Handbook of Propagation Effects for Vehicular and ... - Courses

12-6
Propagation Effects for Vehicular and Personal Mobile Satellite Systems
measurements were obtained using a tracking helix antenna with beamwidths in the
principal planes of approximately 36°. (3) Low and high elevation angle measurements
at 20 GHz were made using a tracking horn antenna with a beamwidth of 27°.
12.4.2 Suggestions for Future Work
The multipath formulation (12-12) was validated at frequencies of 870 MHz, 1.5 GHz
and 20 GHz for three specific antenna types. It is suggested this formulation be further
validated at intermediate frequencies and with other antennas having wider beamwidths.
12.5 Fade and Non-Fade Durations and Phase Spreads (Chapter 5)
Fade and non-fade duration models are given for tree-lined roads at L-Band. These were
derived from measurements made in Central Maryland and Southeastern Australia and
are presently ITU-R Recommendations. Also given are cumulative distributions of phase
spreads for roadside tree scenarios exhibiting moderate and extreme shadowing.
12.5.1 Fade Duration Model for L-Band
The conditional cumulative distribution of fade duration for tree-lined roads exhibiting
moderate to extreme shadowing (presently an ITU-R Recommendation) was found to
follow the following lognormal distribution given by
For dd ≥ 0. 02 m
1 ⎧ ⎡(ln
dd − ln ⎤⎫
P( FD > dd| A > Aq ) = ⎨ − erf ⎢
⎥⎬
2 ⎩ ⎣
⎦⎭
1
α
, (12-13)
2σ
where P( FD > dd| A > Aq ) represents the probability that the fade duration FD exceeds
the duration distance dd under the condition that the attenuation A exceeds Aq . Also,
erf is the error function, σ is the standard deviation of ln dd , and lnα represents the
mean value of ln dd . The left-hand expression of (12-13) was estimated by computing
the percentage number of “duration events” which exceed dd relative to the total number
of events for which A > Aq . An event of duration distance dd occurs whenever the fade
crosses a threshold level Aq and persists “above that level” for the driving distance dd .
For the case in which the threshold Aq = 5 dB ,
α = 0. 22 m, σ = 1215 . m . (12-14)
The RMS deviations of actual measured fade duration distributions, when compared to
the above model, was smaller or equal to 18%. The formulation (12-13) was derived
from Australian measurements (elevation angle of 51°) and validated in central
Maryland, USA, at elevation angles of 30°, 45°, and 60°.