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6-16 6.7 Conclusions and Recommendations Propagation Effects for Vehicular and Personal Mobile Satellite Systems The following salient conclusions and recommendations are based on the results of this chapter. 1. Simultaneous employment of co- and cross-polarized transmissions in a “frequency re-use” system should not be used except to potentially help isolate different CDMA systems because of the potential for poor isolation caused by multipath scattering into the cross-polarized channel (Figure 6-1). 2. Where ground multipath effects do not arise, small equi-probability fade differences of 1 to 2 dB may occur (at L-Band) for mobile antennas having different antenna gains (Figure 6-2). At low elevation angles where ground multipath effects may arise, higher gain antenna has been found to substantially reduce fading by as much as 10 dB at 20 GHz. 3. Changing lanes may substantially reduce the equi-probability fading because of the shortening of the path length through roadside tree canopies (Figure 6-3). At a 10 dB fade at UHF and L-Band, lane changing has been found to reduce the equi-probability fade for 60° elevation by approximately 5 dB (Figure 6-4 and Figure 6-5). Equation (6-4) gives a model describing the reduced fading at equi-probability levels, where the coefficients are summarized in Table 6-2 and Table 6-3. 4. For a 5 m separation between antennas and single antenna fades of 3 dB and 6 dB, diversity gains at L-Band (based on simulations using measurements made in Australia) are approximately 1.5 dB and 3.5 dB (Figure 6-8). These results are within 0.5 dB of those derived from measurements made in Japan (Table 6-4). 5. Satellite diversity measurements at L-Band for urban areas gave rise to diversity gains as high as 14 dB for percentages as low as 1% (Figure 6-10). Nevertheless, even applying diversity gain methods, fade margin levels have been found to exceed 17 to 20 dB at the 1% probability (Figure 6-9 and Figure 6-11). Such high fade margins for urban areas may preclude direct earth-satellite voice communications that require near instantaneous two-way responses. 6.8 References Akturan, R. and W. J. Vogel [1997], “Path Diversity for LEO Satellite-PCS in the Urban Environment,” IEEE Transactions on Antennas and Propagation,” Vol. 45, No. 7, July, pp. 1107-1116. Goldhirsh, J. and W. J. Vogel [1987], “Roadside Tree Attenuation Measurements at UHF for Land-Mobile Satellite Systems,” IEEE Transactions on Antennas and Propagation, Vol. 35, No. 5, May, pp. 589-596. Goldhirsh, J. and W. J. Vogel [1989], “Mobile Satellite System Fade Statistics for Shadowing and Multipath from Roadside Trees at UHF and L-Band,” IEEE Trans. Antennas Propagation, Vol. AP-37, No. 4, April, pp. 489-498. Hodge, D. B. [1978], “Path Diversity for Earth-Space Communication Links,” Radio Science, Vol. 13, No. 3, pp. 481-487.
Polarization, Antenna Gain and Diversity Considerations 6-17 Mayer, C. E. [1996], “Multipathing Effects on a Low Elevation Angle Mobile Experiment at KA-Band,” USNC/URSI Radio Science Meeting, July 21-26, p. 232. Ryuko, H. and T. Saruwatari [1991], “Propagation Characteristics for Land Mobile Satellite Systems in 1.5 GHz Band,” Journal of the Communications Research Laboratory, Vol. 38, No. 2, July, pp. 295-302. Schindall, J. [1995], “Concept and Implementation of the Globalstar Mobile Satellite System,” Proceedings of the Fourth International Mobile Satellite Conference, Ottawa, Canada, June 6-8, pp. A-11 to A-22. Vogel, W. J. [1997], “Satellite Diversity for Personal Satellite Communications - Modeling and Measurements,” Proceedings of the Tenth International Conference on Antennas and Propagation,” Publication #436, Edinburgh, UK, 14-17 April, pp. 269-272. Vogel, W.J., J. Goldhirsh, and Y. Hase [1992], “Land-Mobile-Satellite Fade Measurements in Australia,” AIAA Journal of Spacecraft and Rockets, Vol. 29, No. 1, Jan-Feb, pp. 123-128.
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Table of Contents 1 Introduction __
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10 Optical Methods for Assessing Fa
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1-2 Propagation Effects for Vehicul
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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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3-24 Percentage of Distance Fade >
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Earth-Satellite Propagation Effects
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9-6 Roughness Parameter, u (Rad) 28
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9-8 Cθ = ( θo − 7) / 2 dB for
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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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