辐射模缝隙馈源激励的2GHz无线电波在室内的传播

本文给出了用辐射模缝隙馈源作为发射天线时，2GHz窄带和宽带无线电波在室内传播特性的测量结果。对于窄带信号，主要测量了传播过程中的衰减，测量结果表明，沿缝隙馈源方向，接收信号电平按指数规律衰减，在垂直于电缆方向上，接收信号电平的衰减较慢，损耗指数较小：在平行和垂直于馈源方向上慢衰落基本服从正态分布，而快衰落分别服从Rayleigh和Rician分布。对于宽带信号，测量了多径脉冲相应，得到了均方根时延扩展及其概率分布。     

空间环境对无线电波传播的影响分析

随着技术的不断进步和更新,无线电通信事业也得到了快速发展,特别是伴随着数字化、自适应及编码纠错等新技术的广泛应用,无线电通信的可靠性有了很大的提高。由于无线电通信离不开电波的传播,而电波传播又与自由空间环境有着密切的关系,因此,本文试图从空间环境特别是电离层给无线电波的传播造成的影响方面入手进行分析,希望能为进一步提高无线电通信可靠性的相关研究提供参考。     

浅谈无线电波传播中受到空间环境的影响

随着我国科学技术的快速发展及不断进步,近年来也促进了无线电通信事业的快速发展,尤其伴随着数字化以及编码纠错等一系列新技术在通信方面的广泛应用,进一步提高了无线电通信的稳定性及可靠性.无线电通信的实现主要依靠电波的传播,电波传播与自由空间环境具有较为密切的关系.因此,在对无线电波传播的空间环境及特性分析的基础上,探讨空间环境对无线电波传播所造成的影响,以盼为进一步提高无线电通信可靠性提供有价值的参考意见.     

隧道内纵向导体对漏泄电缆通信中传播衰减率的影响

以矩形隧道为例给出了研究纵向导体对电磁波沿漏泄电缆传播特性影响的一般方法，计算了单线模和双线模衰减率。     

预测隧道中传播损耗的混合模型

本文运用Fresnel区域理论,得到了计算转折点距离的公式,结合自由空间传播模型和修正的波导模型,提出了一种新的混合模型.各种条件下的实验数据都验证了模型的合理性.结果表明,转折点以前的传播损耗可用自由空间的传播模型预测,而在转折点之后,可通过修正的波导模型预测.     

无线电波在隧道微蜂窝环境中传播特性的UTD预测

本文用一致性几何绕射理论，预测了频率为９００ＭＨｚ，１８００ＭＨｚ的窄带和宽带无线电波在隧道中的传播特性，并讨论了隧道的分支，弯曲障碍物对传播特性的影响，其中，窄带和宽带传播特性是分别在空域和时域中研究的。结果表明：在空直隧道中，不同边界条件对窄带信号具有各不相同的传播衰减率，宽带信号具有宽的相关带宽。在弯曲和有分支空隧道中传播衰减较高。在有车辆等障碍物的隧道中接收信号具有宽的相关带宽。在弯曲和在     

Propagation at 2.0 GHz in an Enclosed Area Using a Coaxial Cable with Leaky Sections as the Transmitting Antenna

This paper presents the results of narrowband and wideband propagation measurements carried out at 2.0 GHz in a large enclosed area using a coaxial cable with leaky sections as the transmitting antenna. The narrowband measurements were devised to measure attenuation of radio signals and the wideband techniques to measure multipath impulse responses and their associated root mean square delay spread. Analysis of the narrowband data files shows that the received signal levels in the direction parallel to the cable generally decay and display peaks in front of leaky sections due to the specific attenuation and special structure of the cable. The received signal levels in the direction radial to the cable decrease slowly and the distance-power law exponent is found to be slightly larger than one. The slow and fast variations of the received signal levels are also examined. The results reveal that the slow variations do not follow the lognormal distribution, while the fast variations fit the Rayleigh distribution in both parallel and radial directions. Analysis of the wideband data files yields that the maximum value of the root mean square delay spread is 86.1 ns and the root mean square delay spread values are less than 55 ns 50% of the time. One therefore can conclude that the enclosed area channel excited by the coaxial cable with leaky sections has a broad coherent bandwidth and can support the data rate up to 2.3 Mb/s without equalization.     

Propagation Properties of Radio Wave in Multipath Scattering Mobile Channel

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On the statistics of multipath fading using a direct sequence CDMA signal at 2 GHz,in microcellular and indoor environment

This paper describes the results of field tests consisting of received signal variations and multipath returns seen by a mobile receiver using direct-sequence (DS) code-division multiple-access (CDMA) waveforms. The experimental data for outdoor (microcellular environment) reveals that the instantaneous received power lost due to fading (sometimes called the fade margin) increases dramatically as the signaling bandwidth decreases below 11 MHz. It also shows that for most outdoor locations the significant multipath was confined primarily to 1s of excess delay with average delay of less than 200 ns. A broader-band CDMA system, having a bandwidth exceeding 10 MHz, could resolve the multipath components and could use a RAKE receiver to further reduce the transmitted power. However, a narrower-band CDMA system could not resolve these multipath components and thereby would suffer signal fading which would have to be compensated by 15 dB or more signal amplification. As a result, a narrower-band CDMA system would interfere with its other users and reduce its user capacity if no other forms of diversity are used. Our results also reveal that at some locations, returns with delays of more than 1s can be seen by the receiver with enough energy that could be collected using a RAKE receiver. However, these locations were found to be confined to a very low probability of existence within a prescribed cell (3-mile radius).     

隧道内圆极化电磁波传播特性的研究

交通隧道的发展要求实现全程的无线通信。运用波导理论及格林函数法对圆极化电磁波在长直圆形隧道中的场分布及传播特性进行了研究,得到了轴向距离的电场分布计算表达式,与已有隧道内传播损耗模型的比较也表明此模型更准确有效,其结果对于隧道内通信网络的优化有一定的指导意义。     

Network Access to 2000 WDM Channels at 2 GHz Granularity with a Single Laser in C-band

As WDM channel spacing continues to decrease in size, and with the application of tunable lasers in DWDM (dense wavelength division multiplexing) systems, we demonstrate the ability of electronically tuned lasers to cope with demanding channel spacing and inevitable low frequency setting error. By finding the stable operating points of a single tunable laser at the desired frequencies, using advanced software for feature extraction a look-up table to drive the laser was generated. Once the drive currents to access 2000 channels in a 2 GHz comb are found, and in order to justify their usability in WDM networks, their frequency setting error and Side Mode Suppression Ratio (SMSR) was found. These results open up new possibilities for DWDM access networks while pointing to new potential for management of versatile wavelength re-allocation as well as providing a limit of achievement for channel density and granularity in the optical fiber network.     

A comparative study of STBC transmissions at 2.4 GHz over indoor channels using a 2 × 2 MIMO testbed

In this paper we employ a 2 × 2 Multiple‐Input Multiple‐Output (MIMO) hardware platform to evaluate, in realistic indoor scenarios, the performance of different space‐time block coded (STBC) transmissions at 2.4 GHz. In particular, we focus on the Alamouti orthogonal scheme considering two types of channel state information (CSI) estimation: a conventional pilot‐aided supervised technique and a recently proposed blind method based on second‐order statistics (SOS). For comparison purposes, we also evaluate the performance of a Differential (non‐coherent) space‐time block coding (DSTBC). DSTBC schemes have the advantage of not requiring CSI estimation but they incur in a 3 dB loss in performance. The hardware MIMO platform is based on high‐performance signal acquisition and generation boards, each one equipped with a 1 GB memory module that allows the transmission of extremely large data frames. Upconversion to RF is performed by two RF vector signal generators whereas downconversion is carried out with two custom circuits designed from commercial components. All the baseband signal processing is implemented off‐line in MATLAB ®, making the MIMO testbed very flexible and easily reconfigurable. Using this platform we compare the performance of the described methods in line‐of‐sight (LOS) and non‐line‐of‐sight (NLOS) indoor scenarios. Copyright © 2007 John Wiley & Sons, Ltd.     

带门槛的环形搜索移动性管理策略中移动台所 越过的位置区环数

位置管理或移动性管理是移动计算研究领域的一个具有挑战性的问题.我国及其他国家目前正在使用的个人通信网络如GSM、IS-41中,用两层数据库HLR/VLR支持位置管理.在这些网络中,每当移动台从一个位置区LA(Location area)移动到另一个位置区,其基本的位置管理策略(简称"基本策略")不管是否必要均立即进行位置更新操作,因而造成系统资源的极大浪费,降低了系统的性能.本文给出一种带门槛的环形搜索策略(简称"门槛环形策略")——将位置区分成环,设定一个门槛(整数),当移动台越过的位置区的环数没有达到门槛时,系统不进行位置更新操作,以减少位置管理的费用.在假定移动台的呼入是一个泊松过程,移动台在各个位置区的逗留时间是符合一般概率分布的随机变量的条件下,推导出在两次呼入之间移动台处于各位置区环的概率及移动台所越过的位置区环数公式,给出了"门槛环形策略"的位置管理费用小于"基本策略"的条件.     

Hydrothermally Treated SnO2 as the Electron Transport Layer in High‐Efficiency Flexible Perovskite Solar Cells with a Certificated Efficiency of 17.3%

Perovskite solar cells (PSCs) are one of the most promising solar energy conversion technologies owing to their rapidly developing power conversion efficiency (PCE). Low‐temperature solution processing of the perovskite layer enables the fabrication of flexible devices. However, their application has been greatly hindered due to the lack of strategies to fabricate high‐quality electron transport layers (ETLs) at the low temperatures (≈100 °C) that most flexible plastic substrates can withstand, leading to poor performances for flexible PSCs. In this work, through combining the spin‐coating process with a hydrothermal treatment method, ligand‐free and highly crystalline SnO₂ ETLs are successfully fabricated at low temperature. The flexible PSCs based on this SnO₂ ETL exhibit an excellent PCE of 18.1% (certified 17.3%). The flexible PSCs maintained 85% of the initial PCE after 1000 bending cycles and over 90% of the initial PCE after being stored in ambient air for 30 days without encapsulation. The investigation reveals that hydrothermal treatment not only promotes the complete removal of organic surfactants coated onto the surface of the SnO₂ nanoparticles by hot water vapor but also enhances crystallization through the high vapor pressure of water, leading to the formation of high‐quality SnO₂ ETLs.