Cellular Concept Mobile Computing Technology
Cellular Concepts refers to the use of a group of cells to provide communication from one place to another place when the user is mobile. A cellular system in mobile computing implements space division multiplexing or SDM. Each transmitter in the cellular system is called a base station.
Base station
The base station covers a specific area that is called a cell.
Cell
Cell radius can vary from tens of meters in building, hundreds of meters in a city, and tens of kilometers in the country.
The shape of a cell depends on the environmental conditions such as type of building, mountains, weather conditions, load, and other conditions. Generally, it is hexagon shape but not an exact hexagon.
Figure: Cell Structure
Mobile computing used cellular system and it has the following advantages:
- Higher Capacity
Cellular system uses SDM. SDM allows frequency reuse. If one transmitter is far away from another transmitter particularly out of the range of the interference area then another transmitter can use the same frequency as shown in the following figure-
Mobile systems assign one specific frequency to a certain user and that frequency is blocked for the use by other users. But frequency is a scarce resource therefore for their optimum utilization of the same frequency, the same frequency is used for other users using the technique frequency reuse.
- Less Transmission Power
Transmission power is not a big issue for the base station but it is important for the mobile receivers. Keeping cell size small facilitate mobile receivers because as they move far from the base station their receiving capacity reduces and due to small cells after a few distances they can again access receiving power from the cell nearby them and the problem of the mobile receiver is solved.
- Local Interference
When the distance is large between the sender and receiver then interference is also more and difficult to manage. There is only local interference when cells are small and that is easy to handle by the base station and the mobile station.
- Robustness
The cellular system is decentralized therefore more robust as compared to when centralized. If any component fails only that specific area affected and the rest of the part remains unaffected and works efficiently.
Cellular System or having small cells have the following disadvantages
- Infrastructure Requirement
Cellular system establishment needs complex infrastructure, storage registers to locate mobile users in local areas and roaming, antennas, transmitters, receivers, and amplifiers, etc. that are expensive.
- Handover Needed
The mobile system needs handovers when they change cells. This is quite often which further incur a cost.
- Frequency Planning
To avoid the interference between transmitters frequencies are planned carefully. Frequency is a limited resource therefore they are distributed intelligently so that they can be reused without any kind of interference.
Reference
Jochen Schiller, “Mobile Communication”, 2nd Edition.