Wireless Network Design: Optimization Models and Solution ...

50 K. V. S. Hari
fading is calculated based on the number of rays and the distance the rays travel.
In addition, the angles of arrival (AOA), and Doppler spread are characterized
using the information about array geometry. The channel is then numerically
simulated and compared with measurements obtained through experiments to
validate the models.
3.4.1 Experiments to Characterize Wireless Channels
Wireless channels are characterized by conducting experiments [5, 6, 8, 9, 11, 14,
15, 17, 26, 27, 29, 35, 38, 39, 40, 47, 49] where real transmitters and receivers are
used to measure the received signal characteristics. Outdoor and Indoor measurements
are carried out for different terrain conditions, different weather conditions
etc, to collect data for modeling.
3.4.1.1 Path Loss Models
Path loss is defined as the difference in power levels (in dB) of the received signal
and the transmitted signal due to the overall effect of ‘path’ or distance between
the transmitter and receiver. The path loss for a line-of-sight (LOS) scenario where
free-space path loss is assumed, is given by
PL(dB) = 32.44 + 20log 10 ( fc) + 20log 10 (d) (3.1)
where d is the distance between the transmitter and receiver in km, fc is the frequency
of operation in MHz. It may be observed that the path loss increases with
frequency and distance. Some terrain locations provide additional path loss due to
large structures (hills, buildings etc) which is called the shadow fading loss.
In the case of a multi-path fading environment and shadowing, several experiments
were carried out by Okumura [51] and the data was later analyzed by Hata
[19] to develop path loss models characterizing the statistical nature of the channel.
The mean path loss is usually obtained using curve fitting techniques. In the
logarithmic domain, these models tend to be linear as a function of distance. As an
example, some of the models for different terrains proposed by Hata are given below
(Note: All path loss models need to be used with caution. If the equation yields a
loss less than the free-space path loss, one must use the free-space path loss value.)
Typical Urban
PL(dB) = 69.55 + 26.16log 10 fc
= (44.9 − 6.55log 10 hb)log10d − 13.82log 10 hb − a(hm)
(3.2)
where fc is the carrier frequency in MHz, d is the distance in km, hb is the height
of the base-station in meters, and a(hm) is a correction term for the receiver antenna
height (hm) given by