降雨对于CAPS微小卫星终端通信的影响

中国区域卫星定位系统（CAPS）是卫星导航通信一体化的系统。当利用CAPS微小卫星终端系统进行卫星通信时,所用的天线口径极小,增益低,终端的有效全向辐射功率EIRP。较小,整个通信链路的余量较小。虽然C波段的降雨衰减远没有Ku波段大,但是相对于微小卫星终端的整个卫星通信链路来说,降雨带来的信号衰减、地球站接收天线G／T值的变化以及对卫星通信上、下行链路载噪比的影响也是不可忽视的。文章对这些影响进行了分析,并利用ITU—R给出的降雨衰减预报模式,给出了C波段的降雨衰减的计算方法及结果,并且分析了降雨对CAPS微小卫星通信系统的整个链路余量的影响。     

降雨对卫星链路的影响分析

Ku 频段的卫星通信系统在我国已经普遍使用，目前正朝着更高的 Ka 频段发展。随着 频率的提高，降雨对卫星通信链路的影响会更加严重，是系统设计必须考虑的重要因素之一。针对降雨 带来的信号衰减、地球站天线 G/T 值的变化以及对卫星通信上/下行链路载噪比的影响进行了分析，并 利用 ITU-R 最新给出的雨衰减预报模式，给出了定量计算方法。     

中国Ka波段卫星通信线路的雨衰分布特性

利用ITU-R给出的降雨衰减预测模型,根据我国主要城市的分钟降雨率数据,计算出我国Ka波段(30/20GHz),轨道位置为92°E的卫星通信系统在线极化波情况下的降雨衰减等值线分布,此结果可作为Ka波段卫星通信系统设计的理论依据。     

Ku频段卫星通信链路计算

卫星通信具有容量大、成本低、抗干扰性能强、覆盖面积广和通信距离远等优势,已成为舰船通信的重要手段。针对Ku频段卫星通信的特点,提出了一种链路计算方法,并给出了岸基发送站、卫星转发器和接收系统的参数,通过实例分析,计算上行发送站的EIRP、接收站天线的方位、链路降雨衰减、链路载噪比及链路余量等,从而设计出合理的链路预算。     

Ka频段卫星通信雨衰特性分析与改进措施研究

Ka频段卫星通信中,降雨引起的信号衰减对通信链路的通断起着非常重要的作用。本文详尽分析了Ka频段卫星通信信道的电波传播特性,重点分析了降雨对卫星通信的影响,并提出了Ka频段抗雨衰的各种对策。     

平流层量子通信系统地空路径传播特性研究

在考虑衰减和去极化效应的情况下,根据电磁波传播与散射理论,建立了平流层量子通信系统地空路径上脉冲单光子源的传播模型;数值分析了大气环境对量子密钥分发的影响.结果表明:在晴空条件下,大气衰减对量子误码率的影响较大;而在降雨条件下,去极化效应对量子误码率的影响不容忽视.     

一种低轨卫星动态链路预算评估模型

针对低轨卫星透明转发通信系统,提出了一种动态链路预算评估模型,为透明转发卫星互联网设计提供参考。该模型给出了星地透明转发两跳链路信噪比（Signal-to-Noise Ratio,SNR）计算方法,在计算信号传播链路中自由空间路径损耗、阴影衰落、大气吸收、云雾衰减和降雨衰减的基础上,分析了我国大陆地区在全球典型低轨卫星星座覆盖下的两跳链路SNR,以及不同位置用户解调所需的信关站等效全向辐射功率要求。仿真结果表明,该方法考虑了馈电链路和用户链路的共同作用,能较好地评估卫星星座设计、用户地理位置对两跳链路SNR的影响。     

不同天顶角的星地信道光链路误码率分析

把复杂的大气衰减和湍流效应分别等效为链路的功率损耗和接收机噪声,建立了星地级联信道光链路模型,分析了不同天顶角下大气衰减和湍流对链路误码率的影响.数值仿真结果表明:大气衰减和湍流均造成链路误码率的增大,小天顸角情况下,链路误码率对大气湍流更为敏感;而大天顶角情况下,大气衰减是造成链路误码率急剧增大的主要原因.     

Ka频段卫星信道的衰减特性

在Ka及以上高频段卫星通信系统中,其链路信号的衰减很严重,主要是大气、降雨、闪烁对卫星信道的影响。本文主要研究了雨衰和对流层闪烁产生衰减的机理与特性,提出雨衰采用DAH模型,闪烁采用Van de Kamp模型。然后根据实测气象数据,计算我国各参考站点的雨衰和闪烁值。为抗衰减对策的提出提供理论依据,为工程设计提供具体的参考数据。     

Ka频段卫星通信系统降雨衰减分析

Ka频段卫星通信因其具有可提供的带宽大(3.5GHz)、通信容量大、波束窄、终端尺寸小,轨道平面内可容纳的卫星多和抗干扰能力强等优势成为未来卫星通信的必然趋势。Ka频段卫星通信面临的一个巨大挑战在于它受气象因素的影响大,这一度使研究人员认为Ka频段卫星通信是不可能实现的。降雨、闪烁、大气吸收等因素都会导致Ka频段地空链路信道质量的恶化。根据Ka频段卫星通信的特点,分析了降雨衰减的特性,提出了几种抗雨衰的办法。     

Atmospheric Attenuation on a Satellite Quantum System at 0.8 <Emphasis Type="Italic">μm</Emphasis>

Satellite-based global quantum secure communication is the challenge of telecommunication. It is necessary to face the interaction between infrared wave and the atmosphere. In this letter, we study the atmospheric attenuation and turbulent effect on a low earth orbit satellite quantum communication system at 0.8 μm. By numerical analyzing the atmospheric attenuation between earth-based station and low earth orbit satellite, it is shown that, when the visibility is below 5 km, atmospheric attenuation is obvious on earth-satellite path. Calculation of effect of turbulent atmosphere on infrared wave is shown that, the atmospheric attenuation from low earth orbit satellite to earth based station is about 6dB when clear condition. By applying the quantum computation language which is used in quantum computation to the research of quantum communication, simulation experiment of a secure communication protocol is achieved. The results of the simulation experiment were tallied with numerical ones, which verified the feasibility of the low earth orbit satellite quantum communication system.     

Ku频段卫星雨衰计算及自动观测系统设计

随着Ku频段卫星通信系统的使用,雨衰对卫星传输链路的影响已经成为卫星通信系统设计与使用过程中的重要影响因素。针对雨衰对Ku频段卫星通信系统可用性的影响,首先对雨衰的产生原因及其对卫星传输链路的影响进行了简要介绍,其次对国际电信联盟推荐的雨衰估算方法进行了分析,最后提出了Ku频段卫星链路传输特性自动观测系统的设计方案。     

Effect of non-spherical atmospheric charged particles and atmospheric visibility on performance of satellite-ground quantum link and parameters simulation

In order to study the relationship between the non-spherical atmospheric charged particles and satellite-ground quantum links attenuation. The relationship among the particle concentration, equivalent radius, charge density of the charged particle, the attenuation coefficient and entanglement of the satellite-ground quantum link can be established first according to the extinction cross section and spectral distribution function of the non-spherical atmospheric charged particles. The quantitative relationship between atmospheric visibility and communication fidelity of satellite-ground quantum link were analyzed then. Simulation results show that the ellipsoid, Chebyshev atmospheric charged particle influences on attenuation of the satellite-ground quantum link increase progressively. When the equivalent particle radius is 0.2 μm and the particle concentration is 50 μg/m³, the attenuation coefficient and entanglement of the satellite-ground quantum link is 9.21 dB/km, 11.46 dB/km and 0.453, 0.421 respectively; When the atmospheric visibility reduces from 8 km to 2 km, the communication fidelity of satellite-ground quantum link decreases from 0.52 to 0.08. It is shown that the non-spherical atmospheric charged particles and atmospheric visibility influence greatly on the performance of the satellite-ground quantum link communication system. Therefore, it is necessary to adjust the parameters of the quantum-satellite communication system according to the visibility values of the atmosphere and the shapes of the charged particles in the atmosphere to improve reliability of the satellite-ground quantum link.     

Up-link power control of satellite earth-stations as a fade countermeasure of 20/30 GHz communications systems

All 20/30 GHz satellite communications systems suffer from atmospheric attenuation in cloudy or rainy weather, particularly if high link availabilities are required. In FDMA systems the power transfer characteristic of each carrier is linear, so any up-link fade degrades the overall performance on a dB-by-dB basis. This, together with the fact that the 30 GHz up-link attenuation is much greater than the 20 GHz down-link attenuation, makes adaptive countermeasures of up-link fades most important. This paper shows how the overall link performance can be improved by applying up-link power control. It is explained how this improvement depends on the up-link/down-link balance, the dynamic range of the up-link power control, and the up-link and down-link atmospheric attenuation. If a small number of carriers can be allocated in an intermodulation-free frequency plan, the satellite transponder can be operated near saturation in order to optimize the down-link performance. Computer simulations of up-link power control for such an FDMA scheme have been performed based on measured three-carrier characteristics of a transponder TWT. It is shown that the overall link performance in faded conditions can be significantly improved with up-link power control. This may be utilized to increase the availability of a satellite link or to relax the earth-station performance in terms of G/T or EIRP if the link margin provided by an earth-station with fixed EIRP is satisfactory.     

Rain Attenuation and Doppler Shift Compensation for Satellite Communications

In high‐speed multimedia satellite communication systems, it is essential to provide high‐quality, economical services by using efficient transmission schemes which can overcome channel impairments appearing in the satellite link. This paper introduces techniques to compensate for rain attenuation and the Doppler shift in the satellite communication link. An adaptive transmission technique with a control algorithm to adaptively allocate transmission schemes is used as a countermeasure to rain attenuation. We introduce a new rain attenuation modeling technique for estimating system performance and propose a novel Doppler shift compensation algorithm with reduced hardware complexity. Extensive simulation results show that the proposed algorithm can provide greatly enhanced performance compared to conventional algorithms. Simulation software and hardware which incorporate the proposed techniques are also demonstrated.     

Evaluation of light beams for short and medium range wireless communications

Technological improvements in free space optical communication systems have reduced the cost and alternatives to fiber optic transmission. The advantages of the free space optical link over fiber optic cabling are primarily economic. In line with the demand for gigabyte link from 10 Mbit/s to 10 Gbit/s in the market, the uses of free space optical communication systems have increased exponentially from 1995 to 2008. However, free space optics is subject to atmospheric effects such as attenuation and scintillation which can reduce link availability and may introduce errors not seen in fiber transmission. In this paper we argue that optical wireless communication is an alternative to fiber optic transmission in short and medium range wireless communications and we discuss that the liability and availability of the free space optical link is mainly determined by the local atmospheric condition, this is to say that the transmission quality may be affected by weather conditions. For the evaluation we constructed an experimental communication network with a free space system. One way to characterize the strength of the turbulence fluctuation is by examining the Rytov variance for a plane wave. This Rytov variance physically represents the intensity fluctuation induced by atmospheric turbulence.     

卫星通信链路中的雨衰动态特性分析

雨衰是高频段(Ka、V等)卫星通信链路传输损耗中的一个重要因素。在进行系统工程设计时,低可用度系统需要预留一定的雨衰余量,高可用度系统需要采取自适应抗雨衰措施。卫星通信向高频段发展是未来趋势,因此,有必要研究雨衰的动态特性,为抗雨衰技术的有效性设计提供依据。介绍了雨衰的动态特性和国内外的一些研究成果,并结合我国某地实测数据进行了分析。     

A unified statistical rain-attenuation model for communication link fade predictions and optimal stochastic fade control design using a location-dependent rain-statistics database

The simultaneous demand for increased capacity of communication satellite channels and the demand for such systems to be designed and operate within increasingly stringent economic constraints places severe requirements on the ability to predict, achieve and maintain the reliable operation of these satellite links throughout the United States. The operating frequencies of satellite links are such that the occurrence of rain anywhere along the link will induce attenuation of the signal and is the major source of link reliability degradation. A unified model is presented that describes the relevant static and dynamic statistics of attenuation on an arbitrarily specified satellite link for any location for which there is a long-term data record of rainfall statistics. In addition to providing accurate, location-dependent statistical predictions of the reliability of satellite links, the generality of the model also establishes a basis for the design of optimal stochastic control algorithms used to mitigate the deleterious effects of attenuation and thus maintain link reliability. The rain statistics that are required to characterize the location of interest are derived from extreme value statistics theory. A rain-statistics database has been compiled that allows one to apply the model anywhere in the continental United States with the resolution of 0.5° in latitude and longitude. Comparison of the model predictions is made with available experimental observations and agreement is found to be quite good.     

Channel Capacity Statistics of an Interfered Broadband Satellite Link

Satellite communication networks play an important role in the “digital divide” problem, by offering broadband services everywhere in the world. The ever increasing demand for multimedia services has led to the use of Ku, Ka and V band in modern satellite communication networks. In these frequency bands, rain attenuation is the most dominant propagation fading mechanism. Moreover, interference due to propagation phenomena deteriorates the performance of the satellite links and should be taken into account for the reliable design of satellite communication networks. In this paper, an analytical physical mathematical propagation model is presented for the prediction of channel capacity statistics of a dual-polarized interfered broadband satellite link. Rain attenuation spatial inhomogeneity is incorporated in the analysis with the employment of correlated slant paths. The obtained numerical results show the significance of these effects to channel capacity estimation. Finally, the proposed model may be used towards the optimum utilization of the satellite channel capacity by means of adaptive fade mitigation schemes.