Published on 31 Dec 2014 | about 1 year ago
Cellular telephone systems must accommodate a large number of users over a large geographic area with limited frequency spectrum, i.e., with limited number of channels.
If a single transmitter/ receiver is used with only a single base station, then sufficient amount of power may not be present at a huge distance from the BS. For a large geographic coverage area, a high powered transmitter therefore has to be used. But a high power radio transmitter causes harm to environment. Mobile communication thus calls for replacing the high power transmitters by low power transmitters by dividing the coverage area into small segments, called cells. Each cell uses a certain number of the available channels and a group of adjacent cells together use all the available channels. Such a group is called a cluster. This cluster can repeat itself and hence the same set of channels can be used again and again.
Each cell has a low power transmitter with a coverage area equal to the area of the cell. This technique of substituting a single high powered transmitter by several low powered transmitters to support many users is the backbone of the cellular concept
In each cell, there are four types of channels that take active part during a mobile
call. These are:
• Forward Voice Channel (FVC): This channel is used for the voice transmission
from the BS to the MS.
• Reverse Voice Channel (RVC): This is used for the voice transmission
from the MS to the BS.
• Forward Control Channel (FCC): Control channels are generally used
for controlling the activity of the call, i.e., they are used for setting up calls
and to divert the call to unused voice channels. Hence these are also called
setup channels. These channels transmit and receive call initiation and service
request messages. The FCC is used for control signaling purpose from the BS
• Reverse Control Channel (RCC): This is used for the call control purpose
from the MS to the BS. Control channels are usually monitored by mobiles.