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Monday, November 4, 2013

Mobile Communication Systems - Basics

Now, let us see what makes up a communication system. A very basic components are

  1. SOURCE the beginning point 
  2. INFORMATION or DATA to be conveyed
  3. CARRIER or MEDIUM that will take data from source to destination
  4. RECIPIENT

Now, the very important requirement for communication, is a MEDIUM through which information will flow from the SOURCE to the RECIPIENT. For wireless systems this medium is called the CARRIER, which consists of 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 signaled from a transmitter. The receiving end has a receiver that captures this signals and demodulates it 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.

MOBILE NETWORKS

mobile network is a radio network distributed over huge land areas. Terminal devices or mobile phones can move around in this land areas and still communicate.

In order to support communication between subscribers we need a pair of RF channels per active call. 1 Channel requires atleast two frequencies, one for forward link and one for reverse link.

In large cities where operators could have thousands of subscribers, we would require a large number of channels. A given base station can transceive only at a given frequency range, and the number of channels would be limited. Also there is a limit to availability of spectrum. 




forward and reverse path communication

If an operators get a 1 MHz band, and has 12 channels to use and  only one base station to cover the entire state, then at any given time it could support only 12 active calls at max. To overcome this limitation, you have to create zones of coverage, which are called as cells. 


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