Co Channel Interference Reduction

7/30/2019 Co Channel Interference Reduction

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Anup GholkarRamhari BhapkarAbhijeet Kumbhojkar


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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 largenumber of users by reusing the channel throughout thecoverage region.


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Each cellular base station is allocated a group of radio channelswithin 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, thechannel 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

footprint of a cell - actual radio coverage

omni-directional antenna vs directionalantenna


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Co-channel Interference andSystem Capacity

To reduce co-channel interference, co-channel cell must beseparated by a minimum distance.

When the size of the cell is approximately the sameco-channel interference is independent of the transmittedpower

co-channel interference is a function ofR: Radius of the cell

D: distance to the centre of the nearest co-channel cell


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For a hexagonal geometryQ = D/R = 3N

A small value of Q provides large capacityA large value of Q improves the transmission quality -smaller level of co-channel interference A trade-off must be made between these two objectives


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Methods for improving capacity in cellular

systems

Cell Splitting: subdividing a congested cellinto smaller cells.

Sectoring: directional antennas to controlthe interference and frequency reuse.


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Increasing the separation between twocochannel cells

Using directional antennas at the base station

lowering the antenna heights at the base station.

The use of directional antennas in each cell canserve two purposes:

- further reduction of cochannel interference

-increasing the channel capacity when thetraffic increases.


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Decrease the co-channel interference and keep thecell radius Runchanged

Replacing single omni-directional

antenna by several directionalantennas

Radiating within a specifiedsector


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The interfering site could cause interferenceat those cells within a 19 sector in front ofthe cell.

In an ideal situation the antenna pattern ofthe serving cell must be rotated clockwise by10 such that the notch can be aimed

properly at the interfering cell


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Purely mechanical tilt

Fixed electrical tilt

variable electrical tilt (VET) Remote electrical tilt (RET)

Continuously adjustable electrical downtilt

(CAEDT).


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Elements playing a major role in justifying

antenna tilting-

The antenna vertical pattern

The antenna height


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For controlling the energy in a confined area,the umbrella-pattern antenna can bedeveloped by using a monopole with a topdisk

The size of the disk determines the tiltingangle of the pattern. The smaller the disk, thelarger the tilting angle of the umbrellapattern.


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Energy is confined to the immediate area ofthe antenna

Reduces cochannel and long-distanceinterference.

We can increase antenna height still reducecochannel interference

The frequency-reuse distance can be

shortened


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Antennas are placed at the outer edges of thecell

Any channel may be assigned to any zone by thebase station

Mobile is served by the zone with the strongestsignal. Handoff within a cell

No channel reassignment Switch the channel to a different zone site

Reduce interference

Low power transmitters are employed


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Ensure each mobile transmits the smallestpower necessary to maintain a good qualitylink on the reverse channel

Can be controlled only by mobile station

long battery life

increase SIR


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Creating a desired pattern in a certaindirection.

currents appearing in several parasiticantennas are caused by radiation from anearby drive antenna.

Ways to combine a driven antenna & a singleparasite :

- Normal spacing- Close spacing


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a)One-quarter wavelength

spacing

b)one-half wavelength spacingc)combination of a and b.


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1. Length of both elements same- Forms a null at the centre

- Directive gain of 3 dB relative to a singleelement

2. Length of parasite greater than active element

- Parasite acts as reflector

- Directive gain of 6 dB

3. Length of parasite less than active element- Parasite acts as director

- Directive gain of 8 dB


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Dominant interfererence likely exists in GSM

Number of nearby co channel interference is rathersmallCancellation of it can improve the receiverperformanceIt depends on the dominant to rest of interference

ratio DIR.


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Receiver algorithm identifies dominant

interfering signal

It removes it by joint phase demodulation

System performance improves by 1.3 dB


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Co Channel Interference Reduction

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