If you are a student, tech hungry, or researching on the World’s
most used devices i.e. cell phone its basic principle and working with network,
here is complete tutorial for you.
Tring !!! tring !!!
Hello everyone!! Hello!!
Hello! Am I audible hello!! Hello! Oops sorry I thought I am talking on phone,
no I am writing. Anyways the above greeting style is not coincidental (aka not
kaalpanik). Our generation is known as the mobile generation. Cell phones have
a great impact on our lives and its true imagining a day without phone is …… don’t ask!!
Starting with types of
mobile communication it is of three types
Simplex: -
only one channel present. A single person communicates at a particular time or
one way communication is there.
Example baby monitors, garage door openers, surveillance cameras.
Half-duplex:-
two channels are present. A single person communicates at a particular time or
one way communication. Example: - walkie-talkie.
Full
duplex: - two channels are present. Two persons or simultaneous
communication is possible. Example: - cell phones.
CELL
The cell-phone carrier receives about 800 frequencies to use across the
city. The carrier chops up the city into cells. Each cell is typically sized at
about 10 square miles (26 square kilometers). Cells are normally thought of as
hexagons on a big hexagonal grid.
A single cell in an
analog cell-phone system uses one-seventh of the available duplex voice
channels. That is, each cell (of the seven on a hexagonal grid) is using
one-seventh of the available channels so it has a unique set of frequencies and
there are no collisions. The combination of all cells of a MTSO is known as a
cluster. All available channels are divided in the cluster accordingly. These
Hexagonal grids are not really present it is just an adaptation for a cell as
after circle hexagon is the shape closer to show uniformity of signal 3600
around the base station. Circular cells are not considered as they will leave
voids.
Every cell has a
single base station which looks after all communication happening involving all
mobile stations and mobile users in that cell. Four channels are used for
communication i.e. forward voice channels responsible for transmission of
voice, reverse voice channels responsible for receiving of voice. Two control
channels are also present one is forward control channel which are responsible
for initiating and setting up of calls.
Well starting from a
cellular system. A cellular system provides a wireless connection to the public
switched telephone network (PSTN) for any location within the range of the
system. A basic cellular system consists of mobile stations, base stations and
a mobile switching center (MSC) or mobile telephone switching office (MTSO)
which is responsible for all communication with PSTN. A cell phone (mobile
station) is like a radio which communicates with the base stations. The base
station consists of several transmitters and receivers which serve as a bridge
between all mobile users in the cell.
All cell phones
have special codes associated with them. When we switch on our phone it looks
for control channels or SID. If the phone is not able to find any control
channel then it is “OUT OF RANGE” and displays “NO SERVICE”. When it receives
the SID or control channel, it compares it with SID programmed in the phone. If
it matches the SID of the phone the phone is in its home network.
Calling a mobile user
When a phone call is made to a mobile user, the MSC sends request to all base stations and the mobile identification number (MIN) is broadcasted over the forward control channel. The mobile receives the broadcasted message and identifies it over the reverse control channel. The base station relays the acknowledgment and informs MSC of handshake.
Then the call is moved to an unused voice channel within the cell. At this instant the base station asks the mobile to move to unused voice channels and instruct the phone to ring by sending it an alert message
Calling from a mobile
When a mobile
originates a call, a call initiation request is sent on reverse channel. With
this the mobile station transmits it MIN, electronic serial number (ESN) and
the number of the called party. The mobile also transmits a station class mark
(SCM) which indicates that transmitter power level is for particular user. The
cell base station receives this data and sends it to MSC which further connects
to the PSTN, and instructs the base station and mobile to move to a unused
frequency.
HAND-OFF
Suppose the call is
in progress and the mobile user moves towards the edge of the cell (assuming
the base station antenna is at the center of the cell) the strength of the
signal gets weaken, Meanwhile, the base station in the cell you are moving
toward (which is listening and measuring signal strength on all frequencies,
not just its own one-seventh) sees your phone's signal strength increasing. and
as the mobile station enters another cell, the MSC then switches the voice
channels according to the new base station to maintain the call. This is called
hand-off.
ROAMING
Cellular systems provide us a service known as roaming.
It is a service which allows users to communicate in areas or regions rather or
away from their home network. MSC issues a command asking all mobiles to verify
their MIN and ESN. If new phones are reported, then MIN/ESN data is used to
request billing status from home location register. Good news is that roaming will be vanished by mid 2013 in INDIA.
FOR MORE DEEP STUDY ON THE CONCEPT OF CELL PHONES
WAIT FOR CELL PHONES PART 2
WAIT FOR CELL PHONES PART 2
I must say you have covered the whole concept in one single article..Keep it up!
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