation rĂ©vĂšlent que MP-OLSR est particuliĂšrement adaptĂ© pour les rĂ©seaux mobiles et denses avec des trafics Ă©levĂ©s grĂące Ă sa capacitĂ© Ă distribuer le trafic dans des chemins diffĂ©rents et Ă des fonctions auxiliaires efficaces. Au niveau application, le service vidĂ©o H.264/SVC est appliquĂ© Ă des rĂ©seaux ad hoc MP-OLSR. En exploitant la hiĂ©rarchie naturelle dĂ©livrĂ©e par le format H.264/SVC, nous proposons dâutiliser un codage Ă protection inĂ©gale (PFEC) basĂ© sur la Transformation de Radon Finie (FRT) pour amĂ©liorer la qualitĂ© de la vidĂ©o Ă la rĂ©ception. Un outil appelĂ© SVCEval est dĂ©veloppĂ© pour simuler la transmission de vidĂ©o SVC sur diffĂ©rents types de rĂ©seaux dans le logiciel Qualnet. Cette deuxiĂšme Ă©tude tĂ©moigne de lâintĂ©rĂȘt du codage Ă protection inĂ©gale dans un routage Ă chemins multiples pour amĂ©liorer une qualitĂ© dâusage sur des rĂ©seaux auto-organisĂ©s
Proceedings of the 5th bwHPC Symposium
In modern science, the demand for more powerful and integrated research
infrastructures is growing constantly to address computational challenges
in data analysis, modeling and simulation. The bwHPC initiative, founded
by the Ministry of Science, Research and the Arts and the universities in
Baden-WĂŒrttemberg, is a state-wide federated approach aimed at assisting
scientists with mastering these challenges. At the 5th bwHPC Symposium
in September 2018, scientific users, technical operators and government
representatives came together for two days at the University of Freiburg. The
symposium provided an opportunity to present scientific results that were
obtained with the help of bwHPC resources. Additionally, the symposium served
as a platform for discussing and exchanging ideas concerning the use of these
large scientific infrastructures as well as its further development
Scalable and rate adaptive wireless multimedia multicast
The methods that are described in this work enable highly efficient audio-visual streaming over wireless digital communication systems to an arbitrary number of receivers. In the focus of this thesis is thus point-to-multipoint transmission at constrained end-to-end delay. A fundamental difference as compared to point-to-point connections between exactly two communicating sending and receiving stations is in conveying information about successful or unsuccessful packet reception at the receiver side. The information to be transmitted is available at the sender, whereas the information about successful reception is only available to the receiver. Therefore, feedback about reception from the receiver to the sender is necessary. This information may be used for simple packet repetition in case of error, or adaptation of the bit rate of transmission to the momentary bit rate capacity of the channel, or both. This work focuses on the single transmission (including retransmissions) of data from one source to multiple destinations at the same time. A comparison with multi-receiver sequentially redundant transmission systems (simulcast MIMO) is made.
With respect to feedback, this work considers time division multiple access systems, in which a single channel is used for data transmission and feedback. Therefore, the amount of time that can be spent for transmitting feedback is limited. An increase in time used for feedback transmissions from potentially many receivers results in a decrease in residual time which is usable for data transmission. This has direct impact on data throughput and hence, the quality of service. In the literature, an approach to reduce feedback overhead which is based on simultaneous feedback exists. In the scope of this work, simultaneous feedback implies equal carrier frequency, bandwidth and signal shape, in this case orthogonal frequency-division multiplex signals, during the event of the herein termed feedback aggregation in time. For this scheme, a constant amount of time is spent for feedback, independent of the number of receivers giving feedback about reception. Therefore, also data throughput remains independent of the number of receivers. This property of audio-visual digital transmission is taken for granted for statically configured, single purpose systems, such as terrestrial television. In the scope of this work are, however, multi-user and multi-purpose digital communication networks. Wireless LANs are a well-known example and are covered in detail herein. In suchlike systems, it is of great importance to remain independent of the number of receivers, as otherwise the service of ubiquitous digital connectivity is at the risk of being degraded.
In this regard, the thesis at hand elaborates at what bit rates audio-visual transmission to multiple receivers may take place in conjunction with feedback aggregation. It is shown that the scheme achieves a multi-user throughput gain when used in conjunction with adaptivity of the bit rate to the channel. An assumption is the use of an ideal overlay packet erasure correcting code in this case. Furthermore, for delay constrained transmission, such as in so-called live television, throughput bit rates are examined. Applications have to be tolerant to a certain level of residual error in case of delay constrained transmission. Improvement of the rate adaptation algorithm is shown to increase throughput while residual error rates are decreased. Finally, with a consumer hardware prototype for digital live-TV re-distribution in the local wireless network, most of the mechanisms as described herein can be demonstrated.Die in vorliegender Arbeit aufgezeigten Methoden der paketbasierten drahtlosen digitalen Kommunikation ermöglichen es, Fernsehinhalte, aber auch audio-visuelle Datenströme im Allgemeinen, bei hoher Effizienz an beliebig groĂe Gruppen von EmpfĂ€ngern zu verteilen. Im Fokus dieser Arbeit steht damit die Punkt- zu MehrpunktĂŒbertragung bei begrenzter Ende-zu-Ende Verzögerung. Ein grundlegender Unterschied zur Punkt-zu-Punkt Verbindung zwischen genau zwei miteinander kommunizierenden Sender- und EmpfĂ€ngerstationen liegt in der Ăbermittlung der Information ĂŒber erfolgreichen oder nicht erfolgreichen Paketempfang auf Seite der EmpfĂ€nger. Da die zu ĂŒbertragende Information am Sender vorliegt, die Information ĂŒber den Erfolg der Ăbertragung jedoch ausschlieĂlich beim jeweiligen EmpfĂ€nger, muss eine Erfolgsmeldung auf dem RĂŒckweg von EmpfĂ€nger zu Sender erfolgen. Diese Information wird dann zum Beispiel zur einfachen Paketwiederholung im nicht erfolgreichen Fall genutzt, oder aber um die Ăbertragungsrate an die KapazitĂ€t des Kanals anzupassen, oder beides. GrundsĂ€tzlich beschĂ€ftigt sich diese Arbeit mit der einmaligen, gleichzeitigen Ăbertragung von Information (einschlieĂlich Wiederholungen) an mehrere EmpfĂ€nger, wobei ein Vergleich zu an mehrere EmpfĂ€nger sequentiell redundant ĂŒbertragenden Systemen (Simulcast MIMO) angestellt wird.
In dieser Arbeit ist die Betrachtung bezĂŒglich eines RĂŒckkanals auf Zeitduplexsysteme beschrĂ€nkt. In diesen Systemen wird der Kanal fĂŒr Hin- und RĂŒckweg zeitlich orthogonalisiert. Damit steht fĂŒr die Ăbermittlung der Erfolgsmeldung eine beschrĂ€nkte Zeitdauer zur VerfĂŒgung. Je mehr an Kanalzugriffszeit fĂŒr die Erfolgsmeldungen der potentiell vielen EmpfĂ€nger verbraucht wird, desto geringer wird die Restzeit, in der dann entsprechend weniger audio-visuelle Nutzdaten ĂŒbertragbar sind, was sich direkt auf die DienstqualitĂ€t auswirkt. Ein in der Literatur weniger ausfĂŒhrlich betrachteter Ansatz ist die gleichzeitige Ăbertragung von RĂŒckmeldungen mehrerer Teilnehmer auf gleicher Frequenz und bei identischer Bandbreite, sowie unter Nutzung gleichartiger Signale (hier: orthogonale Frequenzmultiplexsignalformung). Das Schema wird in dieser Arbeit daher als zeitliche Aggregation von RĂŒckmeldungen, engl. feedback aggregation, bezeichnet. Dabei wird, unabhĂ€ngig von der Anzahl der EmpfĂ€nger, eine konstante Zeitdauer fĂŒr RĂŒckmeldungen genutzt, womit auch der Datendurchsatz durch zusĂ€tzliche EmpfĂ€nger nicht notwendigerweise sinkt. Diese Eigenschaft ist aus statisch konfigurierten und fĂŒr einen einzigen Zweck konzipierten Systemen, wie z. B. der terrestrischen FernsehĂŒbertragung, bekannt. In dieser Arbeit werden im Gegensatz dazu jedoch am Beispiel von WLAN Mehrzweck- und Mehrbenutzersysteme betrachtet. Es handelt sich in derartigen Systemen zur digitalen DatenĂŒbertragung dabei um einen entscheidenden Vorteil, unabhĂ€ngig von der EmpfĂ€ngeranzahl zu bleiben, da es sonst unweigerlich zu EinschrĂ€nkungen in der GĂŒte der angebotenen Dienstleistung der allgegenwĂ€rtigen digitalen Vernetzung kommen muss.
Vorliegende Arbeit zeigt in diesem Zusammenhang auf, welche Datenraten unter Benutzung von feedback aggregation in der Verteilung an mehrere EmpfĂ€nger und in verschiedenen Szenarien zu erreichen sind. Hierbei zeigt sich, dass das Schema im Zusammenspiel mit einer Adaption der Datenrate an den Ăbertragungskanal inhĂ€rent einen Datenratengewinn durch Mehrbenutzerempfang zu erzielen vermag, wenn ein ĂŒberlagerter idealer Paketauslöschungsschutz-Code angenommen wird. Des weiteren wird bei der Ăbertragung mit zeitlich begrenzter AusfĂŒhrungsdauer, z. B. dem sogenannten Live-Fernsehen, aufgezeigt, wie sich die erreichbare Datenrate reduziert und welche Restfehlertoleranz an die Ăbertragung gestellt werden muss. Hierbei wird ebenso aufgezeigt, wie sich durch Verbesserung der Ratenadaption erstere erhöhen und zweitere verringern lĂ€sst. An einem auf handelsĂŒblichen Computer-Systemen realisiertem Prototypen zur Live-FernsehĂŒbertragung können die hierin beschriebenen Mechanismen zu groĂen Teilen gezeigt werden
Closed-loop control system and hardware-aware compilation protocols for quantum simulation with neutral atoms in optical trap arrays
Quantum materials offer tremendous potential for advancing electronic devices beyond traditional semiconductor-based technologies. Understanding the dynamics of these materials requires the use of quantum simulators. Quantum simulators are controlled many-body quantum systems that mimic the dynamics of a targeted quantum system. The three key
features of a quantum simulator are controllability, scalability, and interactability. Controllability denotes the ability to address an individual quantum system. Scalability refers to extending this control to multiple quantum systems while maintaining their interconnectivity with a polynomial increase in resources. Interactability, on the other hand, denotes the capability to establish strong tunable interactions between a pair of quantum systems.
This thesis addresses the challenges of attaining controllability and scalability within the current Noisy Intermediate-Scale Quantum (NISQ) era, characterized by limited and error-prone qubits, for a neutral atom-based quantum simulator.
The constraints in qubit interconnectivity necessitate the use of additional swap gates for operations between non-adjacent qubits, increasing errors. To reduce these gate-based errors, we improve qubit interconnectivity by displacing atoms during simulation, thus enhancing our simulatorâs scalability. We compare approaches with and without atom displacement analytically and numerically, employing metrics like circuit fidelity and quantum volume. Our analysis introduces a novel metric, denoted as , for comparing compilation protocols incorporating atom displacement. Additionally, we establish an inequality involving the metric to compare operational protocols with and without atom displacement. We conclude from our quantum volume study that protocols assisted by atom displacement can achieve a quantum volume of 2^7, a significant improvement over the 2^6 attainable without atom displacement with the state-of-the-art two-qubit gate infidelity of 5e-3 and atom displacement infidelity of 1.8e-4.
Implementing a dedicated closed-loop control and acquisition system showcases our simulatorâs controllability. The system integrates machine learning techniques to automate experiment composition, execution, and analysis, resulting in faster and automated control parameter optimization. A practical demonstration of this optimization is conducted through imaging an atomic cloud composed of Rb-87 atoms, the first step in undertaking quantum simulations with neutral atom arrays.
The research presented in this thesis contributes to the understanding and advancement of quantum simulators, paving the way for developing new devices with quantum materials
Energy-aware adaptive solutions for multimedia delivery to wireless devices
The functionality of smart mobile devices is improving rapidly but these devices are limited
in terms of practical use because of battery-life. This situation cannot be remedied by simply
installing batteries with higher capacities in the devices. There are strict limitations in the
design of a smartphone, in terms of physical space, that prohibit this âquick-fixâ from being
possible. The solution instead lies with the creation of an intelligent, dynamic mechanism for
utilizing the hardware components on a device in an energy-efficient manner, while also
maintaining the Quality of Service (QoS) requirements of the applications running on the
device.
This thesis proposes the following Energy-aware Adaptive Solutions (EASE):
1. BaSe-AMy: the Battery and Stream-aware Adaptive Multimedia Delivery (BaSe-AMy)
algorithm assesses battery-life, network characteristics, video-stream properties and
device hardware information, in order to dynamically reduce the power consumption of
the device while streaming video. The algorithm computes the most efficient strategy for
altering the characteristics of the stream, the playback of the video, and the hardware
utilization of the device, dynamically, while meeting applicationâs QoS requirements.
2. PowerHop: an algorithm which assesses network conditions, device power consumption,
neighboring node devices and QoS requirements to decide whether to adapt the
transmission power or the number of hops that a device uses for communication.
PowerHopâs ability to dynamically reduce the transmission power of the deviceâs
Wireless Network Interface Card (WNIC) provides scope for reducing the power
consumption of the device. In this case shorter transmission distances with multiple hops
can be utilized to maintain network range.
3. A comprehensive survey of adaptive energy optimizations in multimedia-centric wireless
devices is also provided.
Additional contributions:
1. A custom video comparison tool was developed to facilitate objective assessment of
streamed videos.
2. A new solution for high-accuracy mobile power logging was designed and implemented
Geostry - a Peer-to-Peer System for Location-based Information
An interesting development is summarized by the notion of âUbiquitous Computingâ: In this area, miniature systems are integrated into everyday objects making these objects âsmartâ and able to communicate. Thereby, everyday objects can gather information about their state and their environment. By embedding this information into a model of the real world, which nowadays can be modeled very realistically using sophisticated 3D modeling techniques, it is possible to generate powerful digital world models. Not only can existing objects of the real world and their state be mapped into these world models, but additional information can be linked to these objects as well. The result is a symbiosis of the real world and digital information spaces.
In this thesis, we present a system that allows for an easy access to this information. In contrast to existing solutions our approach is not based on a server-client architecture. Geostry bases on a peer-to-peer system and thus incorporates all the advantages, such as self-organization, fairness (in terms of costs), scalability and many more. Setting up the network is realized through a decentralized bootstrapping protocol based on an existing Internet service to provide robustness and availability. To selectively find geographic-related information Geostry supports spatial queries. They - among other things - enable the user to search for information e.g. in a certain district only. Sometimes, a certain piece of information raises particular interest. To cope with the run on the single computer that provides this specific information, Geostry offers dynamic replication mechanisms. Thereby, the information is replicated for as long as the rush lasts. Thus, Geostry offers all aspects from setting up a network, providing access to geo-related information and replication methods to provide accessibility in times of high loads
A STUDY ON WIRELESS COMMUNICATION ERROR PERFORMANCE AND PATH LOSS PREDICTION
One channel model that characterises multipath fading eïŹect of a wireless channel is
called Flat Rayleigh Fading channel model. Given the properties of Flat Rayleigh Fading
channel, an equation to ïŹnd the capacity of a Flat Rayleigh fading channel with hard
decision decoding is derived. The diïŹerence of power requirement to achieve the Additive
White Gaussian Noise (AWGN) capacity over a Flat Rayleigh Fading channel fading is
found to increase exponentially with Es /N0 . Upper and lower bounds of error performance
of linear block codes over a Flat Rayleigh Fading channel are also studied.
With the condition that the excess delay of a channel is known earlier, it is shown that a
correlator with shorter length, according to excess delay of the channel, can be constructed
for use in wireless channel response measurements. Therefore, a rule of construction
of a shorter length correlator is deïŹned, involving concatenation of parts of a Constant
Amplitude Zero Auto-Correlation (CAZAC) sequence.
Simulation of [136,68,24] Double Circulant Code with Dorsch List Decoding is also
done in order to evaluate error performance of the channel coding scheme over one of the
IEEE Wireless Metropolitan Area Network (WirelessMAN) channel models, the Stanford
University Interim Channel Model No. 5 (SUI-5) channel. Performance of the channel cod-
ing was severely degraded over the SUI-5 channel when it is compared to its performance
over the AWGN channel.
Indoor path losses within three multiïŹoor oïŹce buildings were investigated at 433
MHz, 869 MHz and 1249 MHz. The work involved series of extensive received signal
strength measurements within the buildings for all of the considered frequencies. Results
have shown that indoor path loss is higher within a square footprint building than indoor
path loss in a rectangular building. Parameters of Log-Distance Path Loss and Floor
Attenuation Factor Path Loss models have been derived from the measurement data. In
addition, a new indoor path loss prediction model was derived to cater for path loss pre-
diction within multiïŹoor buildings with indoor atriums. The model performs with better
prediction accuracy when compared with Log-Distance Path Loss and Floor Attenuation
Factor Path Loss models.Ministry of Higher Education of Malaysia, Universiti Teknologi Malaysi
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