Advanced Communications Technology Satellite (ACTS): four-yearsystem performance

The Advanced Communications Technology Satellite (ACTS) was conceived at the National Aeronautics and Space Administration (NASA) in the late 1970s as a follow-on program to ATS and CTS to continue NASA's long history of satellite communications projects. The ACTS project set the stage for the C-band satellites that started the industry, and later the ACTS project established the use of Ku-band for video distribution and direct-to-home broadcasting. ACTS, launched in September 1993 from the Space Shuttle, created a revolution in satellite system architecture by using digital communications techniques employing key technologies such as a fast hopping multibeam antenna, an on-board baseband processor, a wide-band microwave switch matrix, adaptive rain fade compensation, and the use of 900 MHz transponders operating at Ka-band frequencies. This paper describes the lessons learned in each of the key ACTS technology areas, as well as in propagation investigations     

Avanced Communications Technology Satellite (ACTS) propagationcampaign in North America

Ka-band propagation measurements with the Advanced Communications Technology Satellite (ACTS) are entering their fifth year of data collection. Beacon-signal levels and radiometric sky noise are being measured at 20.2 and 27.5 GHz, with supporting meteorological information, at seven experiment sites in the US and Canada, using ACTS propagation terminals (PSTs) supplied by NASA. Uniform system-calibration, data-collection and data-processing procedures and software, prescribed and developed by the NASA Propagation Experimenters (NAPEX) Group, promote commonality of the data sets and permit comparison among results from the various sites. Goals of the program are to develop basic Ka-band propagation knowledge, and to supply information needed to improve propagation-prediction models and to develop impairment-mitigation techniques. The APT sites were selected to sample a variety of North American climate regions and their associated propagation features. Statistical results from the propagation measurements are presented and compared to the predictions of new and existing prediction models. Other aspects of the measurements, including unusually strong antenna-wetting effects observed with the APTs, plus analyses related to impairment dynamics, rain-rate modeling, and clear-air effects, are discussed     

The Ka-band propagation measurements campaign at JPL

OLYMPUS, the NASA sponsored, JPL-managed, Ka-band propagation measurement campaign carried out at Virginia Tech and many European sites, is discussed. The basic physics involved, the OLYMPUS experiment itself, and the advanced communications technology satellite (ACTS) program, the purpose of which is to demonstrate the feasibility of the Ka-band (20 and 30 GHz) spectrum for satellite communications, as well as to help maintain US leadership in satellite communications. are described     

Ka频段低轨卫星跟踪技术研究

大口径天线在跟踪Ka频段低轨遥感卫星时,由于半功率波束宽度很窄,对天线跟踪提出了更高的要求。从提升天线跟踪精度角度出发,提出了通过采用变积分PID控制及计算机辅助跟踪的方法,有效减小天线伺服环路的动态滞后,提高天线跟踪精度;从优化Ka频段跟踪捕获流程角度,提出了低仰角捕获跟踪及高仰角捕获跟踪时的不同策略,提高大口径天线Ka频段窄波束捕获成功率。采用上述方法和策略,通过仿真及工程调优可以显著提升天线跟踪精度,实现天线高精度跟踪。     

Advanced Communications Technology Satellite (ACTS) fadecompensation protocol impact on very small-aperture terminal bit errorrate performance

The Advanced Communications Technology Satellite (ACTS) communications system operates at Ka band. ACTS uses an adaptive rain fade compensation protocol to reduce the impact of signal attenuation resulting from propagation effects. The purpose of this paper is to present the results of an analysis characterizing the improvement in VSAT performance provided by this protocol. The metric for performance is VSAT bit error rate (BER) availability. The acceptable availability defined by communication system design specifications is 99.5% for a BER of 5E-7 or better. VSAT BER availabilities with and without rain fade compensation are presented. A comparison shows the improvement in BER availability realized with rain fade compensation. Results are presented for an eight-month period and for 24 months spread over a three-year period. The two time periods represent two different configurations of the fade compensation protocol     

ACTS propagation experiment: rain-rate distribution observationsand prediction model comparisons

Empirical distribution functions for one-minute average rain-rate values were compiled for nine station years of observations at five of the Advanced Communications Technology Satellite (ACTS) propagation experiment terminal sites. The empirical distribution functions were compared with cumulative distribution functions generated by three different rain-rate distribution prediction models. On the basis of the expected differences between model predictions and experimental measurements, not one of the model combinations provided good predictions     

Analysis of the effects of water on the ACTS propagation terminal antenna

The NASA advanced communications technology satellite (ACTS) propagation experiment was designed to observe the attenuation produced by rain on Earth-satellite paths operating in the Ka-band. Unwanted effects of water on the antenna reflector surface were noted. Wet-antenna attenuation could be attributed to the combined effect of a water layer on the reflector surface and water wetting the feed window surface. A model was developed to calculate the antenna reflector and feed surface water layer thickness values as a function of position on each surface. The thickness values were used to calculate the additional attenuation produced by the water layers as a function of rain rate on the antenna. The wet-antenna-attenuation prediction model was verified by sprayer tests. The goal of the ACTS propagation experiment was to obtain path attenuation statistics, statistics that represent the effects of rain on the Earth-satellite path but not on the antenna itself. The wet-antenna attenuation prediction model was used to remove the effects of water on the antenna from the combined antenna-plus-path attenuation statistics produced by the experiment. The overall efficacy of the model was demonstrated by comparing the corrected path loss statistics from two ACTS propagation experiment sites with earlier COMSTAR path loss measurements made at or near those sites. The empirical distribution functions from both the ACTS and COMSTAR experiments were identical within the expected uncertainty of an empirical annual distribution of attenuation by rain.     

ACTS propagation experiment: experiment design, calibration, anddata preparation and archival

The National Aeronautics and Space Administration Advanced Communications Technology Satellite (ACTS) propagation experiment was designed to obtain slant-path attenuation statistics for locations within the United States and Canada for use in the design of low-margin Ka-band satellite communication systems. Experimenters at seven different locations have collected propagation data for move than two years. The propagation terminals used for the experiment were identical. A single preprocessing program was used by the experimenters to provide for automatic calibration, generation of attenuation histograms, and data archival. In this paper, the calibration procedures are described mid estimates given for measurement accuracy. ACTS provided beacons at 20.2 and 27.5 GHz for use in making attenuation measurements. In addition to the beacon receivers, each ACTS propagation terminal has two total power radiometers with center frequencies at the beacon frequencies. The radiometers are used to establish the beacon signal reference levels needed for calculating beacon attenuation values. For the combined radiometer and beacon measurement system, the attenuation measurement error was less than a maximum of 1.0 dB and was generally less than 0.3 dB. The dynamic range for attenuation measurement varied from site to site depending on location relative to the peak of the satellite beacon antenna pattern. For locations within the continental United States, the dynamic range was better than 20 dB     

机载Ku、Ka频段卫星通信系统综述

叙述了Ku频段和Ka频段机载卫星通信系统的国内外发展现状,列举了几个典型的卫星通信系统技术指标,并简述了研制机载卫星通信系统应注意的事项和技术途径,其中包括选择天线系统形式,合理分配系统指标,消除多普勒效应的影响等。     

Multipath propagation measurements on an overwater path in NewZealand

The results are described of a 140 Mb/s, 16 QAM digital microwave radio field trial to characterize multipath fading on a 60-km overwater route in New Zealand. Propagation data have been collected from the path between September 1985 and September 1986, and include one fading season of the Southern Hemisphere. The authors specifically apply and extend work on multipath fading by W.D. Rummler and others (1979, 1981, 1986). To the spectral data collected from the trial, a Rummler-type model (echo delay 6.35 ns) has been fitted. Distributions for the parameters a, b, and f_o ar observed to be similar to those presented by Rummler (1979) for the 26.4-mile Atlanta to Palmetto, Georgia path. Data which cannot be characterized well by the Rummler model include samples which show the evidence of a ray with equivalent long delay (⩾10 ns). This ray is either conjectured to be a sea reflection (however sea reflections are blocked at an Earth radius factor of k=4/3), or is indicative of the presence of more than one secondary ray     

使用Matlab实现对Ka波段卫星通信衰减信道的性能仿真

介绍了利用Matlab6．1的通信系统工具包进行通信仿真实验的一般方法，对各模块间的矢量(Vector)与标量(Scalar)的转换进行了介绍．对Ka波段卫星系统的性能进行了仿真。     

ADVANCED COMMUNICATIONS TECHNOLOGY SATELLITE (ACTS): DESIGN AND ON-ORBIT PERFORMANCE MEASUREMENTS

The advanced communications technology satellite (ACTS), developed and built by Lockheed Martin Astro Space for the NASA Lewis Research Center, was launched in September 1993 on the Shuttle STS 51 mission. ACTS is a digital experimental communications test bed that incorporates gigahertz bandwidth transponders operating at Ka band, hopping spot beams, on-board storage and switching and dynamic rain fade compensation. This paper describes the ACTS enabling technologies, the design of the communications payload, the constraints imposed on the spacecraft bus, and the measurements conducted to verify the performance of the system in orbit.     

Millimeter-wave propagation measurements at the Ballistic ResearchLaboratory

Results of measurements made with radars from 35 to 217 GHz of near-Earth propagation in rain, fog, snow, and humidity are presented and discussed     

Normalization of propagation measurements with respect to terrain effect

In this paper, we introduce a method for the reliable modelling of propagation loss using measurements data. Using point to point effective height calculation, we apply a methodology for the normalization of signal propagation loss measurements with respect to terrain effect. Moreover, by applying the proposed normalization methodology on two different measurement data sets, taken in the same urban environment (Athens, Greece), it is experimentally proved that the effective height is accurately expressing the influence of terrain morphology in the vicinity of mobile unit on signal variability. Copyright © 2001 John Wiley & Sons, Ltd.     

Early results: Very low-level propagation measurements on the Ottawa River

The effects of anomalous propagation on the accuracy of low-angle radar tracking are discussed, perhaps for the first time. A novel technique is described for carrying out very low-level propagation measurements. It is based on a large sampled aperture antenna system which is instrumented with both radio and meteorological sensors. Early results are given of collocated radio (angle-of-arrival) and meteorological measurements which were recorded on the Ottawa River near Ottawa, Canada. In particular, a direct comparison is given of measured angle-of-arrival deviations and values predicted from meteorological measurements, as well as results showing angle-of-arrival errors for propagation in evaporation ducts.     

基于LTCC技术的C频段星载接收机混频器

利用低温共烧陶瓷(LowTemperature Co-fired Ceramic,简称LTCC)技术,设计制作了一种可应用于C频段星载接收机的双平衡混频器。该混频器将射频和本振巴伦等无源器件集成在多层LTCC基板内,实现了电路的小型化、高集成度和高可靠性。测试表明,当射频输入为5.925～6.425GHz、本振频率为2.225GHz、中频输出频率为3.7～4.2GHz时,混频器的变频损耗≤9.3dB,P1dB为5.7dBm,本振到射频和本振到中频的隔离度分别为39.44dB和35.58dB。混频器的尺寸为40×22×1.92mm3。     

Comparison of a diffraction based radiowave propagation model with measurements

A comparison between a theoretical diffraction based radio propagation model and measured path loss data for flat terrain in New Zealand in terms of variation in path length, frequency and environment is described. Results of measured town planning data for the model are also given.<>     

串行级联Turbo码在Ka频段卫星通信中的仿真研究

在分析Ka频段静止卫星信道特点的基础上,建立了信道仿真模型并进行了基带仿真,研究了不同天气条件下静止卫星通信系统的误比特率性能,基于这一模型通过仿真研究了串行级联Turbo码在静止卫星信道条件下的性能。仿真结果表明,除了中雨、雷雨等恶劣天气状况之外,在通常的天气条件下,串行级联Turbo码可以提供约10dB左右的编码增益,可有效改善系统性能。