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9-2 Propagation Effects for Vehicular and Personal Mobile Satellite Systems ranged from 15° to 0°. Measurements were performed over a period 40 hours during which the ship was en route from Norfolk, VA to Texas City, Texas. Time-division multiplexing (TDM) carriers for Teletype and voice carriers for telephone and data transmissions were monitored and analyzed. These signals were monitored at the shore station, Southbury, Connecticut, and the ship terminal. The frequencies for these signals were within 1.537 and 1.541 GHz. At satellite elevation angles below 2°, the mean carrier reduction and peak-to-peak fluctuations were noted to be severe. For example, down to two degrees, the peak-to-peak fluctuations of the carrier to noise ratio were smaller than 4 dB. These fluctuations followed the two-component multipath model from a calm sea relatively well after a 1-dB bias was added for gaseous fading. Below 2° elevation, the peak-to-peak fluctuations increased to levels as high as 10 dB and deviated considerably from the two-component multipath model. Cumulative signal distributions relative to the mean values demonstrated that peak-to-peak fluctuations exceeded 10 dB with a probability of 42% in the angular interval of 0.5-2°. The spectrum properties of a 10-minute sample at 2° elevation indicated the presence of turbulent-type scattering in the troposphere or ionosphere. Measurements showed that in passing from 10° to 5° elevation angle, a mean carrier to noise ratio drop of less than 2 dB was observed. The maximum fade level at 5° caused by signal fluctuations was less than 6.5 dB 99% of the time. On the other hand, at an elevation angle of 10°, the fading was less than 4.4 dB for 99% of the time. 9.2.2 Evolution of a Simplified Multipath Fading Prediction Model A number of investigators have analyzed the characteristics of multipath fading due to sea surface reflections. Karasawa and Shiokawa [1984a] applied the Kirchhoff approximation theory and developed a model for the coherent and incoherent scattered power as a function of sea surface conditions for L-Band. Using their developed model, fade depths were determined as a function of elevation angle, wave height and antenna gain. They showed that at an elevation angle of 5°, the fade depth under rough sea conditions was dependent on small antenna gains and had little dependence on wave height. For example, at 5° elevation and 99% of the time, the fade depth varied between 4.5 to 6.5 dB for an antenna gain of 20 dBi; (BW ≈ 17°, BW is the half power beamwidth). The fade depth varied between 7 to 9 dB for an antenna gain of 15 dBi (BW ≈ 30°) and 8 dB to 10.5 dB for an antenna gain of 10 dBi (BW ≈ 53°). These results assume wave heights smaller than 4 m. In a later paper, Karasawa and Shiokawa [1986] reported on a series of measurements using shore-to-shore, satellite-to-shore and satelliteto-ship paths and antennas with gains from 13 dBi (BW = 37°) to 21 dBi (BW = 15°). Based on these and other measurements and previously developed concepts, simplified prediction models were developed by them [Karasawa and Shiokawa; 1988, 1987] and adopted by the ITU-R [1994, pp. 352-354]. These simplified models are described in Section 9.3.
Maritime-Mobile Satellite Propagation Effects 9-3 9.3 Characteristics of Multipath Fading Due to Sea Surface Reflection 9.3.1 Fundamental Concepts We use here the developments of Karasawa and Shiokawa [1988] in describing fundamentals of fading due to sea surface reflections. Their model adopted concepts described by Sandrin and Fang [1986] who proposed a method for determining the fading depth using a multipath power diagram as a function of antenna gain, elevation angle and Nakagami-Rice statistics [ITU-R-1994, pp. 59-61]. Although the model of Karasawa and Shiokawa was confirmed for circular polarization, it is believed also applicable for horizontal and vertical polarizations with appropriate caveats. Multipath reflections from the sea are comprised of “specular” and ”diffuse” contributions, also referred to as “coherent” and “incoherent” components, respectively. For calm seas, the specular component dominates but decreases rapidly for increasingly rough seas. The total power received is obtained by combining the power contributions of coherently scattered and incoherently scattered waves, and the direct wave component. Under calm sea conditions, the forward-scattered wave is composed entirely of the coherent component that can be estimated by v ∗ 2 PCO = EiRDr , (9-1) where r E i is the incident wave vector and where i denotes either the horizontal or vertical components (H,V) and * denotes the complex conjugate. That is, v E = ( E , E ) . (9-2) i iH iV Also, R is the Fresnel reflection coefficient matrix of the sea given by ⎛ RHH RHV ⎞ R = ⎜ ⎟ , (9-3) ⎝ RVH RVV ⎠ where for the calm sea case, RHV = RVH = 0. DR is the directivity of the antenna in the direction of the specular reflection point and given by D R D = D ⎛ ⎜ ⎝ H V ⎞ ⎟ . (9-4) ⎠ The intensity of the coherent and incoherent components depends on the roughness of the sea expressed by the roughness parameter u given by 4π u = ho sin( θo ) , (9-5) λ where λ is the wavelength in m, θ o is the elevation angle to the satellite, h0 is the RMS wave height in m related to the significant wave height H by
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A2A-98-U-0-021 (APL) EERL-98-12A (E
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Table of Contents 1 Introduction __
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10 Optical Methods for Assessing Fa
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Table of Contents 1 Introduction __
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1-2 Propagation Effects for Vehicul
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Table of Contents 2 Attenuation Due
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Chapter 2 Attenuation Due to Trees:
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Attenuation Due to Trees: Static Ca
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Table of Contents 3 Attenuation Due
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Figure 3-23: Fade distributions at
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3-4 Relative Signal Level (dB) 5 0
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3-10 Percent of Distance the Fade >
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3-12 Propagation Effects for Vehicu
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3-14 3.4.3 Austin, Texas at K-Band
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3-20 Relative Signal Level (dB) 5 0
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3-24 Percentage of Distance Fade >
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3-26 and where 1 2 Propagation Effe
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3-28 Percentage of the Time Fade >
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3-32 3.7.5 Comparative Summary of M
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Chapter 4 Signal Degradation for Li
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Table of Tables Table 4-1: Summary
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4-4 Percentage of Distance Fade > A
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4-14 Percentage of Distance or Time
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Table of Contents 5 Fade and Non-Fa
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Chapter 5 Fade and Non-Fade Duratio
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Fade and Non-Fade Durations and Pha
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Table of Contents 6 Polarization, A
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Chapter 6 Polarization, Antenna Gai
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Polarization, Antenna Gain and Dive
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Table of Contents 7 Investigations
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was derived from measurements over
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7-6 7.3 Belgium (PROSAT Experiment)
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7-10 Probability Fade > Abscissa (%
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7-14 Percentage of Time Fade > Absc
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7-24 Probability (%) > Abscissa 100
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Table of Contents 11 Theoretical Mo
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Chapter 11 Theoretical Modeling Con
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Theoretical Modeling Considerations
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Table of Contents 12 Summary of Rec
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Table 12-7: Tabulation of azimuth a
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12-14 Standard Deviation (dB) 4 3 2
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12-18 Fade Depth (dB) 7.0 6.5 6.0 5
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Index 13-1 Index 2 2-state Markov m
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Index 13-3 Jongejans, A. et al., 3-
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