submitted by:
Ramhari Bhapkar
Anup Gholkar
Abhijeet Kumbhojkar

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CO CHANNEL INTERFERENCE REDUCTION IN GSM
Introduction to Cellular Systems
 Solves the problem of spectral congestion and user capacity.
 Offer very high capacity in a limited spectrum without major technological changes.
 Reuse of radio channel in different cells.
 Enable a fix number of channels to serve an arbitrarily large number of users by reusing the channel throughout the coverage region.
Frequency Reuse
 Each cellular base station is allocated a group of radio channels within a small geographic area called a cell.
 Neighbouring cells are assigned different channel groups.
 By limiting the coverage area to within the boundary of the cell, the channel groups may be reused to cover different cells.
 Keep interference levels within tolerable limits.
 Frequency reuse or frequency planning seven groups of channel from A to G
Co-channel Interference and System Capacity
 To reduce co-channel interference, co-channel cell must be separated by a minimum distance.
 When the size of the cell is approximately the same
co-channel interference is independent of the transmitted power
 co-channel interference is a function of
R: Radius of the cell
D: distance to the centre of the nearest co-channel cell
 For a hexagonal geometry
Q = D/R = √3N
 A small value of Q provides large capacity
 A large value of Q improves the transmission quality - smaller level of co-channel interference
 A trade-off must be made between these two objectives
Improving Capacity in Cellular System
 Methods for improving capacity in cellular systems
– Cell Splitting: subdividing a congested cell into smaller cells.
– Sectoring: directional antennas to control the interference and frequency reuse.
Reducing cochannel interference
 Increasing the separation between two cochannel cells
 Using directional antennas at the base station
 lowering the antenna heights at the base station.
 The use of directional antennas in each cell can serve two purposes:
- further reduction of cochannel interference
- increasing the channel capacity when thetraffic increases.
Cell Sectoring
 Decrease the co-channel interference and keep the cell radius R unchanged
– Replacing single omni-directional antenna by several directional
antennas
– Radiating within a specified sector