Performance Analysis and Power Allocation for Cooperative SSK System with Receive Correlation in Rayleigh Fading Channel

In this paper,the performance analysis of cooperative space shift keying(SSK)system with dual-hop amplify and forward(AF)in receive-correlated Rayleigh channel is presented. By means of the performance analysis,a closed-form approximate expression of the average bit error rate(BER)is derived for the performance evaluation.With this expression,in a high signal-to-noise-ratio(SNR)region,a tight closed-form asymptotic BER of the system is also derived. It can simplify the calculation of average BER and provide effective evaluation for asymptotic performance. By minimizing this asymptotic BER expression,a suboptimum power allocation(PA) scheme is developed,and the closed-form PA coefficients are obtained. Simulation indicates that the suboptimal PA scheme outperforms the conventional equal PA scheme,and its performance is very close to that of the exhaustive search based optimal PA scheme but with low complexity. Moreover,the system performance under the spatially correlated channel is worse than that in spatially independent channel due to the effect of spatial correlation.     

An Adaptive Transmission Scheme for Deep Space Communication

Deep space communication is quite different from conventional ground communication due to its time-varying,complexity and large signal delay,which consequently affects communication quality and system efficiency.Adjusting the transmission parameters when the channel environment changes during the communication can guarantee the performance index of the system,and therefore improve communication efficiency. An adaptive transmission scheme of transceiver based on Consultative Committee for Space Data Systems(CCSDS)protocols is proposed in this paper. According to the variation of the deep space channel,the symbol rate of transmission data is adjusted dynamically by estimating the signal-to-noise ratio(SNR) of the receiver in real time and adjusting the channel environment. This scheme can improve the channel utilization and system throughput under the premise of limiting the system bit error rate. Furthermore,this scheme is successfully implemented in Xilinx Virtex-5 FPGA board.     

无线流媒体系统的多模式自适应缓冲设计

针对无线传输流媒体带宽不足和信道具有时变特性的问题,文章提出了一种基于服务器端和客户端联合控制的多模式自适应缓冲方案,经过工程实践证明,该方案可提高无线视频QoS。该方案的基本思想是:系统分模式创建缓冲区;针对无线传输时延抖动大和丢包率高的特点,设计了改进的二维索引表进行RTP包快速排序;综合应用了关键帧丢失自动请求重发和阈值内错误掩盖策略。接收端自适应缓冲RTP数据包,统计网络信道参数,返回给本机和服务器动态调整相应缓冲区参数;服务器调整H.264编码器码率和发送速率完成拥塞控制。     

Analysis on Output Power for Multi-direction Piezoelectric Vibration Energy Harvester

To predict the performance of multi-direction piezoelectric vibration energy harvester,an equation for calculating its output power is obtained based on elastic mechanics theory and piezoelectricity theory.Experiments are performed to verify theoretical analysis.When the excitation direction is along Y direction,a maximal output power about 0.139 mW can be harvested at a resistive load of 65kΩ and an excitation frequency of 136 Hz.Theoretical analysis agrees well with experimental results.Furthermore,the performance of multi-direction vibration energy harvester is experimentally tested.The results show that the multi-direction vibration energy harvester can harvest perfect energy as the excitation direction changes in XY plane,YZ plane,XZ plane and body diagonal plane of the harvester.     

微机控制能量补偿型TIG焊电源的研究

本文通过对电弧形态的分析,弧长波动对熔宽和电弧电流分散度的影响等测试,提出在纯氩气氛中,当弧长波动时,欲使有效热功率恒定,最佳电源外特性应用是能量补偿型电源外特性,通过大量薄板ＴＩＧ焊接实验,建立了能量补偿电源外行性数学模型,并成功地研制了８０９８单片微机控制的能量补偿型ＴＩＧ焊电源系统。     

Fault Tolerant Control Scheme Design for Formation Flight Control System of Multiple Unmanned Aerial Vehicles

The command tracking problem of formation flight control system(FFCS)for multiple unmanned aerial vehicles(UAVs)with sensor faults is discussed.And the objective of the addressed control problem is to design a robust fault tolerant tracking controller such that,for the disturbances and sensor faults,the closed-loop system is asymptotically stable with a given disturbance attenuation level.A robust fault tolerant tracking control scheme,combining an observer with H∞ performance,is proposed.Furthermore,it is proved that the designed controller can guarantee asymptotic stability of FFCS despite sensor faults.Finally,a simulation of two UAV formations is employed to demonstrate the effectiveness of the proposed approach.     

移动Ad Hoc网络中一种前向机密的匿名路由方案

传统移动Ad Hoc网络匿名路由方案主要基于公钥加密手段构建匿名路径.然而,一旦参与通信的节点私钥泄满,则匿名路径也会连带泄漏.针对这一问题,本文提出一种具有前向机密性的匿名路由(Forward secureanonymous routing,FSAR)方案.在FSAR中,节点通过基于伪名和双线性对的密钥协商机制动态协商会话密钥,并以此构建前向机密的洋葱路由完成匿名通信.理论分析和仿真实验表明,FSAR可有效解决传统匿名路由方案的前向机密隐患,同时在网络性能方面有更好的表现.     

Sliding Mode Fault Tolerant Attitude Control Scheme for Spacecraft with Actuator Faults

An active fault tolerant control scheme is investigated for the attitude control systems of spacecraft with external disturbance and actuator faults by using the sliding mode technique. Firstly,the dynamic equations and kinematic equations of spacecraft are given. For the dynamic mode of spacecraft in faulty case,a fault diagnosis component is used for fault detection and estimation by using a nonlinear observer. According to the fault estimation information obtained during the fault diagnosis,the fault tolerant control scheme is developed by adopting the backstepping sliding mode control technique. Meanwhile,the Lyapunov theory is used to analyze the stability of the closed-loop attitude systems. Finally,simulation results for the attitude dynamics models show the feasibility of the proposed fault tolerant scheme.     

小阻尼动态系统的时域自适应反馈主动阻尼设计

针对在前馈／反馈混合控制中提高控制通道阻尼的问题,基于自适应滤波理论,提出适用于单输入单输出(SISO)和多输入多输出(MIMO)控制通道的时域自适应反馈主动阻尼设计方法。研究了自适应过程的理想期望信号的构造、SISO情况下闭环控制通道与反馈控制器同时进行自适应设计以及MIMO控制通道阻尼问题的简化与设计方法的拓展等问题;同时,基于某主动隔振试验平台的实测结果,对所有研究内容进行SIMULINK模型仿真。时域自适应反馈主动阻尼设计是高效的主动阻尼设计方法,并且为小阻尼动态系统的增阻设计提供了统一的方法框架。     

Geo-location for Ground Target with Multiple Observations Using Unmanned Aerial Vehicle

In order to improve the target location accuracy of unmanned aerial vehicle(UAV),a novel target location method using multiple observations is proposed.Firstly,the camera intrinsic parameters are calibrated.Then,the weighted least squares estimation is used to improve the localization precision because the traditional crossover method is vulnerable to noise and has low precision.By repeatedly measuring the same target point,a nonlinear observation equation is established and then covered to linear equations using Taylor expansion.The weighted matrix is obtained according to the height of the measurement point and the camera optic axis pointing angle,and then the weighted least squares estimation is used to calculate the target position iteratively.Finally,the effectiveness and robustness of this method is verified by numerical simulation and flight test.The results show that this method can effectively improve the precision of target location.     

多随机变量的桁架结构系统的可靠性分析及优化设计

针对桁架结构系统,采用随机有限元法（SFEM）计算结构系统的响应量,考虑内力重新分配,建立失效模式的安全余量方程,用验算点法计算失效模式安全余量的可靠性指标,用改进的分枝限界法,寻找主要失效模式,通过对主要失效模式方程线性化研究,计算失效模式安全余量之间的相关系数,寻找主要失效模式,通过对主要失效模式方程线性化研究,计算失效模式安全余量之间的相关系数,最后用PNET法计算出结构系统的失效概率,同时给出多随机变量的结构系统可靠度的敏度表达式,采用最佳矢量法,求解了大型桁架结构系统基于可靠性指标约束下的最小重量的优化设计问题,最后,给出了实际算例,计算结果表明;采用随机有限元法能更好地考虑结构系统的多个随机变量对系统可靠性产生的影响;所采用的可靠性分析方法和优化方法是有效的。     

具有Fuzzy约束的非光滑多目标规划的Fuzzy有效解的充分必要条件

本文研究具有Fuzzy约束的多目标规划（FVP）。在[6]的基础上,利用右上Dini导数,在目标函数和约束函数非光滑的情形下,讨论了FVP的Fuzzy有效解的几何型存在性及Fritz John型和Kunh Tucker型充分必要条件。     

Coalition Formation for Multiple UAVs Cooperative Search and Attack with Communication Constraints in Unknown Environment

A coalition formation algorithm is presented with limited communication ranges and delays in unknown environment,for the performance of multiple heterogeneous unmanned aerial vehicles(UAVs)in cooperative search and attack missions.The mathematic model of coalition formation is built on basis of the minimum attacking time and the minimum coalition size with satisfying resources and simultaneous strikes requirements.A communication protocol based on maximum number of hops is developed to determine the potential coalition members in dynamic network.A multistage sub-optimal coalition formation algorithm(MSOCFA)with polynomial time is established.The performances of MSOCFA and particle swarm optimization(PSO)algorithms are compared in terms of complexity,mission performance and computational time.A complex scenario is deployed to illustrate how the coalitions are formed and validate the feasibility of the MSOCFA.The effect of communication constraints(hop delay and max-hops)on mission performance is studied.The results show that it is beneficial to determine potential coalition members in a wide and deep range over the network in the presence of less delay.However,when the delays are significant,it is more advantageous to determine coalitions from among the immediate neighbors.