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The growing demand on the performance of transparent computing systems requires good cache schemes in order to overcome the prolonged network latency. However, evaluating cache schemes, especially measuring the performance of a transparent computing system with particular cache scheme remains challenging. This is because neither method is available to evaluate the effectiveness and efficiency of the cache schemes in transparent computing, nor the simulator has been developed to measure the system performance under particular cache schemes. In this paper, we propose TranSim, a full-featured, high-performance simulation framework for transparent computing. For the first time, TranSim introduces a methodology to evaluate the performance of multi-level cache hierarchies in transparent computing under different cache configurations and cache replacement policies. TranSim can also demonstrate the behavior and performance of the entire transparent computing system rather than only the cache miss/hit rate. Using TranSim, the system designer can quickly evaluate the effectiveness of cache schemes along with the system performance. We construct several experiments to evaluate the effectiveness and efficiency of TranSim. Results show that TranSim can accurately output the performance of both the cache hierarchy and the entire transparent computing system. [ABSTRACT FROM AUTHOR]

Provisioning buffer management mechanism is especially crucial in resource-constrained delay tolerant networks (DTNs) as maximum data delivery ratio with minimum overhead is expected in highly congested environments. However, most DTN protocols do not consider resource limitations (e.g., buffer, bandwidth) and hence, results in performance degradation. To strangle and mitigate the impact of frequent buffer overflows, this paper presents an adaptive and efficient buffer management scheme called size-aware drop (SAD) that strives to improve buffer utilization and avoid unnecessary message drops. To improve data delivery ratio, SAD exactly determines the requirement based on differential of newly arrived message(s) and available space. To vacate inevitable space from a congested buffer, SAD strives to avoid redundant message drops and deliberate to pick and discard most appropriate message(s) to minimize overhead. The performance of SAD is validated through extensive simulations in realistic environments (i.e., resource-constrained and congested) with different mobility models (i.e., Random Waypoint and disaster). Simulation results demonstrate the performance supremacy of SAD in terms of delivery probability and overhead ratio besides other metrics when compared to contemporary schemes based on Epidemic (DOA and DLA) and PRoPHET (SHLI and MOFO). [ABSTRACT FROM AUTHOR]

Flight envelope protection algorithm is proposed to improve the safety of an aircraft. Flight envelope protection systems find the control inputs to prevent an aircraft from exceeding structure/aerodynamic limits and maximum control surface deflections. The future values of state variables are predicted using the current states and control inputs based on linearised aircraft model. To apply the envelope protection algorithm for the wide envelope of the aircraft, online linearisation is adopted. Finally, the flight envelope protection system is designed using adaptive neural network and least-squares method. Numerical simulations are conducted to verify the performance of the proposed scheme. [ABSTRACT FROM PUBLISHER]

This paper describes the High Order (Seventh-order) Predictor-Corrector approach which uses the two previous points and external interpolation to predict the location and energy of the next point based on CFD**-Bofill scheme. The experiment results show the Seventh-order approach is far better than Verlet approach. Parts of the experiment results prove the Seventh-order approach is better than CFD-Bofill updating scheme. However, the other results are not better than CFD-Bofill since the Seventh-order approach, which uses two points to predict the next point indirectly, increases the step size. The external interpolation is worse than the internal interpolation in some cases at the same time. This article proposes a High Order (Seventh-Order) Predictor-Corrector approach which uses the two previous points and external interpolation to predict the location of the next time step. The simulation results show the Seventh-Order approach is far better than Velocity Verlet approach and as well as CFD-Bofill for molecules without hydrogen atoms, while new method is simpler than CFD-Bofill. This is due to the Seventh-Order approach which uses two points to predict the next point indirectly, increases the step size and the external interpolation is worse than the internal interpolation. [ABSTRACT FROM AUTHOR]

A robot interacting with the environment requires that the end effector \hboxposition is tracked and that the forces of contact are kept below certain reference values. For instance, in a rehabilitation session using a robotic device, the contact forces are limited by the allowed strength of the human limbs and their complex-joints. In these cases, a control scheme which considers both position and force control is essential to avoid damage to either the end effector or the object interacting with the robot. This paper therefore develops a real-time force/position control scheme for a three-DOF parallel robot whose end effector holds a DOF one translation (1 T) and two rotations (2 R). The implemented hybrid force/position control considers, as a reference, the normal force on the mobile platform, which is measured by means of a load cell installed on the platform. The position control is designed to track the orientations of the robot either in joint or task space using a model-based control scheme with identified parameters. Moreover, the force control is based on a PD action. The control scheme is developed through simulations, before being applied to an actual parallel robot. The findings show that with the implemented controller, the actual robot accomplishes the reference values for the normal force on the mobile platform, while at the same time the platform accurately follows the required angular orientation. [ABSTRACT FROM AUTHOR]

Guidance with traditional trajectory correction scheme usually starts from the trajectory apex time to reduce drag penalties early in flight; however, this method cannot get the max trajectory correction capability of canards according to our analysis. This paper presents an optimized trajectory correction scheme by taking different control phases of canards in ballistic ascending segment and ballistic descending segment. Simulation indicates that the optimized trajectory correction can improve the trajectory correction capability greatly. The result of an example trajectory and Monte Carlo simulations with the predictive guidance law and the trajectory tracking guidance law testifies the effectiveness of the optimized trajectory correction scheme. [ABSTRACT FROM AUTHOR]

Here we report a precise computer simulation study of the static critical properties of the two-dimensional q -states Potts model using very accurate data obtained from a modified Wang–Landau (WL) scheme proposed by Caparica and Cunha-Netto (2012). This algorithm is an extension of the conventional WL sampling, but the authors changed the criterion to update the density of states during the random walk and established a new procedure to windup the simulation run. These few changes have allowed a more precise microcanonical averaging which is essential to a reliable finite-size scaling analysis. In this work we used this new technique to determine the static critical exponents β , γ , and ν , in an unambiguous fashion. The static critical exponents were determined as β = 0.10811 ( 77 ) , γ = 1.4459 ( 31 ) , and ν = 0.8197 ( 17 ) , for the q = 3 case, and β = 0.0877 ( 37 ) , γ = 1.3161 ( 69 ) , and ν = 0.7076 ( 10 ) , for the q = 4 Potts model. A comparison of the present results with conjectured values and with those obtained from other well established approaches strengthens this new way of performing WL simulations. [ABSTRACT FROM AUTHOR]

In this study, a numerical model based on the non-oscillatory and non-free parameter dissipation (NND) finite difference scheme for shallow water wave equations including sediment concentration is established in order to simulate the phenomena for dam-break flow and the development of alluvial plain in an estuary. Some numerical experiments show that the numerical model is feasible and efficient for simulating the phenomena for dam-break flow and the development of alluvial plain in an estuary. [ABSTRACT FROM AUTHOR]

In this paper, we consider a control problem of a non-holonomic multi-agent system. We assume that agents and obstacles are in a circular shaped work area. We propose a novel potential-function-based control scheme that drives agents from the initial to the goal configuration while avoiding collision with other agents, obstacles, and the boundary of the work area. The control scheme enables agents to avoid being trapped at local minima by forcing them to exit from the regions that may contain local minima. A numerical simulation is presented to demonstrate the validity of the proposed control scheme. [ABSTRACT FROM PUBLISHER]

This paper proposes a cooperative diversity transmission scheme by superposition coding relaying (SC-relaying) for a wireless system with multiple relays. In this scheme, two layer signals, i.e., signal $${x_1}$$ and $${x_2}$$ , are transmitted from a base station (BS) in the first and the second time slot, while signal $${x_1}$$ is also forwarded from multiple relays to a user in the second time slot. The two layer signals ( $${x_1}$$ and $${x_2}$$ ) meet and superimpose with each other in the air in the second time slot. Then successive interference cancellation (SIC) is used for decoding at the user. In this paper, the optimal power allocation that maximizes the sum throughput of $${x_1}$$ and $${x_2}$$ is first studied. Then the optimal number of selected relays and optimal transmission rate at the BS is derived. Finally the outage probability and diversity gain of the transmission of $${x_1}$$ and $${x_2}$$ is evaluated for system robustness. Simulation results show that the proposed scheme realizes the goal of increasing spectral efficiency and enhancing system robustness. [ABSTRACT FROM AUTHOR]

For multi-field simulations involving a larger number of different physical fields and in cases where the involved fields or simulation codes change due to new modelling insights, e.g., flexible and robust partitioned coupling schemes are an important prerequisite to keep time-to-solution within reasonable limits. They allow for a fast, almost plug-and-play combination of existing established codes to the respective multi-field simulation environment. In this paper, we study a class of coupling approaches that we originally introduced in order to improve the parallel scalability of partitioned simulations. Due to the symmetric structure of these coupling methods and the use of 'long' vectors of coupling data comprising the input and output of all involved codes at a time, they turn out to be particularly suited also for simulations involving more than two coupled fields. As standard two-field coupling schemes are not suited for such cases as shown in our numerical results, this allows the simulation of a new range of applications in a partitioned way. [ABSTRACT FROM AUTHOR]

A fault-tolerant and practically stabilizing simulation of an atomic register is presented. The simulation works in asynchronous message-passing systems, and allows a minority of processes to crash. The simulation stabilizes in a practically stabilizing manner, by reaching a long execution in which it runs correctly. A key element in the simulation is a new combinatorial construction of a bounded labeling scheme accommodating arbitrary labels, including those not generated by the scheme itself. [ABSTRACT FROM AUTHOR]

This paper presents an agile simulation-aided shape editing system for personal fabrication applications. The finite element structural analysis and geometric design are seamlessly integrated within our system to provide users interactive structure analysis feedback during mesh editing. Observing the fact that most editing operations are actually local, a domain decomposition framework is employed to provide unified interface for shape editing, FEM system updating and shape optimization. We parameterize entries of the stiffness matrix as polynomial-like functions of geometry editing parameters thus the underlying FEM system can be rapidly synchronized once edits are made. A local update scheme is devised to re-use the untouched parts of the FEM system thus a lot repetitive calculations are avoided. Our system can also perform shape optimizations to reduce high stresses in model while preserving the appearance of the model as much as possible. Experiments show our system provides users a smooth editing experience and accurate feedback. [ABSTRACT FROM AUTHOR]

Cognitive radio (CR) is a promising technology to improve the utilisation of wireless spectrum resources. Spectrum sensing is the core functionality in CR networks (CRN). When there exist malicious users (MUs) in CRN and MUs start to attack the network after accumulating reputation to some extent, the performance is deteriorated. In this paper, a scheme is proposed by employing Orthogonalized Gnanadesikan–Kettenring (OGK) to mitigate the effect of MUs without the assistance of trusted nodes, and it can improve the robustness of CRN. Simulations verify the effectiveness of the proposed scheme. [ABSTRACT FROM AUTHOR]

Accuracy of velocity–vorticity ( V → , ω → )-formulations over other formulations in solving Navier–Stokes equation has been established in recent times. However, the issue of non-satisfaction of solenoidality conditions on vorticity is not addressed in the literature which can possibly lead to non-physical solution. In this respect, here, we have developed and reported conservative rotational form of the ( V → , ω → )-formulation which preserves the solenoidality condition on vorticity in a much simpler way compared to other formulations. Superiority of rotational form over the conventional Laplacian form of ( V → , ω → )-formulation is also shown [by comparing the results for flows inside cubical lid driven cavity (LDC)]. For solving the 3D Navier–Stokes equation using a staggered grid, we use optimized compact schemes for (a) interpolation and (b) evaluation of first and second derivatives. As illustrations, we have solved problems of (i) flow inside a 3D lid driven cavity (LDC), whose solutions are compared with experimental results reported by Koseff and Street [19] and (ii) 3D transitional flow of an equilibrium zero pressure gradient (ZPG) boundary layer over a flat plate as demonstration of the effectiveness of the rotational form of ( V → , ω → )-formulation. [ABSTRACT FROM AUTHOR]

Abstract: This paper addresses estimation fusion in the presence of possible mismatches of sensor model. The main concerns of the paper lie in two aspects. One is to improve the filter performance of the single sensor when there are possible mismatches about the sensor model. The other one is to adopt a good fusion scheme to combine local estimates. For these purposes, the measurement process of the local sensor is modeled by multiple models firstly, and the IMM (interacting multiple model) estimator is implemented to produce estimates for individual models. Next, we describe the local estimate by a Gaussian mixture rather than a single Gaussian density in the baseline IMM filter. Such a GMM (Gaussian mixture model) representation of the system state allows us to keep the detailed information about the local tracker, which contributes to the further fusion if treated properly. Finally, the fusion of two Gaussian mixtures is done in the probabilistic framework, and a close-form solution is derived without complex numerical operations. Simulation results demonstrate the effectiveness of the proposed approach. [Copyright &y& Elsevier]

Molecular simulation could provide detailed description of fluid systems when compared to experimental techniques. They can also replace equations of state; however, molecular simulation usually costs considerable computational efforts. Several techniques have been developed to overcome such high computational costs. In this paper, two early rejection schemes, a conservative and a hybrid one, are introduced. In these two methods, undesired configurations generated by the Monte Carlo trials are rejected earlier than it would when using conventional algorithms. The methods are tested for structureless single-component Lennard–Jones particles in both canonical andNVT-Gibbs ensembles. The computational time reduction for both ensembles is observed at a wide range of thermodynamic conditions. Results show that computational time savings are directly proportional to the rejection rate of Monte Carlo trials. The proposed conservative scheme has shown to be successful in saving up to 40% of the computational time in the canonical ensemble and up to 30% in theNVT-Gibbs ensemble when compared to standard algorithms. In addition, it preserves the exact Markov chains produced by the Metropolis scheme. Further enhancement forNVT-Gibbs ensemble is achieved by combining this technique with the bond formation early rejection one. The hybrid method achieves more than 50% saving of the central processing unit (CPU) time. [ABSTRACT FROM AUTHOR]

With the emergence of petascale computing platforms, high-fidelity computational aeroacoustics (CAA) simulation has become a feasible, robust and accurate tool that complements theoretical and empirical approaches in the prediction of sound levels generated by aircraft airframes and engines. Differentiating itself from the broader discipline of computational fluid dynamics, CAA is particularly challenging as it demands high accuracy, good spectral resolution, and low dispersion and diffusion errors from the underlying numerical methods. Large eddy simulation based on space-implicit high-order compact finite difference schemes has been shown to meet such stringent requirements. In this paper, we discuss a new, scalable parallelization scheme with a three-dimensional computational space partitioning. Unlike many traditional multiblock computational fluid dynamics (CFD) methods, our partitioning is non-overlapping. We use the truncated SPIKE algorithm to solve the governing equations accurately and limit one-sided biased differentiation to just the physical boundaries. We present experimental performance data collected on Kraken and Ranger, two near-petascale computing platforms. [ABSTRACT FROM AUTHOR]

P4 polyphase code is well known in pulse compression technique. For P4 code with length 1000, peak sidelobe level (PSL) and integrated sidelobe level (ISL) are −36dB and −16dB, respectively. In order to increase the performance, there are different reduction techniques to reduce the sidelobes of P4 code. This paper presents a novel sidelobe reduction technique that reduces the PSL and ISL to −127dB and −104dB, respectively. Also, other sidelobe reduction techniques such as Woo filter are investigated and compared with the novel proposed technique. Simulations and results show that the proposed technique produces a better peak side lobe ratio (PSL) and integrated side lobe ratio (ISL) than other techniques. [ABSTRACT FROM AUTHOR]

Highlights: [•] A new approach of using computationally cheap surrogate models for optimization of SMB chromatography is presented. [•] Two different types of surrogate models are developed to replace the detailed but expensive full-order SMB model for optimization. [•] The trust-region framework is proposed to implement an efficient and reliable management of both types of surrogates. [•] The results show that the new scheme not only converges to the optimum obtained with the full-order system, but also yields significant computational advantages. [Copyright &y& Elsevier]

Abstract: Delay preemption that combines the techniques of preemption and small buffers is an efficient solution for burst contention. However, due to the phenomenon of over-usage on buffer, the low-loss demand of high priority is not ensured especially in high traffic states. In this article, to improve the blocking of delay preemption, we propose a modified scheme named limited delay preemption based priority (limited-DPP) that constrains the buffered right of low priority within the moderate and high traffic states. To validate the efficiency of limited-DPP, the comprehensive analysis and simulation are performed in terms of loss and buffering time. [Copyright &y& Elsevier]

Abstract: Iterative learning control (ILC) has been successfully employed for trajectory tracking of uncertain dynamic systems with less system information. This paper attempts to adopt the benefits of ILC to improve the trajectory tracking performance of spatially interconnected systems. By utilizing the ILC update law along the iteration domain repetitively, a perfect reference trajectory tracking can be ensured. It is the key benefit of using ILC that less system model information is used in the design of a trajectory tracking controller for spatially interconnected systems. Through a numerical simulation, the validity of the proposed control scheme is illustrated. [Copyright &y& Elsevier]

Considering the circumstance of heterogeneous voice flows, first, by applying Markov chain, this paper proposes an unsaturated analytical model for the IEEE 802.11e EDCA protocol, which considers the condition of non-ideal transmission channel and the character of the occurrence of backoff countdown at the beginning of time slot in EDCA protocol. Furthermore, according to the proposed model, the media access delay and throughput of a flow are analysed, and the flow-oriented call admission control (CAC) scheme is proposed. Finally, the simulation results are shown to confirm that the proposed CAC scheme can guarantee the requirements of throughput and delay of voice flows, and can admit more voice flows to improve the utilisation efficiency of network resources by choosing the appropriate values of the minimum contention window or the appropriate varieties of voice flows. [ABSTRACT FROM PUBLISHER]

Abstract: In this paper, we propose a novel high-speed stream cipher encryption scheme based on the true random key generated by a chaotic semiconductor laser. A 5-Gbits/s non-return-to-zero plaintext is successfully encrypted and decrypted using this cryptography by numerical simulations. Compared with chaos-based optical communications for a single channel utilizing analog chaotic optical carrier, the performance of the proposed setup of stream ciphers based on true random numbers generated by chaotic light is improved. The scheme overcomes the shortcoming of quality decrease of chaos communications caused by decline of chaos synchronization. The proposed setup can be applied in the areas of real-time high-speed physical encryption. [Copyright &y& Elsevier]

We develop an information theoretic characterization and a practical coding approach for segmented deletion channels. Compared to channels with independent and identically distributed (i.i.d.) deletions, where each bit is independently deleted with an equal probability, the segmentation assumption imposes certain constraints, i.e., in a block of bits of a certain length, only a limited number of deletions are allowed to occur. This channel model has recently been proposed and motivated by the fact that for practical systems, when a deletion error occurs, it is more likely that the next one will not appear very soon. We first argue that such channels are information stable, hence their channel capacity exists. Then, we introduce several upper and lower bounds with two different methods in an attempt to understand the channel capacity behavior. The first scheme utilizes certain information provided to the transmitter and/or receiver while the second one explores the asymptotic behavior of the bounds when the average bit deletion rate is small. In the second part of the paper, we consider a practical channel coding approach over a segmented deletion channel. Specifically, we utilize outer LDPC codes concatenated with inner marker codes, and develop suitable channel detection algorithms for this scenario. Different maximum-a-posteriori (MAP) based channel synchronization algorithms operating at the bit and symbol levels are introduced, and specific LDPC code designs are explored. Simulation results clearly indicate the advantages of the proposed approach. In particular, for the entire range of deletion probabilities less than unity, our scheme offers a significantly larger transmission rate compared to the other existing solutions in the literature. [ABSTRACT FROM AUTHOR]

\boldmath In this paper, computationally efficient schemes for enumerating the so-called inliers of a wide range of permutations employed in pruned variable-size (turbo) interleavers are proposed. The objective is to accelerate pruned interleaving time in turbo codes by computing a statistic known as the pruning gap that enables determining a permuted address under pruning without serially permuting all its predecessors. It is shown that for any linear or quadratic permutation, including variations such as dithered relative prime or almost regular, the pruning gap can be computed in logarithmic time. Moreover, it is shown that Dedekind sums form efficient building blocks for enumerating inliers of the widely adopted polynomial-based permutations. An efficient algorithm for computing such sums in vector form using integer operations is presented. The results are extended to 2D and higher dimensional interleavers that combine multiple permutations along all dimensions, and closed-form expressions for inliers are derived. It is shown that the inliers statistic is a linear combination of the constituent permutation inliers. A lower bound on the minimum spread of serially pruned interleavers using the inliers statistic is also derived. Moreover, it is shown that serially pruned interleavers inherit the content-free property of the mother interleaver, and hence they are parallelizable. Simulation results of practical pruned turbo interleavers demonstrate a speedup improvement of several orders of magnitude compared to serial interleaving. [ABSTRACT FROM AUTHOR]

Autonomous operation of mechanical systems often requires the ability to detect and locate a particular phenomenon occurring in the surrounding environment. Being implemented to articulated manipulation, such a capability may realize a wide range of applications in autonomous maintenance and repair. This paper presents the sensor-driven task space control of an end-effector that combines the field estimation and the target tracking in an unknown spatial field of interest. The radial basis function network is adopted to model spatial distribution of an environmental phenomenon as a scalar field. Their weight parameters are estimated by a recursive least square method using collective measurements from the on-board sensors mounted to the manipulator. Then the asymptotic source tracking has been achieved by the control law based on the gradient of the estimated field. A new singularity tolerant scheme has been suggested to command the task space control law despite singular configurations. Simulation results using the three-link planar robot and the 6-revolute elbow manipulator are presented to validate the main ideas. [ABSTRACT FROM AUTHOR]

Abstract: Climate change is assumed to have a regionally specific impact on the soil moisture regime. The impact of climate change on soil moisture can be expected to depend on the soil texture. Because soil moisture observations are not available operationally, models can be used to predict these changes. In this study, a soil vegetation atmosphere transfer scheme (SVAT) was applied to virtual soil columns to assess the soil texture-specific sensitivity of simulated soil moisture to projected climate change. For each of the 31 soil texture classes of the German soil texture classification, long-term simulations were carried out based on the observed and scenario-based climate data representing five different climate regions in Germany. The simulation results indicate that soil moisture regimes considerably differ from region to region and among different soil texture classes. Different soil texture classes showed different sensitivities of soil moisture with respect to the projected climate change. While the differences in soil moisture between the current conditions and the climate scenarios were largest for silt soils, they were smallest for clay soils for both continental and humid climates. Sand and loam soils behaved intermediately, showing a moderate sensitivity. The results also showed that the soil texture-specific sensitivity of soil moisture to climate change was largest for soils that were not affected by groundwater (no capillary rise). Differences between soil texture classes decreased with an increasing influence of groundwater. In contrast, increasing vegetation density, rooting depths and transpiration demand induced the sensitivity of soil moisture to climate change, except in continental climates. This study indicates that validated, physically based soil hydrological models serve as suitable tools to assess the response of soil moisture to changing climate conditions. Based on virtual soil columns, modelling experiments systematically reveal soil texture-dependent sensitivities that cannot readily be identified in real world studies due to the limited availability and accessibility of the wide spectrum of different soil textures. [Copyright &y& Elsevier]

Abstract: In this work, we present a symplectic integration scheme to numerically compute space debris motion. Such an integrator is particularly suitable to obtain reliable trajectories of objects lying on high orbits, especially geostationary ones. Indeed, it has already been demonstrated that such objects could stay there for hundreds of years. Our model takes into account the Earth’s gravitational potential, luni-solar and planetary gravitational perturbations and direct solar radiation pressure. Based on the analysis of the energy conservation and on a comparison with a high order non-symplectic integrator, we show that our algorithm allows us to use large time steps and keep accurate results. We also propose an innovative method to model Earth’s shadow crossings by means of a smooth shadow function. In the particular framework of symplectic integration, such a function needs to be included analytically in the equations of motion in order to prevent numerical drifts of the energy. For the sake of completeness, both cylindrical shadows and penumbra transitions models are considered. We show that both models are not equivalent and that big discrepancies actually appear between associated orbits, especially for high area-to-mass ratios. [Copyright &y& Elsevier]

Abstract: The term ‘Convected Scheme’ (CS) refers to a family of algorithms, most usually applied to the solution of Boltzmann’s equation, which uses a method of characteristics in an integral form to project an initial cell forward to a group of final cells. As such the CS is a ‘forward-trajectory’ semi-Lagrangian scheme. For multi-dimensional simulations of neutral gas flows, the cell-centered version of this semi-Lagrangian (CCSL) scheme has advantages over other options due to its implementation simplicity, low memory requirements, and easier treatment of boundary conditions. The main drawback of the CCSL-CS to date has been its high numerical diffusion in physical space, because of the 2nd order remapping that takes place at the end of each time step. By means of a modified equation analysis, it is shown that a high order estimate of the remapping error can be obtained a priori, and a small correction to the final position of the cells can be applied upon remapping, in order to achieve full compensation of this error. The resulting scheme is 4th order accurate in space while retaining the desirable properties of the CS: it is conservative and positivity-preserving, and the overall algorithm complexity is not appreciably increased. Two monotone (i.e. non-oscillating) versions of the fourth order CCSL-CS are also presented: one uses a common flux-limiter approach; the other uses a non-polynomial reconstruction to evaluate the derivatives of the density function. The method is illustrated in simple one- and two-dimensional examples, and a fully 3D solution of the Boltzmann equation describing expansion of a gas into vacuum through a cylindrical tube. [Copyright &y& Elsevier]

In this study, the authors present a resource allocation scheme that determines both a set of multicast basestations and a transmission scheme minimising the aggregate number of multicast resources in all of the multicast basestations while satisfying the multicast coverage requirement in an orthogonal frequency division multiple access-based single frequency networks (SFNs). In particular, the proposed scheme consists of two phases. In the first phase, a multicast basestation set and a transmission scheme are initially found to minimise the aggregate number of multicast resources. Then, in the second phase, the transmission scheme is adjusted according to the multicast users' performance reports. In addition, the multicast basestation set is adaptively updated if the aggregate number of multicast resources significantly changes as compared to that after the set was most recently updated. Using computer simulations, the authors demonstrate that the proposed scheme can efficiently utilise the radio resources for multicast transmission. [ABSTRACT FROM AUTHOR]

Realizing application systems that match people's expectations and providing adequate network services for various users under various network and platform environments are difficult challenges. To overcome these problems, we have studied application systems based on multiagent systems and design models of multiagent systems. We propose a method to observe and control the behavioral characteristics of multiagent systems to support the design, development, and operation of such systems. More specifically, we propose a Flexible Distributed System and a Behavioral Characteristics Model, and we apply these two models to the design of an actual multimedia communication system and evaluate the effectiveness of the proposed scheme. [ABSTRACT FROM AUTHOR]

Abstract: Dynamic balancing of computation and communication load is vital for the execution stability and performance of distributed, parallel simulations deployed on the shared, unreliable resources of large-scale environments. High Level Architecture (HLA) based simulations can experience a decrease in performance due to imbalances that are produced initially and/or during run time. These imbalances are generated by the dynamic load changes of distributed simulations or by unknown, non-managed background processes resulting from the non-dedication of shared resources. Due to the dynamic execution characteristics of elements that compose distributed applications, the computational load and interaction dependencies of each simulation entity change during run time. These dynamic changes lead to an irregular load and communication distribution, which increases overhead of resources and latencies. A static partitioning of load is limited to deterministic applications and is incapable of predicting the dynamic changes caused by distributed applications or by external background processes. Therefore, a scheme for balancing the communication and computational load during the execution of distributed simulations is devised in a scalable hierarchical architecture. The proposed balancing system employs local and cluster monitoring mechanisms in order to observe the distributed load changes and identify imbalances, repartitioning policies to determine a distribution of load and minimize imbalances. A migration technique is also employed by this proposed balancing system to perform reliable and low-latency load transfers. Such a system successfully improves the use of shared resources and increases distributed simulations’ performance by minimizing communication latencies and partitioning the load evenly. Experiments and comparative analyses were conducted in order to identify the gains that the proposed balancing scheme provides to large-scale distributed simulations. [ABSTRACT FROM AUTHOR]

Based on the basic principle of spread spectrum systems, this paper proposes a hybrid automatic-repeat-request (HARQ) scheme with interference mitigation for multiple-input-multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems. The proposed hybrid media access control (MAC) and physical layer (PHY) design orthogonally spreads signals in the transmission domain to separate the desired signals from interferences. It not only improves the signal-to-noise ratio (SNR) but also suppresses intercarrier interference (ICI) and interantenna interference (IAI). Almost without increasing complexity, mathematical analyses and numerical simulations show that the proposed scheme outperforms the conventional Chase combining HARQ. [ABSTRACT FROM AUTHOR]

Abstract: A duplex radio-over-fiber (RoF) link with a novel scheme to generate 60-GHz millimeter (mm)-wave using 20 GHz double sideband (DSB) optical mm-wave with signal carried only by its optical carrier is investigated. In the RoF downlink, the modulation frequency to generate the DSB optical mm-wave is reduced greatly. The theoretical analysis and numerical simulation show that this scheme cannot only eliminate the code form distortion caused by the time shifting of the sidebands, but also reduce the influence of the fading effect as the DSB optical mm-wave signal is transmitted along the fiber. Based on the scheme, the duplex RoF link with the frequency up- (down-) conversion of the down- (up-) link mm-wave signal is built and the uplink transmission performance is analyzed theoretically. [Copyright &y& Elsevier]

It is known that neither the Alamouti nor the V-BLAST scheme achieves the Zheng—Tse diversity—multiplexing tradeoff (DMT) of the multiple-input multiple-output (MIMO) channel. With respect to the DMT curve, the Alamouti scheme achieves the point corresponding to maximum diversity gain only, whereas V-BLAST meets only the point corresponding to maximum multiplexing gain. It is also known that D-BLAST achieves the optimal DMT for n transmit and n receive antennas, but only under the assumption that the leading and trailing zeros are ignored. When these zeros are taken into account, D-BLAST achieves the point corresponding to zero multiplexing gain, but not the point corresponding to zero diversity gain. The first scheme to achieve the DMT is the coding scheme of Yao and Wornell for the case of two transmit and two receive antennas. In this paper, we introduce the notion of an asymptotic-information-lossless (AILL) design and obtain a necessary and sufficient condition under which a design is AILL. Analogous to the result that full-rank designs achieve the point corresponding to the zero mulliplexing gain of the optimal DMT curve, we show AILL to be a necessary and sufficient condition for a design to achieve the point on the DMT curve corresponding to zero diversity gain. We also derive a lower bound on the tradeoff achieved by designs from field extensions and show that the tradeoff is very close to the optimal tradeoff in the case of a single receive antenna. A lower bound to the tradeoff achieved by designs from division algebras is presented which indicates that these designs achieve both extreme points (corresponding to zero diversity and zero multiplexing gain) of the optimal DMT curve. Finally, we present simulations results for n transmit and n receive antennas, for n = 2, 3, 4, which suggest that designs from division algebras are likely to have the property of being DMT achieving. [ABSTRACT FROM AUTHOR]

Time domain synchronous orthogonal frequency division multiplexing (TDS-OFDM) modulation scheme can improve the spectrum efficiency over the traditional Cyclic Prefix (CP) OFDM technology at the cost of computational efforts due to the iterative padding subtraction (IPS) at the receiver to mitigate the inter symbol interference caused by the multipath propagation. In this paper, a simplified equalization scheme is presented for the dual PN-sequence padding (DPNP) TDS-OFDM systems. Although the length of the padded PN sequence needed is double compared to what needed by the IPS, leading to slight decrease of the spectrum efficiency, this method can save about 90% computational effort in practice compared with that of the IPS algorithm. It also outperforms IPS method under the time-varying fading channel in terms of symbol error rate and maximum Doppler frequency, verified by the computer simulation. [ABSTRACT FROM AUTHOR]

The nonlinear stability of thermal lattice BGK models is examined by means of computer simulation for the case of one-and two-dimensional compressible flows. It is shown that in one dimension (1D) the method is stable on a sizeable range of flow speeds and temperatures. In two dimensions (2D) the method is stable even in the presence of negative distribution functions, but on a smaller stability domain. The computational efficiency of the method compares favorably with classical algorithms for compressible flows, such as the λ-scheme and the Lax-Wendroff scheme. [ABSTRACT FROM AUTHOR]

Unequal spaced channel allocation (USCA) is a technique to reduce Four wave mixing (FWM). In this paper, system performance of 8 channel WDM system considering different optical transmitter formats (RZ, NRZ, Raised cosine and Gaussian) using USCA has been evaluated in terms of Q-factor. The simulation results reveal that four wave mixing is minimum for NRZ format. Also the effect of changing the laser power and increasing the bit rate has been observed. [ABSTRACT FROM AUTHOR]