10-08-2012, 11:54 AM
CELLULAR SYSTEM
[attachment=30902]
How they used in olden days?
During the olden days a single, high powered transmitter with antenna was mounted on a tall tower and it used to cover a large service area (as shown in figure below) and the problem due to this method was spectral congestion.
Here the service providers could not make use of the spectrum allocations in proportion to the increasing demand for the mobile services.
The radio telephone system was restructured to achieve high capacity with limited radio spectrum while at the same time covering very large areas.
The Cellular Concept
#) The cellular concept was a major breakthrough in solving the problem of spectral congestion and user capacity.
#) It offered very high capacity in a limited spectrum.
#) In the cellular concept, single high power transmitter is replaced with many low power transmitter search providing coverage to one small portion of the service are as shown in the figure below
#) Each base station is a allocated a portion, the total number of channels, and nearby base stations are assigned different group of channels.
#)By systematically spacing base stations and their channel groups throughout a market, the available channels are distributed and may be reused as many times as possible or as many times as necessary.
#) The interference between the co channel cells is kept below the acceptance level.
#) As the demand for the service increases, the number of base stations may be increased to provide additional radio capacity with no additional increase in radio spectrum
Frequency Reuse
#) Each cellular base station is allotted a group of radio channels to be used within a small geographic area called cell.
#) The design process of selecting and allocating groups or all the cellular base stations within a system is called frequency reuse or frequency planning.
#) The figure below illustrates the concept of cellular frequency reuse, where cells labeled with the same letter/number use the same group of channels. The picture below the 7 cell reuse pattern where the letter F denotes Frequency.
[attachment=30902]
How they used in olden days?
During the olden days a single, high powered transmitter with antenna was mounted on a tall tower and it used to cover a large service area (as shown in figure below) and the problem due to this method was spectral congestion.
Here the service providers could not make use of the spectrum allocations in proportion to the increasing demand for the mobile services.
The radio telephone system was restructured to achieve high capacity with limited radio spectrum while at the same time covering very large areas.
The Cellular Concept
#) The cellular concept was a major breakthrough in solving the problem of spectral congestion and user capacity.
#) It offered very high capacity in a limited spectrum.
#) In the cellular concept, single high power transmitter is replaced with many low power transmitter search providing coverage to one small portion of the service are as shown in the figure below
#) Each base station is a allocated a portion, the total number of channels, and nearby base stations are assigned different group of channels.
#)By systematically spacing base stations and their channel groups throughout a market, the available channels are distributed and may be reused as many times as possible or as many times as necessary.
#) The interference between the co channel cells is kept below the acceptance level.
#) As the demand for the service increases, the number of base stations may be increased to provide additional radio capacity with no additional increase in radio spectrum
Frequency Reuse
#) Each cellular base station is allotted a group of radio channels to be used within a small geographic area called cell.
#) The design process of selecting and allocating groups or all the cellular base stations within a system is called frequency reuse or frequency planning.
#) The figure below illustrates the concept of cellular frequency reuse, where cells labeled with the same letter/number use the same group of channels. The picture below the 7 cell reuse pattern where the letter F denotes Frequency.