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In the upcoming 5G networks and following the emerging Software Defined Network/Network Function Virtualization (SDN/NFV) paradigm, demanded services will be composed of a number of virtual network functions that may be spread across the whole transport infrastructure and allocated in distributed Data Centers (DCs). These services will impose stringent requirements such as bandwidth and end-to-end latency that the transport network will need to fulfill. In this paper, we present an orchestration system devised to select and allocate virtual resources in distributed DCs connected through a multi-layer (Packet over flexi-grid optical) network. Three different on-line orchestration algorithms are conceived to accommodate the incoming requests by satisfying computing, bandwidth and end-to-end latency constraints, setting up multi-layer connections. We addressed end-to-end latency requirements by considering both network (due to propagation delay) and processing delay components. The proposed algorithms have been extensively evaluated and assessed (via a number of figures of merit) through experimental tests carried out in a Packet over Optical Flexi-Grid Network available in the ADRENALINE testbed with emulated DCs connected to it. This work has been partially funded by the EC H2020 5GTransformer Project (grant No. 761536).

We consider design of asynchronous orthogonal frequency division multiplexing (OFDM) based diamond two-way-relay (DTWR) systems in a time-varying frequency-selective (doubly-selective) fading channel. In a DTWR system, two users exchange their messages with the help of two relays. Most of the existing works on asynchronous DTWR systems assume only small relative propagation delays between the received signals at each node that do not exceed the length of the cyclic-prefix (CP). However, in certain practical communication systems, significant differences in delays may take place, and hence existing solutions requiring excessively long CPs may be highly inefficient. In this paper, we propose a delay-independent CP insertion mechanism in which the CP length depends only on the number of subcarriers and the maximum delay spread of the corresponding channels. We also propose a symbol detection algorithm that is able to tolerate very long relative delays, that even exceed the length of the OFDM block itself, without a large increase in complexity. The proposed system is shown to significantly outperform other alternatives in the literature through a number of specific examples. © 2015 IEEE.

The present paper details a technique for adjusting in a smart manner the position estimates of any user equipment given by different geolocation/positioning methods in a wireless radiofrequency communication network based on different strategies (observed time difference of arrival , angle of arrivals, propagation delay(Formula presented.)). The main advantage of our proposal is to improve in a remarkable way the accuracy and to mitigate the adverse effect of multipath and other sources of errors that induce to inaccuracy in the terminals position estimates. Accordingly, the estimation of the geographical positions associated to all reported mobile terminals will be remarkable improved independent on the geolocation technique employed. The proposed method will move each position estimate towards a previously calculated area of confidence in a smart manner. This reduced area of confidence is generated to guarantee that the real position of any mobile terminal is inside it with a (Formula presented.) of probability of certainty.

A number of congestion control schemes which adopt the max-min fairness criterion and do not require maintenance of per flow states within the network have been proposed in the literature. The establishment of global asymptotic stability remains an open challenging research topic. In this paper, we show global asymptotic stability of two decentralized max-min congestion controllers in the absence and presence of queueing dynamics when the propagation delays are assumed to be zero. In particular, we show that these max-min congestion control schemes applied to a network of arbitrary topology, guarantee that the user sending rates converge asymptotically to the max-min allocation values for any arbitrary feasible initial condition. The second algorithm which accounts for queueing dynamics, typical in store and forward networks, does not only guarantee convergence of the sending rates to their max-min allocation values but also guarantees that the queue sizes within the network all converge to zero when there is only one bottleneck link at each path. © The authors 2015. 34 1 179 201

Cataloged from PDF version of article. Throughput model for non-persistent CSMA networks which was proposed by Kleinrock and Tobagi has been widely used, although it provides a loose lower bound when nodes are distributed in a large area because the analysis assumes that the propagation delay between each pair of users equals to the largest propagation delay in the network. We present a throughput analysis which considers the spatial distribution of nodes. We obtain a simple throughput expression which predicts throughput with an 8% maximum error whereas the earlier model results in a 44% error when the maximum propagation delay equals to the packet transmission time.

Cataloged from PDF version of article. In this paper, we explore design aspects of adaptive modulation based on orthogonal frequency-division multiplexing (OFDM) for underwater acoustic (UWA) communications, and study its performance using real-time at-sea experiments. Our design criterion is to maximize the system throughput under a target average bit error rate (BER). We consider two different schemes based on the level of adaptivity: in the first scheme, only the modulation levels are adjusted while the power is allocated uniformly across the subcarriers, whereas in the second scheme, both the modulation levels and the power are adjusted adaptively. For both schemes we linearly predict the channel one travel time ahead so as to improve the performance in the presence of a long propagation delay. The system design assumes a feedback link from the receiver that is exploited in two forms: one that conveys the modulation alphabet and quantized power levels to be used for each subcarrier, and the other that conveys a quantized estimate of the sparse channel impulse response. The second approach is shown to be advantageous, as it requires significantly fewer feedback bits for the same system throughput. The effectiveness of the proposed adaptive schemes is demonstrated using computer simulations, real channel measurements recorded in shallow water off the western coast of Kauai, HI, USA, in June 2008, and real-time at-sea experiments conducted at the same location in July 2011. We note that this is the first paper that presents adaptive modulation results for UWA links with real-time at-sea experiments. © 2013 IEEE.

Propagation delay across long on-chip buses is significant when adjacent wires are transitioning in opposite direction (i.e., crosstalk transitions) as compared to transitioning in the same direction. By exploiting Fibonacci number system, we propose a family of Fibonacci coding techniques for crosstalk avoidance, relate them to some of the existing crosstalk avoidance techniques, and show how the encoding logic of one technique can be modified to generate codewords of the other technique. � 2011 IEEE.

Sub-threshold operation has been proven to be very effective to reduce the power consumption of circuits when high performance is not required. Future low power systems on chip are likely to consist of many sub-systems operating at different frequencies and VDDs from super-threshold to sub-threshold region. Synchronizers are therefore needed to interface between these sub-systems. However, VDD scaling rapidly degrades synchronizers performance making them unsuitable for sub-threshold operation. For the first time, we analyze the synchronizer performance at ultra low voltages and propose to apply forward body bias to extend the operation of synchronizers to the sub-threshold region and to make them resilient to process variation. We show that applying full-VDD bias significantly increases the transconductance of the bi-stable in synchronizers without adding capacitance to the switching nodes. As a result all the circuit parameters (τ metastability time constant, T\d normal propagation delay and T\w metastability window) determining synchronizer performance or mean time between failure (MTBF) can be improved by more than 80% (i.e. by five times) in the sub-threshold region. We also study the impact of process variation on the synchronizer performance in the sub-threshold region and conclude that with full-VDD bias the synchronizer MTBF can be improved from seconds to years for the worst case corner. Finally, we propose an implementation scheme of full-VDD body-biased synchronizer, which is able to work for a wide range of VDDs from sub-threshold region to nominal VDD with nearly zero overhead. © 2011 Elsevier Ltd. All rights reserved.

Date of Conference: 16-19 Feb. 2015 Conference name: 2015 International Conference on Computing, Networking and Communications (ICNC) We consider design of asynchronous OFDM-based diamond two-way-relay (DTWR) systems in time-varying frequency-selective (doubly-selective) fading channels such as underwater acoustic (UWA) channels. In a DTWR channel, two users exchange their messages with the help of two relays. Most of the existing work on asynchronous DTWR systems assume only small relative propagation delays between the received signals at each node. However, in practical systems, significant delays may take place. Our proposed system is able to tolerate the delay even if it exceeds the length of the OFDM block which is almost inevitable in UWA channels. We provide analytical and numerical results to verify the advantages of the proposed scheme in mitigating large delays in different fading conditions.

An all-digital self-adaptive clock generation system capable of adapt the clock frequency to compensate the effects of PVTA variations on the IC propagation delay and satisfy an externally set propagation length condition is presented. The design uses time-to-digital converters (TDCs) to measure the propagation length and a variable length ring oscillator (VLRO) to synthesize the clock signal. The VLRO naturally adapts its frequency to the PVTA variations suffered by its logic gates while the TDCs are used to track these variations across the chip and modify the VLRO length in order to adapt the clock frequency to them. The system measurements, for a 45nm FPGA, show that it adapts the VLRO length, and therefore the clock frequency, to satisfy the propagation length condition. Measurements also prove the system capabilities to act as a dynamic frequency scaling clock source since the propagation length condition value act as a frequency selection input and a strong linear relation between the input value and the resultant clock period is present.

The convergence of two popular access technologies, namely Worldwide interoperability for Microwave Access (WiMAX) and passive optical network (PON) is a promising access solution that combines the mobility feature of WiMAX and the ample bandwidth of PONs. In such a converged optical-wireless access network, the provision of quality of service (QoS) support is a challenging issue, mainly because of the different bandwidth allocation mechanisms of the two access technologies. Since the considered convergence seems to be dominant, it deserves assiduous analysis and evaluation. In this study, the authors investigate the delay performance of a converged optical-wireless network that provides QoS support by considering multiple service-classes with different priorities. In the wireless domain, the IEEE 802.16 standard is applied, whereas in the optical domain a wavelength division multiplexing ethernet PON provides connectivity to both wired and wireless users. The authors present an analytical framework for the calculation of the average end-to-end packet delay of each service-class, by developing two queuing models for each domain of the converged network. The end-to-end delay is calculated as the sum of the queuing delay in both domains, and the transmission and propagation delay in the optical domain. The accuracy of the proposed analysis has been verified by simulation and found to be quite satisfactory.

There are different tools to estimate the end to end available bandwidth (AB). These tools use techniques which send pairs of packets to the network and observe changes in dispersion or propagation delays to infer the value of the AB. Given the fractal nature of Internet traffic, these observations are prompt to errors affecting the accuracy of the estimation. This article presents the application of a clustering technique to reduce the estimation error due to wrong observations of the available bandwidth in the network. The clustering technique used is K-means which is applied to a tool called Traceband that is originally based on a Hidden Markov Model to perform the estimation. It is shown that using K-means in Traceband can improve its accuracy in 67.45 % when the cross traffic is about 70% of the end-to-end capacity.

This thesis deals with mesoscopic models of cortex called neural fields. The neural field equations describe the activity of neuronal populations, with common anatomical / functional properties. They were introduced in the 1950s and are called the equations of Wilson and Cowan. Mathematically, they consist of integro-differential equations with delays, the delays modeling the signal propagation and the passage of signals across synapses and the dendritic tree. In the first part, we recall the biology necessary to understand this thesis and derive the main equations. Then, we study these equations with the theory of dynamical systems by characterizing their equilibrium points and dynamics in the second part. In the third part, we study these delayed equations in general by giving formulas for the bifurcation diagrams, by proving a center manifold theorem, and by calculating the principal normal forms. We apply these results to one-dimensional neural fields which allows a detailed study of the dynamics. Finally, in the last part, we study three models of visual cortex. The first two models are from the literature and describe respectively a hypercolumn, i.e. the basic element of the first visual area (V1) and a network of such hypercolumns. The latest model is a new model of V1 which generalizes the two previous models while allowing a detailed study of specific effects of delays; Cette thèse traite de modèles mésoscopiques de cortex appelés champs neuronaux. Les équations des champs neuronaux décrivent l'activité corticale de populations de neurones, ayant des propriétés anatomiques/fonctionnelles communes. Elles ont été introduites dans les années 1950 et portent le nom d'équations de Wilson et Cowan. Mathématiquement, elles consistent en des équations intégro-différentielles avec retards, les retards modélisant les délais de propagation des signaux ainsi que le passage des signaux à travers les synapses et l'arbre dendritique. Dans la première partie, nous rappelons la biologie nécessaire à la compréhension de cette thèse et dérivons les équations principales. Puis, nous étudions ces équations du point de vue des systèmes dynamiques en caractérisant leurs points d'équilibres et la dynamique dans la seconde partie. Dans la troisième partie, nous étudions de façon générale ces équations à retards en donnant des formules pour les diagrammes de bifurcation, en prouvant un théorème de la variété centrale et en calculant les principales formes normales. Nous appliquons tout d'abord ces résultats à des champs neuronaux simples mono-dimensionnels qui permettent une étude détaillée de la dynamique. Enfin, dans la dernière partie, nous appliquons ces différents résultats à trois modèles de cortex visuel. Les deux premiers modèles sont issus de la littérature et décrivent respectivement une hypercolonne, /i.e./ l'élément de base de la première aire visuelle (V1) et un réseau de telles hypercolonnes. Le dernier modèle est un nouveau modèle de V1 qui généralise les deux modèles précédents tout en permettant une étude poussée des effets spécifiques des retards

This thesis deals with mesoscopic models of cortex called neural fields. The neural field equations describe the activity of neuronal populations, with common anatomical / functional properties. They were introduced in the 1950s and are called the equations of Wilson and Cowan. Mathematically, they consist of integro-differential equations with delays, the delays modeling the signal propagation and the passage of signals across synapses and the dendritic tree. In the first part, we recall the biology necessary to understand this thesis and derive the main equations. Then, we study these equations with the theory of dynamical systems by characterizing their equilibrium points and dynamics in the second part. In the third part, we study these delayed equations in general by giving formulas for the bifurcation diagrams, by proving a center manifold theorem, and by calculating the principal normal forms. We apply these results to one-dimensional neural fields which allows a detailed study of the dynamics. Finally, in the last part, we study three models of visual cortex. The first two models are from the literature and describe respectively a hypercolumn, i.e. the basic element of the first visual area (V1) and a network of such hypercolumns. The latest model is a new model of V1 which generalizes the two previous models while allowing a detailed study of specific effects of delays, Cette thèse traite de modèles mésoscopiques de cortex appelés champs neuronaux. Les équations des champs neuronaux décrivent l'activité corticale de populations de neurones, ayant des propriétés anatomiques/fonctionnelles communes. Elles ont été introduites dans les années 1950 et portent le nom d'équations de Wilson et Cowan. Mathématiquement, elles consistent en des équations intégro-différentielles avec retards, les retards modélisant les délais de propagation des signaux ainsi que le passage des signaux à travers les synapses et l'arbre dendritique. Dans la première partie, nous rappelons la biologie nécessaire à la compréhension de cette thèse et dérivons les équations principales. Puis, nous étudions ces équations du point de vue des systèmes dynamiques en caractérisant leurs points d'équilibres et la dynamique dans la seconde partie. Dans la troisième partie, nous étudions de façon générale ces équations à retards en donnant des formules pour les diagrammes de bifurcation, en prouvant un théorème de la variété centrale et en calculant les principales formes normales. Nous appliquons tout d'abord ces résultats à des champs neuronaux simples mono-dimensionnels qui permettent une étude détaillée de la dynamique. Enfin, dans la dernière partie, nous appliquons ces différents résultats à trois modèles de cortex visuel. Les deux premiers modèles sont issus de la littérature et décrivent respectivement une hypercolonne, /i.e./ l'élément de base de la première aire visuelle (V1) et un réseau de telles hypercolonnes. Le dernier modèle est un nouveau modèle de V1 qui généralise les deux modèles précédents tout en permettant une étude poussée des effets spécifiques des retards

Sub-threshold operation has been proven to be very effective to reduce the power consumption of circuits when high performance is not required. Future low power systems on chip are likely to consist of many sub-systems operating at different frequencies and VDDs from super-threshold to sub-threshold region. Synchronizers are therefore needed to interface between these sub-systems. However, VDD scaling rapidly degrades synchronizers performance making them unsuitable for sub-threshold operation. For the first time, we analyze the synchronizer performance at ultra low voltages and propose to apply forward body bias to extend the operation of synchronizers to the sub-threshold region and to make them resilient to process variation. We show that applying full-VDD bias significantly increases the transconductance of the bi-stable in synchronizers without adding capacitance to the switching nodes. As a result all the circuit parameters (τ metastability time constant, T\d normal propagation delay and T\w metastability window) determining synchronizer performance or mean time between failure (MTBF) can be improved by more than 80% (i.e. by five times) in the sub-threshold region. We also study the impact of process variation on the synchronizer performance in the sub-threshold region and conclude that with full-VDD bias the synchronizer MTBF can be improved from seconds to years for the worst case corner. Finally, we propose an implementation scheme of full-VDD body-biased synchronizer, which is able to work for a wide range of VDDs from sub-threshold region to nominal VDD with nearly zero overhead. © 2011 Elsevier Ltd. All rights reserved.

With CMOS process technology scaling to deep submicron level, propagation delay across long on-chip buses is becoming one of the main performance limiting factors in high-performance designs. Propagation delay is very significant when adjacent wires are transitioning in opposite direction as compared to transitioning in the same direction. As opposite transitions on adjacent wires (called as crosstalk transitions ) have significant impact on propagation delay, several bus encoding techniques have been proposed in literature to eliminate such transitions. We propose selective shielding technique to eliminate crosstalk transitions. We show that the selective shielding technique requires ⌈3 n /2⌉ wires to encode a n -bit bus. SPICE simulations by considering 90nm technology nodes reveal that, for uniformly distributed random data, our technique achieves nearly 39% (21%) delay savings over 10 mm -length uncoded 32-bit bus for pipelined (nonpipelined) data transmission at the cost of nearly 7% energy overhead.

On-chip buses in deep-submicron designs have large propagation delay due to dominant coupling capacitance. As delay impacts system performance, several techniques have been proposed in the literature to minimize it. A common point in most of the existing techniques is to consider uniformly distributed random data, but propagation delay is data dependent and data is application dependent. Different applications may have different data behaviors. The existing techniques which consider uniformly distributed random data may not exploit the exact data behavior of an application and hence can give inferior performance results. By exploiting similarity in the data transmitted on on-chip buses, we propose three delay minimization techniques, namely, data packing (DPack), data permutation (DPerm), and data replication with shielding and two-phase transmission (RESTP). We show that for a 5-mm 32-bit on-chip bus in 90 nm CMOS technology, the DPack, DPerm, and RESTP techniques achieve more than 25%, 32%, and 51% delay savings, respectively, in both address and data buses. For a 32-bit bus, the DPack, DPerm, and RESTP techniques require 38, 34, and 48 wires, respectively. � 2009 Elsevier B.V. All rights reserved.

In this note we analyse various stability properties of the max-min fair Rate Control Protocol (RCP) operating with small buffers. We first tackle the issue of stability for networks with arbitrary topologies. We prove that the max-min fair RCP fluid model is globally stable in the absence of propagation delays, and also derive a set of conditions for local stability when arbitrary heterogeneous propagation delays are present. The network delay stability result assumes that, at equilibrium, there is only one bottleneck link along each route. Lastly, in the simpler setting of a single link, single delay model, we investigate the impact of the loss of local stability via a Hopf bifurcation., 13 pages, no figures. Submitted to IEEE Transactions on Automatic Control

Two aspects of DVB-RCS standard can worsen performance of TCP data connections: DAMA access scheme, since it introduces additional and variable delay to the already significant propagation delay and the adoption of Adaptive Coding on the return link to maximize bandwidth efficiency to face variable weather conditions, because it results in variable bandwidth allocation. Both aspects can severely impact TCP performance, especially for what concerns flow adaptation to varying channel conditions and channel usage efficiency. To optimize performance, in this paper cross-layer signaling among transport, MAC and physical layers of a DVB-RCS system is addressed. In particular MAC-TCP cross-layer is analyzed through the use of NS2 network simulator, showing the possible benefit in a DVB-RCS scenario.

High speed networks that are characterized by large bandwidth propagation delay products are expected to support applications with diverse traffic characteristics and Quality of Service (QoS) requirements. Thus, flow control schemes are needed for an efficient usage of the network bandwidth. A proactive feedback (PF) based flow control scheme developed by the author attempts to eliminate the bandwidth mismatch problem seen in such networks by generating and transmitting early feedbacks based on the application characteristics. In this paper, an extension of this scheme to large scale networks is presented. Due to the bottlenecked network nodes, some best effort applications may not be able to use their assigned bandwidth. For such cases, a modified version of the proactive feedback based (MPF) flow control scheme is introduced. It is observed that without affecting the other applications the best effort traffic can be significantly increased. International Institute of Informatics and Systemics (IIIS) Publisher's Version WOS:000254642700012