单脉冲雷达速度量折射误差高精度修正方法

单脉冲雷达是高精度外弹道测量系统中的一种主要测量设备之一,为了提高其测量精度,对所有测量参数都需要进行电波折射误差修正.针对目前单脉冲雷达测速参数折射误差修正精度较低的现状,在距离和角度折射误差修正基础上,提出了基于方向余弦的速度量折射误差高精度修正方法.首先根据经折射修正后的目标精确位置,利用二阶中心平滑微分方法求出目标的真实速度向量;然后再利用测站、地心的位置得到目标到雷达站、地心的方向余弦,进而求出目标与雷达站间电波射线在目标处切矢方向余弦;最后进行距离变化率的折射误差修正.实验证明,该方法比常用的直接微分方法的精度高出20％,且具有较好的实用性和有效性.     

基于两跳匹配的OFDMA中继网络联合资源分配算法

针对OFDMA中继网络的两跳特性,提出一种基于两跳匹配的中继网络联合资源分配算法。首先根据中继网络的两跳性建立两跳速率匹配模型,然后利用对偶分解理论将中继网络资源分配的主问题分解为：中继选择、子载波分配和功率分配三个主要的子问题并进行联合优化,同时基于中继网络两跳性在子载波分配的过程中考虑两跳子载波配对,以逼近系统最优解。最后为了保证算法的公平性,考虑子载波分配因子约束以优化子载波分配。仿真结果表明：所提算法将中继选择、两跳子载波配对与功率分配联合优化以进一步提升系统吞吐量,同时引入子载波分配因子约束,保证了算法的公平性。     

一种低误报率的新型光纤分布式振动传感系统

针对目前-OTDR光纤分布式振动传感器由于散射光波光强不稳定造成误报率较高的问题,文中提出一种-OTDR和Mach-Zehnder干涉仪相结合的光纤分布式振动传感新系统,-OTDR和Mach-Zehnder干涉仪分别对外界振动进行探测,从而降低单一-OTDR探测的误报率。实验研究了-OTDR和提出的新的复合结构系统对外界振动探测的误报率,实验结果表明:在复杂环境下,与现有-OTDR方案相比,提出的基于-OTDR和M-Z干涉仪复合结构的方案可以有效降低系统的误报率,使系统的误报率由单一-OTDR的25%降至2%。     

一种基于无线网络的智能温室群监控系统设计

针对现代农业的发展,温室群智能监控成为当前现代农业建设的重点。毒刺本文设计一种基于 ZigBee 和Internet温室群环境远程监控,通过由若干个基于 ZigBee的独立温室网络,将不同温室的相关数据通过 Internet网络的方式接入到最终的管理服务平台,从而使得现代农业企业通过无线网络和因特尔网络实现对企业农业数据的智能监控。     

一种基于FPGA的可变速率帧结构设计与实现

在简述V.35接口的基础上针对V.35接口速率可变的应用需求提出了一种速率可变的帧结构,该帧结构可支持N×64kb/s(3≤N≤32)速率,从而在V.35接口上实现了多种速率的低速业务传输.     

Analysis of capacity and coverage region for Rayleigh fading MIMO relay channel

In this paper, we consider Rayleigh fading MIMO relay channel with channel state information at the receivers. First, we extend the previously obtained results for the ergodic capacity of uncorrelated and semi‐correlated MIMO channels and derive closed‐form expressions for the capacity bounds of MIMO relay channel. Next, we study this channel from a new point of view, maximizing coverage region for a desired transmission rate, and investigate the optimal relay location in the sense of maximizing coverage region. However, in order to overcome the mathematical complexity in desired transmission rate analysis, because of the randomness of the multiple antenna channel matrices, we evaluate this rate by using an existing exact formula and also by an approximation we find in the high signal‐to‐noise ratio regime. Numerical results show a perfect match between the Monte Carlo simulations and the obtained analytical closed‐form expressions and also confirm the effectiveness of our approach in cooperative vehicular communication for determining optimal relay location at which the coverage region is maximum. Copyright © 2013 John Wiley & Sons, Ltd.     

大功率LED散热用微通道铝基板的有限元仿真

对带微通道的铝基板上封装的不同功率LED,用Comsol Multiphysics软件对其温度场进行了有限元模拟,重点研究了微通道的孔大小、孔间距、绝缘层的厚度和热导率对基板散热性能的影响,结果表明:铝基板厚度为1.5mm左右,微通道方形孔,孔长0.8mm,孔间距0.8mm,绝缘层厚度50μm,热导率1.5 W/(m·K),为最佳散热性能铝基板.微通道铝基板封装3W灯珠与普通铝基板和氮化铝基板相比,热阻分别下降了5.44和3.21℃/W,表明微通道铝基板能更好地满足大功率LED散热的需求.     

环氧树脂及其增强材料回顾

本文回顾了PCB制造常用的环氧树脂及其增强材料的性能和用途。同时,还介绍了代用树脂材料和代用增强材料的最新进展,如改性环氧树脂、无卤树脂、Thermount、PTFE、氰酸酯等,并就其性能进行了探讨。     

Transparent flexible plastic substrates for organic light-emitting devices

In this paper, we describe the properties of flexible plastic substrates with a transparent conducting electrode (TCE), which are important for organic light-emitting devices (OLEDs). Specifically, we have evaluated the TCE electrical resistivity, surface roughness, electrode patterning, optical transmission, and the substrate water vapor/oxygen transmission. We have studied the effect of ultraviolet (UV)-ozone treatment on the TCE surface by using contact angle measurements and x-ray photoelectron spectroscopy (XPS). A decrease in the advancing contact angle by 30–40° and an increase of oxygen content on the TCE surface by 10 at.% were observed after the UV-ozone treatment. These changes facilitate the polymer adhesion to the TCE surface and increase the TCE surface work function, respectively. A sheet resistance of 12–13 Ω/□, an optical transmission greater than 80% over the visible range, and a surface roughness of 1.4–2.2-nm RMS over 50×50 μm² have been obtained for the plastic substrates. These properties are adequate for OLED applications based on United States Display Consortium specifications. Finally, we have found that a combination of hydrogenated amorphous silicon-nitride and silicon-oxide layers deposited on one side of the substrate at low-temperature reduces the water vapor and oxygen transmission rates (TRs) to less than 10⁻⁵ g/cm²-day-atm and about 10⁻⁷ cc/cm²-day-atm, respectively.     

Wireless video streaming with TCP and simultaneous MAC packet transmission (SMPT)

Video streaming is expected to account for a large portion of the traffic in future networks, including wireless networks. It is widely accepted that the user datagram protocol (UDP) is the preferred transport protocol for video streaming and that the transmission control protocol (TCP) is unsuitable for streaming. The widespread use of UDP, however, has a number of drawbacks, such as unfairness and possible congestion collapse, which are avoided by TCP. In this paper we investigate the use of TCP as the transport layer protocol for streaming video in a multi‐code CDMA cellular wireless system. Our approach is to stabilize the TCP throughput over the wireless links by employing a recently developed simultaneous MAC packet transmission (SMPT) approach at the link layer. We study the capacity, i.e. the number of customers per cell, and the quality of service for streaming video in the uplink direction. Our extensive simulations indicate that streaming over TCP in conjunction with SMPT gives good performance for video encoded in a closed loop, i.e. with rate control. We have also found that TCP is unsuitable (even in conjunction with SMPT) for streaming the more variable open‐loop encoded video. Copyright © 2004 John Wiley & Sons, Ltd.