A cellular mobile communications system consists of a large number of low power wireless transmitters to create cells. These cells cover a certain area and typically called as base station. Depending upon the power level the size of cells can be decided. In this way, the radii of a cell may vary from tens of meters to tens of kilometers in a building to a city respectively.
It will also depend upon the subscriber density and demand within a particular area. The shape of cell may not be a perfect hexagon or circle and depends upon the environment. When a mobile user travels from cell to cell, their conversations are "handed oft'" between cells in order to maintain seamless service. Cells can be added as per the demands based upon the user density or newly created areas. Channels (frequencies) used in one cell can be reused in another cell after some distance and therefore it uses Space Division Multiplexing (SDM).
Frequencies for communication may vary from very high frequency (VHF) to microwave range. Regulation bodies of the concerned countries regulate these. The signal may be analog or digital with amplitude, frequency and phase modulation. The multiplexing and access techniques are space division multiplexing (SDM), frequency division multiplexing (FDM), time division multiplexing (TDM), and code division multiplexing (CDM).
The advantages of mobile communication may be looked into higher capacity, higher number of users, less transmission power needed, more robust, decentralized base station deals with interference transmission area etc. The disadvantages are fixed network needed for the base stations, handover (changing from 'one cell to another) necessary. Interference with other cells such Ii co-channel adjacent-channel.
It is now evident that cellular networks are, essential for wireless transmission. We ought to know about the cellular concept, frequency reuse, channel allocation, call setup, location management, cell handoffs, optimizations in terms of power control and cell capacity and implementations of GSM, GPRS, and 3G etc. The important issues on wireless communication 'are cell sizing, frequency reuse planning and channel allocations strategies.
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