基于FDTD方法的无线信道衰落特性模拟研究

为了表述无线信道衰落的时变及远区分布特性，提出了利用时域有限差分(FDTD)方法研究由多径效应引起的时变无线信道衰落的方法。在此将无线信道的衰落建模为随机过程，而不是通常的确定性随机变量。首先基于Clarke统计模型，利用FDTD方法研究了时变无线信道的小尺度平坦衰落特征；然后利用Monte Carlo方法和FDTD方法产生了具有信道多普勒功率谱特性的色高斯随机过程，再基于无线信道的时变统计特性建模，用Suzuki模型研究了时变无线信道的快衰落；最后将无线信道衰落特性分布和理论分布做了比较，验证了方法的有效性。     

无线信道特性分析

本文对无线信道中的大尺度衰落、小尺度衰落等特性和多径信道建模进行了分析和介绍,有利于从事无线通信研究工作的人员进行信道分析和仿真研究。     

短波信道衰落特性试验研究与仿真

利用电离层斜向探测系统对中低纬地区一条地面距离约1 000 km的电路进行了连续的试验探测,依据探测数据对不同电离层条件下各个传播模式信号的衰落特性进行了瞬时变化特性描述和统计分析,并从Vogler模型出发,结合实测分析结果对短波信道进行建模,文中称为广义Vo-gler模型。通过模型输出散射函数与实测散射函数的对比证实,广义Vogler模型能较准确地描述短波时变信道的特性。     

多径衰落信号循环平稳特性研究及其应用

利用信号的循环平稳特性可有效解决通信中的很多问题。在通信双方未知干扰信号先验知识时,信干噪比（SJNR, Signal-to-Jamming-Plus-Noise Ratio）可以描述人为有意干扰和噪声对通信信道的综合影响。分析典型人为音调干扰、加性高斯白噪声及多径衰落信号的循环平稳特性,得出结论：可利用通信信号、干扰及噪声三者不同的循环平稳特性进行SJNR估计,表征信道质量,为通信中的信道质量判决提供可靠依据。     

蒸发波导微波超视距信道衰落特性研究思路漫谈

简单分析了蒸发波导传播的信道特征,试探性地构建了一个蒸发波导信道传输的模型并通过仿真实验得到了相关数据,最后对信道传播损耗功率进行分析,得出了蒸发波导微波超视距信道衰落的相关特性,以供广大同行参考与借鉴,以期推动我国海面蒸发波导超视距信道研究工作的发展。     

卫星通信中的衰落以及抗衰落技术概述

卫星通信以其覆盖面广，通信容量大、经济效益高等优点，已经运用到各个领域，如：军事、气象、海洋、科研、广播等。卫星通信也有其固有的缺点，即除了自由空间造成的传输损耗外，受大气层的影响较大。所以要采取一定的技术手段来克服大气层对信号造成的这种损耗。本文就大气层对信号造成的衰落做了详细的分析，并研究了抗衰落的技术措施。     

Nakagami衰落信道的仿真方法研究

Nakagami衰落能够描述实际中所遇到的大多数衰落环境。文章提出了一个新的Nakagami衰落信道的仿真方法,用它仿真了Nakagami衰落信道的一阶、二阶统计特性并通过与其理论值进行比较验证了该方法的可靠性。该仿真方法直接基于瑞利衰落信道仿真基础之上,是对Nakagami衰落信道的一种新的研究探讨。     

无人机空地信道衰落包络统计特性研究

针对电平通过率和平均衰落持续时间能有效反映信道衰落包络的恶劣状况,提出了一种基于几何随机的无人机信道模型,该模型支持任意三维轨迹运动。在此基础上,分析推导了电平通过率和平均衰落持续时间的理论表达式,并得到二维散射情况下的闭式解。针对无人机高速飞行场景的仿真结果表明,本文推导的电平通过率和平均衰落时间理论值与仿真值吻合,并且与实际测量结果基本一致,可极大降低评估计算的复杂度,对UAV通信系统的差错控制编码和分组交织设计具有理论指导意义。      

浅谈超短波监测站技术性能要求

随着无线电管理事业在国民经济发展中作用和地位的不断提高．无线电监测网基础设施建设步伐不断加快，全国超短波无线电监测网的格局正在逐步形成。如何围绕超短波监测站的任务职责和建设目标，科学论证超短波监测站技术性能要求和功能设置．提高基础设施建设的针对性和有效性，是无线电监测网设施建设的重要研究课题。本文着眼于超短波监测站的作用和用途．对超短波监测站技术性能要求及监测接收机选型原则进行了分析讨论。     

Modified rain attenuation model for tropical regions for Ku‐Band signals

Attenuation measurement on Ku‐ band satellite signal in a tropical site, Fiji is presented. Rain‐attenuation prediction by ITU‐R and the Crane Global models showed noticeable deviation to the measured values. Unlike the monotonic decrease predicted by these models, exceedance of rain‐rate and attenuation in Fiji and other tropical regions showed the presence of breakpoints. For Suva, the breakpoint in rain‐rate and attenuation were at 58 mm/h and 9.4 dB with exceedances of 0.009 and 0.018%, respectively. Modifications to the ITU‐R model are proposed in this paper, for adopting it in the tropics. These modifications are based on the properties that in the tropics (i) the accumulation time factor at the breakpoints is an invariant (ii) for elevation angles <60° and at high rain rates multiple rain cells intersect the slant path. The attenuation exceedance is predicted by two expressions similar to the ITU‐R model, one for rain‐rates lower than the breakpoint rain‐rate and the other above it. The modified prediction model show remarkable agreement with the measured Ku‐band attenuation in seven tropical sites. Copyright © 2006 John Wiley & Sons, Ltd.     

舰船超短波通信系统初探

对舰船超短波通信系统进行了介绍,讨论了海上舰船超短波视距通信的特点,并分析了舰船超短波通信的抗干扰、反侦察能力,最后对舰载超短波通信的发展趋势作了探讨.     

关于超短波无线电台站管理的思考

近几年来，公众移动通信发展迅速，蜂窝移动电话已拥有庞大的用户群。相比之下，超短波无线电台的用户群较小。然而超短波无线电台是一种社会必需的无线电台站，主要应用于民航、铁路、公安、防汛、防火等部门专用通信和电力、银行、学校、酒店、宾馆、商场、建筑工地等单位的指挥调度系统，以及一些应急通信系统。超短波无线电台是地方无线电管理部门管理的重点和难点之一，如何加强超短波无线电台管理，满足用户和社会发展需要是无线电管理部门亟需解决的问题之一。本文介绍江西省信息产业厅无线电管理处赵经文对超短波无线电台管理的思考，供同行借鉴。[编者按]     

海浪谱的选择对海面电磁波散射建模的影响

海浪谱的选择对Bragg共振散射建模的影响是海面电磁波散射建模的关键问题。首先简介了海浪谱的概念,然后选择RA(Romeiser-Alpers)谱进行了Bragg共振散射建模,最后选择另一种具有代表性的PM(Pierson-Moskowitz)谱进行了Bragg共振散射建模,并通过仿真实验对两种海浪谱及其用于Bragg共振散射建模的效果进行了比较分析。获得的结论对合理地选择海浪谱具有指导意义。     

Millimeter wave attenuation in relation to rain rate distribution over a tropical station

Rain, perhaps, is the worst offender for utilising Millimeterwaves in practice. This paper describes the rain rate distribution from which millimeterwave attenuation distribution have been attempted. Results reveal that in our location (Calcutta: lat 23°N long 88.5°E) the rain rate distribution fits well with normal distribution. The cumulative distribution of rain rate also prompted the present authors to find out rain attenuation cumulative distribution for both terrestrial and earth-space paths in millimeterwave band.     

Fading characteristics of distributed antennas

Distributed antennas have been suggested as a possible method of providing reliable coverage for indoor wireless communication systems. A potential problem with them however is the possibility of increased channel fading caused by interference between individual antennas in the distributed antenna. The authors present measurement and simulation results of the fading characteristics of distributed antennas to exactly determine whether they will play a significant role in the coverage provided. and how they will affect system design     

超短波频谱监测网络化接收机设计

随着物联网和通信技术的迅速发展,频率资源供需矛盾日益突出。为了对电磁环境进行测试和数据采集,掌握各种无线电业务和通信系统,特别是宽带无线接入、物联网等新业务用频的背景噪声和频率使用情况,设计了一种超短波频谱监测网络化接收机。该接收机监测的频率范围为20MHz～3GHz,可提供多种IF处理带宽以适应处理不同信号的要求,具有较高的接收灵敏度和抗干扰性能,并具有最佳信噪比,能适应较宽动态范围的监测需要。     

超短行波放大自发辐射的研究

用泵浦能量具有梯度分布的横向同步泵浦方案,产生超短行波自发辐射光脉冲。以N_2激光为泵浦源,获得约50ps的染料光脉冲输出,以锁模Nd:YAG倍频光作泵浦源,获得8～15ps光脉冲。用条纹照相机和光学多道分析器测量了脉冲波形和光谱。 计算机模拟了行波放大自发辐射的瞬态行为,计算结果与实验结果相符合。     

Elevation angle dependence in tropical regions

The variation of path attenuation with elevation angle has been generally considered to approximate a cosecant law, certainly between elevation angles of about 10° and 50°. Such a theory relies on the assumption that the attenuation layer is statiform for most of the time, and is therefore probably reasonable for temperate regions. In tropical areas however the incidence of convective rain is much higher than in temperate regions, so that during rainy periods, particularly at times of high rain rate, the assumption that the attenuating layer is stratiform is no longer valid. The cosecant law does not therefore hold in such conditions. An experiment has been carried out in the tropical rain belt of northern Australia over several years to investigate the elevation-angle dependency. Four radiometers were co-sited, with the same azimuth. Three of these, with a half power beamwidth of 2.2°. were elevated to 15°, 45° and 85°. The fourth. with a beamwidth of 0·6° was elevated to 45° so as to allow an investigation into aperture effects. The antennae were all orientated for horizontal polarization. Rain-gauges were co-sited with the radiometers and placed along the look path. The results obtained clearly indicate that, in tropical regions. the cosecant law is inappropriate for predicting the elevation angle effects of path attenuation. particularly at high rain rates. The presence of rain cells with rates exceeding 300 mm/h ensures that the assumption of a stratiform attenuating layer is invalid.