Does fragmentation avoidance improve the performance of dynamic spectrum allocation in elastic optical networks?

Most spectrum allocation algorithms in elastic optical networks apply a greedy approach: A new connection is allocated as long as there are enough spectrum slots to accommodate it. Recently, a different approach was proposed. Named Deadlock–Avoidance (DA), it only establishes a new connection if the portion of spectrum left after allocating it is zero (full-link utilization) or is big enough to accommodate future requests. Otherwise, the connection request is blocked as a way to avoid fragmentation. The performance of DA has been evaluated in a single-link scenario, where its performance is not affected by the slot continuity constraint. In this paper, we evaluate for the first time the blocking performance and fragmentation level of DA in a fully dynamic network scenario with different bitrates and number of slots for a single link, a 4-node bus and a mesh topology. The performance was evaluated by simulation, and a lower bound was also derived using a continuous Markov chain model. Results are obtained for DA and three greedy algorithms: First Fit, Exact Fit and First–Last Fit. Results show that DA significantly decreases fragmentation, and thus, it exhibits a much lower blocking due to fragmentation than the greedy algorithms. However, this decrease is compensated by a new type of blocking due to the selective acceptance of connections. As a result, the extra computational complexity of DA does not compensate a gain in performance.     

Throughput performance of distributed applications in switched networks in presence of end‐system bottlenecks

The steady state throughput performance of distributed applications deployed in switched networks in presence of endsystem bottlenecks is studied in this paper. The effect of various limitations at an endsystem is modelled as an equivalent transmission capacity limitation. A class of distributed applications is characterised by a static traffic distribution matrix that determines the communication between various components of the application. It is found that uniqueness of steady state throughputs depends only on the traffic distribution matrix and that some applications (e.g., broadcast applications) can yield nonunique values for the steady state component throughputs. For a given switch capacity, with traffic distribution that yield fair unique throughputs, the tradeoff between the endsystem capacity and the number of application components is brought out. With a proposed distributed rate control, it has been illustrated that it is possible to have unique solution for certain traffic distributions which is otherwise impossible. Also, by proper selection of rate control parameters, various throughput performance objectives can be realised.     

Testbed analysis of video and VoIP transmission performance in?IEEE 802.11 b/g/n networks

The aim of the work is to analyze capabilities and limitations of different implementations of IEEE 802.11 technologies (IEEE 802.11 b/g/n), utilized for both video streaming and VoIP calls directed to mobile devices. Our preliminary research showed that results obtained with currently popular simulation tools can be drastically different than these possible in real-world environment, so, in order to correctly evaluate performance of such transfers, a wireless test-bed infrastructure has been created. The results show a strong dependence of the quality of multimedia transmission on the chosen transmission technology and a particular implementation. The overall results demonstrate, that, while multimedia transmission quality in different products is still varied and often requires additional configuration, it is possible to select a WiFi access point model and determine the best system parameters to ensure a good audio/video transfer conditions in terms of acceptable QoP/E (Quality of Perception/Excellence) or MOS (Mean Opinion Score).     

User’s mobility effect on the performance of wireless cellular networks serving elastic traffic

The objective of the present paper is to give an analytic approximation of the performance of elastic traffic in wireless cellular networks accounting for user’s mobility. To do so we build a Markovian model for users arrivals, departures and mobility in such networks; which we call WET model. We firstly consider intracell mobility where each user is confined to remain within its serving cell. Then we consider the complete mobility where users may either move within each cell or make a handover (i.e. change to another cell). We propose to approximate the WET model by a Whittle one for which the performance is expressed analytically. We validate the approximation by simulating an OFDMA cellular network. We observe that the Whittle approximation underestimates the throughput per user of the WET model. Thus it may be used for a conservative dimensioning of the cellular networks. Moreover, when the traffic demand and the user speed are moderate, the Whittle approximation is good and thus leads to a precise dimensioning.     

Impact of the radio channel modelling on the performance of?VANET communication protocols

The expected traffic safety and efficiency benefits that can be achieved through the development and deployment of vehicular ad-hoc networks has attracted a significant interest from the networking research community that is currently working on novel vehicular communication protocols. The time-critical nature of vehicular applications and their reliability constraints require a careful protocol design and dimensioning. To this aim, adequate and accurate models should be employed in any research study. One of the critical aspects of any wireless communications system is the radio channel propagation. This is particularly the case in vehicular networks due to their low antenna heights, the fast topology changes and the reliability and latency constraints of traffic safety applications. Despite the research efforts to model the vehicle-to-vehicle communications channel, many networking studies are currently simplifying and even neglecting the radio channel effects on the performance and operation of their protocols. As this work demonstrates, it is critical that realistic and accurate channel models are employed to adequately understand, design and optimize novel vehicular communications and networking protocols.     

Piloting the spanning tree protocol in home?networks using a?multi-agent system

Broadband access to the Internet at home was the first step in the emergence of so called Home Networks. In a close future, the number of appliance connected will rise and the network will become the home backbone. Its architecture has to evolve to tackle those new challenges. After a study of the network requirements, this paper introduces a complete system to pilot the forwarding ensuring a proper QoS. This is achieved by a knowledge plane composed of agents embedded on devices, which are optimizing the Ethernet layer.     

Study on the performance of the A*Prune QoS routing algorithm for intelligent optical networks and its improvements

1 Introduction In the past few years, many routing algorithms for compu- ting constrained paths have been proposed in the networking community. In the earlier days, research study has been concentrated on a single additive constraint, especially the delay…     

Resampling the output of switched networks†

The use of switches has given the engineers a new tool for modifying the characteristic of networks. Their use is usually that of a modulating process, i.e. to convert the signal wave into a series of amplitude-modulated pulses which are then further handled by a suitable network, usually a filter. The possibility of resampling the output has been investigated; it was found that the phase angle of the second sampler with respect to the first has a significant effect on both the phase and the magnitude of the time function that can be reproduced from the output of the second sampler.     

A new role-switching mechanism optimizing the coexistence of?bluetooth and Wi-Fi networks

Unlicensed ISM band is used by various wireless technologies. Therefore, issues related to ensuring the required efficiency and quality of operation of coexisting networks become essential. The paper addresses the problem of mutual interferences between IEEE 802.11b transmitters (commercially named Wi-Fi) and Bluetooth (BT) devices. An optimization approach to modeling the topology of BT scatternets is introduced, resulting in more efficient utilization of ISM environment consisting of BT and Wi-Fi networks. To achieve it, the Integer Linear Programming approach has been proposed. Example results presented in the paper illustrate significant benefits of using the proposed modeling strategy.     

How is the capacity of ad hoc networks improved with directional antennas?

The capacity of wireless ad hoc networks is constrained by the interference caused by the neighboring nodes. Gupta and Kumar have shown that the throughput for such networks is only Θ bits per second per node in a unit area domain when omnidirectional antennas are used [1]. In this paper we investigate the capacity of ad hoc wireless networks using directional antennas. Using directional antennas reduces the interference area caused by each node, thus increases the capacity of the network. We will give an expression for the capacity gain and we argue that in the limit, when the beam-width goes to zero the wireless network behaves like the wired network. In our analysis we consider both arbitrary networks and random networks where nodes are assumed to be static. We have also analyzed hybrid beamform patterns that are a mix of omnidirectional/directional and a better model of real directional antennas. Simulations are conducted for validation of our analytical results. Su Yi received the B.S. and M.S degrees in automation from Tsinghua University, China, in 1998 and 2001, respectively. She received her Ph.D. degree in electrical engineering from Rensselaer Polytechnic Institute, in December 2005. Her research interests include various topics in wireless ad hoc networks, including capacity of wireless networks, error control coding, and multimedia communications over wireless. Yong Pei is currently a tenure-track assistant professor in the Computer Science and Engineering Department, Wright State University, Dayton, OH. Previously he was a visiting assistant professor in the Electrical and Computer Engineering Department, University of Miami, Coral Gables, FL. He received his B.S. degree in electrical power engineering from Tsinghua University, Beijing, in 1996, and M.S. and Ph.D. degrees in electrical engineering from Rensselaer Polytechnic Institute, Troy, NY, in 1999 and 2002, respectively. His research interests include information theory, wireless communication systems and networks, and image/video compression and communications. He is a member of IEEE and ACM. Shivkumar Kalyanaraman is an Associate Professor at the Department of Electrical, Computer and Systems Engineering at Rensselaer Polytechnic Institute in Troy, NY. He received a B.Tech degree from the Indian institute of Technology, Madras, India in July 1993, followed by M.S. and Ph.D. degrees in computer and Information Sciences at the Ohio State University in 1994 and 1997 respectively. His research interests are in network traffic management topics such as congestion control, reliability, connectionless traffic engineering, quality of service (QoS), last-mile community wireless networks, low-cost free-space-optical networks, automated network management using online simulation, multicast, multimedia networking, and performance analysis. His special interest lies in developing the interdisciplinary connections between network architecture and fields like control theory, economics, scalable simulation technologies, video compression and optoelectronics. He is a member of ACM and IEEE. Babak Azimi-Sadjadi received his B.Sc. from Sharif University of Technology in 1989, his M.Sc. from Tehran University in 1992, and his Ph.D. from the University of Maryland at College Park in 2001 all in Electrical Engineering. He is currently with Intelligent Automation Inc. where he is a Senior Research Scientist He also has a joint appointment with the department of Electrical, Systems, and Computer Engineering of Rensselaer Polytechnic Institute where he is a research assistant professor. His research interests include, nonlinear filtering, networked control systems, and wireless networks.     

Does the IEEE 802.11 MAC protocol work well in multihop wireless adhoc networks?

The IEEE 802.11 MAC protocol is the standard for wireless LANs; it is widely used in testbeds and simulations for wireless multihop ad hoc networks. However, this protocol was not designed for multihop networks. Although it can support some ad hoc network architecture, it is not intended to support the wireless mobile ad hoc network, in which multihop connectivity is one of the most prominent features. In this article we focus on the following question: can the IEEE 802.11 MAC protocol function well in multihop networks? By presenting several serious problems encountered in an IEEE 802.11-based multihop network and revealing the in-depth cause of these problems, we conclude that the current version of this wireless LAN protocol does not function well in multihop ad hoc networks. We thus doubt whether the WaveLAN-based system is workable as a mobile ad hoc testbed     

Bit-per-joule performance of power saving ad hoc networks with a mobile backbone

Energy efficient MAC protocols have been developed for wireless sensor and mobile ad hoc networks so that inactive nodes can transition into sleep state to conserve energy. It has been recognized that maintaining a continuously awake connected dominating set (CDS) serves to reduce the route setup latency. Under the mobile backbone network (MBN) architecture introduced by Rubin et al., a mobile backbone (Bnet) is dynamically constructed to provide a topological covering of the network. The MBN employs a hybrid routing algorithm under which flows that travel a distance longer than a threshold are directed along routes across the Bnet. In turn, a limited span network-wide global route discovery process is applied for routing shorter distance flows. In this paper, we introduce and analyze an MBN based power saving protocol (MBN-PS) that employs this hybrid routing scheme. Under the MBN-PS scheme, dynamically elected backbone nodes are kept awake, while inactive non-backbone nodes can reside in sleep state. We analytically show that, when the number of network flows is above a minimal level, the throughput per watt efficiency attained in an ad hoc network under complete backbone coverage is better than that achieved by a corresponding network that does not form a backbone. We present a model for the calculation of the bit-per-joule performance of the network as a function of the distance threshold. We confirm the validity of our analytical approach through simulations. Using our method, a network designer is able to choose the optimal distance threshold to be used by this scheme, based on traffic loading conditions.     

Simulation‐based performance evaluation of routing protocols for mobile ad hoc networks

In this paper we evaluate several routing protocols for mobile, wireless, ad hoc networks via packetlevel simulations. The ad hoc networks are multihop wireless networks with dynamically changing network connectivity owing to mobility. The protocol suite includes several routing protocols specifically designed for ad hoc routing, as well as more traditional protocols, such as link state and distance vector, used for dynamic networks. Performance is evaluated with respect to fraction of packets delivered, endtoend delay, and routing load for a given traffic and mobility model. Both small (30 nodes) and medium sized (60 nodes) networks are used. It is observed that the new generation of ondemand routing protocols use much lower routing load, especially with small number of peertopeer conversations. However, the traditional link state and distance vector protocols provide, in general, better packet delivery and endtoend delay performance.     

How significant is the assumption of the uniform channel phase distribution on the performance of spatial multiplexing MIMO system?

Spatial multiplexing (SMX) multiple-input multiple-output (MIMO) systems are promising candidates to enhance the achievable throughput and the overall spectral efficiency in future wireless systems. Performance studies of these systems over different channel conditions assume simplified models for the channel phase distribution. This paper highlights the impact of the channel phase distribution assumption on the performance of SMX MIMO systems. The Nakagami-m and the \(\eta -\mu\) fading channels are considered in this study. In existing literature, performance studies of SMX MIMO systems over Nakagami-m fading channel assume uniform phase distribution. Though, it has been reported recently that the Nakagami-m channel phase distribution is not uniform. In this article, we show that the assumption of the channel phase distribution has a major impact on the performance of SMX MIMO systems. The obtained results demonstrate that the performance of SMX MIMO systems significantly varies with different channel phase distributions. Furthermore, it is shown that uniform assumption of channel phase distribution is incorrect and leads to erroneous conclusions. Detailed performance analysis for more accurate channel models are provided and results are sustained through Monte-Carlo simulations.     

Effect of joint spatial correlation on the diversity performance of space?time block codes

We characterize the effect of joint spatial correlation on the diversity performance of multiple-input multiple-output (MIMO) systems. The joint spatial correlation is structured by the coupling matrix whose elements determine the average power coupling between the transmit and receive eigenmodes. We first derive the closed-form expression for the exact symbol error probability (SEP) of orthogonal space?time block codes over jointly correlated MIMO Rayleigh-fading channels. We then show that the achievable diversity order is equal to the number of nonzero elements of the power coupling matrix and establish the Schur monotonicity theorems on the SEP and the effective fading figure as a functional of elements of the power coupling matrix. Diversity, orthogonal space?time block code (OSTBC), Schur monotonicity, spatial correlation, symbol error probability (SEP).     

Selection of PCEs＇ location in multi-domain optical networks

Path computation elements （PCEs） are employed to compute end-to-end paths across multi-domain optical networks due to the advantages of powerful computation capability. However, PCEs＇ location selection is still an open problem which is closely related to the communication overhead. This paper mainly focuses on the problem of PCEs＇ location selection to minimize the overall communication overhead in the control plane. The problem is formulated as a quadratic integer programming （QIP） model, and an optimal decision rule is gained from the solution of the QIP model. Then based on the decision rule, a distributed heuristic algorithm is proposed for dynamic network scenario. Simulation results demonstrate the benefit and the effectiveness of our proposed approach by comparing it with random selection policy.     

An efficient handover decision in heterogeneous LTE-A networks under the assistance of users’ profile

The increasing demand for wireless networks calls for the use of heterogeneous networks in order to fulfil user requirements. Mobility management is considered one of the important entities for such networks. The handover is one of the main features of mobility management in regard to the long term evolution advanced (LTE-A) system, which depends purely on the hard handover. The vertical handover decision is a significant component of heterogeneous networks; it authorizes the user equipment (UE) to migrate between the two-tier LTE-A wireless networks. Femtocell, or also known as the home-evolved nodeB (HeNB), has turned out to be a promising arrangement, as it enhances the coverage and the quality of service for users on one hand, and offloads the eNB on the other hand. In this paper, an advanced handover technique is presented, in terms of adding new and critical parameters, as well as combining between the present UE trajectory and the HeNB cell location. A polynomial function is used to predict the future UE position while the cosine function along with distance are used for the selection of an appropriate target cell. The proposed algorithm is evaluated and then compared to the present work based on the handover number, number of signaling measurements, packet delay ratio, packet loss ratio, and system throughput. Simulation of the LTE-Sim demonstrates that the proposed algorithm significantly reduces the number of handovers, the transmission measurement number, the packet delay ratio, and the packet loss ratio and increases system throughput.     

Protocol for the application of cooperative MIMO based on clustering in sparse wireless sensor networks

Wireless sensor networks (WSN) using cooperative multiple-input multiple-output (MIMO) communication are effective tools to collect data in several environments. However, how to apply cooperative MIMO in WSN remains a critical challenge, especially in sparse WSN. In this article, a novel clustering scheme is proposed for the application of cooperative MIMO in sparse WSN by extending the traditional low-energy adaptive clustering hierarchy (LEACH) protocol. This clustering scheme solves the problem that the cluster heads (CH) cannot find enough secondary cluster heads (SCH), which are used to cooperate and inform multiple-antenna transmitters with CHs. On the basis of this protocol, the overall energy consumption of the networks model is developed, and the optimal number of CHs is obtained. The simulation results show that this protocol is feasible for the sparse WSN. The simulation results also illustrate that this protocol provides significant energy efficiencies, even after allowing for additional overheads.     

Modeling the Electrical Conduction in Epoxy–BaTiO3 Nanocomposites

Epoxy–BaTiO₃ nanocomposites are widely used as the dielectric material in embedded planar capacitors. To maximize the effective dielectric constant of this nanocomposite, the loading of BaTiO₃ is kept as high as possible, but at high loadings of BaTiO₃ the magnitude of undesirable leakage current in the dielectric also increases. This paper investigates the conduction mechanism in epoxy–BaTiO₃ nanocomposites. Further, the effects of BaTiO₃ loading and the size of BaTiO₃ particles on the electrical conduction are investigated and also modeled. To investigate the conduction mechanism, capacitor structures (Cu/dielectric/Cu) with nanocomposite dielectric were fabricated using the colloidal process. The loading and size of BaTiO₃ particles were varied in the nanocomposite dielectric. Once the capacitor structures were fabricated, the leakage current was measured across the capacitor dielectric as a function of temperature and voltage. The leakage current data were checked for any consistency with the standard conduction models using regression analysis, and the dominant conduction mechanism was identified. Finally, the activation energy of the dominant conduction mechanism was trended as a function of BaTiO₃ loading and particle size both experimentally and theoretically.     

Three-Component Zone-Melting Method: Modeling of the Concentration-Component Distribution in Single Crystals of Ge–Si Solid Solutions

Semiconductors - The concept and theoretical basis of the three-component zone melting method is given for growing single crystals of semiconductor solid solutions using seeds from constituent...