CO CHANNEL INTERFERENCE REDUCTION IN GSM
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 seminar class Active In SP Posts: 5,361 Joined: Feb 2011 19-02-2011, 04:22 PM submitted by: Ramhari Bhapkar Anup Gholkar Abhijeet Kumbhojkar   COCHANNEL INTERFERENCE REDUCTION IN GSM.ppt (Size: 3.16 MB / Downloads: 138) 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