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Discuss about frequency reuse used in cellular system
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Answer:

Frequency reuse is the process in which the same set of frequencies(channels) can be allocated to more than one cell, provided the cells are a certain minimum distance apart, referred to as the frequency reuse distance.

Cells using the same set of radio channels must be apart by a specific distance in order to avoid mutual interference (co-channel interference).

The frequency reuse distance depends on the following factors:

  • Number of co-channel cells in the vicinity of the central cell.
  • Type of geographic terrain contour.
  • Antenna height
  • Transmitted power at each cell site

The frequency reuse distance (D) is determined by the formula: D=R*√3N

Where N=No. Of cells in the frequency reuse pattern.

          R=Cell radius.

The figure above illustrates the concept of cellular frequency reuse. Here the cells labelled with same letters use the same group of channels.

Each cellular base station is allocated a group of radio channels to be used within a same geographic area called a cell. Base stations in adjacent cells are assigned channel groups which contain completely different channels than neighbouring cells. In the figure above, A, B, C, D, E and F denote the channel groups of adjacent cells. The base station antennas are designed to achieve the desired coverage pattern (footprint) within the particular cell. By limiting the coverage area to within the boundaries of the cell, the same group of channels may be used in different cells, provided they are sufficiently separated from one another. This is illustrated in the figure above. The minimum separation distance is governed by the tolerable co-channel interference.

Advantages of frequency reuse:

In the frequency reuse system, users in different cells may simultaneously use the same frequency channel. Hence, it can drastically increase the spectrum efficiency.

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Frequency reuse:

Frequency Reuse is the scheme in which allocation and reuse of channels throughout a coverage region is done. Each cellular base station is allocated a group of radio channels or Frequency sub-bands to be used within a small geographic area known as a cell. The shape of the cell is Hexagonal. The process of selecting and allocating the frequency sub-bands for all of the cellular base station within a system is called Frequency reuse or Frequency Planning.

Features of using Frequency Reuse:

1.Frequency reuse improve the spectral efficiency and signal Quality (QoS).

2.Frequency reuse classical scheme proposed for GSM systems offers a protection against interference.

3.The number of times a frequency can be reused is depend on the tolerance capacity of the radio channel from the nearby transmitter that is using the same frequencies.

4.In Frequency Reuse scheme, total bandwidth is divided into different sub-bands that are used by cells.

5.Frequency reuse scheme allow WiMax system operators to reuse the same frequencies at different cell sites.

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