Concept of Cell Sectoring and Clustering in Wireless Communication

1 Cell

A Cell is the basic geographical unit of a cellular system. Commonly represented as a hexagon.

The term cellular comes from the hexagonal or honeycomb shape of the coverage area. Each cell has a BS transmitting over a cell. Because of constraints imposed by natural terrain and man made structure . The true shapes of cell are not hexagonal. The coverage area of cell is called the footprint. The BS simultaneously communicates with many mobile using one channel (pair of frequencies) per mobile. One frequency is for the forward link (Base station to the mobile) and other frequency is for the reverse link (Mobile to the Base station). Each cell size varies depending on landscape, subscriber density and demand within particular region. Cells can be added to accommodate growth e.g.; creating new cells by overlaying, splitting, or sectoring existing cells. This technique increases the capacity of the system. Sectoring existing cells and then using directional antenna can also increase capacity.

2 Cluster

A cluster is a group of cells. No frequencies are reused within a cluster. Frequencies used in one cell cluster can be reused in another cluster of cells. A large number of cells per cluster arrangement reduces interference to the system.

3 Frequency Reuse

Frequency reuse is a technique of allocating channels to the cellular system. Because of the unavailability of the spectrum at the cellular band, channels frequencies must be reused. Cells are assigned group of channels that are completely different from those of neighboring cells. Cells with the same number have the same set of frequencies, if the number of available frequency is 7, the frequency reuse factor is 1/7, which implies that each cell is using 1/7 of available frequencies . Frequency reuse introduces interference into the system.

In Cellular Communication there are two types Interference when we want to do Frequency Re-use. They are Known as: Adjacent Channel Interference (ACI), Co-Channel Interference (CCI).

1.Adjacent Channel Interference(ACI):

ACI is the interference between signal's having frequencies close together.

For example suppose channel 1 has frequencies 825.030 MHz (Mobile) and 870.030 MHz (BS) and channel 2 has frequencies 825.060 and 870.060 MHz. Channels 1 and 2 have frequencies close to one another, which will results in ACI.

2.Co-Channel Interference (CCI):
CCI is the interference between signal's having the same frequency(i.e; re-use frequency).
For example suppose channel 1 has frequencies 825.030 MHz (Mobile) and 870.030 MHz (BS).

Any othe signals having the frequencies of channel 1 825.030 (Mobile) and 870.030MHz (BS) are co-channel signals and will suffer from co-channel interference (CCI).