FREQUENCY PLANNING IN WIRELESS SYSTEMS ETI 2511 Thursday, 13 April - - PowerPoint PPT Presentation

FREQUENCY PLANNING IN WIRELESS SYSTEMS

ETI 2511 Thursday, 13 April 2017

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FREQUENCY PLANNING

• Frequency planning refers to the

process of analysing and assigning frequencies in a wireless system

• perating on multiple transmitters in a

given geographic area in order to: a) minimize interference b) maximize frequency utilization.

• Two key factors that guide frequency

planning are: (a)Interference tolerance (b)Distance to reuse ratio

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RE-USE DISTANCE

• Reuse Distance is a measure of

the minimum distance between two transmitters in a cellular system and is given by: Where

• N is the number of cells in a

cluster.

• R is the radius of a cell

𝐸 = 𝑆 3𝑂

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N = 7

FREQUENCY REUSE FACTOR

• Frequency reuse factor refers to the rate at which the same frequency

can be used in a network.

• If the are K cells per clusters, then the frequency reuse factor is given

by: 𝐺𝑆𝑓𝑣𝑡𝑓 = 1 𝐿

• Common frequency reuse factors are:

1 3 , 1 4 , 1 7 , 1 9 , 1 12

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SECTORED ANTENNAS

• 1. Most sites employ sectored antennas at one

site.

• 2. If a site has N sectors, then we say it has a

reuse pattern of N/K

• 3. The following reuse patterns have been used

in cellular communications:

• 3/4 (GSM)
• 3/7 (North American AMPS)
• 6/4 (Motorola NAMPS)

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USE OF DIRECTIONAL ANTENNAS

• 1. Most base stations use directional

antennas in order to improve coverage

• n highways, stadium and buildings.
• 2. In most GSM systems, this is realized by

using a hexadecimal arrangement where towers are located at the corners

• f the hexadecimals.
• 3. Each tower has three sets of directional

antennas aimed in three directions 120o apart and receiving/transmitting at different frequencies into three different cells as shown.

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IMPROVING CAPACITY IN CELLULAR NETWORKS

• 1. Cell Splitting is the process of sub-

dividing congested cells into smaller

• nes.
• 2. Advantages:
• Splitting preserves the geometry and

architecture.

• By increasing the number of cells, we

also increase the number of clusters which increases the capacity.

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• 1. Sectoring introduces more

directional antennas to further improve frequency usability.

• 2. Advantages:
• Uses the same base station site

and therefore reduces the site acquisition costs.

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IMPROVING CAPACITY IN CELLULAR NETWORKS

• Femto Cells (Microcell Zone ) extends

cell boundaries by using fibre optic cables (or microwave relay) links to hard to reach places.

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IMPROVING CAPACITY IN CELLULAR NETWORKS