基于磁势梯度与高斯过程的空间磁场构建方法

构建准确的空间磁场是实现地磁室内定位的基础,针对传统构建模型未考虑磁场分布规律,导致其构建磁场精度差的问题,本文提出了基于磁势梯度与高斯过程的磁场构建方法.首先,将磁势梯度和磁场的关系中引入高斯过程,并用平方指数核函数的空间梯度与地球磁场分布的方差和作为高斯过程核函数;然后,将带有约束的超参数优化问题转换为无约束优化问题,并利用Rprop算法优化超参数;最后,通过仿真分析了新方法相比于传统方法的优势,讨论了超参数对构建精度的影响,并且使用三轴矢量磁传感器,分别在小区域较强磁场异常环境、开阔区域强磁场异常环境和弱磁场异常环境中开展磁场构建实验,结果证明提出的方法能够用于真实环境下空间磁场的准确构建.     

基于改进神经网络算法控制开关电源的研究

针对数字开关电源的控制策略问题,提出一种改进共轭梯度算法的BP神经网络PID控制系统.以BUCK变换器为研究对象,在BP神经网络PID算法的基础上,通过改进共轭梯度算法优化控制系统的调节时间和恢复速度,以提高数字开关电源系统的控制性能和输出性能.基于MATLAB软件完成系统建模进行仿真研究.结果表明:改进后的控制系统比...     

An improved quasi-static finite-difference scheme for induced field evaluation based on the biconjugate gradient method

This paper presents a biconjugate gradient (BiCG) method that can significantly improve the performance of the quasi-static finite-difference scheme, which has been widely used to model field induction phenomena in voxel phantoms. The proposed BiCG method offers remarkable computational advantages in terms of convergence performance and memory consumption over the conventional iterative, successive overrelaxation algorithm. The scheme has been validated against other known solutions on a lossy, multilayered ellipsoid phantom excited by an ideal coil loop. The wide application capability and computational performance of the BiCG method is demonstrated by modeling the exposure of MRI healthcare workers to fields produced by pulsed field gradients. This is an important topic of research in light of the Physical Agents Directive 2004/40/EC because a variety of realistic operator postures near the bore entrance of an MRI system are modeled.     

Echo projection imaging-a method to obtain NMR images undistorted by magnetic field inhomogeneities

It is proposed to use a modified form of Mansfield's echo planar imaging to obtain NMR images which are entirely undistorted by background inhomogeneities of the magnetic field. In the proposed method, a train of 180 degrees pulses is applied in the presence of a periodically switched or sinusoidally modulated linear field gradient. The time-domain signal is sampled at half the distance between the 180 degrees pulses. At these points the magnetization will be modulated by the gradient, but will be independent of any mechanisms of inhomogeneous broadening, such as static field inhomogeneities, local susceptibility effects, or chemical shifts. A Fourier transform of the function comprising these points will therefore yield a faithful projection of the spin density, although the magnitude of the superimposed gradient need not be large compared to the inhomogeneous broadenings. This paper demonstrates the application of the proposed pulse sequence to a small-scale one-dimensional phantom. The major problem in upscaling this technique to human-scale dimensions lies in the limited available and allowed RF power, which in turn limits the maximal tolerable field inhomogeneities as well as the maximal practical field strength. An analysis of the tolerance of the proposed technique to these factors is presented, based on numerical simulation of its performance, using the Bloch equations. It is concluded that its use may be feasible on low-field systems, providing the advantages of increased signal-to-noise, lower required gradient strength, and drastically reduced sensitivity to the homogeneity and stability of the magnetic field, at the expense of larger RF power.     

机间数据链系统的功率分配控制方法

针对想定战场中机间数据链网络通信模型的上行链路功率控制问题,采用了一种基于多目标灰狼算法(Multi-objective Grey Wolf Optimizer,MOGWO)的功率控制方法.将功率控制建模为多目标优化问题,以最小化上行链路中各节点功率、使各节点在接收机处的信干噪比值(Signal-to-In-terfe...     

基于多天线波束赋形的CRN分布式上行功率控制算法

针对工作于underlay模式的认知无线网络（CRN,Cognitive Radio Network）上行功率控制问题,本文提出一种基于多天线波束赋形,由认知基站和认知用户联合优化的分布式上行功率控制算法.联合优化的具体步骤为认知基站通过求解最大广义特征值问题完成多天线波束赋形优化;认知用户先将非线性功率优化问题转换为几何规划凸优化问题,再使用梯度法完成分布式发送功率优化;认知基站和认知用户交替优化,实现网络效用最大化.数值仿真显示,同只优化认知用户功率的上行功率控制算法相比,认知基站和认知用户联合优化的上行功率控制算法不仅能得到更大的网络效用值,而且对主用户的干扰具有鲁棒性.     

An FDTD model for calculation of gradient-induced eddy currents in MRI system

In most magnetic resonance imaging (MRI) systems, pulsed magnetic gradient fields induce eddy currents in the conducting structures of the superconducting magnet. The eddy currents induced in structures within the cryostat are particularly problematic as they are characterized by long time constants by virtue of the low resistivity of the conductors. This paper presents a three-dimensional (3-D) finite-difference time-domain (FDTD) scheme in cylindrical coordinates for eddy-current calculation in conductors. This model is intended to be part of a complete FDTD model of an MRI system including all RF and low-frequency field generating units and electrical models of the patient. The singularity apparent in the governing equations is removed by using a series expansion method and the conductor-air boundary condition is handled using a variant of the surface impedance concept. The numerical difficulty due to the "asymmetry" of Maxwell equations for low-frequency eddy-current problems is circumvented by taking advantage of the known penetration behavior of the eddy-current fields. A perfectly matched layer absorbing boundary condition in 3-D cylindrical coordinates is also incorporated. The numerical method has been verified against analytical solutions for simple cases. Finally, the algorithm is illustrated by modeling a pulsed field gradient coil system within an MRI magnet system. The results demonstrate that the proposed FDTD scheme can be used to calculate large-scale eddy-current problems in materials with high conductivity at low frequencies.     

A Multiple Criteria Decision-Making Knowledge-Based Scheme for Real-Time Power Voltage Control

A new real-time power voltage control strategy is proposed in this paper. This scheme utilizes a novel offline evolutionary multiobjective optimization algorithm called jumping genes for generating the widespread control solutions and be readily stored into a knowledge data base. A separate online multiple criteria decision-making scheme is established for selecting the appropriate control solution. This concept of power voltage control has been demonstrated by the New England 39-bus power system. The system output performance was speedy and accurate.     

用于WCDMA系统的MMSE接收机的功率与数据速率相结合的分配算法

该文针对3GPP WCDMA系统的反向链路,提出了一种基于MMSE接收机的功率和数据速率相结合的控制算法。该算法可以保证用户在达到目标信干比的同时,减小平均发射功率、加快收敛速度,从而提高系统的整体性能。仿真结果验证了所提出方案的正确性和优化算法的有效性。采用该文提出的算法,与MMSE功率控制算法比较,系统容量可增加近10％,而收敛速度可提高30％左右。     

Nelder‐Mead–based power optimization for secrecy enhancement in amplify‐and‐forward cooperative relay networks

Cooperative communication based on relaying nodes has been considered as a promising technique to increase the physical layer security (PLS) performance in wireless communications. In this paper, an optimal power allocation (OPA) scheme based on Nelder‐Mead (NM) algorithm is proposed for improving the secrecy rate of amplify‐and‐forward (AF) cooperative relay networks employing cooperative jamming (CJ) scheme. The proposed hybrid jamming scheme allows the source and selected relay to transmit the jamming signal along with the information to confound the eavesdropper. The path selection probability of ant colony optimization (ACO) algorithm is used for selecting the relay for transmission. The performance based on secrecy rate is evaluated for “n” trusted relays distributed dispersedly between the source and destination. Gradient‐based optimization and three‐dimensional exhaustive search methods are used as benchmark schemes for comparison of the proposed power optimization algorithm. The secrecy performance is also compared with conventional AF scheme and CJ scheme without power optimization (EPA). The impact of single and multiple relays on secrecy performance is also evaluated. Numerical results reveal that, compared with the gradient method and exhaustive search algorithm, the proposed power allocation strategy achieves optimal performance. Also, the derived OPA results show a significantly higher secrecy rate than the EPA strategy for both CJ and AF schemes.     

基于不确定非线性智能电网感知网络控制系统方法研究

针对传统的不确定时滞的鲁棒控制系统不能满足现代电力系统发展的需求,提出一种基于不确定非线性智能电网感知云网络化控制识别方法。使用传统的数据值和基于电力网络到网络系统模型作为电力感知网络到网络模型的电力云网络,控制数据优化使用电源感知网络,而不是利用控制节点的预测值,突破了鲁棒控制的不确定时滞系统的控制效果。运用感知模型中的正向云算法修正加权系数,仿真实验证明,该识别方法能够很好地优化传统的不确定时滞鲁棒控制电力系统,具有良好的适应性和鲁棒控制性,进一步提高了智能电网传感云网络控制的各项性能指标。     

Worst-case performance optimization for robust power control in downlink beamforming

In this paper,¹ we examine the problem of robust power control in a downlink beamforming environment under uncertain channel state information (CSI). We suggest that the method of power control using the lower bounds of signal-to-interference-and-noise ratio (SINR) is too pessimistic and will require significantly higher power in transmission than is necessary in practice. Here, a new robust downlink power control solution based on worst-case performance optimization is developed. Our approach employs the explicit modeling of uncertainties in the downlink channel correlation (DCC) matrices and optimizes the amount of transmission power while guaranteeing the worst-case performance to satisfy the quality of service (QoS) constraints for all users. This optimization problem is non-convex and intractable. In order to arrive at an optimal solution to the problem, we propose an iterative algorithm to find the optimum power allocation and worst-case uncertainty matrices. The iterative algorithm is based on the efficient solving of the worst-case uncertainty matrices once the transmission power is given. This can be done by finding the solutions for two cases: (a) when the uncertainty on the DCC matrices is small, for which a closed-form optimum solution can be obtained and (b) when the uncertainty is substantial, for which the intractable problem is transformed into a convex optimization problem readily solvable by an interior point method. Simulation results show that the proposed robust downlink power control using the approach of worst-case performance optimization converges in a few iterations and reduces the transmission power effectively under imperfect knowledge of the channel condition.     

Resource Management Techniques for OFDM Systems with the Presence of Inter-Carrier Interference

The aim of the paper is to study the problems of resource management in the presence of inter-carrier interference (ICI) and multipath fading channel for orthogonal frequency division multiplexing (OFDM) systems. OFDM is a promising technique for the broadband wireless communication systems. However, the OFDM communication system is sensitive to ICI which arises because of Doppler spread and carrier frequency offset (CFO). To solve these problems, an optimization method has been exploited, and a computationally efficient method using numerical optimization techniques is proposed. The simulation results show that these derived optimal solutions and proposed suboptimal algorithms as compared with the uniform power allocation algorithm or conventional water-filling algorithm can significantly improve the performance of the OFDM systems.     

Erlang Capacity of a Voice/Data Cellular CDMA Uplink System Using Prioritized Admission Control and Adaptive Power Control

A CDMA uplink system that carries both voice and data traffic is investigated. The reservation-based admission control scheme is used to prioritize voice mobiles, and the truncated channel inversion power control scheme is used by data mobiles to improve system capacity. The performance of the system is measured by the Erlang capacity. Two methods of determining the Erlang capacity are presented. The first method decouples the analysis of blocking and outage performance, thus simplifying numerical search. The second method takes into account the impact of mobile traffic fluctuations on interference statistics, and thus yields more accurate results. Numerical results are provided that show significant differences between the two methods. Finally, the Erlang capacities of the system are compared for different power control schemes.     

一种关于水文RTU电源稳定性的优化方案

本文简要的介绍了水文RTU(Remote Terminal Unit)远程测控终端的电源系统,针对传统水文RTU电源系统中电源切换电路、3.3V电源电路和现场仪表供电电路的缺点,分别提出了优化方法与改进措施。对于电源切换电路,利用Liner公司的LTC4412芯片控制MOSFET的导通,解决了电源在切换时产生纹波的现象;对于3.3V供电电路,利用磁环电感替换相同感值的柱状电感,使磁力线会集中在磁环电感中,避免了漏磁的产生;对于现场仪表供电电路,用MOSFET代替电磁继电器,解决了电磁继电器误动作和机械寿命短的问题。通过这三个部分优化了RTU电源系统,提高了电源系统的稳定性。     

Comparison of GA and DDE for optimizing coverage in indoor environment

This paper presents a method for determining the required number and locations of transmitting antennas to optimize wireless propagation coverage in indoor ultra‐wideband communication system. In the coverage prediction model, we use the three‐dimensional ray‐tracing technique associated to a genetic algorithm and a dynamic differential evolution for optimizing the transmitting antennas location in an indoor environment. The ray‐tracing method is employed to calculate the field strength from one or more transmitting antennas, and the optimization algorithm is used to determine the required number and locations of these antennas to achieve optimized wireless coverage in the indoor environment. The combined three‐dimensional ray‐tracing and optimization algorithm was applied in the indoor environment to find the best location of the transmitting antennas by maximizing the power in the coverage area. The use of deployments to minimize the transmitting antennas and maximize the power in the coverage area was proposed. Obtained simulation results illustrate the feasibility of using the integrated ray‐tracing and optimization method to find the optimal transmitter locations in determining the optimized coverage of a wireless network. The dynamic differential evolution has better optimization results compared with the genetic algorithm. The investigated results can help communication engineers improve their planning and design of indoor wireless communication. Copyright © 2013 John Wiley & Sons, Ltd.     

基于射频隐身的采样周期和辐射功率控制方法研究

为进一步提高雷达的射频隐身能力,合理分配相控阵雷达的工作参数,在目标跟踪时,对雷达的采样周期和辐射功率控制方法进行研究。首先,根据目标运动状态的不同,对雷达采样周期与辐射功率自适应设计方法进行分析,在满足系统跟踪性能要求的前提下,建立了控制参数的优化模型;然后,利用粒子群算法优化自适应采样周期和自适应辐射功率等参数,有效地降低了跟踪性能误差,提高了雷达系统的射频隐身性能。与传统的雷达采样周期和辐射功率算法进行了仿真比较,结果表明所提的算法取得了较好射频隐身效果。     

An Adaptive Fuzzy C Means with Seagull Optimization Algorithm for Analysis of WSNs in Agricultural Field with IoT

In recent years, the environmental monitoring in agriculture field is an essential required application. To achieve the environmental monitoring of agriculture fields, the wireless sense networks (WSN) and internet of things is utilized. In the WSN, the energy consumption is a main issue to access the medium and transfer the networks. Hence, in this paper, adaptive fuzzy C means clustering and seagull optimization algorithm is developed for monitoring environmental conditions in agriculture field. Two main objective functions are utilized to empower the presentation of the WSN such as load balancing and energy efficient operation. The proposed method is a combination of fuzzy C means clustering and seagull optimization algorithm (SOA). The energy efficient and load balancing is achieved by optimal routing scheme by proposed method. The fuzzy C-means clustering is utilized to empower the energy efficient operation and load balancing. In the fuzzy C-means clustering, the SOA is utilized to select the optimal path selection. The proposed method is executed by NS2 simulator and performances are compared with existing methods such as atom search optimization and emperor penguin optimization respectively. The performance metrics are delay, drop, throughput, energy consumption, network lifetime, overhead and delivery ratio.

     

基于改进量子粒子群的红外图像增强算法

为了提高红外图像增强的效果,采用改进量子粒子群算法。首先构造粒子群多层空间结构,粒子运行空间划分为主层空间、次层空间,粒子信息交流通过主层空间、次层空间分别进行,交流过程受自身信息度因子和交流度因子影响;接着量子旋转门更新通过镜像门操作,梯度方法自适应调整量子门的旋转角度,提高了算法性能;最后将红外图像高频分量和低频分量分离,对其分别进行增强。实验仿真显示本文算法对红外图像增强结果相比其他算法较清晰,优质系数评价指标相比HE、NSCT、MSR、PSO、RSQS算法分别提高了43.60、36.52、25.60、19.24、12.14,对比度指标相比HE、NSCT、MSR、PSO、RSQS算法分别提高了27.99、20.70、15.28、13.97、10.85,性能指标较优。     

X 波段衍射输出相对论磁控管的粒子模拟研究

：本文报道了一个X 波段18 腔衍射输出相对论磁控管的初步模拟研究结果。利用高频场分析软件和粒子模拟软件, 通过分析和优化器件的结构参数,合理选取电磁场取值大小,最终得到：在二极管电压350 kV,外加磁场0.41T 条件下, 可以得到输出功率1.09 GW、功率转换效率为22%、频率9.59GHz 的微波。