Start this tutorial from : Introduction
Primitively mobile networks (that should probably be called the 0g mobile network such as IMTS),were designed like TV networks... one very powerful base station catered to a large area.
The IMTS by AT&T for instance in New York, had 12 channels only. This means that at a given time only 12 calls could be active. Because of limited channels, AT&T had to limit subscribers to 2000. On an average users had to wait around 20 minutes before there calls could be placed.
Primitively mobile networks (that should probably be called the 0g mobile network such as IMTS),were designed like TV networks... one very powerful base station catered to a large area.
The IMTS by AT&T for instance in New York, had 12 channels only. This means that at a given time only 12 calls could be active. Because of limited channels, AT&T had to limit subscribers to 2000. On an average users had to wait around 20 minutes before there calls could be placed.
This user capacity limitation was overcome by using a Cellular Topology
A land area to be covered is divided into regular shaped cells(as big as 10-15 miles), which can be hexagonal, square, circular or some other regular shapes.Hexagonal cells are conventional because hexagons best resemble a circle. (as a BTS would radiate around itself in more or less a circular radius)
A land area to be covered is divided into regular shaped cells(as big as 10-15 miles), which can be hexagonal, square, circular or some other regular shapes.Hexagonal cells are conventional because hexagons best resemble a circle. (as a BTS would radiate around itself in more or less a circular radius)
 |
| A cluster of cells |
Each cell is served by one or more fixed-location transceiver, known as a cell site or base station. A mobile device would communicate with a cell-site most closest to it. Every radio base stations transmits/receives information in its cell at a particular frequency range from f1 - f6 . The group of frequencies can be reused in other cells, provided that the same frequencies are not reused in adjacent neighboring cells as that would cause co-channel interference.
In IMTS :
How capacity is improved by cellular topology?
In IMTS :
we can think the entire area A as one big cell with one BTS.
Let total number of channels = 14Number of Active calls that can be supported in area A = 14In Cellular:
Let A be divided in 10 clusters
No. Of cells in one cluster = 7 Number of channels per cluster = 14/7 = 2This was a short description of channel multiplication using frequency reuse. Now, that we know basic concepts behind cellular topology, we shall for now, stop here. There's a lot more to frequency re-use and cell planning which is a major field research and application. Cell planning is a science in itself.
Number of channels in area A = (14*10)/7=20Number of Active calls that can be supported in area A = 20
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