Page 210 - Integrated Wireless Propagation Models

188 C h a p t e r F o u r

as many major cities reside on top of varying terrains. For example, in Los Angles,
San Francisco, Tokyo, and Seoul, the terrain undulation over a few feet has a great
impact on the accuracy of the model. The Lee model was also enhanced to deal with
attributes, such as water and foliage. The water in Amsterdam and the trees in Atlanta
have a profound impact on the accuracy of the model.
Later, the Lee microcell prediction model will be used to determine the path loss
statistical properties of the cell site based on multiple breakpoints. This microcell path
loss prediction model predicts the signal strength based on both theory and experiments,
that is, multiple-break-point formulas, cell site parameters, and measured data. As the
prediction model will be shown later, the results of this model are very promising.
The Lee model provides a baseline for integrating the microcell to the macrocell so
that coverage, interference, and handoffs among microcells and macrocells can be prop­
erly simulated and integrated. This model has been validated with the measured data
from drive tests performed in various countries and cities, with different transmitter
heights, unique frequencies, and separate cell site parameters as well as different kinds
of mobile environments. The initial findings are that this empirically and theoretically
based microcell model performs well in all areas under various conditions. Further­
more, this model can be reinforced based on the collected measured data.
Many other microcell prediction models, including their empirical, theoretical, and
physical approaches and site specifics, are discussed as well. Note that the FDTD model
and the TLM model for the microcell and the picocell will be discussed in Chaps. 5 and 6.

l
4.2 The Basic Lee M i croce l Predi c tion Model
2
4. . 1 Basic Principle and Algorithm
4.2. 1 . 1 Near-In Distance in the Microcell Prediction Model
Near-in distance has been derived from the simple plane earth model, which has been
described in Sec. . 9.1.3. Actually, it is a two-ray model, and the Lee model has been
1
derived from this fundamental model. Because in the microcell region, the distance
between the base station and the mobile is much longer than the antenna height of each
of them, the incident angle between the reflected wave and the ground is very small. In
this model, the signal s received at the mobile as shown in Fig. 4.2 1 . 1 . 1 :
.
-
s = �( � ) exp(j<j>1 ) [ 1 + a exp(-j(<j>1 <j> ))]
2
4 / t- · v
1
= �( ) . exp(j<j>1 ) [1 + a v e - iM ] (4.2. . 1 . 1 )
4rc� / t-
2
I
.
i
The received power P , a t the mobile s I s 1 • t was expressed in Eq. (1.9 1 . 3.1) as
1 2 2
( ) 1 1 + a e
j
P, - P o rtd v - l>$ I
-
4 /A.
where a = -1 for small incident angle.
v
The phase difference between two wave paths is shown in Eq. (1.9.1.3.6) as
�<1> � �d "" 2rc 2h1h 2
= A. d