Methods for improving capacity in cellular systems :
- Cell Splitting
- Microcell zone concept
While cell splitting increases the number of base stations in order to increase capacity, sectoring and microcell zone concept rely on base station antenna placements to improve capacity by reducing co channel interference.
Cell Splitting: It is the process of splitting a congested cell in smaller cells (called microcells), each with its own base station and a corresponding reduction in antenna height and transmitter power.
Sectoring: The co-channel interference in a cellular system may be decreased by replacing a single omni directional antenna at the base station by several directional antennas, each radiating within a specified area called a sector. The technique for decreasing co-channel interference and thus increasing system performance by using directional antennas is called sectoring. The factor by which co-channel interference is reduced depends on the amount of sectoring used. A cell is normally partitioned into three 120° sectors or six 60° sectors as shown in the above fig (a) and (b). The channels used in a particular cell are broken down into sectored groups and are used only within particular sector.
Microcell zone concept: The fig. below illustrates the microcell zone concept. Typical Plan of a cell in the Service area
In this scheme each cell is split into smaller areas referred to as zones. In the fig. above there are 3 such zones. Each zone is covered by a separate antenna and low power Transmitter/Receiver [Tx/Rx]. The 3 antenna are strategically placed at the outer edges of the cell. The zones are connected to by coaxial cable, fibre optic cable or microwave link to a base station and hence share the same radio equipment. The multiple zones with their respective antenna and Transmit/Receive equipment and base station make up a cell. Since the coverage area of each zone within the cell is distinct, any base station channel may be assigned to any zone by any base station.