In the past decade, cellular communications have experienced an explosive growth due to recent technological advances in cellular networks and cellular telephone manufacturing.
Early schemes for radio telephones schemes used a single central transmitter to cover a wide area. These radio telephone systems suffered from the limited number of channels that were available.
The need for a spectrum efficient system:
- To illustrate the need for efficient spectrum usage for a radio communications system, take the example where each user is allocated a channel.
- Each channel needs to have a bandwidth of around 25 kHz to enable sufficient audio quality to be carried as well as enabling there to be a guard band between adjacent signals to ensure there are no undue levels of interference.
- Using this concept it is only possible to accommodate 40 users in a frequency band 1 MHz wide.
- Even of 100 MHz were allocated to the system this would only enable 4000 users to have access to the system.
- Today cellular systems have millions of subscribers and therefore a far more efficient method of using the available spectrum is needed.
Cell Systems:
In order to accommodate more subscribers, the size of cells must be reduced
to make more efficient use of the limited frequency spectrum allocation. This will add to the challenge of some fundamental issues in cellular networks.
In a cellular network, a service coverage area is divided into smaller hexagonal areas referred to as cells.
Each cell is served by a base station. The base station is fixed. It is able to communicate with mobile stations such as cellular telephones using its radio transceiver. The base station is connected to the mobile switching center (MSC) which is, in turn, connected to the public switched telephone network (PSTN).
- Cellular radio is a technique that was developed to increase the capacity available for mobile radio telephone service.
- It is an underlying technology for mobile phones, personal communication systems, wireless networking, etc.
- This technology is developed for a mobile radio telephone to replace high power transmitter/receiver systems.
- Cellular network uses lower power, shorter range and more transmitters for data transmission.
- A cellular network divides any given area into cells where a mobile unit in each cell communicates with a base station.
- A hexagon cell shape is highly recommended for its easy coverage and calculations. It offers the following advantages −
- Provides equidistant antennas.
- Distance from center to vertex equals length of side.
Cell Cluster
Cell cluster is a group of cells in which cells are arranged such that no frequency channels are reused. The size of cluster is defined by number of cells in the cluster. Following figure shows three clusters with size of 7.
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