Chapter 3 Attenuation Due to Roadside !Ikees: Mobile ... - DESCANSO

Chapter 3 Attenuation Due to Roadside !Ikees: Mobile Case 3.1

Background

As of this writing,a limitednumberof LMSSrelatedpropagationinvestigationshavebeen executedat UHF and L-Band wherethe transmitterplatformswerelocated on satellites.A summaryof other investigationsis given in Chapter 7. LMSS propagation measurements with satellitetransmitterplatformswereconductedby the authorsin centralMarylandwith MARECS-B2, ~ogel and Goldhirsh,1990],and in Australiawith the JapaneseETS-V and INMARSAT-Pacificsatellites[Vogelet al., 1991; Hase et al., 1991]. Other types of transmitter platformsused for mobile measurementswere also employedto derive propagation informationfor LMSS configurations.Vogel and Hong [1988]reportedon stratosphericballoons carryingtransmittersat 870 MHz and 1502MHz wheremeasurementsweremade in westernTexasand NewMexico . Goldhirshand Vogel [1989;1987]and Vogel and Goldhirsh [1988]also describe helicopterexperimentsat both 870 MHz and 1.5 GHz in the central Marylandand north-centralColoradoregionsof the United States.

3

Time-Series Fade Measurements

3.2

16 .

Time-Series Fade Measurements

In the analysisof times-seriesroadsidefadesfor LMSSscenarios,the attenuationlevelswere representedby the dB ratio of the shadowedpower receivedrelative to the unshadowed levelsunder conditions of negligiblemultipath. Figures3.1 and 3.2 are examplesof measurementsdepicting nominal characteristicsof time-seriesof fades (a) and phases (b) for non-shadowedand shadowedline-of-sightcases,respectively.These measurementswereperformedby Vogelet al. [1991]in AustraliawhereL-Bandtransmissions(1.5 GHz) emanating fromthe JapaneseETS-V werereceivedat an elevationangleof 50°. For the casesindicated in Figures3.1 and 3.2, the vehiclespeedswereapproximately17.4 m/s and 11 m/s for the unshadowedand shadowedcases, respectively. The receivernoise had fluctuationswhich werewithin 1 dB (rms). The unshadowedenvironment(Figure3.1) may be characterizedas a “flatruralregion” and the shadowedcase (Figure3.2), a suburbanlocation havingroadside trees. Fluctuationsoutsidethe one dB noiselevelin Figure3.1 (a) are due to multipath. Nomvariations of less than 5 dB of power and 25° of phase were observed inally,pea.k-tc)-pd for non-shadowed cases. We note the shadowed case (Figure 3.2) has fades which are highly variable with fluctuations exceeding 15 dB. Some of these deep fades are also accompanied by rapid phase shifts. Time-series of fade and phase of the above types were obtained for various LMSS geometries and environments and corresponding cumulative distributions were derived as described in the following paragraphs.

3.3

Empirical Roadside ShadowingModel

CumulativeL-Band fade distributionssystematicallyderived from helicopter-mobileand satellite-mobilemeasurementsin centralMarylandenabledthe formulationof an Empirical Roadside Shadowing(ERS) model. The measurementswere obtained over approximately 600 km of driving distancecomprisingpath elevationanglesof 21°, 30°, 45°, and 60°. The 21° case was executed employingMARECS-B2 ~ogel and Goldhirsh, 1990], whereasthe measurements for the otherangleswereobtainedemployingthe helicopteras the transmitter platform. The configurationscorrespondto maximumshadowingconditions; namely,the

17

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