Lenovo I360 Maintenance Manual page 7

I360 Mobile Phone Maintenance Manual
D. Security and privacy -- While analog calls can be easily intercepted by portable
wireless receivers, GSM calls are encrypted and transmitted digitally, which are of high
security.
E. High quality voice – Problems such as channel interference, switching interrupts
and attenuation are properly handled in the digital system, and error code correction
(reorganizing missed data) also helps to improve voice quality.
F. Efficiency -- The GSM system can utilize the frequency band more efficiently than
traditional analog systems.
As shown in Figure 2 given below, the area bounded by the bold line represents the
total area to be covered by the imagined system. The whole area is divided into multiple cells,
with a base station in each cell. The cells work with specific channels and connect the
wireless phone subscribers to the mobile switching center. A mobile phone can utilize any of
the channels of the system, which means the mobile phone can be used in any of the cells.
Within any specific cell, the wireless communication requires lower power, so the channels
can be reused by cells which do not intersect with each other.
For instance, in Figure 2, cell A utilizes channels 1--8, cell B utilizes channels 9--16,
cell C utilizes channels 17--24, and cell D utilizes channels 1--8 again. So channels 1--8 are
used repeatedly, which means subscribers in cell A and cell D can use channels 1--8
simultaneously.
This frequency multiplexing increases the calls processing capability of the wireless
system, and it is unnecessary to increase the number of channels available. When the same
frequency is multiplexed within a community, the interference between the channels cannot
LENOVO
Lenovo Mobile Telecommunications Co., Ltd.（OPEN DOC）
CELL B
CHANNELS
9-16
CELL A CELL D
CHANNELS CHANNELS
1-8 1-8
CELL C
CHANNELS
17-24
Figure 2: Hypothetical
CELL E
CHANNELS
9-16
CELL F
CHANNELS
17-24
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