Using Cellular Networks for Wireless Communications

Instructor: Vignesh Sivabalan
A cellular network is a mobile network (radio network) for wireless mobile communication. The cellular networks face great growth with the invention of technologies like GSM, GPRS, CDMA, and so on. This lesson gives an overview of cellular networks and how they work, their applications and major features.

What are Cellular Networks?

Cellular networks are radio or mobile networks that are divided into fundamental units called cells. Each cell has a functional base station with restricted power that makes it easier to re-use frequencies within different cells without interference. For example, the frequency used by a base station in a cell can be used by any other cells that are separated by a relative distance. The cellular networks are very efficient ways of making use of scarce frequencies.

A cell serves a particular area and its size is based on the number of users and varies depending on the maximum number of users to be served in that particular area and the traffic. The cell size in densely-populated areas are comparatively larger than cell clusters in rural places. The shape of a cell can be square or hexagonal though hexagonal is most recommended for better coverage and easy mathematical calculations.

Popular examples for cellular networks are GSM (Global System for Mobile communication), GPRS (General Packet Radio Service), CDMA (Code Division Multiple Access) and 3GSM.

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Figure 1: Frequency Reuse in Cells
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Major Characteristics of Cellular Networks

  • Cellular networks were developed as an alternative to high power receiver/transmitter systems for mobile systems, wireless networks, personal area networks.
  • They use short range and low power transmitters for communication.
  • Their communication always happens between a mobile and a base station; no direct mobile to mobile communication.
  • Each base station has a dedicated collection of radio channels or frequencies within a cell; a cell covers a particular geographic area.
  • As the coverage area is limited to a particular cell, these radio channels/frequencies can be reused between various cells. This is called a frequency reuse.
  • Cellular networks manage interference levels in tolerance.

Frequency Reuse and Its Applications

Frequency reuse is making use of the same frequencies between various coverage areas or cells which are separated by a significant distance to prevent interference. Following are the benefits of frequency reuse in cellular networks:

  • Nearby cells can use same frequencies without interference
  • Escaping power is limited to adjacent cells
  • Same frequency can be used for multiple conversations
  • Allows from ten to fifty frequencies per each cell.

If N is the total number of cells and K is the number of frequencies. The cell frequency or frequency of each cell can be calculated using a mathematical formula: K/N.

Working of Cellular Networks

The base stations that are present inside each cell act as a hub for connecting all the mobile devices within that cell. The radio frequency signals that are transmitted by the mobile phones are first received by these base stations; these signals are then re-transmitted to corresponding receiver mobile phones through these base stations. Both transmission and reception are done at two different frequencies.

Each base station is connected to another base station using a central switching center that is capable of tracking calls and transferring them between base stations of different cells. When a mobile user moves from one cell to another, one geographical area to another, then there is a functionality of these central switching centers. The process of transferring data from one cell's base station to another cell's base station is called a hand over. Every base station also has connection with the MTN (Main Telephone Network) for relaying mobile calls to landline phones.

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