Cellular System

In cellular systems, the service area is subdivided into smaller geographic areas called cells, each served by its own base station.In order to minimize interference between cells, the transmit-power level of each base station is regulated to be just enough to provide the required signal strength at the cell boundaries.Therefore, the same frequency channels can be reassigned to different cells, as long as those cells are spatially isolated.

The rate at which frequencies can be reused (freq-reuse ratio) should be determined such that the interference between base stations is kept to an acceptable level. In this context, frequency planning is required to determine a proper frequency-reuse factor.The frequency-reuse factor f = 1 means that all cells reuse all the frequencies. Accordingly, f = 1/3, implies that a given frequency band is used by only one of every three cells.

Above figure shows a hexagonal cellular system model with frequency-reuse factor of 4, where cells labeled with the same letter use the same frequency channels. In this model, a cluster is outlined in boldface and consists of four cells with different frequency channels.

But this will create a problem of CCI (Co-channel Interference) between the adjecent cell using the same frequency. And also it wastes much bandwidth and power by radiating power in complete cell.

Cell Sectoring is the best way to tackle this situation. Using directional antennas instead of an omnidirectional antenna at the base station can significantly reduced the cochannel interference. So it increases both bandwidth and system capacity by the number of time sectoring is done !!