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Proceedings of the IEEE

Issue 6 • Date June 1997

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Displaying Results 1 - 18 of 18
  • Edwin H. Colpitts: A pioneer in communications engineering [Scanning the Past]

    Publication Year: 1997 , Page(s): 1020 - 1024
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  • Ka-band propagation measurements: an opportunity with the Advanced Communications Technology Satellite (ACTS)

    Publication Year: 1997 , Page(s): 853 - 862
    Cited by:  Papers (14)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (176 KB)  

    The Advanced Communications Technology Satellite (ACTS) was conceived at the National Aeronautics and Space Administration (NASA) as a follow on program to its long history in satellite communications projects that have reduced the risk of developing new technologies that fall outside the sponsorship capability of the private sector. To counter the foreign challenge that developed in the late 1970's to the once insuperable US lead in this field, ACTS was developed to maintain the US preeminence. Launched in September 1993 from the space shuttle, key technologies on ACTS include a multibeam antenna, a baseband processor, a 900 MHz wideband microwave switch matrix, adaptive rain fade compensation techniques, and the use of Ka-band frequencies. Since this is the United States' first effort in using Ka-band for satellite communications, beacons are incorporated on the satellite, which provide an opportunity for propagation measurements. NASA is sponsoring a network of propagation experimenters using these beacons and receive-only terminals identical in design. This paper provides some history that leads to the eventual development of ACTS. Also, a system overview of the spacecraft is provided for those less familiar with it View full abstract»

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  • Cumulative fade distributions and frequency scaling techniques at 20 GHz from the Advanced Communications Technology Satellite and at 12 GHz from the digital satellite system

    Publication Year: 1997 , Page(s): 910 - 916
    Cited by:  Papers (14)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (176 KB)  

    Cumulative fade distributions were derived from measured transmissions at 20 GHz emanating from the geostationary Advanced Communications Technology Satellite (ACTS) and at 12 GHz from the television broadcasting digital satellite system (DSS) over the one-year period September 1, 1995-August 31, 1996. The transmissions were acquired at two collocated receivers at the Applied Physics Laboratory of The Johns Hopkins University (central Maryland). Since both geostationary satellites are positioned within 1° from one another, the geometric pointing parameters at the receiver locations are approximately coincident (e.g., 38° elevation angle). The 20-GHz fades were noted to be two-four times larger than those measured at 12 GHz. Two frequency scaling techniques were employed for estimating the distribution at one frequency given a measurement at the other. The methods pertained to the frequency scaling formulation of the radiocommunications sector of the International Telecommunications Union and the ratio of attenuations in terms of an equal probability rain rate along an effective path. The latter method gave agreement to within 1 dB when adjusted for antenna-wetting signal degradation View full abstract»

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  • System requirements for Ka-band Earth-satellite propagation data

    Publication Year: 1997 , Page(s): 810 - 820
    Cited by:  Papers (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (224 KB)  

    Accurate estimates of the propagation impairments that affect link quality and availability and determine signal interference fields are essential for the reliable design of telecommunication systems and the efficient use of the electromagnetic spectrum. Recent announcements by commercial entities of their intent to use Ka-band spectrum to supply satellite services have heightened interest in propagation data and models for these frequencies. This paper provides a brief overview of Ka-band Earth-satellite systems and requirements in relation to the need for specific types of propagation data View full abstract»

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  • ACTS propagation experiment: experiment design, calibration, and data preparation and archival

    Publication Year: 1997 , Page(s): 863 - 878
    Cited by:  Papers (21)
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    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 View full abstract»

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  • Ka-band Earth-space propagation research in Japan

    Publication Year: 1997 , Page(s): 821 - 842
    Cited by:  Papers (13)
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    Earth-space propagation studies in Japan were originally concerned with measuring atmospheric absorption and rain attenuation by means of a suntracker and a radiometer, following which a number of long-term experiments were performed using various experimental and commercial satellites. The first experiments involving Ka-band Earth-space propagation measurements in Japan were carried out in 1977 using the Engineering Test Satellite Type II, and since 1978, these experiments have been conducted using Japan's domestic communication satellite. Based on these studies to date, the understanding of Earth-space propagation characteristics at higher frequency bands, modeling of propagation channels, and development of countermeasure technologies have shown dramatic progress. In Japan at present, advanced propagation studies are under way in wideband digital-transmission satellite systems for the forthcoming multimedia era. This paper summarizes recent study activities concerning wave propagation in Ka-band Earth-space paths and related topics, such as radiometeorology in Japan. Last, future plans for conducting Ka-band and millimeter-wave propagation experiments by using the Japanese experimental satellite “COMETS” and rain observations in tropical regions by “TRMM” are introduced briefly View full abstract»

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  • A three-site comparison of fade-duration measurements

    Publication Year: 1997 , Page(s): 917 - 925
    Cited by:  Papers (5)
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    Important elements in the design of Ka-band communication systems are the duration of fade and nonfade events at a particular fade depth. The choice of modulation and forward error correcting codes will depend on both the fading time dynamics and annual fade occurrence statistics. This paper examines the fade duration measured at locations in three of the Advanced Communications Technology Satellite (ACTS) propagation experimental regions, namely, Florida (rain zone N of the radiocommunications sector of the International Telecommunications Union [ITU-R] model), New Mexico State University (ITU-R rain zone M), and Alaska (ITU-R rain zone C). Within each region, measures of the underlying uniformity are described and an interregional comparison examines the ability to scale the local results View full abstract»

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  • European research on Ka-band slant path propagation

    Publication Year: 1997 , Page(s): 843 - 852
    Cited by:  Papers (25)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (180 KB)  

    Europe saw two major initiatives in the mid-1980's to verify the viability of 20-50 GHz frequency bands for high capacity radio transmission. The first was the experimental telecommunication satellite OLYMPUS commissioned by the European Space Agency; the second was the ITALSAT program planned by the Italian Space Agency. Both spacecraft were equipped with highly stable propagation beacon payloads for accurate measurement of propagation conditions. Two international groups of experimenters (OPEX for OLYMPUS and CEPIT for ITALSAT), who had agreed on a set of common procedures for the earth stations' design, experiment management, and comparison of results, carried out the propagation measurements in a collaborative manner. This paper gives a summary of these activities and their results View full abstract»

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  • ACTS propagation experiment: rain-rate distribution observations and prediction model comparisons

    Publication Year: 1997 , Page(s): 946 - 958
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (260 KB)  

    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 View full abstract»

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  • Transoceanic communication by means of satellites [classic paper]

    Publication Year: 1997 , Page(s): 1011 - 1019
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    The existence of artificial Earth satellites and of very low-noise maser amplifiers makes microwave links using spherical satellites as passive reflectors seem an interesting alternative to cable or tropospheric scatter for broadband transatlantic communication. A satellite in a polar orbit at a height of 3000 mi would be mutually visible from Newfoundland and the Hebrides for 22.0% of the time and would be over 7.25° above the horizon at each point for 17.7% of the time. Out of 24 such satellites, some would be mutually visible over 7.25° above the horizon 99% of the time. With 100-ft diameter spheres, 150-ft diameter antennas, and a noise temperature of 20°K, 85 kw at 2000 mc or 9.5 kw at 6000 mc could provide a 5-mc baseband with a 40-dB signal-to-noise ratio. The same system of satellites could be used to provide further communication at other frequencies or over other paths View full abstract»

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  • ACTS propagation experiment: attenuation distribution observations and prediction model comparisons

    Publication Year: 1997 , Page(s): 879 - 892
    Cited by:  Papers (20)
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    Empirical cumulative distribution functions for satellite-to-ground path attenuation relative to clear-sky values were compiled for 22 path years of data collected by the ACTS propagation experiment. These statistics are for two frequencies, 20.2 and 27.5 GHz, with elevation angles ranging 8-52°, latitudes ranging 28-65°, and five different rain-rate climate regions. The attenuation estimation accuracy was better than 0.3 dB. The availability of the equipment for making measurements was higher than 90% for 18 of 22 path years of observation. The empirical distribution functions were compared with predicted cumulative distribution functions generated by four different attenuation-prediction models: the model recommended by the radiocommunications sector of the International Telecommunications Union (ITU-R); the Dissanayake, Allnutt, and Haidara (DAH) rain-attenuation model; and the Crane-Global and Crane-Two Component models when combined with three different rain-rate distribution prediction models: the ITU-R model the Crane-Global model and the Rice-Holmberg model. On the basis of the expected differences between model predictions and experimental measurements, the only attenuation model that provided acceptable predictions was the DAH model when combined with either the Crane-Global rain-zone model or the Rice-Holmberg rain-race model. A major problem in interpreting the results of the model-versus-measurement comparison is the unmodeled contribution of water on the surface of the ACTS propagation terminal antenna reflector View full abstract»

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  • Ka-band scintillations: measurements and model predictions

    Publication Year: 1997 , Page(s): 936 - 945
    Cited by:  Papers (21)
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    New propagation data from a 30/20-GHz propagation experiment at several US sites, including Fairbanks, AK, and Norman, OK, are presented to examine existing models for scintillations. Beacon measurements were collected at one sample per second continuously and at 20 samples per second for selected intervals. The widely separated measurement frequencies and the wide range of measurement elevation angles of about 8-52° provide a solid set of measurements to test existing models and formulate new ones. It is found that current scintillation prediction models overestimate the magnitude of scintillation. The Karasawa model was modified to fit the Fairbanks data, with this modification valid for the climate zone containing Fairbanks. The model of the radiocommunication sector of the International Telecommunication Union was examined for several sites, and an elevation angle modification was attempted to bring it into agreement with the data sets. Measurements indicate a frequency dependence of f7/12 View full abstract»

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  • Channel characterization and modeling for Ka-band very small aperture terminals

    Publication Year: 1997 , Page(s): 981 - 997
    Cited by:  Papers (22)  |  Patents (102)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (484 KB)  

    An increasing number of commercial applications are being promoted for future Ka-band satellite communication systems. Many of these systems will involve low-margin very small aperture terminals (VSATs). These systems are subject to important atmospheric propagation degradations that affect the quality of transmission and the link availability. The objective of this paper is to characterize the Ka-band channel and evaluate the performance degradation in VSATs resulting from atmospheric propagation, impairments. In particular microwave propagation through a turbulent atmosphere is discussed, and the statistical characterization and modeling of tropospheric scintillation is reviewed. Moreover, the paper extends the method proposed by Filip and Vilar (1990) for the long-term characterization and modeling of the combined effect of rain impairments and scintillation. Specifically, the increase in noise temperature during rain events is added to the Filip-Vilar model. This leads to a five-parameter global fading distribution that is used to predict typical Ka-band satellite link outage time, the mathematical formalism is illustrated by applying the method to the selected case of the Advanced Communications Technology Satellite (ACTS)-Georgia Tech experimental downlink. Numerical results confirm that both rain impairments and scintillation are important factors in the design of Ka-band VSAT systems View full abstract»

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  • The application of S-band polarimetric radar measurements to Ka-band attenuation prediction

    Publication Year: 1997 , Page(s): 893 - 909
    Cited by:  Papers (4)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (512 KB)  

    In September 1993, the National Aeronautics and Space Administration's Advanced Communications Technology Satellite (ACTS) was deployed into a geostationary orbit near 100° W longitude. The ACTS satellite employs two Ka-band beacons, one at 20.185 GHz and another at 27.505 GHz. Impairments due to rain attenuation and tropospheric scintillations will significantly affect new technologies for this spectrum. Heavy rain at Ka-band can easily produce 30 dB of attenuation along the propagation path. Propagation experiments being conducted in seven different climatic zones involve multiyear attenuation measurements along the satellite-Earth slant path. Measurements in the B2 climatic zone are made with an ACTS propagation terminal located in northeast Colorado. In order to gain move understanding about the physical processes that are responsible for Ka-band attenuation, the Colorado State University CHILL S-band polarimetric radar is used to take radar measurements along the slant path. The Colorado Front Range experiences a variety of weather conditions throughout the year ranging from upslope rain conditions to winter storms. Four such events measured along the slant path are illustrated in this paper. They include two convective cases and two “bright-band” cases. The S-band polarimetric radar data is used to initialize radar-based attenuation-prediction models, which are applied to the four precipitation events described. The comparisons of predicted attenuation to measured attenuation are quite good. It was also found during the course of the experiment that water droplets standing on the antenna surface can cause appreciable attenuation at Ka-band frequencies. That finding needs to be recognized in future model development and statistical analysis View full abstract»

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  • Application of open-loop uplink power control in Ka-band satellite links

    Publication Year: 1997 , Page(s): 959 - 969
    Cited by:  Papers (16)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (236 KB)  

    Propagation impairments impose a limit on the use of the 20/30-GHz frequency band for satellite communication applications. Power control is one of the techniques that can be used to mitigate such impairments. Results of an experiment conducted using the Advanced Communications Technology Satellite (ACTS) to evaluate the efficacy of open-loop uplink power control are presented. A power control system is required to maintain the power flux received at the satellite at a constant level irrespective of the fading along the propagation path. The control parameter for the power controller was derived from the fading and enhancements observed on a downlink beacon signal thus requiring frequency translation of the propagation effects to the uplink frequency. In this scheme, the controller performance is largely a function of the frequency translation accuracy, which is determined by the prevailing propagation conditions. In addition, equipment-induced variations in the control parameter can produce power control errors. To maintain the control accuracy within reasonable limits, an algorithm that can differentiate various propagation factors as well as equipment effects was devised. It was found that under most conditions, the power control accuracy could be maintained within ±2.5 dB View full abstract»

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  • Fade slope analysis for Alaska, Florida, and New Mexico ACTS propagation data at 20 and 27.5 GHz

    Publication Year: 1997 , Page(s): 926 - 935
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (164 KB)  

    This paper analyzes fade slope for the Alaska, Florida, and New Mexico Advanced Communications Technology Satellite (ACTS) propagation data at 20 and 27.5 GHz for the first two years of the experiment (December 1, 1993-November 30, 1995). The propagation experiment will continue to collect data for at least another 21 months. Fade slope is examined on a statistical basis for the three sites. The Florida and New Mexico receiver sites have very different weather characteristics but almost identical elevation angles, while the Alaska receiver terminal has an extremely low elevation angle. The cumulative statistics illustrate the relationship between fade slope, fade level, transmission frequency, and elevation angle for all three sites View full abstract»

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  • Satellite communications

    Publication Year: 1997 , Page(s): 998 - 1010
    Cited by:  Papers (12)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (140 KB)  

    This paper provides an introduction to the classic paper “Transoceanic Communication by Means of Satellites,” which was written by J.R. Pierce and R. Kompfner and appeared in the March 1959 issue of the Proceedings of the IRE. This paper also provides a periscopic view of satellite communications development since then. Surprisingly, in some aspect, the fundamental ideas have not changed much after 40 years. Conceptually, most technical development falls within these ideas. Practically, however, technological advances and significant progress has been made in all areas of space segment, ground segment, and launch vehicles. Today, due to its impact and usefulness, satellite communications is no longer the domain of the technologists alone. Instead, it has created industries, established relevant institutions, coordinated regulations and standards, provided employment, and financially benefitted many persons. This paper addresses these issues, which have been indirectly created by the scientists and engineers who developed satellite communications View full abstract»

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  • Three-site space-diversity experiment at 20 GHz using ACTS in the Eastern United States

    Publication Year: 1997 , Page(s): 970 - 980
    Cited by:  Papers (10)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (244 KB)  

    A three-site rain-fade space-diversity measurements experiment at 20 GHz has been in near continuous operation since September 1, 1994. Two receiver sites (at the Applied Phys. Laboratory [APL] of The Johns Hopkins University and COMSAT Laboratories) are located in Central Maryland, and the other is located in Virginia. The APL and COMSAT locations are separated by 33 km. The Virginia site is separated from APL by 44.5 km and from COMSAT by 30.5 km. Receivers at each of the sites measure the 20-GHz CW signal level from the radiating beacon onboard the geostationary Advanced Communications Technology Satellite (ACTS). Because of the lateral variability of rain, the likelihood is diminished that intense rain cells will simultaneously intersect all three Earth-satellite paths. There is also a reduced likelihood that intense rain will simultaneously intersect two Earth-satellite paths associated with different two-site scenarios. Hence, a substantially smaller rain-fade margin is required when the sites operate in a diversity mode (e.g., connected together such that the largest signal is used) vis-a-vis uncoupled single terminal operation. In this effort, we examine the efficacy of employing three-site and two-site space-diversity systems to reduce the required fade margin. Single- and joint-terminal rain-fade distributions are calculated for both the three-site and different combinations of two-site scenarios. Diversity gains, which give a measure of the reduced fade margin, are determined from these distributions. The distributions and diversity gains are also individually determined for two six-month periods of the year for which precipitation is predominantly convective or stratiform, respectively. Comparisons between measured diversity gains and those estimated using the model of the radiocommunications sector of the International Telecommunications Union are made View full abstract»

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