Bert H. Musiani

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

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.

Dimension statistics of rain cell cores and associated rain rate isopleths derived from radar measurements in the mid-Atlantic coast of the United States

Employing a multi-year radar database of precipitation in a mid-Atlantic coast region, the authors have characterized rain cell size statistics. The measurements were made with a high resolution, high power radar in which equicircle diameter contours of resolutions of 1 km and greater were identified out to ranges of 100 km from the radar. The rain cell was constructed by its core intensity isopleth and a family of enveloping contours having defined rain rate intervals in the regions between them. The isopleth statistics were extracted from a database of cores with rain level number 7 (18-24 mm/h) and greater. >

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

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/spl deg/ from one another, the geometric pointing parameters at the receiver locations are approximately coincident (e.g., 38/spl deg/ 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.

Three years of C band signal measurements for overwater, line‐of‐sight links in the mid‐Atlantic coast: 1. Fade statistics

Three years of fade statistics are described for two overwater, line-of-sight propagation linksalong the mid-Atlantic coast of the United States operating at 4.7 GHz. Single-terminal, joint fade, and fade duration statistics derived from time series of received signal losses due to refractive and diffractive effects are described for combined-year, annual, and monthly cases. In particular, year-to-year and month-to-month variabilities in the statistics and also the efficacy of employing space diversity for the two links to mitigate fade margin requirements are examined. Sustained deep fade (SDF) events due to severe subrefraction during the 3-year period tended to dominate the statistics. Statistics have been culled in terms of contiguous month groupings during which SDF events occurred (November–July) and did not occur (August–October) over the 3-year period. Although the year-to-year variability in the annual fade statistics was relatively small, the year-to-year variability in the monthly statistics was large, especially during the April–July period, which separated the periods during which deep subrefractive fades were maximum and the periods during which they were nonexistent.

Signal level statistics and case studies for an over‐the‐horizon mid‐Atlantic coastal link operating at C‐band

We examine the results of 1 year of near-continuous measurements for a 128-km over-the-horizon C-band coastal propagation link. The link extends between Dam Neck, Virginia (16 km south of Virginia Beach), and Wallops Island, Virginia (approximately 150 km southeast of Washington, D. C.). The objectives of this effort are to explore the different mechanisms of propagation through an analysis of several case studies and to assess the statistical connectivity over the 1-year period. Case studies involving the linking of environmental information and measured signal levels are analyzed. Propagation factor levels due to evaporation ducts, surface ducts, and scattering from irregularities of the refractive index in the common volume are determined. Cumulative distributions of the measured propagation factor for the annual, fall–winter, and spring–summer periods are presented. Conditional and absolute distributions of propagation factor time durations are also presented and analyzed. It is demonstrated that during the spring–summer period, received signal levels were consistent with ducting and not with troposcatter. The fall–winter levels may be due to troposcatter from irregularities of the refractive index. The months giving the smallest and largest propagation factors were January and June, respectively.

Rain Measurement Results Derved from a Two-Polarzation Frequency-Diversity S-band Radar at Wallops Island, Virginia

A dual-polarization radar located at the NASA Wallops Flight Facility, Wallops Island, Virginia is described. This radar operates with a slow polarization switch having a cycle time of 0.7 s and also incorporates a frequency diversity technique to achieve independent sampling over short intervals of time. Rain-rate measurements derived from the dual-polarization radar and low-and high-resolution rain gauges located at a remote site are compared. Average percent differences in rainfall of less than 5 and 16 percent were demonstrated when comparing the dual-polarization radar measurement with the low-and high-resolution rain gauges, respectively. Excellent correlation of the rain rates was in evidence during one rain day. All rain measurement cases examined were limited to only light rain rates (less than 7 mm/h).