RADIO PROPAGATION IN THE MOBILE ENVIRONMENT
buildings on either side, verdure such as trees and inside buildings, to name a few typical
situations. There are two notable results. Transmission loss increases notably and such an
environment is rich with multipath scenarios. Paths can be highly dispersive, as much as
µsec of delay spread (Ref. 2). If a user is in motion, Doppler shift can be expected.
The radio-frequency bands of interest are UHF, especially around 800 and 900 MHz,
and 17002000 MHz. In certain parts of the world, there is usage in the 400-MHz band.
We concentrate on cellular operation. There is a fixed station (FS) and mobile stations
(MSs) moving through the cell. A cell is the area of responsibility of the fixed station, a
cell site. It usually is pictured as a hexagon in shape, although its propagation profile is
more like a circle with the fixed station in its center. Cell radii vary from 1 km (0.6 mi)
in heavily built-up urban areas to 30 km (19 mi) or somewhat more in rural areas.
Path Loss or Transmission Loss
. We recall the free-space loss (FSL)
formula in Section 9.2.3. It simply stated that FSL was a function of the square of the
distance and the square of the frequency plus a constant. It is a very useful formula if the
strict rules of obstacle clearance are obeyed. Unfortunately, in the cellular situation, it is
impossible to obey these rules. Then to what extent must this free-space loss formula be
modified by the proximity of the earth and by the effects of trees, buildings, and hills in,
or close to, the transmission path?
There have been a number of models that have been developed that are used as a basis
for the calculation of transmission loss, several assumptions are made:
That we will always use the same frequency band, often 800 or 900 MHz. Thus it
is common to drop the frequency term (the 20 log
F term) in the FSL formula and
include a constant that covers the frequency term. If we wish to use the model for
another band, say 1800 MHz, a scaling factor is added.
That we will add a term to compensate for the usual great variance between the cell
site antenna height when compared to the mobile (or hand-held) antenna height. We
often call this the height-gain function, and it tends to give us an advantage. It is
often expressed as
), where h
is the height of the transmit antenna
(cell site) and
is the height of the receive antenna (on the mobile platform). These
are comparative heights. Commonly, the mobile platform antenna height is taken as
6 ft or 3 m.
That there is a catch-all term for the remainder of the losses, which in some references
is expressed as
That at least three models express the free-space loss as just 40 log
The Okumura Model
. Okumura et al. (Ref. 3) carried out a detailed anal-
ysis for path predictions around Tokyo for mobile terminals. Hata (Ref. 4) published an
empirical formula based on Okumura's results to predict path loss. The Okumura/Hata
model is probably one of the most widely applied path loss models in the world for
cellular application. The formula and its application follow.
= 69.55 + 26.16 log f - 13.82 log h
+ (44.9 - 6.55 log h
) log d,