Mobile Phones
From the early days of communication systems the aim of personal communication systems was to provide maximum access to an individual anytime anywhere. Cellular phones have seen a long haul of evolution period. Starting from the first days of analog push-to-talk phones with a central transmitter base station which are sill used by the forces, mobile phones have seen consistent development, and we have WAP enabled phones today.
The first prototype similar to mobile phones we see today were the ones using Advanced Mobile Phone System (AMPS). This was very much similar to the present day cellular phones in that they divided the region to cells and implemented frequency reutilization. The major difference was that it was an analogue system and was lot more simpler, and offeren much lesser features than today�s cell phones.
Cellular phones have two basic characteristics; the entire physical region where the cellular service is provided is divided into cells, with one base station in each cell. When a mobile unit is in a cell it communicates with the base station in that cell. Since the size of a cell is in the range of a mile or so, the transmitter of the mobile unit need not transmit at too high powers. When a mobile unit moves from one unit to other, the control is transferred from the base station of the first cell to the next. This process is called handoff. Another characteristic of Cellular telephony is frequency reuse. Since each transmitter is meant for a cell of radius near a mile, the same frequency can safely be reused in a cell at a safe distance from it.
All present day mobile phones follow the GSM standard. Today the mobile phones have evolved into an all-purpose communication device. You can make and receive voice calls, send and receive messages, and even surf the net or send and receive videos in 3G mobile phones.
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