Page 84 - Integrated Wireless Propagation Models

62 C h a p t e r T w o

provide earth terrain information. TIREM takes into account (1) the transmitting
medium (surface refractivity and humidity), (2) antenna properties (height, frequency,
and polarization), and (3) geometrical environment (relative permittivity, conductivity,
)
and terrain elevations . The calculation of path loss also includes the effects of reflec­
tion, surface wave propagation, diffraction, tropospheric scatter propagation, and
atmospheric absorption but not ducting phenomena, fading, ionosphere propagation,
and absorption due to rain or foliage.
TIREM computes radio frequency propagation loss over irregular terrain and sea­
water for ground-based and airborne transmitters and receivers. TIREM is capable of
predicting the signal coverage for land mobile radios, sensor acquisition ranges, and
television and radio broadcast stations.
.
Figure 2.7 1 . 1 depicts a radio path over a curved earth involving both rough earth
terrain and seawater. TIREM examines the terrain type (including seawater) and eleva­
tion profile and selects the optimum model(s) for calculating propagation loss along the
path. Based on the geometry of the profile, all appropriate modes of TIREM are used to
calculate the path loss either within line of sight (LOS) or beyond line of sight (BLOS).
Figure 2.7.1.2 illustrates both LOS and BLOS zones in a propagation path.
Under the NLOS condition, TIREM's modeling of multiple-knife-edge diffraction is
illustrated in Fig. 2.7.1.2. Figure 2.7.1.3 shows a larger image of the multiple-knife-edge
diffraction illustration. The calculation of diffraction loss was shown in Sec. . 9.2.
1

2 . 7 . 2 Summary of Land Propagation Formulas
The path loss predicted by TIREM depends on whether the path is LOS, BLOS, or tro­
poscatter. The total terrain-dependent propagation loss for LOS and BLOS path is

LOS (2.7.2.1)
BLOS

F
where Aws is the excess loss for line of sight as determined by the frequency, A01 is
the excess loss for the diffracting region, and A 850R8 is the molecular absorption loss.

Land/sea path

FIGURE 2.7.1.1 TIREM propagation paths.