某Ku频段卫星通信系统的设计

为了让两个地面站通过卫星链路进行无线通信,设计了一个Ku频段卫星通信系统 ,数据速率是512 kbit/s～4.096 Mbit/s,速率可调步进1 bit/s。选取了一 种较简洁的Ku频段地面 站设计方案,信道的本振为固定点频,调制解调器的中频范围是950～1 450 MHz。对卫 星通信 链 路功率进行了预算。地面站的组成设备,如调制解调器、低噪声放大器、上变频单元、下变 频单元等均选用成熟的商用货架产品,降低了设计风险和成本。本系统研制周期短,通信稳 定可靠,得到了用户的认可。     

Simulation approach for optimization of ZnO/c-WSe2 heterojunction solar cells

Taking into account defect density in WSe₂, interface recombination between ZnO and WSe₂, we presented a simulation study of ZnO/crystalline WSe₂ heterojunction (HJ) solar cell using wxAMPS simulation software. The optimal conversion efficiency 39.07% for n-ZnO/p-c-WSe₂ HJ solar cell can be realized without considering the impact of defects. High defect density (> 1.0 × 10¹¹ cm^-2) in c-WSe₂ and large trap cross-section (> 1.0 × 10^-10 cm²) have serious impact on solar cell efficiency. A thin p-WSe₂ layer is intentionally inserted between ZnO layer and c-WSe₂ to investigate the effect of the interface recombination. The interface properties are very crucial to the performance of ZnO/c-WSe₂HJ solar cell. The affinity of ZnO value range between 3.7-4.5 eV gives the best conversion efficiency.     

A secure authentication with key agreement scheme using ECC for satellite communication systems

Recently, Liu et al came up with an authentication with key agreement scheme for securing communication over the low‐earth‐orbit satellite communication systems. However, this paper demonstrates that this scheme cannot provide perfect forward secrecy or defend against the smart card stolen attack, and has some very bad design defects, making it unpractical. Thus, to design a truly secure authentication scheme for satellite communication systems, this paper presents a new scheme, making use of the advantages of elliptic curve cryptography and symmetric cryptography. The security analyses by the widely used BAN logic and heuristic discussions demonstrate that our new scheme possesses perfect security properties and can defend against various well‐known malicious attacks. Moreover, our new scheme allows users to update passwords locally in accordance with their wishes, achieving a good user experience.     

石墨烯纳米带电极区N掺杂电子输运性质研究

运用密度泛函理论和非平衡格林函数结合的方法,研究电极区N掺杂对扶手椅型石墨烯纳米带电子输运特性的影响.结果表明,与本征扶手椅型石墨烯纳米带电流-电压曲线相比,宽度为7的石墨烯纳米带电流-电压曲线表现出明显的不对称性,其中心N掺杂表现强烈的整流特性,整流系数达到102数量级,且将N原子从电极区中心位置移动到边缘,整流特性减弱.研究结果表明宽度为7的扶手椅型石墨烯纳米带出现强整流现象的原因主要是负向偏压下能量窗内没有透射峰引起的,该研究结果对将来石墨烯整流器件的设计具有重要的意义.     

二维多群辐射输运程序LARED-R-1的并行化

利用有向图描述数据依赖关系,应用已有的并行流水线通量扫描算法,实现基于非协调网格的二维辐射输运程序LARED-R-1的并行化.同时,采用消息缓冲技术提高并行程序的性能.经测试,对于典型的问题规模(100群、3800个网格单元、40个方向),在某并行机的64个和128个处理器上,并行程序分别获得80%和53%的并行效率.     

An end‐to‐end alternative to TCP PEPs: Initial Spreading,a TCP fast start‐up mechanism

While Transmission Control Protocol (TCP) Performance Enhancing Proxy (PEP) solutions have long been undisputed to solve the inherent satellite problems, the improvement of the regular end‐to‐end TCP congestion avoidance algorithms and the recent emphasis on the PEPs drawbacks have opened the question of the PEPs sustainability. Nevertheless, with a vast majority of Internet connections shorter than ten segments, TCP PEPs continue to be required to counter the poor efficiency of the end‐to‐end TCP start‐up mechanisms. To reduce the PEPs dependency, designing a new fast start‐up TCP mechanism is therefore a major concern. But, while enlarging the Initial Window (IW) up to ten segments is, without any doubt, the fastest solution to deal with a short‐lived connection in an uncongested network, numerous researchers are concerned about the impact of the large initial burst on an already congested network. Based on traffic observations and real experiments, Initial Spreading has been designed to remove those concerns whatever the load and type of networks. It offers performance similar to a large IW in uncongested network and outperforms existing end‐to‐end solutions in congested networks. In this paper, we show that Initial Spreading, taking care of the satellite specificities, is an efficient end‐to‐end alternative to the TCP PEPs. Copyright © 2015 John Wiley & Sons, Ltd.     

Cr、Co、Mn磁性对ZnO压敏特性影响的机理研究

研究了不同浓度Cr、Co和Mn的掺杂对ZnO-PbO-B2O3陶瓷压敏特性的影响.实验表明,ZnO平均晶粒尺寸随各元素掺杂量增加而逐渐变大,压敏电压也随之升高,非线性系数随各元素掺杂量增加而先增大后减小,漏电流先减小后增大.分析认为,过渡族金属元素掺杂对ZnO压敏材料电性能的影响不仅与电子的能级有关,与其自旋特性也紧密相连.ZnO中掺杂的Cr、Mn、Co元素随机取代其中的部分Zn原子后,Cr2+、Mn2+、Co2+在ZnO中产生局域磁矩,会对与其取向不同的自旋电子产生强的散射,这样可增大ZnO陶瓷电阻率和提高其非线性特性.     

“北斗”救生终端海上自适应功率退避算法

受海况、浸水、结冰、对星等因素影响,飞行员海上遇险后报位可靠性较低,工作时长较短。为此,提出一种自适应功率退避方法,在对报位影响因素分析基础上,利用深度神经网络,通过对经纬度、高度、俯仰角、方向、加速度、速度、浸水、信号、电量等多维度数据进行学习,拟合出覆冰、浪涌、液面等信号特征与环境特征联想模型,自适应控制信号发射时机,实现功耗的有效控制。试验表明,该方法将通信成功率及工作时长分别由36.3%、6.0 h提升至73.3%、8.6 h。     

一维线性非共轭石墨烯基(CH2)n分子链的电子输运

一维非共轭烷烃链虽不具富电子或少电子特征,但常存在于单分子器件或多肽、蛋白质等生物分子中,对电子传输产生重要影响.为理解这类物质的电子输运特征,本研究设计了一维线性非共轭(CH2)n分子结模型,并利用密度泛函理论结合非平衡态格林函数的方法,对(CH2)n(n=1—12)线性分子链与两个石墨烯电极耦合而成的分子结进行了第...     

卫星定位中伪距的广义延拓外推

GPS当丢失部分伪距不能正常定位时,采用广义延拓外推法外推伪距来实现对用户位置的定位.仿真结果和理论推理表明,这种伪距外推法在外推步数一定的条件下能满足用户接收机定位的要求.