HOW CELL PHONES WORK
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How does a cell phone work?
Cell phones are housed with low-power transmitters.
They mostly operate on either 0.6 or 0.3 watts. The base stations also have
low-power transmitters. Low-power transmitters mean that the cell phone doesn’t
need to use much power, which is helpful when using a cell phone because they
can lose power quite quickly and the low-power transmitter means that they have
a smaller battery and therefore, use less power. Another advantage to the
low-power transmitter is that the same frequencies can be used over quite a far
distance. Many different cells are needed in order for the cellular system to
work properly. In a large city there can be hundreds of cells with hundreds of
towers. There is still a relatively low cost attached because cell phones are in
such high demand. For each carrier that is in each city, there must also be a
Mobile Telephone Switching Office (MTSO.) This is where all of the connections
to the land-line phones will be handled and the base stations are also
controlled and maintained through these city offices.
Although this may seem fairly basic so far, there
is much more that goes into a cell phone. One of the components of a cell phone
is the different codes that they carry. These codes are used to identify the
phone, the owner of the phone, and the service carrier of the phone. These codes
are used every time that the phone is used. When you turn on your phone and
receive a call, an entire process takes place in a matter of less than a second.
Here is how that process works:
- As soon as the phone is turned on, it begins to
listen for the System Identification Code (SID). It listens for this signal
on the control channel. The control channel is a frequency that the phone
and the base station use to communicate with each other to tell each other
what is happening with the phone. If there are no control channels that can
be found, the phone cannot be used and will display a “No Service” message.
- Once the phone has received the SID the phone
will then check to make sure that it matches the SID to ensure that it is
communicating with part of its home system.
- The phone will also send out a registration
request. This request lets the home office (MTSO) know where you are so that
if any calls come in, the office will know which cell to send it to.
- The MTSO will also choose a frequency pair that
your phone can use during the call.
- The MTSO uses the control channel to tell your
phone which frequencies to use. After that, the phone and the tower connect
to those frequencies and then the phone is connected to the person who is
calling. The two people can now talk through a two-way radio.
- Once you move toward the outer edges of the
cell, the base station will notice that the signal strength of the phone is
getting weaker. The base station that you are moving towards will also
notice that your phone’s signal strength is getting stronger. The two base
stations will communicate through the MTSO and a hand off process will take
place that will transfer the call from one cell to the other.
If the cell that the signal is moving towards has a
base station that is from another carrier other than the carrier for your phone,
the base station will still pick up the call. Because the carrier will be
different than the SID on your phone, the phone will go into roaming mode. The
MTSO of the other carrier will contact the MTSO of your carrier to ensure that
the SID is valid. After your carrier has verified the MTSO it will watch your
phone as it moves through the cells. This is an incredible process as you will
not notice any distance in your call except that you may see the word “roaming”
on your display. However, roaming charges themselves are incredible so if the
word should appear, you better get off the call quickly or be prepared to pay a
lot of money for it.
It’s amazing what these small devices, that are
only getting smaller by the day, can do in a matter of microseconds. Now when
you know that you are out of range, you will understand that you are not near a
tower and that the phone cannot find the control channel. You will be able to
understand that because you are in a concrete building, the control channel
cannot penetrate the strong walls to reach your phone. But you can also be just
as certain that someday, probably very soon, a manufacturer will design a phone
that will not see determine these things as obstacles. The signal will be so
strong that it will be able to get through just about anything.
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