Page 165 - Integrated Wireless Propagation Models

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M a c r o c e I P r e d i c t i o n M o d e I - s P a r t 2 : P o i n - t o - P o i n t M o d e I s 143
Three antenna patterns are chosen to demonstrate the effects of mechanical down­
tilting of the antenna. The vertical beam main-lobe widths of those antennas are 8°, 30°,
and 60°. Their horizontal and vertical beam patterns are listed in Figs. 3.1.7.1.3.1,
3.1.7.1.3.2, and 3.1.7.1.3.3. According to our optimal condition, the first one has a 30°
beam width in the horizontal pattern, and its vertical beam is narrow, so we should
expect to see a useful notch. However, when either the horizontal beam width is too
narrow (see Fig. 3.1.7.1.3.2) or the vertical pattern is too wide (see Fig. 3.1.7.1.3.3), no
useful notch can be obtained. So it is impossible to generate a useful notch under these
conditions.
Our simulation result shows that all three cases can generate a notch by downtilt,
and the notch tilt angle is approximately at the joint angle of their first and second lobes
of the vertical pattern. The notch for the first antenna (in Fig. 3.1.7 1 . 3.1) is shown as a
.
useful one. The other two notches (see Figs. 3.1.7.1.3.2 and 3.1.7.1.3.3) may not be useful
because they are too weak and have a large side or back lobe, and that will interfere the
co-channel cells behind it.
As our simulator shows, not all patterns can generate useful downtilted patterns.
Antenna downtilt might actually create problems for some systems. As shown in
Fig. 3.1.7.1.3.2, although a notch is generated, it is not useful for improving system
performance. With this simulator, engineers can simulate the effect of downtilt in 3D
and decide whether mechanical downtilt is the right approach to improving the sys­
tem performance.

3 . 1 . 7.2 Smart Antenna and Lee's Microcell System
3.1.7.2.1 Smart Antenna A "smart antenna" is viewed as a means of significantly
improving spectral efficiency and achieving better quality of service and higher capac­
1
ities while also achieving considerable savings in base station costs. 8 The smart
)
antenna system uses a small number of antenna panels (usually three . Each of these
antenna panels has multiple beams generated by a passive electronic phasing matrix.
With the smart antenna, the number of cellular subscribers continues to stay within the
antenna coverage. The signals received on the narrow beams of the smart antenna are
dynamically connected to the base site radios via an electronic matrix switch. The sys­
tem capacity is increased in two ways. First, the use of high-gain narrow beams dra­
matically improves the C/I ratio, thus reducing frequency reuse factor K for the same
quality of service. A lower frequency reuse factor means more channels per cell, that is,
higher capacity. Second the smart antenna system maintains its channels in one trunk
pool. Therefore, it has a higher capacity compared with the sectorial cell, in which
three sectors do not share their resources.

3.1.7.2.2 Lee's Microcell System19 In Lee's patented microcell system, each microcell
consists of three zones (noted as zone A, zone B, and zone C), as shown in Fig. 3.1. 7.2.1. Each
zone has its own small base station just like an access point. This should be the first time
the access points were used in the cellular system. A zone switch connects the three zones
such that a signal channel can be switched from one zone to another. Thus, within the three
zones, a mobile will stay at one signal channel until it moves out from its microcell. Based
on the regular cells, the system is K = 7, but based on the zones, the system become K = 3,
as shown in Fig. 3.1.7.2.2. Since the signal channel is confined in one zone at a time, we
use K = 3 and find that the capacity increases by 2 to 2.5 over that of K = 7. The implement
of microcell system is very cost effective. The modification of existing cellular equipment