What is a cellular phone?

           Cellular telephone or radio telephone is a type of mobile telephone which is integrated with existing telephone systems, allowing mobile users to contact any one with a standard telephone and vice-versa. Each mobile telephone has its own number which can be dialed from any other telephone. The cellular telephone can cover the entire country; even inter-continental telephone calls are possible with cellular telephone.

           A cellular telephone network is setup by dividing the country into a series of cells, each with its own radio transmitter controlled by a central switching computer. Each cell is about 5km across and it broadcasts and receives low power signals on its own set of frequencies. Since each cell is so small, the same set of frequencies can be reused in any other cell whose transmitter’s range does not overlap the first cell. As a cellular telephone is mobile and moves from one cell to another, the broadcast frequency needs to be changed.

            Cellular radio phone signals follow a route starting from the mobile, then of the radio transmitter. The signal is sent along the conventional telephone lines to an exchange. The analog signal is converted to digital signal, ready for switching to the correct destination. After switching, the signal is reconverted to analog and sent along telephone lines to the destination transmitter, where it is transmitted and consequently received by another mobile.

           There are at present three types of cellular telephones. These are – automobile based, pocket or briefcase portables and trans-portables which can be moved in a vehicle and used in the hand.

           Cellular phones are being used by many countries besides India such as Saudi Arabia, U.S.A., Sweden, Britain, Japan, Middle East countries etc.