In most types of radio transmission systems, the object is to transmit your signal as far as possible, in order to maximize the amount of listeners or viewers you may have. In cellular systems, the object is to transmit a controlled signal. This is done to maximize the amount of channels that are given to each cellular provider for use.
Cellular systems break the coverage area into a series of cells.
Each cell can cover anywhere from a one mile radius from the base station in the city and urban areas to a 10 mile radius in the countryside and rural areas. Usually an arrangement of seven repeating cells is used. This makes use of the most important part of the cellular system, frequency re-use. There are only a limited amount of channels available in any cellular system, and this system makes the same channel available in different geographic parts of the system, to different users. There are two main frequencies used for wireless telephone communications in the United States.