Rain attenuation measurements over New Delhi with a microwave radiometer at 11 GHz

Rain attenuation measurements over New Delhi carried out with a microwave radiometer installed at the National Physical Laboratory (NPL), New Delhi and operating on 11 GHz for a period of more than three years are presented. For 0.01 percent of time for the period June 1977-April 1978, the attenuation exceeded for the monsoon period is 14.0 dB whereas for the whole year, it exceeds 10.4 dB. During the winter for the same percentage of time, the attenuation exceeded 1.5 dB, whereas for March-April it exceeds 0.5 dB. For the period May 1978-June 1980, it is observed that for 0.01 percent of time the attenuation for the whole year exceeds 9.0 dB. During the winter for the same percentage of time, the attenuation exceeds 1.4 dB whereas for March-April it exceeds 0.4 dB. A comparison of attenuation over New Delhi and those reported elsewhere are discussed. Yearly and worst month time ratio over New Delhi are given also as the values reported for the European region. Comparison of the attenuation distribution and the rate of surface rainfall measured with a rapid-response rain gauge are also given. The comparison shows that for the monsoon period and for 0.01 percent of time, the attenuation value exceeded for 14 dB corresponds to the surface rainfall rate of 140 mm/h. For the monsoon of 1978, 1979, comparison shows that for 0.1 percent of time, the attenuation value exceeded for 9.0 dB corresponds to the surface rainfall rate of 90 mm/h. Variation of attenuation and effective path length for various rainfall rates and elevation angles are also given.     

A data broadcasting system expanding the information capacity of existing analog communication systems

This paper presents the physical layer functions powering a new wireless data broadcasting system over analog television signals, referred to as dNTSC system (for data over National Television System Committee (NTSC) standard). Novel data insertion techniques at the transmitter and data extraction techniques at the receiver allow data rates of 1-4 Mbps that coexist with existing analog transmission but do not adversely affect normal television reception. Novel digital signal processing (DSP) techniques include a video abatement system that reduces data-to-video crosstalk for unimpaired analog television reception, adaptive nonlinear amplifier compensation, and advanced video cancellation and adaptive data equalization methods in the receiver. An analysis of the dNTSC system through noisy, multipath channels reveals the subtleties of the dNTSC system, compared to a conventional, dedicated digital communication link.     

914 MHz path loss prediction models for indoor wirelesscommunications in multifloored buildings

Qualitative models are presented that predict the effects of walls, office partitions, floors, and building layout on the path loss at 914 MHz. The site-specific models have been developed based on the number of floors, partitions, and concrete walls between the transmitter and receiver, and provide simple prediction rules which relate signal strength to the log of distance. The standard deviation between measured and predicted path loss is 5.8 dB for the entire data set, and can be as small as 4 dB for specific areas within a building. Average floor attenuation factors, which describe the additional path loss (in decibels) caused by floors between transmitter and receiver, are found for as many as four floors in a typical office building. Path loss contour plots for measured data are presented. In addition, contour plots for the path loss prediction error indicate that the prediction models presented are accurate to within 6 dB for a majority of locations in a building     

Atmospheric emission measurements of attenuation by microwaveradiometer at 19.4 GHz

Attenuation measurements on an Earth space path are presented using a passive microwave radiometer operating at 19.4 GHz in the emission mode. Attenuation measured under clear weather showed variation between 0.2 to 1.1 dB, whereas for cloud conditions attenuation as high as 1.0 dB have been recorded. Attenuation measurements for rain events have been correlated with rainfall rate using a fast-response 10 seconds opto-electronic rain gauge. The values of attenuation versus rainfall rate varied between A (dB)=0.01+0.18 R(mm/h) at the minimum and A (dB)=0.01+0.25 R(mm/h) at the maximum, showing considerable variability in the values of attenuation from year to year. The attenuation statistics for different seasons have also been computed and they show considerable changes from season to season-the largest attenuation in excess of 10 dB recorded in July-August-September, whereas minimum attenuation in excess of 2 dB recorded in December-March for nearly two years of data. Comparison of measurements made over New Delhi with those reported elsewhere show that for 0.02% of time attenuation values lie between those of Slough, England, and Crawford Hill, NJ. The concept of effective path length has been discussed based on the relationship between effective path length and the rain rate     

Integrated circuits for a 200 Mbit/s fiber-optic link

A set of three bipolar integrated circuits for a new fiber-optic link is described. The link operates at data rates of 5-200 Mb/s NRZ. The optical transmitter and receiver modules are compact and fit into standard 16-pin dual-in-line sockets. The power consumption of the transmitter module is 530 mW and the receiver module dissipates 310 mW. The optical loss budget is 20 dB, which is sufficient for link lengths of up to 5 or 6 km. The circuits have been designed in a 3-/spl mu/m bipolar process. The chip sizes are 2 mm/spl times/1.75 mm each.     

UHF Band Short Range Propagation Model

The purpose of this study is to characterize the indoor and indoor–outdoor propagation in different scenarios, using monopole antennas working at 410 and 890 MHz. Propagation of narrow band and wide bands have been studied. In scenarios with a continuous variation of the distance between the transmitter and receiver antenna (1 D scenarios), we use a log-distance path loss model to determine the equations that describe the mean value of the path loss. In scenarios where the position of the receiver is not a uniform function of the distance between the transmitter and the receiver, we represent the basic propagation gain as a function of the measurement point index. Results show that the indoor propagation gain can be described using two slopes propagation model. For the multiwall attenuation loss it is shown that each wall has an attenuation of almost 2.5 dB at 410 MHz increasing to almost 4 dB at 890 MHz. The obstruction gain (loss) due to human beings shows that this can be within a 40 dB interval.     

Multispot diffusing configuration for wireless infrared access

In order to combine the advantages and to overcome the drawbacks of a direct line-of-sight or a diffuse configuration for wireless infrared access, a multispot diffusing concept utilizing a holographic spot array generator is presented. Simulation results are presented and compared with those for a pure diffuse configuration in terms of link characteristics, when a single-element or a multibranch composite receiver is employed. The multispot transmitter ensures a more uniform signal power distribution. Improvements of about 2 dBo (optical decibels) can be achieved compared to a Lambertian pattern illumination. The increased power path loss at the edges of the communication cell is accompanied with a decrease in the delay spread resulting in an extension of the coverage range. Utilization of angle diversity detection improves the signal-to-noise ratio by more than 7 dB when selecting the best receiver branch and more than 10.5 dB in the case of maximal-ratio combining. Use of a multibeam transmitter and an angle diversity receiver reduces the likelihood of shadowing of the receiver due to an obstacle standing along the path between the receiver and the transmitter     

Normalized differential spectral attenuation (NDSA): a novel approach to estimate atmospheric water vapor along a LEO-LEO satellite link in the ku/K bands

We introduce here the normalized differential spectral attenuation (NDSA) approach, which is a novel differential measurement way for estimating the total content of water vapor integrated water vapor (IWV) along a tropospheric propagation path between two Low Earth Orbit (LEO) satellites. The NDSA approach requires a transmitter onboard the first LEO satellite and a receiver onboard the second one. It is based on the simultaneous measurement of the total attenuation at two relatively close frequencies in the Ku/K bands, and on the estimate of a "spectral sensitivity parameter" that can be directly converted into IWV. NDSA is potentially able to emphasize the water vapor contribution, to cancel out all spectrally flat unwanted contributions and to limit the impairments due to tropospheric scintillation. The objective of the paper is to analyze the level of correlation between the spectral sensitivity parameter and the IWV at a given altitude from ground of the LEO-LEO link (tangent altitude), in order to single out the best performing frequencies. Simulation results are based on microwave propagation models and on radiosonde data. The results shows the potential of the NDSA approach to provide direct estimates of IWV along LEO-LEO tropospheric propagation paths in the 15-25 GHz frequency range, under different atmospheric conditions.     

Microwave link dual-wavelength measurements of path-averageattenuation for the estimation of drop size distributions and rainfall

Microwave attenuation measurements at 25 and 38 GHz made on a 2.3-km microwave link are employed to estimate drop size distributions (DSD), rainfall rate, and rainfall accumulation. A theoretical model for the propagation of microwaves in a link system sets forth the basis for the development of a dual-wavelength analytical technique to invert two parameters of a path-average gamma DSD. The DSDs obtained from the technique are evaluated in conjunction with point measurements performed with a 2-D video disdrometer. Additionally, the DSDs yield path-average rainfall rates and rainfall accumulation which are compared with path-average measurements from a network of optical and tipping bucket rain gauges located beneath the link path, and with estimates based on empirical power law relations     

Multipath effects due to rain at 30-50 GHz frequency communicationlinks

This study makes predictions about signal degradation along terrestrial radio links, operated at wide bandwidth and 30-50-GHz frequencies, caused by inhomogeneities in fairly severe rain storms. While the line-of-sight path may experience moderate to severe attenuation, the real problem at hand is to estimate the effect of multipath via scatterings from rain drops on side paths. These longer-path contributions can cause pulse distortions and related high-bandwidth effects which are deleterious to the information content, even upon successful reception of attenuated signals. The results show that significant degradation of high-bandwidth signals accompanying attenuations of more than ~40 dB are possible under intermittent rainfall conditions     

Cumulative Fading and Rainfall Distributions for a 2.1 km, 38 GHz, Vertically Polarized, Line-of-Sight Link

Between February 1,1997 and January 31,1998, a 2.1 km vertically polarized 38 GHz communications link was studied in the subtropical city of Brisbane, Australia. According to the current ITU fading prediction method the link would be expected to experience a rainfall intensity of approximately 50 mm/h for 52.6 min during the year, when averaged over a 60 s integration time. This should have caused approximately 20 dB of fading for 52.6 min [1]-[3]. However the link actually experienced 20 dB of fading for 150.5 min, with fading of 37 dB exceeded for 53.5 min during the year. A rainfall intensity of 84 mm/h was exceeded for 64 min at the receive end, and a rainfall intensity of 72 mm/h was exceeded for 52 min at the transmit end of the hop.     

Power budget optimization of STARNET II: an optically amplifieddirect-detection WDM network with subcarrier control

STARNET-II is a novel optically amplified direct-detection multi-Gb/s WDM LAN developed at Stanford University, Stanford, CA. STARNET-II is simpler than the coherent STARNET-I yet is functionally equivalent. Here, STARNET-II power budget is investigated and optimized. Power allocation between payload and subcarrier control streams at the transmitter, and power splitting ratio between the payload and subcarrier control receivers are investigated and optimized theoretically and experimentally. Critical parameter variations such as electro-absorption modulator nonlinearity, transmitter wavelength and power instability are investigated, and their effect on the power budget is analyzed. With the optimized design, experimental STARNET-II optical layer has a receiver sensitivity of -31.5 dBm at BER=10^-9 corresponding to 23.9 dB SNR, for simultaneous transmission and reception of 1.25 Gb/s payload and 125 Mb/s control data. Including the computer interface, STARNET-II has a power budget of 28.6 dB. For a 10-km network diameter, STARNET-II dispersion margin can support the modulation bandwidth up to 13 Gb/s     

盐城地面数字电视发射传输网络系统分析

主要以广播电视信号的流程为顺序,从信号的传输、编码器的设置、发射机的组成、激励器的设置、天馈线系统的选择和地面数字电视信号的接收6个方面,对系统的组成做了详细介绍。在介绍各个环节的同时,根据运行、维护经验,针对该部分设备中的不同选项对发射和接收会产生怎样的影响做了详细说明。     

适于视频应用的高数据传输率集成CMOS收发机

这篇文章给出了一个5GHz CMOS射频收发机的设计方案。此设计采用0.18微米射频CMOS加工工艺,集合了最新IEEE802.11n的特性例如多输入多输出技术的专利协议以及其他无线技术,可提供应用在家庭环境中的实时高清电视数据的无线高速传输。设计频率涵盖了从4.9GHz到5.9GHz的ISM频带,每个射频信道的频宽为20MHz。收发机采用了直接上变频发射器和低中频接收器的结构。在没有片上校准的情况下,设计采用双正交直接上变频混频器,得到了超过35dB的镜像抑制。测试结果得到6dB接收机噪声系数以及在-3dBm输出功率时得到发射机EVM结果优于33dB。     

Absorption and scintillation effects at 3 mm wavelength on a short line-of-sight radio link

Measurements on a path 150m long, with narrow-beam transmitting and receiving antennas 2m above the ground at one end of the path, and a reflecting plate at the other end, at the same height, have shown attenuation in rain to be about 17dB/km and 8dB/km for rainfall rates of 48mm/h and 7mm/h, respectively. Amplitude variations of up to ±0.4dB can occur in a time interval of the order of 1s during sunny, humid conditions in summer.     

Channel capacity analysis of non-line-of-sight ultraviolet communication in noncoplanar geometry based on traversing tiny unit method

Channel capacity reflects the ability of the system to transmit information without errors.The path loss and impulse response of the system were calculated based on traversing tiny unit method,and then the frequency response of the system was obtained by the discrete Fourier transform of the impulse response sampling sequence,and the 3 dB bandwidth of the system was calculated.Considering the shot noise caused by signal light,the signal-to-noise ratio of the system was obtained according to the quantum limit method,and then the relationship between the channel capacity and the geometric parameters of transmitter and receiver in non-line-of-sight noncoplanar ultraviolet communication system were simulated and analyzed by Shannon formula.The results show that the channel capacity decreases with the increase of the off axis angle and the communication distance.When the elevation angles of transmitter and receiver are less than 40°,the channel capacity decreases rapidly with the increase of the elevation angles of transmitter and receiver,and the transmitter elevation angle has a great influence on the channel capacity.The system channel capacity is almost constant with the increase of divergence angle,and the larger the receiver field of view angle,the greater the system channel capacity.     

Effect of Atmospheric Parameters on Satellite Link

The rainfall path attenuation measured at Universiti Sains Malaysia (USM) for 4 years (January 02 to January 06) is presented. The data obtained are useful to investigate the impairment due to rainfall attenuation in satellite links operating in tropical and equatorial climates. It shows that the logarithmic function with ground rain rate deviates at very high rain rate. A rainfall rate of 130 mm/h causes the rainfall attenuation threshold (> 20 dB) to be exceeded. Maximum exceedences for rain rate and attenuation were observed during the wet months. The cumulative distributions of attenuation derived from the measured data are presented and compared with those obtained with existing prediction methods.     

Simultaneous analysis of downlink beacon dynamics and skybrightness temperature. Part II. Extraction of amplitude scintillations

This paper addresses the long-standing problem of separating the tropospheric amplitude scintillations from the dominant trend of atmospheric attenuation in a satellite downlink. Following extensive theoretical and experimental work, it is shown how the use of a radiometer coaxial with the communications beacon receiver constitutes an excellent tool for an optimum separation regardless of the meteorological conditions along the propagation path and avoids the use of the long-traditional high-pass filter approach. The experimental and theoretical work has revealed that the angular resolution of the radiometer together with the dynamics of rain attenuation and tropospheric scintillations determine the success of the extraction. This is because fast fadings require large radiometer antennas in order to resolve the sky temperature fluctuations. The dynamic behavior of rain attenuation has been reanalyzed and adapted for this study with special focus on the Maseng-Bakken (MB) model and the impact of the slant path on attenuation dynamics. The importance of the antenna pattern in the time response of the radiometer is studied in detail and permits to derive the maximum Fourier component observable for a given antenna size. The theoretical work has been verified by means of extensive experimental results obtained using a dual radiometer system and a beacon receiver tracking the ITALSAT 39.5 GHz F40 beacon. Finally, because of its importance and direct relevance to future communication systems benefiting from fade countermeasure strategies, the minimum size of the radiometer antenna for a successful extraction of amplitude scintillations is determined as a function of the elevation angle and carrier frequency     

The influence of heavy rainfall on attenuation at 18.5 and 30.9 GHz

Percent-of-time distributions of rain-induced fades obtained on a 6.4-km path in New Jersey operating at a frequency of 18.5 GHz are discussed for the period of 1968-1969; data obtained at 30.9 GHz on a 1.9-km path for the same period are also discussed. The attenuation distributions are compared with attenuations calculated from the distributions of average rain rates on the paths. With these data, it is found that distributions of attenuation can be predicted from the path-average rain-rate distributions for a given sample period. Detailed rain-rate and attenuation measurements at 18.5 GHz on the 6.4-km path are presented for the most intense storm observed in a three year recording period. Point rain rates in excess of 250 mm/h and path-average rates exceeding 180 mm/h were observed; the attenuation exceeded the 50-dB dynamic measuring range of the equipment for more than seven minutes.     

Normalized Differential Spectral Attenuation (NDSA) Measurements Between Two LEO Satellites: Performance Analysis in the Ku/K-Bands

Normalized differential spectral attenuation (NDSA) is a novel differential measurement method to estimate the total content of water vapor [integrated water vapor (IWV)] along a tropospheric propagation path between two low Earth orbit (LEO) satellites. A transmitter onboard the first LEO satellite and a receiver onboard the second one are required. The NDSA approach is based on the simultaneous estimates of the total attenuation at two relatively close frequencies in the Ku/K-bands and of a “spectral sensitivity parameter” that can be directly converted into IWV. The spectral sensitivity has the potential to determine the water vapor contribution, to cancel out all spectrally flat unwanted contributions, and to limit the impairments due to tropospheric scintillation. In this paper, we focus on the measurement accuracy of the spectral sensitivity parameter. Specifically, we examine this accuracy at three different frequencies and for two models of atmospheric structure. We first provide an approximate expression of the accuracy and then validate this expression through Monte Carlo simulations based on microwave propagation models.