39 Delay spread dependency with data collection threshold.
In fact, the results were taken for both the micro- and macrocellular environments operating in the
910 MHz frequency band.
The above characteristic is useful knowledge especially when comparing the measured data
presented herein. This will allow comparisons to be made on the same as well as fair playing
ground.
Let??™s continue with a discussion on the PDP using Fig. 3.40 to support our point. We have
shown earlier to RMS delay spread was not only dependent on the surrounding environment but
also on distance (L) from the BS. Let??™s consider Fig. 3.40 which consists of essentially three regions
that source the scattering signals: local scattering, large building scattering, and mountainous
scattering [91].
WIRELESS MULTIPATH CHANNEL 147
Base
Station
Mobile
Station
??†L ~ 100 m
??†t ~ 333 nsec
msec
msec t
??†L
??†t
FIGURE 3.40 General delay spread characterization for three scattering regions.
What is important to note here is that signals scattered from large building and mountains will be
rescattered by objects near the mobile resulting in a cascade of multipath arrivals at the MS antenna.
This clustering concept was earlier proposed by Saleh and Valenzuela in [92].
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