19-12-2012, 06:54 PM
Cellular Concept
1Cellular Concept.ppt (Size: 534 KB / Downloads: 24)
Cellular concept is a major breakthrough in solving problems of
Spectral congestion
User Capacity
Cellular concept is a system level idea to replace a single high power transmitter with many low power transmitters.
Concept of “Frequency reuse”
Definitions / Terminology
Frequency reuse
Frequency reuse factor=1/N, N=cluster size
A cell / sector is a logical network element that uses given resources.
A cell site (or site or base station) can include multiple of cells/sectors at the same physical location.
Cell coverage is defined as geographical area where the cell is likely to serve mobiles.
Network coverage refers to sum of individual cell coverage.
Actual radio coverage of a cell is called footprint and is determined from the field measurement or propagation prediction models.
Cellular Architecture
In practice the cells are not regular hexagons, but instead are distorted and overlapping areas.
The hexagon is an ideal choice for representing macrocellular coverage areas, because it closely approximates a circle and offers a wide range of tesellating (a regular tiling of polygons) reuse cluster sizes.
A tesellating reuse cluster of size N can be constructed if,
where i and j are non-negative integers, and i ≥ j. It follows that the allowable cluster sizes are N=1,3,4,7,9,12,…..
Co-channel Reuse Factor
The co-channel reuse factor D / R (sometimes also referred as Q), is defined as the ratio of the co-channel reuse distance D between cells using the same set of carrier frequencies and the radius of the cells R.
For hexagonal cells, the reuse cluster size N and the co-channel reuse factor D / R are related by,
Microcellular Deployment
For microcellular systems with lower BS antenna heights, regular hexagons are no longer appropriate for approximating the radio coverage zones.
Typical microcell BSs use an antenna height of about 15 m, well below the skyline of any buildings that might be present.
For microcells, the choice of cell shape depends greatly upon the particular deployment.
Interference and system capacity
Interference limits the system capacity and the performance of a single radio link.
The higher is the interference level, the lower is the system capacity and poorer is the quality of communication links.
Interference can origin from
Mobiles under the same cell
Mobile under different cell
Base stations operating at the same frequency (or in general using simultaneously the same resources)
From non-cellular systems
Co-channel interference is the most problematic.
Also adjacent channel interference affect the system capacity.
However, adjacent channel interference is also filtering problem, which can be decreased by assigning channels intelligently.
1Cellular Concept.ppt (Size: 534 KB / Downloads: 24)
Cellular concept is a major breakthrough in solving problems of
Spectral congestion
User Capacity
Cellular concept is a system level idea to replace a single high power transmitter with many low power transmitters.
Concept of “Frequency reuse”
Definitions / Terminology
Frequency reuse
Frequency reuse factor=1/N, N=cluster size
A cell / sector is a logical network element that uses given resources.
A cell site (or site or base station) can include multiple of cells/sectors at the same physical location.
Cell coverage is defined as geographical area where the cell is likely to serve mobiles.
Network coverage refers to sum of individual cell coverage.
Actual radio coverage of a cell is called footprint and is determined from the field measurement or propagation prediction models.
Cellular Architecture
In practice the cells are not regular hexagons, but instead are distorted and overlapping areas.
The hexagon is an ideal choice for representing macrocellular coverage areas, because it closely approximates a circle and offers a wide range of tesellating (a regular tiling of polygons) reuse cluster sizes.
A tesellating reuse cluster of size N can be constructed if,
where i and j are non-negative integers, and i ≥ j. It follows that the allowable cluster sizes are N=1,3,4,7,9,12,…..
Co-channel Reuse Factor
The co-channel reuse factor D / R (sometimes also referred as Q), is defined as the ratio of the co-channel reuse distance D between cells using the same set of carrier frequencies and the radius of the cells R.
For hexagonal cells, the reuse cluster size N and the co-channel reuse factor D / R are related by,
Microcellular Deployment
For microcellular systems with lower BS antenna heights, regular hexagons are no longer appropriate for approximating the radio coverage zones.
Typical microcell BSs use an antenna height of about 15 m, well below the skyline of any buildings that might be present.
For microcells, the choice of cell shape depends greatly upon the particular deployment.
Interference and system capacity
Interference limits the system capacity and the performance of a single radio link.
The higher is the interference level, the lower is the system capacity and poorer is the quality of communication links.
Interference can origin from
Mobiles under the same cell
Mobile under different cell
Base stations operating at the same frequency (or in general using simultaneously the same resources)
From non-cellular systems
Co-channel interference is the most problematic.
Also adjacent channel interference affect the system capacity.
However, adjacent channel interference is also filtering problem, which can be decreased by assigning channels intelligently.