Page 275 - Integrated Wireless Propagation Models

M i c r o c e l l P r e d i c t i o n M o d e l s 253

0.7({ - 1 ) for medium-size cities and suburban centers with medium tree density
9 5

1.5({ - 1 ) for metropolitan centers
9 5
(4.5.5.3.1.12)

For the calculation of L sd for l < d,,
m
(4.5.5.3.1.13)

[ �; Jf] o.9
b
2.35 for hb > h,
QM = b for hb h , (4.5.5.3.1.14)
""
d
b #[1 1
2nd p 8 - 2n+8 J for hb < h,

8 a rctan[ �] (4.5.5.3.1.15)
b
=
2
p = ��h� + b (4.5.5.3.1.16)
We have described the model for the typical NLOS case 1 in this section. The follow­
ing section will introduce different approaches.

4.5.5.3.2 Different Approaches for Rooftop Diffraction Calculations For calculating the
multiple diffraction loss over building rooftops, diffraction can occur around the
sides of individual buildings. The diffraction angle over most rooftops is usually less
than 1 o for typical base station heights and distances, and the diffraction is largely
unaffected by the particular shape of the obstacles. It is appropriate to treat the build­
ings by equivalent knife edges. The calculation of multiple diffraction loss will be
separated into two parts. The first part considers the multiple diffractions across the
first (n - 1) buildings, treated as knife edges. The second part treats a final building
(see Fig. 4.5.5.3.2.1) either as a knife edge or as some more complex shape for which
the diffraction coefficient is known.
For dealing with small diffraction angle much less than ° , special methods have
1
been developed to enable reasonably rapid calculation of the multiple diffraction inte­
gral for cases where accurate results are required and where the necessary data on the
building positions and heights is available.46

4.5.5.3.3 Propagation along Street Canyons Figure 4.5.5.3.3.1 depicts the situation of a
BS to MS link in a typical microcellular NLOS case. This case is called NLOS2.
2
3