Rain attenuation at 15 and 35 GHz

In order to satisfy future earth-to-space communications needs, new regions of the electromagnetic spectrum must be exploited. A program to determine the feasibility of using millimeter waves for this application has been conducted at Air Force Cambridge Research Laboratories (AFCRL) for approximately 6 years and it has been shown that at frequencies of 15 GHz (lambda = 2.0cm) and 35 GHz (lambda = 8.6mm) atmospheric attenuation is relatively low except for conditions of heavy clouds and precipitation. A portable radiometric system designed to measure attenuation at 15 and 35 GHz under conditions of precipitation was constructed and located in Hilo, Hawaii, a region where it rains frequently thus making it possible to conduct many attenuation measurements for varying rainfall rates. Attenuation was determined from both extinction and emission measurements as a function of zenith angle and rain rate. On the basis of the results that were obtained, it is concluded that for orographic rain up to rates of 50 mm/h in Hawaii: 1) attenuations up to approximately 10 dB can be calculated quite accurately from an emission measurement; 2) zenith attenuations are well correlated with rain rate and can be estimated from the regression lines which have been obtained; 3) attenuations at angles off zenith are not as well correlated with rain rate and thus the values obtained from the regression lines are only approximate; 4) attenuations at 15 and 35 GHz are well correlated.     

A flexible transmission technique for the satellite ISDB system

A new transmission technique which can achieve suitable quality and reliability for satellite ISDB (Integrated Services Digital Broadcasting) is introduced. The transmission system for satellite ISDB must have high spectrum efficiency, continuous service availability and also superior flexibility in its transmission scheme. This paper first studies appropriate transmission schemes, taking account of the 12 GHz band DBS (direct broadcasting satellite) system. Then, employing a hierarchical transmission technique and a newly proposed TMCC (transmission and multiplexing configuration control) signal, it describes the requirements for satellite ISDB. The hierarchical transmission extends the service availability under heavy rainfall conditions. The TMCC signal can change the transmission configuration depending on the program content and the weather conditions. In addition, a generalized method for the design of transmission configurations for satellite ISDB is presented     

Microwave attenuation due to rain at 110 GHz in south-east England

Fading due to precipitation has been recorded at 110 GHz for a period of one year over a 2.65 km path near Slough, England. The results show that frequencies as high as this could be used for relay links over short distances with acceptable reliability, despite the large attenuation due to heavy rain.     

First attempts at modelling earth-to-space radio propagation using SIRIO measurements in the 11 and 18 GHz bands

A bi-dimensional statistical model for earth-to-space radio links, characterized by effective rain rates and rain path lengths is proposed. These parameters refer to an equivalent homogeneous slab of rain having depth and rain rate such as to produce similar values of measured attenuations. Input data for the present study were attenuation data at 11.6 GHz (absolute and differential over a 520 MHz band) and 17 GHz, collected by the Sirio satellite: these data were found to be jointly log-normally distributed as were the effective rain rate and path length. A straightforward application of the model is the extrapolation of attenuation statistics to higher frequencies: the effectiveness of the method, when applied to 11.6 GHz data is tested against the data at 17 GHz; both the statistics and the time profiles are excellently reproduced. This suggests the use of a differential radiometer working at a relatively low frequency in order to acquire reliable higher frequency statistics and effective model parameters.     

Modelling attenuation by rain in tropical regions

The data in the CCIR data banks were employed for a statistical study of the relative performance of several rain attenuation prediction procedures in temperate and tropical regions. The results show that the models worked well, in general, when used for prediction at latitudes more than 30° from the equator, but, in the equatorial region, significant prediction errors were observed for all the models. Three sources of error were discovered. The most important is the use of too few rain climate zones to span the wide range of rain conditions present in the equatorial region. The second is an inadequate procedure for taking the naturally occurring vertical variations of specific attenuation into account. Finally, for the CCIR attenuation prediction model, the use of a universal shape for the cumulative distribution of path attenuation must be called into question.     

Adjacent satellite interference effects as applied to the outage performance of an earth- space system located in a heavy rain climatic region

Interference effects are of utmost importance to the reliable design of modern satellite communication systems operating at Ku and Ka bands. In these frequencies rain attenuation is the dominant fading mechanism particularly for Earth-space systems located in subtropical and tropical regions. On the other hand, the main propagation effect on interference between two adjacent satellite systems is considered to be the differential rain attenuation. The subject of the paper is the development of a procedure for the prediction of carrier-to-noise plus interference ratio (cnir) statistics, under the presence of rain fading conditions, applied to heavy rain climatic regions. The method is based on a model of convective raincells and the gamma distribution assumption for point rainfall rate statistics, which fits better than lognormal distribution in subtropical and tropical regions. A tropical raindrop size distribution is also adopted for the calculation of the power-law parameters of specific rain attenuation. The numerical results are concentrated on the analytical examination of various operational parameters upon the CNIR statistics and the subsequent outage performance of the system. Comparison of the proposed model with an already existing one is attempted and the necessity of the present procedure for application to locations belonging to subtropical/tropical zones becomes obvious.     

时相调制的循环相关匹配滤波技术研究

针对传统数字调制信号的边带衰减缓慢,造成频谱扩展问题,从相位突变调制出发,提出具有较快边带衰减特性的调制方式——时相调制(TPM)。提出以非平稳信号分析方法分析通信信号,并针对TPM调制的循环平稳特性,利用谱相关分析理论,给出TPM调制的循环相关匹配滤波设计方法,并进行了性能仿真分析。仿真结果表明:与传统匹配滤波方法相比较,循环相关匹配滤波方法能够充分利用TPM信号的循环平稳特性,可以有效提高TPM调制系统信息传输可靠性。     

5G毫米波短距离链路雨衰减特性分析

雨衰减严重影响第5代(the 5th Generation,5G)移动通信系统性能.在路径长度小于1 km的短距离链路情况下,现有雨衰减预测模型调整因子大于1,导致预测雨衰减随路径变短而增大,无法支撑毫米波短距离链路系统设计.通过分析国际电信联盟无线电通信部(Radiocommunication Sector of International Telecommunication Union,ITU-R)短距离链路雨衰减试验数据,发现湿天线衰减与路径雨衰减相当,得到毫米波短距离链路必须考虑湿天线衰减的结论.建立了湿天线衰减与降雨率的关系模型,分频段对模型参数进行了拟合,拟合结果与实测数据吻合得较好.提出了考虑湿天线衰减的短距离雨衰减建模新思路,可解决短距离雨衰减预测问题.研究结果有助于提高5G毫米波系统余量设计的可靠性.     

Annual and diurnal slant path rain attenuation statistics in Athens obtained with the synthetic storm technique

We present annual/seasonal rainfall rate statistics derived from a 29-month data bank of 1 sample/min, measured by a disdrometer located inside the National Technical University of Athens Campus. We discuss both the inaccuracy and the unavailability of the measuring equipment, as well as the statistical reliability of the rainfall rate sample. Additionally, after applying the Synthetic Storm Technique on the measured rainfall rate time series, we present the first long term simulated annual/seasonal and diurnal rain attenuation statistics, at 12 GHz for a hypothetical downlink from Hellas Sat 2 to Athens. According to the results, we predict that communication downlinks working in the afternoon and early evening hours must be given an extra power margin, to compensate for high rain attenuation.     

测量噪声功率谱作为筛选光电耦合器件的方法研究（Ⅱ）

在文献「１」中作者曾提出用测量光电耦合器件噪声功能率谱的方法,筛选光电耦合器件。此 根据低频噪声的幅值。但在实验中发现,由于１／ｆ、ｇ－ｒ和爆裂噪声三者之间相关性较弱,在剔除掉１／ｆ噪声值较大的器件后,ｇ－ｒ噪声和爆裂噪声较大的器件却可能未被易除。     

Survival probability of precipitations and rain attenuation in tropical and equatorial regions

This contribution presents a stochastic model useful for the generation of a long-term tropospheric rain attenuation time series for Earth space or a terrestrial radio link in tropical and equatorial heavy rain regions based on the well-known Cox–Ingersoll–Ross model previously employed in research in the fields of finance and economics. This model assumes typical gamma distribution for rain attenuation in heavy rain climatic regions and utilises the temporal dynamic of precipitation collected in equatorial Johor, Malaysia. Different formations of survival probability are also discussed. Furthermore, the correlation between these probabilities and the Markov process is determined, and information on the variance and autocorrelation function of rain events with respect to the particular characteristics of precipitation in this area is presented. The proposed technique proved to preserve the peculiarities of precipitation for an equatorial region and reproduce fairly good statistics of the rain attenuation correlation function that could help to improve the prediction of dynamic characteristics of rain fade events.     

基于频域插值的信道化原型滤波器设计

针对信道化原型滤波器设计复杂度较高的问题,提出一种满足线性相位要求的原型滤波器频域插值设计算法。该算法采用无约束迭代优化办法获得了阻带衰减较高的低阶滤波器模型,然后根据所推导的频域插值模型构建满足线性相位特性的原型滤波器频谱,最后通过快速傅里叶逆变换获得了满足信道化滤波器组完全重构特性要求的原型滤波器。所提设计算法将频域插值与迭代优化相结合,有效地解决了设计高阻带衰减的原型滤波器时待优化参数数目较大的问题,并且不会产生镜像频谱,省去了镜像抑制滤波器的设计。仿真结果表明,所提算法相比传统的时域插值设计算法具有显著的性能改善,并且降低了设计复杂度。     

Limitation of the Kirchhoff boundary conditions for aerial imagesimulation in 157-nm optical lithography

The aerial images of half-wavelength features with 0° and 180° phases obtained by using the Kirchhoff boundary conditions are compared with those obtained by using rigorous electromagnetic field computation for 248-nm lithography and 157-nm lithography. The discrepancies between the aerial images computed by the two methods are large at both wavelengths, but they are much larger for TM polarization at the wavelength λ=157 nm. These discrepancies are due to diffraction effects in the aperture regions, which are more pronounced at λ=157 nm because of the larger ratio of the thickness of the chromium absorber to the wavelength required at λ=157 nm for a given attenuation factor. This shows that diffraction effects in the aperture regions must be included when simulating aerial images in 157-nm lithography     

A Journey from Traditional to Machine Learnig of Radio Wave Attenuation Caused by Rain: A State of Art

Given the massive rapid growth for capacity in wireless data telecommunications every year, wireless carriers must be planned for a thousand-fold increase in mobile traffic in 2020. It compels scientists to explore for new wireless airwaves that can accommodate large data rates. Next-generation technologies must address issues such as increased spectrum allocation in millimetre wave frequency bands, the installation of directional antennas beam forming antennas, better battery life, high data transmission rates with reduced outage probability, lower capital costs, and increased capacity for multiple simultaneous users. There are two types of telecommunication links: terrestrial and satellite. Terrestrial links are also known as radio relay links. This connects the troposphere, which is located between the earth’s surface and the high atmosphere, to the propagation of radio waves. Gases, water vapour, and other weather phenomena such as rain, storms, snow, and hail all interfere with higher frequency radio signals in this region. Due to these difficulties, energy is absorbed and diffused, resulting in signal attenuation. Another form of obstruction generated by radio waves on terrestrial paths is buildings, trees, lampposts, grill, and other urban features. Under these conditions, reflection, diffraction, refraction, scattering, depolarization, and other phenomena are studied. This study discusses the effects of rain on satellite and terrestrial communications.

     

频谱校正技术在频率步进探地雷达中的应用研究

频率步进方法是探地雷达的工作体制之一。由于地下介质在各个频点对电磁波的衰减程度不同,导致频率步进探地雷达中回波信号频谱已经严重变形。文中基于恒Q模型推导了当考虑地下介质衰减特性时回波频谱的表达式,提出采用频谱校正技术对回波谱白化后进行匹配滤波。仿真结果表明,该技术大大提高了距离像的主旁瓣抑制比和分辨率,提高了地下目标检测能力。     

On the possibility of high power gyrotrons for super range resolution radar and atmospheric sensing

High power gyrotrons have been developed recently; this makes a number of high power millimeter wave oscillators available. Currently their main application is the heating of fusion plasmas. This examines other potential applications for these RF sources. If used in multipulse radar mode, the pulses may be somewhat different from each other and this must be considered. A variant of coherent-on-receive data processing can be used. With this, the entire pulse, not only the phase, is renormalized to a reference pulse. The data are analysed off line. Possible applications of the quasi-optical gyrotron in a radar mode include exploiting its wide tuning range to achieve super range resolution and also remotely sensing the distribution of the size of ice crystals in cirrus clouds. Possible applications of a fixed frequency (94 GHz) gyrotron in the radar mode include studying the structure of clouds. In a forward scatter mode, these high power sources could provide the capability to remotely sense the structure of clear air turbulence. The tunability of the quasi-optical gyrotron could also be exploited to perform rapid path average measurements of relative humidity on the ground and in clouds, and to perform two way earth-to-space measurements of upper atmosphere trace element concentrations.     

Effect of waveguide optical scattering on the integrated optical spectrum analyzer dynamic range

The dynamic range limited by optical scattering in the integrated optical spectrum analyzer is considered. Calculations of dynamic range as a function of waveguide attenuation and surface roughness characteristics are presented. Dynamic range is found to decrease with increasing attenuation, to be nearly independent of the surface roughness correlation length for a fixed attenuation, and to be independent of the Fourier transform lens focal length. Adjacent channel rejection is found to fall off slowly. The effect of lens scattering is shown only to be important for cases in which waveguide scattering is very small and lens scattering is very high.     

Attenuation and fluorescence characteristics of optical signalspropagating in an erbium-doped fiber

For a monochromatic input signal launched into an erbium-doped fiber (EDF), a broadband fluorescence spectrum will be generated with total power approximately 30 dB lower than input signal power. The forward fluorescence power decays slowly at long EDF length due to smaller absorption cross section for wavelength components away from absorption peak. Care must be taken when the conventional cutback method is used to measure the attenuation of the optical signals in an EDF. The backward fluorescence power is saturated to a constant level, and the spectrum does not change for long EDF     

Secure centralized spectrum sensing for cognitive radio networks

Spectrum utilization becomes more and more important while new communication techniques keep increasing and the spectrum bands remain finite. Cognitive radio is a revolutionary technology to make use of the spectrum more effectively. In order to avoid the interference to the primary user, spectrum sensing must be sensitive and reliable. Cooperative spectrum sensing (CSS) is one of the ways to increase the reliability of spectrum sensing. The information fusion technique is a key component of CSS. In this paper, we proposed a novel fusion scheme based on spatial correlation technique. We utilize geographical information with reputational weights to propose a two-level fusion scheme called secure centralized spectrum sensing (SCSS). The simulation results show that as the attackers present high density aggregation at some areas, the correct sensing ratio of SCSS is increasing as well even when the number of attackers is very large.     

FPGA implementation of dynamic channel assignment algorithm for cognitive wireless sensor networks

The reliability of wireless sensor networks (WSNs) in industrial applications can be thwarted due to multipath fading, noise generated by industrial equipment or heavy machinery and particularly by the interference generated from other wireless devices operating in the same spectrum band. Recently, cognitive WSNs (CWSNs) were proposed to improve the performance and reliability of WSNs in highly interfered and noisy environments. In this class of WSN, the nodes are spectrum aware, that is, they monitor the radio spectrum to find channels available for data transmission and dynamically assign and reassign nodes to low-interference condition channels. In this work, we present the implementation of a channel assignment algorithm in a field-programmable gate array, which dynamically assigns channels to sensor nodes based on the interference and noise levels experimented in the network. From the results obtained from the performance evaluation of the CWSN when the channel assignment algorithm is considered, it is possible to identify how many channels should be available in the network in order to achieve a desired percentage of successful transmissions, subject to constraints on the signal-to-interference plus noise ratio on each active link.