非对称衰落信道下无人机中继传输方案及性能分析

 无人机(UAV)作为中继传输平台受到了国内外研究人员的广泛关注。本文研究了非对称衰落信道下的无人机中继传输系统,提出了输出信噪比最大化准则下的波束形成(BF)优化方案,并推导出系统中断概率、遍历容量和平均误符号率等无线通信系统主要性能指标的理论表达式。通过计算机仿真验证了本文提出的中继传输方案及性能分析的正确性,并定量分析了天线数量、信道参数以及功率分配对系统性能的影响,为无人机中继传输系统的设计及性能评估提供了参考和依据。     

字符发生器的一种设计方案

提出了一种采用SOC单芯片设计字符发生器的方法;介绍了SOC芯片的特性;给出了字符发生器的设计框图;并讨论了设计过程中的若干问题。     

Survivable communication concept via multiple low Earth-orbitingsatellites

An overview of a reliable cross-link communication system using multiple low-Earth-orbit satellites is presented, covering the overall network concept, data packet routing, communication techniques including antenna subsystems, communication parameter tradeoffs, signal processing, and the overall radio design concept definition. The critical issue addressed is the maximum cross-link distance coverage obtained under stressed conditions by utilizing an optimal coding technique for a given prime power of the satellite     

多渐消因子Kalman滤波器在SINS初始对准中的应用(英文)

针对系统模型和统计信息不能精确已知的条件下Kalman滤波无法给出最优解这一问题,单一渐消因子Kalman滤波算法对于简单的系统是有效的,但是对于复杂的多变量系统,仅仅利用单个的渐消因子是不够的。本文提出了一种多渐消因子滤波算法,通过利用开窗法计算新息序列协方差的无偏估计获得渐消因子矩阵。利用渐消因子矩阵调节一步预测均方误差矩阵k|k1P,对不同的滤波通道提供不同的渐消速率。将该方法应用于SINS的初始对准中,仿真和试验结果表明:当真实系统噪声统计特性同设定参数不一致时,对准精度明显高于其他滤波算法。其对不确定性噪声具有较低的敏感度,对系统参数具有较好的滤波效果。因而,在实际应用中具有重要的参考价值。     

一种可齐平安装的机载复合结构宽带天线的设计

设计了一种可齐平安装的宽带超高频(UHF)天线.该天线由含有背腔结构的盘锥天线、盘锥顶盘与地板之间的短路结构、以及多板天线3个部分复合而成.这3个部分分别在频率的中端、低端和高端产生3个邻近的独立谐振点,从而有效地展宽了天线的工作带宽.分析了天线各主要结构参数对谐振频点和阻抗带宽的影响,给出了这些参数的最优值,并据此制...     

复合材料层板一维穿透脱层的能量释放率

建立了含穿透脱层的正交各向异性层合板在承受面内轴向压缩载荷作用时的一维分析模型。在一阶剪切层板理论的基础上,利用一维可动边界变分问题,结合断裂力学知识导出了脱层扩展的能量释放率G及其分量G_Ⅰ、G_Ⅱ的表达式,且验证了该方法的正确性。通过计算,讨论了外载和脱层长度对能量释放率的影响。     

用于雷达波形的无损压缩编码

讨论了用算术编码实现波形数据的无损压缩。对波形数据进行无损压缩时 ,如果把每个可能的样本值看作一个符号 ,符号表会非常庞大 ,导致算法不可行。基于这种原因 ,本文用一个符号表示一定范围内波形数据 ,而不是单个波形数据 ,然后在此基础上设计了一种编码方案。先是无损线性预测 ,去除了波形数据之间的相关性。并假定产生的差值序列具有白功率谱 ,幅度服从高斯分布 ,第二步是算术编码。最后给出了对雷达回波数据进行压缩的实验结果。     

Error Analysis of the Optimal Antenna Array Processors

The optimal weights of an antenna array processor, which maximizes the output signal-to-noise ratio (SNR) in the absence of errors, are computed using the noise-alone matrix inverse (NAMI) and the steering vector in the look direction or the signal-plus-noise matrix inverse (SPNMI) and the steering vector. In practice the estimated steering vector as well as the estimated optimal weights are corrupted by random errors. This paper has analyzed the effects of these errors on the performance of the NAMI processor and the SPNMI processor by deriving analytic expressions for the output signal power, output noise power, output SNR, and the array gain as a function of the error variance. The treatment is for a general array configuration and no assumption about a particular array geometry is made.     

复合材料薄壁加筋抛物面天线仿真与优化

采用Patran/Nastran有限元软件对复合材料薄壁加筋抛物面天线进行了建模和仿真分析。重点分析了反射面铺层方式、加筋结构形式以及加强筋铺层对抛物面天线基频的影响。分析结果表明:采用[0/45/-45/90]s铺层形式的反射面基频最高;增加径向和环向筋可大幅提高天线基频,其中加筋结构采用[0/30/90/-30]s铺层可进一步提高天线基频。通过有限元分析确定了基频最佳的复合材料抛物面天线结构,为制备薄壁加筋抛物面天线提供了指导。     

Jerusalem十字架型FSS的仿真设计

在飞行器隐身技术的研究中发现,雷达天线系统通常在飞行器鼻锥方向产生很强的RCS贡献[1]。因此,如何减少雷达天线带外的RCS而又保证自身雷达正常工作已成为目标隐身技术中的一个关键课题。文中介绍了由Jerusalem十字架型振子单元构成的带阻式频率选择表面来有效的控制电磁波的传输和反射,利用单个单元和周期性边界条件的性质,采用理想匹配层(PML)吸收边界、周期边界相结合的方法对无限大频率选择表面进行仿真。借助于有限元软件Ansoft HFSS对Jerusalem十字架型FSS进行了软件建模,并对Jerusalem十字架外形及平面波入射角对频率特性的影响分别进行了仿真,给出了表面波频率选择特性随Jerusalem十字架几何参数和平面波入射角的变化而变化的趋势。     

Adaptive processing at the subarray level

This paper describes a class of partially adaptive arrays with adaptive processing applied to the outputs of steered subarrays. The problem is to detect a signal or estimate its direction of arrival in the presence of jammers. The advantage of applying adaptive processing to subarrays is that it requires much less CPU time than the corresponding fully adaptive processing. The subarray processing equations for the two kinds of problem are described. In this paper, we compare partially adaptive processing performance with fully adaptive processing performance in the case of the following antenna and signal sources:

• •- array with regularly spaced sensors ;
• •- between 20 and 100 elements ;
• •- between 3 and 20 subarrays ;
• •- a single jammer ;
• •- desired signal from the antenna zenith.

We suggest a method for determining the optimal subarray configurations in this case. An example is given to show that the performance of an antenna with five subarrays is comparable to that of a fully adaptive thirty-element array for eliminating a single jammer with a target at the zenith.     

基于FPGA的自适应阵列协方差矩阵特征分解的实现

卫星导航抗干扰的过程中，对空间信号波达方向估计、干扰个数检测、最优权矢量的求解直接影响着导航接收机的抗干扰性能，而协方差矩阵的特征分解是这些算法实现的核心部分。根据自适应阵列天线获得的协方差矩阵的特性，基于双边并行Jacobi算法，实现了基于FPGA的协方差矩阵特征值和特征向量的求解，并通过在信号波达方向估计的应用进行了验证。另外，在实现的过程中对直接调用CORDIC IP核的方式进行了精度误差分析，并用一种双精度浮点的方式进行修正，提高了矩阵特征分解FPGA的实现精度，为导航抗干扰接收机性能的提升提供了有效的工程基础。     

一类基于颤振行列式的颤振分析新方法

提出了一类基于颤振行列式的颤振分析新方法,分别采用颤振行列式值的模,或颤振矩阵的模最小特征值这两个指标的频域下界,来直接确定颤振临界点.根据这两个指标在颤振临界点附近取极小值的特点,编制了相应的算法.数值算例验证了这两个指标在确定颤振临界点时的等价性.该方法与传统颤振分析方法的结果精度相当,并且根据颤振临界点处的颤振特征向量还可以定量给出各模态参与颤振耦合的程度.      

基于CAD模型的碳纤维复合材料天线反射面精度测量

针对天线反射面研制过程中的精度测量,提出一种基于CAD模型的自动测量技术和反射面数据处理技术的精度测量方法。在测点均匀布局规划和工件与模型对齐的基础上,自动获取反射面的完整测量数据,利用最优化算法使实测数据和理论模型达到最佳匹配,实现反射面面形精度的准确评价并获得变换矩阵。最终通过偏差矢量图表达天线反射面的面形偏差趋势,并利用获得的变换矩阵修正加工基准,有效保证了反射面的成型精度和加工精度,工程应用表明该方法较好地满足了反射面制造过程中的测量需求。     

Nonredundant error correction DQPSK for the aeronautical-satellitechannel

The performance of differentially encoded quadrature phase-shift keying (DQPSK) system employing nonredundant error correction (NEC) receivers with single- and double-error correction capability is analyzed and evaluated for the aeronautical satellite channel. The NEC is an attractive coding technique which employs differential detectors with more than one symbol delay elements and which does not introduce any redundancy as other coding schemes do. As typical for aeronautical satellite communications, a Rician fading channel with Gaussian power spectrum has been considered. Unlike the additive, uncorrelated from symbol to symbol interference such as additive white Gaussian noise (AWGN) or static cochannel interference (CCI) which has been investigated in the past, analysis of the performance in a fading channel is much more difficult. The difficulty arises from the multiplicative and correlative nature of the fading interference. Bit error rate (BER) performance evaluation results have been obtained by means of computer simulation for various channel conditions, including different values of the K-factor and the fading B_DT. These results have indicated that considerable performance gains as compared with conventional differentially detected systems are achieved for high values of K and for very fast fading. Both of these conditions are encountered in typical aeronautical communication systems. Wherever possible, heuristic explanations of the trend of the obtained BER performance evaluation results are also given     

Experiments on aeronautical satellite communications using ETS-Vsatellite

The world's first aeronautical satellite communication experiments, conducted at L-band frequencies using a commercial aircraft, are described. An airborne antenna with electronically steerable beam and communication equipment was installed in a B-747F freighter flying over transoceanic flight routes. The satellite used in these experiments is the Engineering Test Satellite-Five (ETS-V). During the test period, various experiments, such as antenna pattern measurements, transmission performances, and voice quality evaluation were conducted. As the airborne antenna is the key component for the aeronautical satellite communication system, emphasis has been placed on antenna characteristics. Its performance is found to be closely related to the fading characteristics in low-elevation areas and to transmission error performance     

天线窗材料热透波特性风洞测试方法

高超声速飞行器天线窗材料在等离子体包覆条件下的热响应和热透波特性测试,是分析天线窗材料特性、研究电磁波在等离子体和天线窗中传输特性的基础。针对等离子体和天线窗中电磁波传输特性,采用矢量网络分析仪和标准增益天线组成的电磁波传输测试系统,获得了一定频率的电磁波经过等离子体和高温天线窗之后的衰减;针对高温天线窗自身热响应特性和电磁波在其中的传输特性,研究了天线窗材料在一定热流作用下的温度分布和烧蚀特性,测试了烧蚀后处于高温状态且无等离子体覆盖的天线窗对电磁波的影响,分析了天线窗高温透波特性与常温透波特性的差异。所建立的方法,为在地面等离子体风洞中开展天线窗热透波特性研究、分析天线窗和等离子体耦合作用对电磁波传输特性的影响建立了基础。     

光波纳米推进技术中的表面等离激元增益光镊作用机理

为研究天线不同结构对表面等离激元（SPP）增益光镊作用的影响,建立天线-基底的电磁波传输耦合激元电场触发光梯度力的数值模型,并利用数值模型分析天线不同结构对SPP电场的影响规律,同时,这种电场变化规律对光镊增益有直接的数学关系,基于上述物理机制,获得不同天线结构对光梯度力产生的优化策略。为验证上述物理机制与优化策略的有效性,开展纳米颗粒的粒子图像测速（PIV）试验,天线材料为银,基底为二氧化硅,纳米颗粒为银,试验能够完好地观测到纳米颗粒在天线通道的运动情况。结果表明,光梯度力的增益机制在于激元电场强度和梯度两方面因素,前者随天线不对称性增强而先增大后减小,后者呈现一直增大趋势;纳米颗粒推动作用力的计算误差约为5.5%~13.8%,且试验值与计算值的趋势相符,一方面验证本文研究机理及优化策略的有效性,另一方面证明PFP技术的原理可行。     

Satellite formation reconfiguration and station-keeping using state-dependent Riccati equation technique

The current paper presents optimal reconfigurations and formation-keeping for formation flying satellites. The state-dependent Riccati equation (SDRE) technique is utilized as a non-linear controller for both the reconfiguration problem and formation-keeping problem. For the SDRE controller, a state-dependent coefficient (SDC) form is formulated to include non-linearities in the relative dynamics and J₂ orbital perturbation. The Taylor series and a transformation matrix are used to establish the SDC form. Optimal reconfiguration trajectories that minimize energy in satellite formation flying are obtained by the SDRE controller and compared with those obtained from a linear quadratic regulator (LQR) and a linear parameter varying (LPV) control method. It is illustrated that the SDRE non-linear controller of the current study obtains relocation accuracy of less than 0.1% of formation base-line length, while the LQR controller and LPV controller yield relatively large relocation errors. The formation-keeping controller developed using the SDRE technique in the current study also provides robustness under severe orbital perturbations.     

扩展酉矩阵束算法实现稀疏可重构天线阵的优化设计

针对方向图可重构天线阵列的稀疏布阵问题,提出一种基于扩展酉矩阵束算法的优化设计算法。首先建立以阵元位置和多组激励为变量的多方向图联合稀疏优化模型,并利用期望方向图采样数据构建Hankel块矩阵。然后通过centro-Hermitian化处理和酉变换将采样矩阵从复数域转换到实数域,舍弃实矩阵中较小的奇异值对可重构线阵进行稀疏。最后通过对等价矩阵束的广义特征值分解估计稀布阵元位置,进而得到每个方向图对应的激励。仿真验证了该方法能够以阵元非均匀稀疏分布的阵列形式有效实现多个方向图的精确重构。