CELLULAR SYSTEM.pptx

8/10/2019 CELLULAR SYSTEM.pptx

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CONTEN

CELLULAR SY

FREQUENCY ROA


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The design objective of early mobile radio systems was tolarge coverage area by using a single, high powered transmit

antenna mounted on a tall tower While this approach ach

coverage, it also meant that it was impossible to reuse t

frequencies throughout the system, since any attempts

frequency reuse would result in interference.

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OLD METHOD OF MOBILE RADIO TRANSMISSION


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TOW

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WHAT ACTUALLY LEAD

FOR THE DESIGN OFCELLULAR SYSTEM?


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NEED FOR THE CELLULAR SY

The demand of the telephone service kept on increasing at a

rate. Hence, the network became more and more congested.

Since the government regulatory agencies could not make

allocations in proportion to the increasing demand for mobile

it became important to reconstruct the radio telephone system

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A

Each base station is allocated a group of channels to be used

small geographic area called a cell.

Base stations in adjacent cells are assigned channel group

contain completely different channels than neighboring ce

base station antennas are designed to achieve the desired c

within the particular cell.

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THE CELLULAR CONC

The cellular concept is a system level idea which calls for rep

single, high power transmitter (large cell) with many low

transmitters (small cells), each providing coverage to only

portion of the service area.

Since neighboring base stations are assigned different gro

channels so that the interference between base stations (a

mobile users under their control) is minimized.

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PROBLEM SOL

So, the problem of the rising demand of service could now be

by increasing the no. of base stations (along with a corres

decrease in transmitter power to avoid added interference),

providing additional radio capacity with no additional incr

radio spectrum.

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HEXAGONAL CELL

ARRANGEMENT


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When using hexagons to modelcoverage areas, base station

transmitters are represented aseither being in the center of the cell(center-excited cells) or on three ofthe six cell vertices (edge-excited cells).

Omni- directional antennas areused in center-excited cells anduni-directional antennas usedin corner-excited cells.

Tessellation: Connection of the cells without any gap.


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BASIC DEFINI

The design process of selecting and allocating channel group

the cellular base stations within a system is called frplanning.

Frequency Reuse implies use of a available channel (frequency

or more cells.

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TERMS RELATED TO FREQUENCY

Cluster: The N cells which collectively use the complete set of afrequencies called a cluster.

Cluster Size: The total number of the cells in a given clustercluster size. It is normally equal to 4,7 or 12. We will represN.

Frequency Reuse Factor: The frequency reuse factor of a

system is given by 1/N , since each cell within a cluster is only1/N of the total available channels in the system.

Footprint: The actual geographical radio coverage of a cell is thefootprint.

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ILLUSTRAT

Illustration of the cellular frequency

reuse concept . Cells with the sameletter use the same set of frequencies.

A cell cluster is outlined in bold andreplicated over the coverage area.

In this example , the cluster size , Nis equal to seven , and the frequency

reuse factor is 1/7 since each cellcontains one - seventh of the total

number of available channels.

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ANALYSIS OF FREQUENCY R

Consider a cellular system which has a total of duplex c

available for use. If each cell is allocated a group of c( < )

The total number of available radio channels can be expressed

= -------------------- Eqn. 1

If a cluster is replicated times within the system, thnumber of duplex channels, can be used as a measure of cand is given

= = [From eqn. 1]-------------E

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CLUSTER SIZ

Due to the fact that the hexagonal geometry of Figure 2.1 hassix equidistant neighbors and that the lines joining the centercell and each of its neighbors are separated by multipledegrees, there are only certain cluster sizes and cell layouare possible. In order to tessellate to connect withobetween adjacent cells the geometry of hexagons is such number of cells per cluster, N, can only have values which

= 2 + + 2------------------ Eqn. 3

where i and j are non-negative integers.

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METHOD OF LOCATING CO-CHANNEL

To find the nearest co-channel neighbors

of a particular cell, one must do thefollowing:

(1) Move cells along any chain ofhexagons and then,

(2) Turn 60counter-clockwise

and move cells. This is illustrated inthe figure for = 3 and = 2.

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QUE

If a total of 33 MHz of bandwidth is allocated to a particula

telephone system which uses a 50 kHz duplex channel to pro

duplex voice and control channels, compute the number of

available per cell if a system uses (a) 4-cell reuse, (b) 7-cell

12-cell reuse.

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ANSW Given:

Total bandwidth =33 MHz

Channel bandwidth = 50 kHz/duplex channel

Total available channels = 33,000/50 = 660 channelsFrom eqn. 1 i.e, =

(a) For N= 4

Total number of channels available per cell = 660/4 165 channels.

(b)For N=7,

Total number of channels available per cell = 660/795 channels.

(c) For N = 12,

Total number of channels available per cell = 660/1255 channels.

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ROAMI Roaming is a fundamental requirement of wireless network

mobile subscriber becomes a roaming subscriber when it le

the coverage area of the MSC (Mobile Switching Center) to w

it was originally subscribed (the home MSC). Existing wireapproaches are not optimized to meet the requirements of

delivery in a wireless network where the users are allowed

roam from switch to switch. To ensure that the PSTN(Pu

Switched Telephone Network ) is able to provide voice acces

all mobile subscribers, the roaming subscriber (even if

engaged in a call) is required to register with the MSC in whicpresently resides (the visitor MSC). Registration is a proces

which each roaming subscriber notifies the serving MSC of

presence and location. This registration is then transferred to

home MSC where the HLR(Home Location Register) is updated.20


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ROAMING(CON

When a call is made to the mobile user, the network selec

path through which the call must be routed in order to ob

connection between the calling party and the called subs

The selection of a path in the network is known as routincalled subscriber is alerted of the presence of an incomin

and a pickup procedure is then initiated by the called subscraccept the call.

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THANKYOU

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CELLULAR SYSTEM.pptx

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