i want to know why celllular phone are called so and other details like
what is bluetooth, gprs gsm there advantages and disadvantages
There were mobile, and even portable, phones before cellphones came along.
But it meant connecting with one (or a few) central stations (and usually
required an operator at that station to do the actual dialing), and relatively
high power was needed. Only a handful of frequencies were assigned to
mobile phone use, and only one person could use a given frequency at a time
in most locations. Thus it could never be a system for the masses, and
the cost was quite high.
Cellphones change all that. They got a slew of frequencies. More important,
the "base stations" are spread out all over town. This means power levels
are much lower, at the base and in the cellphone. If you're in area A,
someone across town in area X can use the same frequency because the
frequencies are high enough in the radio spectrum so they won't travel far,
and the power levels additionally limit the range of the signals. This means
the frequencies can be reused throughout a city, just making sure that
adjacent cell "bases" don't use the same ones. As someone moves along,
they will move into a new cell, and the network will automatically switch
them over to the next one (ie change the frequency, and pass them on to
the next cell, so the user never notices that anything has changed. The
cellphones are a lot "smarter" than the old mobile phones, that had
nothing but the radio transmitter and receiver.
Michael
