05
Free space 2
Dhaka, India 2.98
Bangkok 3.6
where x 10*log(X) measured in units of dB, xm area average measured in dB, X the received
signal level, standard deviation measured in dB.
The typical values of the standard deviation ( ) of the log-normal shadowing is in the range of
5??“12 dB.
This log-normal fading has been suggested to be a result of a cascade of events along the propagation
path. Each event multiplies the signal by a randomly varying amount. Now when expressed in
dBs, the product of random events becomes the sum of random variables, which approaches a
Gaussian distribution [6].
Suburban environments would have a larger dues to the large variations in the environment,
where as urban would have a lower , but recall the path loss would be higher for this urban
environment.
We can address the question of how does the log-normal fading vary with carrier frequency.
A relationship was fitted to Okumura??™s data and is given as follows for the macrocell case [128].
(3.83)
with
It is worth mentioning that the log-normal standard deviation difference between 900 MHz and
1.9 GHz has been shown to be approximately 1 dB. Figure 3.50 plots the above equation.
A e5.2 urban
6.6 suburban
s 0.
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