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Unit 4: Physical Layer-2

4.4 Mobile Telephone System Notes

The development of mobile telephone system or cellular phones is recent one. This is also
known as mobile phone and as its name implies it is designed for mobile users who need to
make telephone calls from different locations when they are usually away from home or office.
The rapid development in hardware technology helps in designing such kind of portable
telephone sets as shown in Figure 4.5 so that user may carry it within their office bag or pocket
during movement. Cellular phone uses radio frequencies to talk to a nearby cell site. Cell site
acts as an access point for cellular calls and the cellular phone regularly communicates with the
nearest cell site to inform the network that it is connected.
Figure 4.5: Cellular Phone

Cell Site
This may be defined as a circular geographical area that handles cellular phones within its
defined physical boundary. A cellular network as shown in Figure 4.5 is considered consisting
of overlapped cells so that a larger area with low probability of call dropping may be provided.
This overlapping structure helps in keeping the call intact as a user moves location from one cell
site to another. In this case, the call is transferred to the nearest cell site responsible for that
physical area.

Cellular telephones are suitable for larger geographical areas including remote sites. It saves
the cost of copper wire and efforts in laying the same in densely populated areas.
Each cell site shown in Figure 4.6 is connected to a master site, which acts as an access point for
a particular cellular network. Master site furnishes an interconnection to the regular telephone
network. Calls handled by each cell site are relayed back to the master cell site, which then
relays it to the telephone network as shown in Figure 4.7

Figure 4.6: Cellular Network Consisting of Individual Cells

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