Littérature scientifique sur le sujet « Tradeoff bandwidth »

One of the most important applications of stimulated Raman scattering (SRS) is the realization of amplifiers or laser sources in bulk materials, in fiber and in integrated optic format as well. We note that, as a general rule, in all laser gain bulk materials, there is a tradeoff between gain and bandwidth: line width may be increased at the expense of peak gain. This tradeoff is a fundamental limitation toward the realization of micro/nano-sources with large emission spectra. In this paper, in order to clarify the possibility of obtaining new materials with both large Raman gain coefficients and spectral bandwidth, SRS investigations in nanostructures, spanning from nanometrically heterogeneous K2O–Nb2O5SiO2 (KNS) glasses to Si nanocrystals, are reported and discussed.

In this work, a novel fractional-order extended state observer (FOESO)-based linear active disturbance rejection control (LADRC) method is firstly proposed for a hypersonic vehicle (HV) to address the measurement noise problem. The uncertainty and external disturbance of an HV was discussed and addressed by the active disturbance rejection control and many different control methods in recent decades. However, the research of an HV with measurement noise is insufficient. For the LADRC, the anti-noise ability is highly dependent on the bandwidth of the extended state observer (ESO). Meanwhile, the control performance of the LADRC is relevant to the bandwidth. The FOESO is presented, aiming to address the tradeoff of the control performance or noise suppression. The FOESO-based LADRC (FOESO-LADRC) introduces fractional calculus. It can enhance the anti-noise ability with little influence on the control performance. The simulation results show that the FOESO-LADRC has a significant improvement in the noise suppression. In addition, compared with the LADRC, it obtains a better solution to address the tradeoff between the bandwidth and noise impact.

Les réseaux orientés contenus (CCN) ont été créés afin d'optimiser les ressources réseau et assurer une plus grande sécurité. Le design et l'implémentation de cette architecture est encore à ces débuts. Ce travail de thèse présente des propositions pour la gestion de trafic dans les réseaux du future. Il est nécessaire d'ajouter des mécanismes de contrôle concernant le partage de la bande passante entre flots. Le contrôle de trafic est nécessaire pour assurer un temps de latence faible pour les flux de streaming vidéo ou audio, et pour partager équitablement la bande passante entre flux élastiques. Nous proposons un mécanisme d'Interest Discard pour les réseaux CCN afin d'optimiser l'utilisation de la bande passante. Les CCN favorisant l'utilisation de plusieurs sources pour télécharger un contenu, nous étudions les performances des Multipaths/ Multisources; on remarque alors que leurs performances dépendent des performances de caches.Dans la deuxième partie de cette thèse, nous évaluons les performances de caches en utilisant une approximation simple et précise pour les caches LRU. Les performances des caches dépendent fortement de la popularité des objets et de la taille des catalogues. Ainsi, Nous avons évalué les performances des caches en utilisant des popularités et des catalogues représentant les données réelles échangées sur Internet. Aussi, nous avons observé que les tailles de caches doivent être très grandes pour assurer une réduction significative de la bande passante; ce qui pourrait être contraignant pour l'implémentation des caches dans les routeurs. Nous pensons que la distribution des caches devrait répondre à un compromis bande passante/mémoire ; la distribution adoptée devrait réaliser un coût minimum. Pour ce faire, nous évaluons les différences de coût entre architectures
Content Centric Network (CCN) architecture has been designed to optimize network resources and ensure greater security. The design and the implementation of this architecture are only in its beginning. This work has made some proposals in traffic management related to the internet of the future.We argue that it is necessary to supplement CCN with mechanisms enabling controlled sharing of network bandwidth by competitive flows. Traffic control is necessary to ensure low latency for conversational and streaming flows, and to realize satisfactory bandwidth sharing between elastic flows. These objectives can be realized using "per-flow bandwidth sharing". As the bandwidth sharing algorithms in the IP architecture are not completely satisfactory, we proposed the Interest Discard as a new technique for CCN. We tested some of the mechanisms using CCNx prototype software and simulations. In evaluating the performance of multi-paths we noted the role of cache performance in the choice of selected paths.In the second part, we evaluate the performance of caches using a simple approximation for LRU cache performance that proves highly accurate. As caches performance heavily depends on populations and catalogs sizes, we evaluate their performance using popularity and catalogs representing the current Internet exchanges. Considering alpha values, we observe that the cache size should be very large, which can be restrictive for caches implementation in routers.We believe that the distribution of caches on an architecture creates an excessive bandwidth consumption. Then, it is important to determine a tradeoff bandwidth/memory to determine how we should size caches and where we should place them, this amounts to evaluate differences, in cost, between architectures

Given the breath-taking pace at which the amount of data being generated on a daily basis is growing, and the keen desire to extract information from this data, there is strong interest within the storage industry, at finding means to efficiently and reliably store this data. Given that individual storage units are prone to failure, data pertaining to a single _le is distributed across storage nodes. Such storage of `Big Data' across a spatially distributed network of nodes, calls for codes than can efficiently handle the issue of node repair. The need for node repair could arise on account of device failure, need for a maintenance reboot, or simply because the node is busy serving other demands. A new branch of coding theory has sprung up in response. Regenerating codes minimize data download during a repair operation, while codes with locality ensure that local operations suffice for node repair. The present thesis makes contributions to both regenerating codes as well as codes with locality. While the reliable storage of data in disks with minimum storage overhead is a well-studied problem, the problem of node repair is relatively new. From the viewpoint of the storage industry, the cost to repair a failed node can be measured in two distinct ways: firstly, in terms of the number of surviving nodes accessed, and secondly, in terms of the amount of data transmitted over the network to ensure repair of the failed node. In a regenerating code having parameter set (n; k; d; (_; _);B), and over a _finite _field Fq, a file consisting of B symbols from Fq is encoded into n_ symbols, and the coded symbols are stored in n distinct nodes, each node storing _ symbols. The parameter _ is referred to as sub-packetization level. The entire _le can be recovered from downloading k_ symbols from any set of k nodes. Under the exact-repair (ER) setting that is of interest here, the contents of a failed node are repaired exactly from a total of d_ symbols downloaded from any d helper nodes, each helper node transmitting _ symbols. In the alternative setting of functional repair (FR), the contents of the replacement node can be different from that of the failed node, however, following node repair, the new configuration is still required to satisfy the data-recovery and node repair properties of a regenerating code. Under the FR setting, there is a trade-off known as storage-repair-bandwidth (S-RB) trade-off between the values of _ and d_, that optimize the size of the _le being stored. The two extreme points of the trade-off, one corresponding to the minimum possible value of _ and the other, to the minimum possible value of d_, are known as the minimum-storage-regenerating (MSR) and minimum-bandwidth-regenerating (MBR) points respectively. It has been shown that the extreme points of the ER trade-off coincide with those of the FR trade-off. However, the characterization of trade-off in the case of ER remains an open and challenging problem. High-rate MSR code constructions the _first problem reported in the thesis, is one of designing exact-repair MSR codes that possess certain additional desirable properties, namely, high rate (i.e., rate greater than half) and a small value of sub-packetization level _. In the present thesis, we construct a family of MSR codes for d = (n 􀀀 1) having a fixed rational rate R = (t 􀀀 1)=t and a sub-packetization that is polynomial in k for a fixed rate. In the construction, _ varies with k as _ = O(kt). This was the first high-rate MSR code construction to have such small value of sub-packetization. Canonical codes: Regenerating codes for the interior points of the S-RB trade-off the next pair of results relate to the construction of interior-point regenerating codes. For the parameter set (n; k; d = k), we first construct as our second result, a class of codes referred to as canonical codes, having an auxiliary parameter w, with w in the range n􀀀k < w < k, these codes operate in the region between the MSR point and the MBR point, and perform significantly better than operating points obtained through space-sharing. The canonical code constructed for the case (n; k = n 􀀀 1; d = n 􀀀 1), turn out to achieve an interior point of the FR trade-off, thus characterizing for the first time, an interior point of the ER trade-off. Generalized Canonical codes We next build on top of a canonical code having parameters (n; d; d) and construct codes corresponding to a more general parameter set of the form (n; k < d; d) using two different approaches. In the first approach, leading to what we refer to as non-canonical codes, an exponential expansion in field size is needed while the parameters _ and _ remain the same as in the case of the (n; d; d) code. In the second approach, the value of _ is increased from that of the (n; d; d) code, but no expansion in field size is needed. The resultant codes are referred to as improved layered codes. Both approaches lead to codes that perform much better than the space-sharing line. Outer bounds on the storage-repair-bandwidth trade-off the next set of results presented here take on the form of two distinct outer bounds for the S-RB trade-off. The first is referred to here as the repair-matrix bound and the second as the improved Muhajir-Tandon bound. The repair-matrix bound lies strictly away from the FR trade-off for every parameter (n; k; d), and thus proves that the ER trade-off is bounded away from the FR trade-off, even when the _le size grows to infinity. This result solved an open problem in the literature. In conjunction with the improved layered codes constructed in the thesis and described above, these outer bounds characterize the ER trade-off for the case when (n; k = 3; d = n 􀀀 1). This is the first family of parameters for which the ER trade-off is characterized. Furthermore, for the parameter set (n; k = 4; d = n 􀀀 1), the operating point of the improved layered code coincides with the outer bound, characterizing yet another interior point of the S-RB trade-off. Codes with hierarchical locality the final set of results relate to the second class of codes developed for efficient node repair, namely, codes with locality. The aim of this class of codes is to reduce the number of nodes accessed while repairing a failed node. In a code with locality having locality parameter r, every symbol can be repaired by accessing r other symbols, where r is typically, much smaller than the dimension k of the code. We introduce in the thesis the notion of hierarchical locality, where the local codes are of varying locality and possess a hierarchical structure. In the case of two-level hierarchical locality, for instance, every symbol is protected both by an inner, short-block-length local code, as well as a middle code of larger block length. The code symbols in the inner code are a subset of the code symbols in the middle code. We first present the case of codes with two-level hierarchy, derive an upper bound on the minimum distance and provide optimal code constructions for a wide parameter range. The minimum-distance bound, and code construction are then generalized for the case of a hierarchical structure having an arbitrary number of levels.

Recent years have witnessed a great technological evolution in video display and capturing technologies leading to the development of new standards of video coding including MPEG-X, H.26X and HEVC. The cost of computations, storage and high bandwidth requirements makes a video data expensive in terms of transmission and storage. This makes video compression absolutely necessary prior to its transmission in order to accommodate for different transmission media's capabilities. Digital video compression technologies therefore have become an important part of the way we create, present, communicate and use visual information. The main aim behind a video compression system is to eliminate the redundancies from a raw video signal. The tradeoff involved in the process of video compression is between the speed, quality and resource utilization. The current chapter explores the techniques, challenges, issues and problems in video compression in detail along with the major advancements in the field.

With the increasing usage of the Internet, electronic commerce (e-commerce) has been catching on fast in a lot of business areas. As e-commerce booms, there comes a demand for a better system to manage and carry out transactions. This leads to the development of agent-based e-commerce. In this new approach, agents are employed on behalf of users to carry out various e-commerce activities. Although the tradeoff of employing mobile agents is still under debate (Milojicic, 1999), using mobile agents in e-commerce attracts much research effort, as it may improve the potential of their applications in e-commerce (Guan & Yang, 1999, 2004). One advantage of using agents is that communication cost can be reduced. Agents traveling and transferring only necessary information saves network bandwidth and reduces the chances of network congestion. Also, users can schedule their agents to travel asynchronously to the destinations and collect information or execute other applications, while they can disconnect from the network (Wong, Paciorek, & Moore, 1999). Although agent-based technology offers such advantages, the major factor holding people back from employing agents is still the security issues involved. On one hand, hosts cannot trust incoming agents belonging to unknown owners, because malicious agents may launch attacks on the hosts and other agents. On the other hand, agents may also have concerns on the reliability of hosts and will be reluctant to expose their secrets to distrustful hosts. To build bilateral trust in an e-commerce environment, the authorization and authentication schemes for mobile agents should be designed well. Authentication checks the credentials of an agent before processing an agent’s requests. If the agent is found to be suspicious, the host may decide to deny its service requests. Authorization refers to the permissions granted for the agent to access whichever resources it requested.

This chapter presents novel passive and active wearable sensors for biomedical systems, energy harvesting, and communication devices. Design tradeoffs, simulation, and measured results of compact efficient sensors for communication, energy harvesting, IoT, and healthcare systems are discussed in this chapter. The new sensors are green sensors with an energy harvesting unit. The sensor electrical parameters near the human body were evaluated by employing RF CAD software. The sensors are flexible passive and active devices with high efficiency and low cost. Low-cost sensor may be developed by printing the printed antenna with the antenna feed network and the active components on the same board. Efficient metamaterial sensors were developed to improve the system electrical performance. The resonant frequency range of the sensors, with Circular Split-Ring Resonators CSRRs, is lower by 5% to 11% than the sensors with CSRRs. The directivity and gain of the sensors with CSRRs are higher by 2.5dB than the sensors without CSRRs. For S11 lower than –6 dB, the bandwidth of the novel metamaterial sensors may be around 15 to 55%. The directivity and gain of the new metamaterial sensors are around 5 dBi to 7.5 dBi. The receiving active sensor gain is 12 ± 3 dB. The transmitting active sensor gain is 13 ± 3 dB.