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Proceedings of the IEEE

Issue 6 • Date Jun 1993

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Displaying Results 1 - 10 of 10
  • Site diversity for satellite earth terminals and measurements at 28 GHz

    Page(s): 897 - 904
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (632 KB)  

    This work reviews site diversity concepts and models and presents the results of a site diversity experiment, in which radiometers were used to measure attenuation on Earth-space paths, performed at Columbus, Ohio, for a period of one year. Attenuation statistics are presented first in the form of the joint probability density function of attenuation at the two sites. From these are derived the cumulative two-dimensional distribution of attenuation at both sites, the cumulative distribution of attenuation at each site, the effective cumulative distribution of attenuation for a diversity system that always switches to the better of two signals, and the effective cumulative distribution of attenuation for a system with maximal-ratio signal combining. The switched-system diversity gain is compared with D.B. Hodge's (1982) predictive model, and the diversity improvement is compared with L. Boithias' (Radiowave Propagation, McGraw-Hill, 1987) model. Fade-duration and interfade-interval statistics are presented for each site and for systems that use switching and maximal-ratio combining. Rain-rate and interrainfall interval statistics are included View full abstract»

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  • Least-square identification with error bounds for real-time signal processing and control

    Page(s): 815 - 849
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3196 KB)  

    Set-membership (SM) identification, which refers to a class of algorithms using certain a priori knowledge about a parametric model to constrain the solutions to certain sets, is considered. The focus is on a class of SM-based techniques that are of particular interest in applications requiring real-time processing. The optimal bounding ellipsoid (OBE) algorithms are interpreted as a blending of the classical least-square error minimization approach with knowledge of bounds on model errors arising from SM considerations. Using this interpretation, a general framework embracing all currently used OBE algorithms is developed, and strategies for adaptation and for implementation on parallel machines are discussed. Computational complexity benefits are considered for the various algorithms. The treatment is tutorial, leaving many of the formal details to an appendix that presents an archival theoretical treatment of the key results. A second appendix gives an overview of current research in the general SM identification field View full abstract»

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  • Interference due to hydrometeor scatter on satellite communication links

    Page(s): 914 - 922
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    A brief review of hydrometeor scatter interference is given, focusing on recent improvements to International Radio Consultative committee (CCIR) texts on interference between terrestrial and earth stations, and research to effect possible future improvements. The following improvements are suggested: smaller reflectivity factor slope above the `rain height' coupled with a revised empirical constant in the transmission loss equations; inclusion of melting layer scatter; improved rain height model; improved horizontal structure model for precipitation cells; consideration of correlation between the wanted and unwanted signals; and consideration of a range of terrestrial elevation angles in coordination View full abstract»

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  • Propagation considerations for emerging satellite communications applications

    Page(s): 923 - 929
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    The effects of rain and other propagation concerns for new applications areas, currently in operation or planned for implementation by the end of this decade, are described. The areas include: VSAT systems employing low operating margins and/or low elevation angles; traditional communications applications operating with inclined geosynchronous orbits; and mobile and personal communications applications employing networks of low earth orbit (LEO) satellites. Prediction modeling and analysis techniques applicable to these areas are described. Analytical results for a range of operational parameters involving low-margin, low elevation angle, inclined geosynchronous, and LEO systems are presented View full abstract»

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  • Estimating risk for Earth-satellite attenuation prediction

    Page(s): 905 - 913
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    Annual cumulative distributions of attenuation measurements and of rain-rate measurements were obtained from several locations in Europe and the United States. They were analyzed to estimate the year-to-year variability to be associated with a prediction of the expected cumulative distribution. Two models were constructed to estimate variability, an ad hoc model that summarized a number of observations when compared to model predictions and a probabilistic model that applied the ideas of order statistics to the prediction problem when the number of independent attenuation or rain-rate events in a sample year could be estimated. Based on these models, the statistical uncertainty in a model prediction may be estimated. The estimation procedure also provides an answer to the question of the number of years of observation needed to provide an estimate of the empirical distribution with a specified statistical uncertainty View full abstract»

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  • INTELSAT propagation experiments: the focus and results of recent campaigns

    Page(s): 856 - 864
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    The work presented here aims at a detailed understanding of propagation impairments likely to be encountered on a given path, which is one of the factors needed in transmission link design to provide satellite service at the quality customers demand. The author discusses the background to INTELSAT's need for propagation information, describes the focus of recent INTELSAT Ku- and Ka-band measurements, and provides some of the results and conclusions of these measurements View full abstract»

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  • Results from 12- to 30-GHz German propagation experiments carried out with radiometers and the OLYMPUS satellite

    Page(s): 876 - 884
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    The rationale for Ka-band propagation studies is discussed, and the relevant measurement program carried out in Germany by the Research Centre of the Deutsche Bundespost Telekom is reviewed. Current problems are briefly presented. Radiometer measurements from a 30 GHz site diversity experiment are discussed. The results indicate that availabilities of 99.9% can be achieved with diversity spacings of about 15 km. If, however, much lower values of around 97-99% are acceptable, margins of 3 dB are sufficient in single-site operation with gaseous and cloud absorption being of similar statistical importance as rain. Measurements carried out with the OLYMPUS satellite at 12.5, 20, and 30 GHz are also discussed. A comparison with the predictions based on the current CCIR procedures shows that rain attenuation is overestimated for time percentages above 0.01%, whereas depolarization is underestimated significantly. Instantaneous frequency scaling of attenuation and scintillations is discussed, and an improved scaling procedure for the latter is presented View full abstract»

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  • Propagation research in Europe using the OLYMPUS satellite

    Page(s): 865 - 875
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    The launch of the European Space Agency's (ESA) large telecommunications satellite OLYMPUS in the summer of 1989 offered a unique opportunity to study the effects of the atmosphere on satellite communication links at Ku-band (14/12 GHz) and Ka-band (30/20 GHz). The community of OLYMPUS Propagation Experimenters (OPEX) operates experiments at more than 50 locations covering all of Western Europe with its different climatic regions. The authors introduce the European propagation research scenario, summarize the major features of the current OLYMPUS campaign, discuss the significance of the first results obtained, and give an outlook for new activities View full abstract»

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  • Image-enhanced estimation methods

    Page(s): 797 - 814
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    The performance of an image-enhanced estimator is contrasted with that of the extended Kalman filter (EKF). A scenario in which a planar agile target moves with intermittent maneuvers is studied. The performance comparison clearly indicates that image enhanced estimation methods are worthy of consideration in applications involving agile targets. A dual-path estimation architecture in which one path infers the likelihood of maneuver from image data is considered. These maneuver likelihoods are used to adapt the filter gains to changing conditions. Although the image-based estimator employs what appears to be an orthodox algorithm, it is less susceptible to delays in detecting a maneuver. In this architecture, the image path uses observations of target shape to change the time constants in the range-bearing path. In effect, one path modulates the other, and the tracking system is able to locate the target and discern changes in its motion pattern, so that it follows target motion more accurately. The results illustrate both the potential and the limitation of image augmentation View full abstract»

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  • Rain fades on low elevation angle Earth-satellite paths: comparative assessment of the Austin, Texas, 11.2 GHz experiment

    Page(s): 885 - 896
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1056 KB)  

    Only a few years of rain attenuation data for Earth-space paths are available for low elevation angle paths, and these show a consistent tendency by the CCIR fade prediction model to underpredict rain fades. The authors contribute to the database four years of 11.2 GHz measurements, taken on a 5.8° elevation path in Austin, Texas, USA and assess higher than predicted fade results with respect to earlier measurements and the CCIR model. At the fiducial 0.01 percent of time, the rain fall rate was 73 mm/h and the attenuation exceeded the 25 dB measurement fade margin. It is found that the monthly variability of rain fall rates and decibel fades follows a normal distribution. Durations of rainfall and fades are classified into events, episodes, interevent gaps (longer than 4.2 h), and interepisode gaps (shorter than 4.2 h). Rainfall interevent gaps and event durations, as well as fade event, episode, and gap durations are log-normally distributed View full abstract»

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