Page 41 - Integrated Wireless Propagation Models

I n r o d u c t i o n t o M o d e I i n g M o b i I e S i g n a I s i n W i r e I e s s C o m m u n i c a t i o n s 19
t

100
90
80
Q)
Ol 70
C1l
c
Q)
� 60
Q)
Cl.
c
0 50 � O mni
.TI
� 3_Sector
-ffi 40
-� .....-6_Sector
"'
B 30
20
10
0
3K 4K 7K 12K
FIGURE 1.7.3.1 The satisfaction percentage of coverage (for C/1 = 18 dB) versus K, forward i n k
l
without power control.
we need only K = 4 for providing a coverage of 100 percent satisfaction. If we lower
the C/I requirement, say, a coverage of 94 percent satisfaction, then we can even have
K = 3. This tells us that for a reasonable satisfaction of coverage, we can have K = 3
(or even lower) for using a sectorized cell.
For considering a reverse link, we studied the cases with and without power con­
trol. The use of power control essentially improves the C/ I ratio at the cell boundary of
the center cell, where the C/ I ratio is the worst. So we can see a significant improvement
of the C/I in the cell. Also, because of the power control, the C/I ratio is the same at the
base regardless of where the mobile is in the cell. This is the reason that we indicate only
0 percent or 100 percent coverage, as shown in Fig. . 7.3.2. In order to have 100 percent
1
coverage, the omni-cell system needs K = 4 and others need only K = 3, as depicted in
Fig. . 7.3.2.
1
Figure 1.7.3.3 is the satisfaction percentage of coverage versus K due to the reverse
1
link transmission without power control. Comparing Fig. 1.7.3.2 with Fig. . 7 .3.3, one
can find that for an omni-cell system, the coverage satisfaction percentage of 68 percent
1
in Fig. . 2.3.3 becomes of 100 percent in a three-sector cell system in Fig. . 7 .3.2 for
1
K = 4 and C/I = 18 dB.
Another interesting thing we found is that the coverage satisfaction percentage is
basically the same for both the forward and the reverse link without power control
1
1
(comparing Figs. . 7.3.1 and . 7 .3.3). Thus, the analysis used for the forward link should
be applied for the reverse link.
The co-channel interference is unchanged at a mobile in a cell on a reverse link.
However, for calculating the forward link, the co-channel interference varies, depend­
ing on the location of the mobile in the cell. We take the location with the worst interfer-
ence in calculating i2 and shown in Fig. 1 . 7 .3.4.
I