Iterative receivers for SFBC-OFDM systems with adaptive training scheme

This paper considers the design of iterative receivers for space-frequencyblock-coded orthogonal frequency division multiplexing (SFBC-OFDM) systems in unknown wirelessdispersive fading channels. An iterative joint channel estimation and symbol detection algorithm isderived. In the algorithm, the channel estimator performs alternately in two modes. During thetraining mode, the channel state information (CSI) is obtained by a discrete-Fourier-transform-basedchannel estimator and the noise variance and covariance matrix of the channel response is estimatedby the proposed method. In the data transmission mode, the CSI and transmitted data is obtainediteratively. In order to suppress the error propagation caused by a random error in identifyingsymbols, a simple error propagation detection criterion is proposed and an adaptive training schemeis applied to suppress the error propagation. Both theoretical analysis and simulation results showthat this algorithm gives better bit-error-rate performance and saves the overhead of OFDM systems.

On the comparison of particle regeneration technique and volume adaptive scheme in the compressible flow based on smoothed particle hydrodynamics

The collapse of a cavitation bubble is an interesting topic and it has many applications in the engineering fields.Due to its compressible nature,the modelling of a cavitation bubble is not easy by the Lagrangian method,like the smoothed particle hydrodynamics(SPH),as there is large variation of particle volume.Currently,there are two kinds of method that have been proposed to deal with this problem:the particle regeneration technique(PRT)and the volume adaptive scheme(VAS).They have all been validated via several numerical tests of compressible flow in the past studies.As is based on totally different concept,the ultimate simulation results and properties may differ.Here,we intend to compare these two methods based on the Riemann-based SPH solver with monotone upwind-centered scheme for conservation laws(MUSCL)reconstruction via several numerical tests.The characteristics of these two methods are discussed and the applicable scope for them are also commented for further usage.

AN ADAPTIVE MEASUREMENT SCHEME BASED ON COMPRESSED SENSING FOR WIDEBAND SPECTRUM DETECTION IN COGNITIVE WSN

An Adaptive Measurement Scheme (AMS) is investigated with Compressed Sensing (CS) theory in Cognitive Wireless Sensor Network (C-WSN). Local sensing information is collected via energy detection with Analog-to-Information Converter (AIC) at massive cognitive sensors, and sparse representation is considered with the exploration of spatial temporal correlation structure of detected signals. Adaptive measurement matrix is designed in AMS, which is based on maximum energy subset selection. Energy subset is calculated with sparse transformation of sensing information, and maximum energy subset is selected as the row vector of adaptive measurement matrix. In addition, the measurement matrix is constructed by orthogonalization of those selected row vectors, which also satisfies the Restricted Isometry Property (RIP) in CS theory. Orthogonal Matching Pursuit (OMP) reconstruction algorithm is implemented at sink node to recover original information. Simulation results are performed with the comparison of Random Measurement Scheme (RMS). It is revealed that, signal reconstruction effect based on AMS is superior to conventional RMS Gaussian measurement. Moreover, AMS has better detection performance than RMS at lower compression rate region, and it is suitable for large-scale C-WSN wideband spectrum sensing.

A NEW ADAPTIVE FILTERING SCHEME BASED ON WAVELET TRANSFORM

Based on the scale function representation for a function in L2(R), a new wavelet transform based adaptive system identification scheme is proposed. It can reduce the amount of computation by exploiting the decimation properties and keep the advantage of quasi-orthogonal transform of the discrete wavelet, transform (DWT). The issue has been supported by computer simulations.

Feature extraction of gear-localized defect using adaptive lifting scheme and local gradient maps

In this paper,the adaptive lifting scheme (ALS) and local gradient maps (LGM) are proposed to isolate the transient feature components from the gearbox vibration signals. Based on entropy minimization rule,the ALS is employed to change properties of an initial wavelet and design adaptive wavelet. Then LGM is applied to characterize the transient feature components in detail signal of decomposition results using ALS. In the present studies, the orthogonal Daubechies 4 (Db 4) wavelet is used as the initial wavelet. The proposed method is applied to both simulated signals and vibration signals acquired from a gearbox for periodic impulses detection. The two conventional methods (cepstrum analysis and Hilbert envelope analysis) and the orthogonal Db4 wavelet are also used to analyze the same signals for comparison. The results demonstrate that the proposed method is more effective in extracting transient components from noisy signals.

Ergodic Capacity Analysis and Adaptive Transsmion Scheme in Multi-user Distributed Antenna Systems

This paper focuses on analyzing the ergodic capacity performance of limited feedback (LFB) beamforming in multi-user distributed antenna system (DAS). In such a system, multi-user interference (MUI) is inevitably due to the channel uncertainties caused by quantization error. Considering this, we propose a parameter named effective ergodic capacity rate (EECR), which denotes the capacity offset between finite rate feedback and perfect channel state information (CSI). The simulation results show that the derived approximated EECR is very tight to actual EECR. Based on the approximated EECR, an adaptive minimum bit feedback scheme is proposed, which can effectively reduce the overhead of feedback channel and the complexity of the system. The simulation results verify the effectiveness of the proposed scheme.

Self-configuring scheduling scheme for IPv6 traffic with multiple QoS classes

This paper proposes a new queuing model and adaptive scheduling scheme which realizes multi-class QoS mechanism under DiffServ architecture. The queuing model is composed of two parallel output subqueues, each output sub-queue adopts random drop algorithm by setting different buffer threshold for different class traffic, so it can provide multi-class QoS. The new proposed scheduling scheme which adaptively changes the parameter A can guarantee the performance target of high class traffic, in the mean time, improve the QoS of low classes traffic.

Analytical and Numerical Investigation for the DMBBM Equation

The nonlinear dispersive modified Benjamin-Bona-Mahony(DMBBM)equation is solved numerically using adaptive moving mesh PDEs(MMPDEs)method.Indeed,the exact solution of the DMBBM equation is obtained by using the extended Jacobian elliptic function expansion method.The current methods give a wider applicability for handling nonlinear wave equations in engineering and mathematical physics.The adaptive moving mesh method is compared with exact solution by numerical examples,where the explicit solutions are known.The numerical results verify the accuracy of the proposed method.

Passivity-based control of synchronous motors in mine hoist systems

An adaptive PBC strategy for SM with a time-varying load torque to track fluxand speed trajectories was proposed.The key point of this method was the identificationof terms,known as workless forces,which appeared in the dynamic equations of SM buthad no effect on the energy balance equation of the closed loop.PBC,combined withadaptive control schemes,not only preserved the advantages of PBC such as nonexistenceof singularity,but also rejected the flux and speed tracking error caused by statorand rotor resistance variation.The rotor currents of SM were estimated via a state observer.This algorithm simplified the control structure and enhanced the robustness of thecontrol system.The feasibility and effectiveness were confirmed by experimental resultsbased on dSPACE.

An efficient unstructured WENO method for supersonic reactive flows

An efficient high-order numerical method for supersonic reactive flows is proposed in this article.The reactive source term and convection term are solved separately by splitting scheme.In the reaction step,an adaptive time-step method is presented,which can improve the efficiency greatly.In the convection step,a third-order accurate weighted essentially non-oscillatory（WENO）method is adopted to reconstruct the solution in the unstructured grids.Numerical results show that our new method can capture the correct propagation speed of the detonation wave exactly even in coarse grids,while high order accuracy can be achieved in the smooth region.In addition,the proposed adaptive splitting method can reduce the computational cost greatly compared with the traditional splitting method.

Unified Vibration Suppression and Compliance Control for Flexible Joint Robot

An adaptive control scheme is presented,which can simultaneously realize vibration suppression and compliance control for flexible joint robot(FJR).The proposed control scheme provides a unified formulation for both vibration suppression mode,where FJR tracks the desired position with little vibration,and compliance mode,in which FJR presents passive.Instead of designing multiple controllers and switching between them,both modes are integrated into a single controller,and the transition between two modes is smooth and stable.The stability of the closed-loop system is theoretically proven via the Lyapunov method,with the considering the dynamics uncertainties in both link side and motor side.Simulation results are presented to illustrate good performances of the proposed control scheme.

Adaptive Gaussian sum squared-root cubature Kalman filter with split-merge scheme for state estimation

The paper deals with state estimation problem of nonlinear non-Gaussian discrete dynamic systems for improvement of accuracy and consistency. An efficient new algorithm called the adaptive Gaussian-sum square-root cubature Kalman filter（AGSSCKF） with a split-merge scheme is proposed. It is developed based on the squared-root extension of newly introduced cubature Kalman filter（SCKF） and is built within a Gaussian-sum framework. Based on the condition that the probability density functions of process noises and initial state are denoted by a Gaussian sum using optimization method, a bank of SCKF are used as the sub-filters to estimate state of system with the corresponding weights respectively, which is adaptively updated. The new algorithm consists of an adaptive splitting and merging procedure according to a proposed split-decision model based on the nonlinearity degree of measurement. The results of two simulation scenarios（one-dimensional state estimation and bearings-only tracking） show that the proposed filter demonstrates comparable performance to the particle filter with significantly reduced computational cost.

Accuracy of the Adaptive GRP Scheme and the Simulation of 2-D Riemann Problems for Compressible Euler Equations

The adaptive generalized Riemann problem(GRP)scheme for 2-D compressible fluid flows has been proposed in[J.Comput.Phys.,229(2010),1448–1466]and it displays the capability in overcoming difficulties such as the start-up error for a single shock,and the numerical instability of the almost stationary shock.In this paper,we will provide the accuracy study and particularly show the performance in simulating 2-D complex wave configurations formulated with the 2-D Riemann problems for compressible Euler equations.For this purpose,we will first review the GRP scheme briefly when combined with the adaptive moving mesh technique and consider the accuracy of the adaptive GRP scheme via the comparison with the explicit formulae of analytic solutions of planar rarefaction waves,planar shock waves,the collapse problem of a wedge-shaped dam and the spiral formation problem.Then we simulate the full set of wave configurations in the 2-D four-wave Riemann problems for compressible Euler equations[SIAM J.Math.Anal.,21(1990),593–630],including the interactions of strong shocks(shock reflections),vortex-vortex and shock-vortex etc.This study combines the theoretical results with the numerical simulations,and thus demonstrates what Ami Harten observed"for computational scientists there are two kinds of truth:the truth that you prove,and the truth you see when you compute"[J.Sci.Comput.,31(2007),185–193].

Chaos Synchronization in the Belousov-Zhabotinsky Chemical Reaction by Adaptive Control Scheme

The adaptive synchronization scheme proposed by John and Amritkar was employed into the Belousov Zhabotinsky (BZ) 4 variable Montanator model system. By the parameter adjustment, chaos synchronization has been obtained. Through calculating the transient time, the optimal combination of the stiffness constant and damping constant was obtained. Furthermore, the relationships among the transient time, conditional Lyapunov exponents, the stiffness constant and damping constant were discussed. Also, the BZ system with the adaptive synchronization scheme might be used for the communication purposes.

Adaptive bit allocation scheme in multi-cell cooperative block diagonalization systems with delayed and limited feedback

In multi-cell cooperative multi-input multi-output （MIMO） systems, base station （BS） can exchange and utilize channel state information （CSI） of adjacent cell users to manage co-channel interference. Users quantize the CSIs of desired channel and interference channels using finite-rate feedback links, then BS can generate cooperative block diagonalization （BD） precoding matrices using the obtained quantized CSI at transmitter to supress co-channel interference. In this paper, a novel adaptive bit allocation scheme is proposed to minimize the rate loss due to imperfect CSI. We derive the closed-form expression of rate loss caused by both channel delay and limited feedback. Based on the derived rate loss expression, the proposed scheme can adaptively allocate more bits to quantize the better channels with smaller delays and fewer bits to worse channels with larger delays. Simulation results show that the proposed scheme yields higher performance than other allocation schemes.

Distributed Adaptive Synchronization of Complex Dynamical Network with Unknown Time-varying Weights

A new approach of adaptive distributed control is proposed for a class of networks with unknown time-varying coupling weights. The proposed approach ensures that the complex dynamical networks achieve asymptotical synchronization and all the closed-loop signals are bounded. Furthermore, the coupling matrix is not assumed to be symmetric or irreducible and asymptotical synchronization can be achieved even when the graph of network is not connected. Finally, a simulation example shows the feasibility and effectiveness of the approach.

Adaptive phase field simulation of quasi-static crack propagation in rocks

In this study,we present an adaptive phase field method(APFM)for modeling quasi-static crack propagation in rocks.Crack initiation due to positive strains is considered,and a numerical simulation is implemented using a commercial software,COMSOL Multiphysics.Two benchmark tests are first examined,namely,a single-edge-notched square plate subjected to respective tension and shear loadings.The crack propagation in Brazil splitting tests,2D notched semi-circular bend(NSCB)tests,and 3D NSCB tests are subsequently simulated and analyzed.All the numerical examples indicate that the propagation of the cracks is autonomous and external fracture criteria are not required for phase field modeling.Furthermore,the adaptive remeshing scheme reduces unnecessary global mesh refinement and exhibits good adaptability for fracture modeling.The simulations are in good agreement with the experimental observations,and thereby indicate the feasibility and practicability of the APFM in rocks(even in 3D cases).

Adaptive controller design for satellite attached by non-cooperative object

When non-cooperative body attachment occurs in space, the inertia of the new combination and the change of the system's momentum are unknown.This uncertainty may lead to the instability of the spacecraft's attitude control.In order to solve this problem, we propose an adaptive control scheme based on the inertia estimation of the new, combined system of non-cooperative body and satellite.This method can allow the new combination of different situations to reach a stable state with a high level of precision and speed.In this paper, the stability of the adaptive control scheme is proven by constructing a Lyapunov function.A simulation environment in which a non-cooperative body attaches to a satellite attaches to is constructed.The simulation shows that the attitude error converges to a small field when using the control scheme, regardless of unfavorable cases, including unknown inertia parameters, added momentum.In addition, the simulation results show the strong robustness of the control scheme for the new combination.

The Variable-Step L1 Scheme Preserving a Compatible Energy Law for Time-Fractional Allen-Cahn Equation

In this work,we revisit the adaptive L1 time-stepping scheme for solving the time-fractional Allen-Cahn equation in the Caputo’s form.The L1 implicit scheme is shown to preserve a variational energy dissipation law on arbitrary nonuniform time meshes by using the recent discrete analysis tools,i.e.,the discrete orthogonal convolution kernels and discrete complementary convolution kernels.Then the discrete embedding techniques and the fractional Gronwall inequality are applied to establish an L^(2)norm error estimate on nonuniform time meshes.An adaptive time-stepping strategy according to the dynamical feature of the system is presented to capture the multi-scale behaviors and to improve the computational performance.

光滑粒子流体动力学框架下的EoSB空化模型及空化流动数值模拟研究

过去十余年来,光滑粒子流体动力学(Smoothed Particle Hydrodynamics,SPH)研究领域一直在探索空化流动的数值模拟,但迄今为止依然没有精确且稳定的SPH空化模型.本文将阐述一种在SPH框架内实现空化流动模拟的数值方法.首先,为了捕捉空化初生及其发展,本文在SPH框架内提出一种基于状态方程的相变模型.特别地,本文还引入一种粒子体积自适应算法(Volume Adaptive Scheme,VAS),以保证空化区域流体剧烈膨胀时粒子体积分布的均一性.此外,本文还采用粒子位移修正技术(Particle Shifting Technique,PST)和张力不稳定性控制技术(Tensile Instability Control,TIC)以提高粒子分布质量和抑制数值空洞的产生.最后,本文还通过引入大涡模拟(Large Eddy Simulation,LES)模型以考虑湍流效应,提高本文提出的SPH空化模型对高雷诺数流动的适用性.研究结果表明,本文提出的基于SPH方法的新空化模型能实现空化区域和压力分布等问题的精确预报.