A Cellular Base Station (tower) transmits a constant signal commonly known as a “pilot” signal or “control channel signal” and this signal is received by the cellular handset (phone). One can think of this signal as a constant sound or voice that is transmitted by the tower and is heard by the phone. When the phone receives this signal the user sees signal bars on the phone’s display. If the phone receives a strong signal, many bars are displayed and when the signal is weak few bars appear. The phone measures all the pilot signals it receives from all the cell towers that it hears, and transmits these measurements to the tower. These measurements report receive signal level (loudness) and signal quality (clarity) of all the towers’ signals received (heard) by the phone.

This information is transmitted by the phone to the tower hundreds of times per second, virtually constantly. The information is received by the tower and sent by the tower to a land-based device known as the “switch”. The switch uses the information received from the phone to create commands based on preset parameters that are programmed in the data banks of the switch. These commands are sent back to the tower and the phone. These commands include the frequency and channel to communicate on, the tower that the phone is to connect to, and the power level at which the phone should transmit (essentially, how loud the phone should be). One can think of the switch as the conductor of a symphony that is made up of cellular towers and cellular phones.

The switch/tower combination controls the phone’s output power and generally commands the phone to reduce power as it approaches the tower and increase power as the phone leaves the tower. (One could think of this as the phone whispering when it is close to the tower and yelling when it is far away). This exchange of information is what keeps a phone connected to a network and allows the phone to travel from place to place successfully. For a cellular conversation to connect and stay connected two things must occur: the phone must receive signal from the tower and the phone must transmit with enough power to reach the tower, in other words, the phone must hear the tower and the tower must hear the phone, as long as this condition occurs, cellular communication is successful.

The Urban Environment:

Cellular communications in cities are usually very reliable because cellular providers deploy numerous towers and transmitter/receiver stations in close proximity to each other. Urban towers are spaced close together and their range is usually quite short, sometimes only a few city blocks or less. This condition exists because a cellular provider has a limited number of channels and each channel has a maximum number of users that it can support at the same time, therefore, when the provider reduces the range of the tower the provider can use the same channels at numerous locations and accommodate more users. The provider controls the range of a tower by increasing or decreasing the pilot signal and pilot signal in cities is typically quite low.

 The Rural Environment:

Cellular communication in rural environments is usually less reliable than cities because there are fewer towers covering larger geographic areas. Cellular providers try to maximize the range of a rural tower because towers are expensive and users are few. To maximize the range of the tower, the provider will increase the power of the pilot signal. This allows phones to receive signal from a given tower at a greater distance; essentially, the phone can hear the tower from further away. Under these conditions a phone can be far enough away from a tower to display “signal bars” maybe one, two or three, but despite this a call cannot be completed. The reason that this occurs is simple: the phone can hear the tower because the tower has a powerful transmitter that is turned up to be quite loud, however, the phone has a less powerful transmitter than the tower and even at its maximum transmit output power, the phone’s signal will not reach the tower. Basically, the phone can hear the tower but it is not loud enough to be heard by the tower, hence, no connection or dropped call.