With the invention and expansion of mobile telephony, mobile
devices such as smartphones and tablets offer more than just making calls, it
has become quite usual to surf the internet, make video calls and download
photos, music and videos and so much more. People want to use their devices
anywhere and everywhere. From the user with the simplest ‘mulika mwizi’ to the
one with the most sophisticated of gadgets, a voice call; the mustard seed of cellular
services can be made. To many the transmission path of mobile communications
appears as a rather simple radio signal transmission from one mobile equipment
to another. In reality however, speech and data will pass through a number of
intermediate stations before reaching the called party.
The transmission path of mobile communications spans the
distance from the mobile phone to the base station of the radio cell in which
the caller is located. From there, the information must be transmitted, at
times over great distances, to the radio cell in which the called party is
located. This is done by the use of mobile switching centres (MSCs).
The mobile phone base station receives the radio signal of a
mobile phone – and the information to be transmitted – with its receiving
antenna. It relays this signal, via a traditional cable connection or a
microwave link, to the MSC. The MSC routes calls and handles the entire
connection, including ringing through to the end connection, carrying out
services such as call forwarding, call waiting or conference calls.
Additionally, it registers the billing data. It (the MSC) will either hand the
call over to the traditional fixed network or to another MSC that will transmit
the call to the base station closest to the called party. It is from here that
it can reach the mobile phone.
The transmission of data
between the base stations and the MSCs uses either cable connections or
microwave links. Microwave links will send and receive signals on frequencies
in the GigaHertz range via circular parabolic antennas. Signals are sent in the
microwave range between 2 GHz and 60 GHz. Microwave links always require a
direct line-of-sight(LOS) connection and will not transmit in case of an
obstacle such as a skyscraper or a hill.
It is the reason as to why they are often installed on rooftops together with transceiver
stations. The microwave radio relays receive and amplify the microwave signals
and retransmit them to the next relay. Maximum distances here depend on the
frequency. The higher the frequency, the less the distance of transmission
covered.
The transmission path of the information changes depending
on the location of the caller and the called party. Whenever a subscriber moves
from one radio cell to another during a call, the system will automatically
switch over (handover) to the adjacent radio cell and terminate the connection
to the old cell without the mobile phone user noticing anything. The
transmission quality is the deciding factor in the decision whether the
handover will occur or not. If changing the radio cell will improve the
transmission quality, a handover to the next cell will take place.
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