history of mobile phones

A cellular phone, in actuality is really a radio, a very sophisticated one at that, but a radio nonetheless. A cellular phone system can be compared to a CB radio system. A CB radio uses the same frequency for transmitting and receiving, therefore only one person can speak at a time and the other has to listen (the practice of saying 'over' is to inform the other person that the speaking person has finished speaking). A communication device using single frequency is categorized as a simplex device. A cell phone on the other hand is a duplex device; i.e. it uses one frequency for transmitting and a second, separate frequency for receiving. Cell phones operate within cells that is the system uses many base stations to divide a service area into multiple 'cells'. Cellular calls are transferred from one station (transmitting tower) to another as the phone moves from cell to cell. This switching mechanism allows cellular phones to have virtually unlimited ranges.

The concept of cellular phones first came to light in 1947, when researchers realized that by dividing service areas into small cells, and reusing frequencies the Car phone traffic could be immensely increased. The only problem was the lack of technology, which hampered the realization of this concept.
Since a cell phone is actually a type of two-way radio, AT&T proposed that the Federal Communications Commission (FCC) allot a large number of radio frequencies so that wide-spread mobile telephone service could become feasible and communication giants could enter the field. This would not only create a bigger market but also provide incentive to research the new technologies. The FCC adopting a conservative approach allocated very few frequencies thus allowing only twenty-three phone conversations to occur simultaneously in the same service area. This was highly inefficient and uneconomical considering the huge investment the companies would have to pump into equipment and research and development. The FCC revised its decision and allowed more frequencies on the condition that a better more sophisticated mobile network be established. AT&T - Bell Labs, again at the forefront of innovation and development, proposed a cellular system based on small, low-powered broadcasting towers, each covering a 'cell' a few kilometers in radius, jointly covering a larger area. Each tower would service the mobiles present in its coverage areas and pass them onto the next tower as they moved out of its coverage area, thus at any particular moment very few frequencies would be required.
With a go ahead from FCC AT&T Bell Labs established a prototype system and by 1978 started public trials in Chicago. While In 1979, the first commercial cellular telephone system began operation in Tokyo. In 1982, FCC authorized commercial cellular service for the USA. Even though the demand for mobile communication system had been very strong all over the industrialized world, it took a long time for the initial concept to materialize into a commercially available mobile communication service. Demand quickly outstripped the system's capabilities and the only way to improve was to develop better technology.
The answer came in the form of PCS (Personal Communication Services). PCS is used to describe a newer class of wireless communication recently authorized by the FCC. PCS systems use a higher radio frequency, the 1.9 GHz band, and generally use all digital technology for transmission and reception.
The Cellular Technology Industry Association (CTIA) was established to work with the cellular service operators to identify and develop new technology. They wanted the new products and services introduced by 1991, with a 10 fold increase in capacity with both AMPS (analog) and digital capability being used in transmission which would allow new data features such as fax and messaging services.
The TDMA Interim Standard 54 or TDMA IS-54 was developed in accordance with the recommendations of CTIA, and released in early 1991.Three widely accepted standards are currently being used. TDMA (time division multiple access) divides cellular channels into three separate time slots in order to increase the amount of data that can be transmitted. TDMA IS-136, also called Digital AMPS or D-AMPS, uses the frequency bands and divides them into time slots with each phone having access to one time slot at regular intervals, creating a continuous cycle. CDMA IS-95 (Code Division Multiple Access) is based on spread spectrum technology that separates voice signals by assigning them digital codes. After digitizing the data, CDMA spreads it out over the entire bandwidth it has available. Multiple calls are overlaid over each other on the channel, with each identified by its unique sequence code.
GSM (Global System for Mobile Communications) is an improvement of TDMA technology. The concept started in Europe where the aim was to allow users to move from country to country (roam). By 1987, the GSM standard was created based on a hybrid of FDMA (analog) and TDMA (digital) technologies. It allowed for fast bit rates and better quality voice. Only GSM provides additional services such as email, fax, Internet browsing etc.
Clearly GSM is the best option among the different choices. Most new phones are running on the GSM technology and all service providers are upgrading to GSM because of its advantages.