FREQUENCY REUSE WITH CELLULAR TOPOLOGY

Primitively (that should probably be called the 0g mobile network such as IMTS), mobile networks 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 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.

How capacity is improved by cellular topology?

MOBILE COMMUNICATION SYSTEM

The very first requirement for communication, is a MEDIUM through which information will flow from the transmitter to the receiver. For wireless systems this medium is called the CARRIER, which consists of signal waves of given frequency. For mobile telephony, radio frequency range is used.

The carrier can be modulated in a variety of ways to embed data/information into it. It is then signalled from one transceiver. The receiving end captures this signals and demodulates to decipher the embedded data/info/message.

Since there are so many different mobile carriers, to avoid exchange of signals and interference, each carrier can use only an allotted  frequency range from the spectrum. That is why the radio spectrum has become a very valuable asset.

More or Less... We're Wireless

Wireless mobile communication systems... They have been there since decades!

What's new about them..?

Well, nothing new about them. But they have evolved for so many years, and are always evolving into something new. From simply "cellular technology" to 3G, 4G and now evolving fast is... 5G or the LTE advanced...

What Qualifies to be called a Wireless Communication System?

Communication : Means transfer of data from one point to another. 
Any transfer of information between two or more points that are not physically connected by wires is wireless communication.

Even when you talk to your friend sitting beside you, logically you are communicating wirelessly.

But as Engineers, we will consider only technologically advanced wireless data transfer as wireless communication. Therefore two simple examples of wireless communication systems would be:

Short Distance : TV controlled by remote

OR

Long Distance : Space Radio Communication

Although there are so many different wireless technologies from WLAN and Bluetooth to radio space communications, for this series we will be limiting ourselves to Wireless Mobile communications, as that is the most widely used wireless technology these days.

A Piece of Fun Fact