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8/2/2019 MAJU Cell 2009 Fall Week 3 4 5 Cellular Concept Mobility RFPlanning Trunking
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Muhammad Ali Jinnah University, Islamabad Campus, Pakistan
Cellular Concept Cellular Concept Cellular Concept Cellular Concept
Lecturer: Associate Prof. Dr Noor M Khan Department of Electronic Engineering,
Dr. Noor M KhanDr. Noor M KhanDr. Noor M KhanDr. Noor M KhanEE, MAJUEE, MAJUEE, MAJUEE, MAJU
EE6733 Cellular Mobile CommunicationsWeek 3Week 3Week 3Week 3- ---4 ; Fall4 ; Fall4 ; Fall4 ; Fall - --- 2009200920092009
Cellular Concept 1
PSTNMSC
Muhammad Ali Jinnah University, Islamabad Campus, Islamabad, PAKISTAN Ph: +92 (51) 111-878787, Ext. 147 Fax: +92 (51) 2822743email: [email protected]
,
8/2/2019 MAJU Cell 2009 Fall Week 3 4 5 Cellular Concept Mobility RFPlanning Trunking
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Muhammad Ali Jinnah University, Islamabad Campus, Pakistan
Cellular Concept
Simple Solution Single high powered transmitter on a tall tower Good coverage but very low capacity
Dr. Noor M KhanDr. Noor M KhanDr. Noor M KhanDr. Noor M KhanEE, MAJUEE, MAJUEE, MAJUEE, MAJU
EE6733 Cellular Mobile CommunicationsWeek 3Week 3Week 3Week 3- ---4 ; Fall4 ; Fall4 ; Fall4 ; Fall - --- 2009200920092009
Cellular Concept 2
No frequency reuse High Capacity Solution
Cellular concept solves problem of low capacity
Replaces a single high power transmitter (large cell)with many low power transmitters (small cells)
Much smaller and more efficient mobile units
8/2/2019 MAJU Cell 2009 Fall Week 3 4 5 Cellular Concept Mobility RFPlanning Trunking
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Muhammad Ali Jinnah University, Islamabad Campus, Pakistan
Operation
The Cellular Concept is a system level idea: Each base station is allocated a portion of the total
number of channels available to the entire system
Dr. Noor M KhanDr. Noor M KhanDr. Noor M KhanDr. Noor M KhanEE, MAJUEE, MAJUEE, MAJUEE, MAJU
EE6733 Cellular Mobile CommunicationsWeek 3Week 3Week 3Week 3- ---4 ; Fall4 ; Fall4 ; Fall4 ; Fall - --- 2009200920092009
Cellular Concept 3
Nearby base stations are assigned different groups of channels All channels are assigned to a relatively small number
of neighboring base stations
The level of interference between base stations(and the mobile users) is controlled
8/2/2019 MAJU Cell 2009 Fall Week 3 4 5 Cellular Concept Mobility RFPlanning Trunking
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Muhammad Ali Jinnah University, Islamabad Campus, Pakistan
Scalability
Frequency can be re-used as many times asnecessary as long as interference between co-channel stations can be kept within acceptable
Dr. Noor M KhanDr. Noor M KhanDr. Noor M KhanDr. Noor M KhanEE, MAJUEE, MAJUEE, MAJUEE, MAJU
EE6733 Cellular Mobile CommunicationsWeek 3Week 3Week 3Week 3- ---4 ; Fall4 ; Fall4 ; Fall4 ; Fall - --- 2009200920092009
Cellular Concept 4
m ts. As the demand increases, the number of base
stations can be increased (with a corresponding
decrease in transmitter power) This fundamental principal is the foundation of all
modern wireless communication systems.
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Muhammad Ali Jinnah University, Islamabad Campus, Pakistan
Frequency Re-use The process of selecting and allocating channel
groups for all base stations within a system isknown as frequency re-use or frequency planning
Dr. Noor M KhanDr. Noor M KhanDr. Noor M KhanDr. Noor M KhanEE, MAJUEE, MAJUEE, MAJUEE, MAJU
EE6733 Cellular Mobile CommunicationsWeek 3Week 3Week 3Week 3- ---4 ; Fall4 ; Fall4 ; Fall4 ; Fall - --- 2009200920092009
Cellular Concept 5
AG
FE
C
D
B
G
FE
C
DA
G
F
E
C
DA
B
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Muhammad Ali Jinnah University, Islamabad Campus, Pakistan
Comments on HexagonalCells
Hexagon geometry approximates omni-directional base station with free spacepropagation
Dr. Noor M KhanDr. Noor M KhanDr. Noor M KhanDr. Noor M KhanEE, MAJUEE, MAJUEE, MAJUEE, MAJU
EE6733 Cellular Mobile CommunicationsWeek 3Week 3Week 3Week 3- ---4 ; Fall4 ; Fall4 ; Fall4 ; Fall - --- 2009200920092009
Cellular Concept 6
When hexagons are used base stations caneither be in the center (center excited) - omni directional
antennas or on 3 of the six cell vertices (edge excited) -
sectored directional antennas
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Muhammad Ali Jinnah University, Islamabad Campus, Pakistan
On Hexagonal Cells..? Hexagon geometry approximates omni-directional base
station with free space propagation
Dr. Noor M KhanDr. Noor M KhanDr. Noor M KhanDr. Noor M KhanEE, MAJUEE, MAJUEE, MAJUEE, MAJU
EE6733 Cellular Mobile CommunicationsWeek 3Week 3Week 3Week 3- ---4 ; Fall4 ; Fall4 ; Fall4 ; Fall - --- 2009200920092009
Cellular Concept 7
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Muhammad Ali Jinnah University, Islamabad Campus, Pakistan
Simple Calculation
Let S be the total number of duplex channels Let k be the number of channels in each cell N cells collectivel use the com lete set of S
Dr. Noor M KhanDr. Noor M KhanDr. Noor M KhanDr. Noor M KhanEE, MAJUEE, MAJUEE, MAJUEE, MAJU
EE6733 Cellular Mobile CommunicationsWeek 3Week 3Week 3Week 3- ---4 ; Fall4 ; Fall4 ; Fall4 ; Fall - --- 2009200920092009
Cellular Concept 8
available channels.
N is the cluster size ( N =4,7 or 12), then S = kN If a cluster is replicated M times Total number of duplex channels = MS= MkN 1/N is called the frequency re-use factor
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Muhammad Ali Jinnah University, Islamabad Campus, Pakistan
More About Cellular Structure
Each cell has exactly six equidistantneighbors Thus there is onl certain cluster sizes and
Dr. Noor M KhanDr. Noor M KhanDr. Noor M KhanDr. Noor M KhanEE, MAJUEE, MAJUEE, MAJUEE, MAJU
EE6733 Cellular Mobile CommunicationsWeek 3Week 3Week 3Week 3- ---4 ; Fall4 ; Fall4 ; Fall4 ; Fall - --- 2009200920092009
Cellular Concept 9
cell layouts possible
It can be shown that the number of hexagonal cells per cluster is given by
N = i 2 + ij + j 2
i & j are non negative integers
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i & j, Co-Channel Neighbors
To find the nearest co-channel neighbors Move i cells along any chain of hexagons
Dr. Noor M KhanDr. Noor M KhanDr. Noor M KhanDr. Noor M KhanEE, MAJUEE, MAJUEE, MAJUEE, MAJU
EE6733 Cellular Mobile CommunicationsWeek 3Week 3Week 3Week 3- ---4 ; Fall4 ; Fall4 ; Fall4 ; Fall - --- 2009200920092009
Cellular Concept 10
Turn 60 degrees counter clockwise, and
move j cells
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Muhammad Ali Jinnah University, Islamabad Campus, Pakistan
Example
i= 3, (move 3 cells alongany chain of hexagons)
Dr. Noor M KhanDr. Noor M KhanDr. Noor M KhanDr. Noor M KhanEE, MAJUEE, MAJUEE, MAJUEE, MAJU
EE6733 Cellular Mobile CommunicationsWeek 3Week 3Week 3Week 3- ---4 ; Fall4 ; Fall4 ; Fall4 ; Fall - --- 2009200920092009
Cellular Concept 11
j=2 (turn 60 degreescounter clockwise andmove 2 cells);
i=3
j=2 This is the way to find thecentral cell of the new cluster
Number of cells in thecluster; N=9+3*2+4=19.
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Channel Assignment
Channel assignment (Frequency reuse) efficient utilization of radio spectrum increased capacity
Dr. Noor M KhanDr. Noor M KhanDr. Noor M KhanDr. Noor M KhanEE, MAJUEE, MAJUEE, MAJUEE, MAJU
EE6733 Cellular Mobile CommunicationsWeek 3Week 3Week 3Week 3- ---4 ; Fall4 ; Fall4 ; Fall4 ; Fall - --- 2009200920092009
Cellular Concept 13
Channel assignment can be fixed dynamic
Affects performance especially handover (handoff )
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Fixed Channel Assignment
Each cell is allocated a predetermined set of channels An call attem t within the cell can onl be
Dr. Noor M KhanDr. Noor M KhanDr. Noor M KhanDr. Noor M KhanEE, MAJUEE, MAJUEE, MAJUEE, MAJU
EE6733 Cellular Mobile CommunicationsWeek 3Week 3Week 3Week 3- ---4 ; Fall4 ; Fall4 ; Fall4 ; Fall - --- 2009200920092009
Cellular Concept 14
served by the unused channels in that cell Variations that allow channel borrowing
exist A cell is allowed to borrow from its neighbor MSC supervises the borrowing procedure
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Muhammad Ali Jinnah University, Islamabad Campus, Pakistan
Dynamic Channel Assignment
Each time a call is attempted, the servingBS request a channel from the MSC The lendin al orithm take into account
Dr. Noor M KhanDr. Noor M KhanDr. Noor M KhanDr. Noor M KhanEE, MAJUEE, MAJUEE, MAJUEE, MAJU
EE6733 Cellular Mobile CommunicationsWeek 3Week 3Week 3Week 3- ---4 ; Fall4 ; Fall4 ; Fall4 ; Fall - --- 2009200920092009
Cellular Concept 15
likelihood of future blocking frequency re-use of candidate channel other cost functions
Dynamic schemes reduces the call blockingprobability and increases system capacity
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Muhammad Ali Jinnah University, Islamabad Campus, Pakistan
Implications
Dynamic schemes require the MSC tocollect real time data on all channels hannel occu anc
Dr. Noor M KhanDr. Noor M KhanDr. Noor M KhanDr. Noor M KhanEE, MAJUEE, MAJUEE, MAJUEE, MAJU
EE6733 Cellular Mobile CommunicationsWeek 3Week 3Week 3Week 3- ---4 ; Fall4 ; Fall4 ; Fall4 ; Fall - --- 2009200920092009
Cellular Concept 16
Traffic distribution Radio signal strength indications (RSSI)
Makes the MSC more complex, andincreases its storage and computational load
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Muhammad Ali Jinnah University, Islamabad Campus, Pakistan
Handover (Handoff)
Need to be performed successfully andinfrequently as possible and be transparent tousers
Dr. Noor M KhanDr. Noor M KhanDr. Noor M KhanDr. Noor M KhanEE, MAJUEE, MAJUEE, MAJUEE, MAJU
EE6733 Cellular Mobile CommunicationsWeek 3Week 3Week 3Week 3- ---4 ; Fall4 ; Fall4 ; Fall4 ; Fall - --- 2009200920092009
Cellular Concept 17
Need to decide the optimum signal level toperform handover
Generally the level is decided the handover
level is set slightly above it = P r handover - P r minimum usable
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Example
Dr. Noor M KhanDr. Noor M KhanDr. Noor M KhanDr. Noor M KhanEE, MAJUEE, MAJUEE, MAJUEE, MAJU
EE6733 Cellular Mobile CommunicationsWeek 3Week 3Week 3Week 3- ---4 ; Fall4 ; Fall4 ; Fall4 ; Fall - --- 2009200920092009
Cellular Concept 18
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Dwell Time
The time a call may be maintained within a cell,without handover, is called the dwell time . Dwell time is dependent on a number of factors
Dr. Noor M KhanDr. Noor M KhanDr. Noor M KhanDr. Noor M KhanEE, MAJUEE, MAJUEE, MAJUEE, MAJU
EE6733 Cellular Mobile CommunicationsWeek 3Week 3Week 3Week 3- ---4 ; Fall4 ; Fall4 ; Fall4 ; Fall - --- 2009200920092009
Cellular Concept 19
propagation interference distance from BS etc.
Therefore even a stationary subscriber may have arandom and finite dwell time
8/2/2019 MAJU Cell 2009 Fall Week 3 4 5 Cellular Concept Mobility RFPlanning Trunking
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Mobile Assisted Handover(MAHO)
In analog systems the signal strength was measuredby the base station and supervised by the MSC,
The MSC decides if a handover is necessary or not
Dr. Noor M KhanDr. Noor M KhanDr. Noor M KhanDr. Noor M KhanEE, MAJUEE, MAJUEE, MAJUEE, MAJU
EE6733 Cellular Mobile CommunicationsWeek 3Week 3Week 3Week 3- ---4 ; Fall4 ; Fall4 ; Fall4 ; Fall - --- 2009200920092009
Cellular Concept 20
assisted Mobile measures signal strength and reports to the
serving BS
Handover is initiated when power received from the BSof a neighboring cell begins to exceed the power receivedfrom the current BS - certain level & duration
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Handover 2
MAHO is faster and more suited for micro cellularenvironments It is also possible to have intersystem handover,
Dr. Noor M KhanDr. Noor M KhanDr. Noor M KhanDr. Noor M KhanEE, MAJUEE, MAJUEE, MAJUEE, MAJU
EE6733 Cellular Mobile CommunicationsWeek 3Week 3Week 3Week 3- ---4 ; Fall4 ; Fall4 ; Fall4 ; Fall - --- 2009200920092009
Cellular Concept 21
Handover from a cell of one MSC to a cell of anotherMSC
Numerous issues
A local call (initially) may become a long distance call Need to deal with incompatibility of the MSC
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Muhammad Ali Jinnah University, Islamabad Campus, Pakistan
Handover Policy Ways of handling handover requests
Same as all initial call requests Give it higher priority Queue requests
Dr. Noor M KhanDr. Noor M KhanDr. Noor M KhanDr. Noor M KhanEE, MAJUEE, MAJUEE, MAJUEE, MAJU
EE6733 Cellular Mobile CommunicationsWeek 3Week 3Week 3Week 3- ---4 ; Fall4 ; Fall4 ; Fall4 ; Fall - --- 2009200920092009
Cellular Concept 22
in mid conversation than being blocked on a newcall attempt
Fraction of the total available channels in a cell isreserved for handover requests from ongoing calls- guard channel
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Practical HandoverConsiderations
Cell dragging - pedestrian users that provide avery strong signal to the BS (LOS), but moved toa close range of another base station causing
Dr. Noor M KhanDr. Noor M KhanDr. Noor M KhanDr. Noor M KhanEE, MAJUEE, MAJUEE, MAJUEE, MAJU
EE6733 Cellular Mobile CommunicationsWeek 3Week 3Week 3Week 3- ---4 ; Fall4 ; Fall4 ; Fall4 ; Fall - --- 2009200920092009
Cellular Concept 23
Difficulty in obtaining physical cell sites Zoning laws (no high rise structures) Public protest (radiation concerns) e.t.c
Too many handoffs for high speed mobiles (on avehicle)
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Handoff Improvements
First generation mobile 10s to make handoff and = 6-12 dB. ( = P r handover - P r minimum usable )
GSM II eneration 1-2s to make handoff with
Dr. Noor M KhanDr. Noor M KhanDr. Noor M KhanDr. Noor M KhanEE, MAJUEE, MAJUEE, MAJUEE, MAJU
EE6733 Cellular Mobile CommunicationsWeek 3Week 3Week 3Week 3- ---4 ; Fall4 ; Fall4 ; Fall4 ; Fall - --- 2009200920092009
Cellular Concept 24
= 0-6 dB.
Better system efficiency and handling high speedvehicles
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Soft Handoff
Channelized wireless systems (such as GSM) haveto switch channels in the process of handoff There is always risk of losing the connection
Dr. Noor M KhanDr. Noor M KhanDr. Noor M KhanDr. Noor M KhanEE, MAJUEE, MAJUEE, MAJUEE, MAJU
EE6733 Cellular Mobile CommunicationsWeek 3Week 3Week 3Week 3- ---4 ; Fall4 ; Fall4 ; Fall4 ; Fall - --- 2009200920092009
Cellular Concept 25
- , o e v s on u t p e ccesssystem provides Soft Handoff . Soft Handoff does not mean changing the channel
but rather deciding which base station will handlethe connection This is a unique property of CDMA concept.
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CDMA Frequency ReusePattern
G CA
B
CDM
Dr. Noor M KhanDr. Noor M KhanDr. Noor M KhanDr. Noor M KhanEE, MAJUEE, MAJUEE, MAJUEE, MAJU
EE6733 Cellular Mobile CommunicationsWeek 3Week 3Week 3Week 3- ---4 ; Fall4 ; Fall4 ; Fall4 ; Fall - --- 2009200920092009
Cellular Concept 26
AG
FE
C
D
BF
ED
G
FE
C
DA
B
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Co-channel Interference
There are several cells that use the same setfrequencies co-channel cells
Dr. Noor M KhanDr. Noor M KhanDr. Noor M KhanDr. Noor M KhanEE, MAJUEE, MAJUEE, MAJUEE, MAJU
EE6733 Cellular Mobile CommunicationsWeek 3Week 3Week 3Week 3- ---4 ; Fall4 ; Fall4 ; Fall4 ; Fall - --- 2009200920092009Cellular Concept 27
Interference between signals from these cells iscalled co-channel interference
Unlike thermal noise, this cannot be overcome by
increasing the signal power The co-channel cells must be physically separated
h d l h l b d k
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Muhammad Ali Jinnah University, Islamabad Campus, Pakistan
Co-channel Interference
Because the cell size is same, co-channelinterference is independent of transmitted power It is a function of the radius of the cell ( R), and
Dr. Noor M KhanDr. Noor M KhanDr. Noor M KhanDr. Noor M KhanEE, MAJUEE, MAJUEE, MAJUEE, MAJU
EE6733 Cellular Mobile CommunicationsWeek 3Week 3Week 3Week 3- ---4 ; Fall4 ; Fall4 ; Fall4 ; Fall - --- 2009200920092009Cellular Concept 28
the distance to the center of the nearest co-channel cell ( D ) For hexagonal geometry, co-channel reuse ratio
Q is given by N
DQ 3==
M h d Ali Ji h U i i I l b d C P ki
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Carrier to Interference Ratio
Carrier to Interference ratio (SIR or S/I) is alsoindependent of transmitted power It is a function of the radius of the cell ( R), and
Dr. Noor M KhanDr. Noor M KhanDr. Noor M KhanDr. Noor M KhanEE, MAJUEE, MAJUEE, MAJUEE, MAJU
EE6733 Cellular Mobile CommunicationsWeek 3Week 3Week 3Week 3- ---4 ; Fall4 ; Fall4 ; Fall4 ; Fall - --- 2009200920092009Cellular Concept 29
the distance to the center of the nearest co-channel cell ( D ) For the first tier in hexagonal geometry, Carrier
to Interference ratio is usually taken as( )
421 1
36 6
S D N
I R
=
free space
E d i t e
d b y F
ox i t R
e a d er
C o p y r i gh
t ( C ) b y F
ox i t
S of t w
ar e C om
p an
y ,2 0 0 5 -2
0 0 8
F or E v
al u a t i on
Onl y .
M h d Ali Ji h U i it I l b d C P ki t
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Some Arithmetic Again
Let i 0 be the number of co channelinterfering cells then carrier signal to interference ratio (SIR)
Dr. Noor M KhanDr. Noor M KhanDr. Noor M KhanDr. Noor M KhanEE, MAJUEE, MAJUEE, MAJUEE, MAJU
EE6733 Cellular Mobile CommunicationsWeek 3Week 3Week 3Week 3- ---4 ; Fall4 ; Fall4 ; Fall4 ; Fall - --- 2009200920092009Cellular Concept 30
S - desired signal power from desired BS; I i -interference power caused by the ithinterfering co-channel cell BS
0
1
i
ii
I I
=
=
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Received Power Ave. received signal strength at any point decays
as a power law of the distance of separation ( d )and is given byn
d
Dr. Noor M KhanDr. Noor M KhanDr. Noor M KhanDr. Noor M KhanEE, MAJUEE, MAJUEE, MAJUEE, MAJU
EE6733 Cellular Mobile CommunicationsWeek 3Week 3Week 3Week 3- ---4 ; Fall4 ; Fall4 ; Fall4 ; Fall - --- 2009200920092009Cellular Concept 31
P 0 - Power received at a close-in reference point inthe far field region of the antenna at a smalldistance; n - path loss component (2-4)
r
d =
00
=
00 log10)()( d
d ndBmPdBmPr
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SIR
If D i is the distance of the ith
interferer, thereceived power at a given mobile due to the i th
interfering cell will be proportional to (D i)-n
Dr. Noor M KhanDr. Noor M KhanDr. Noor M KhanDr. Noor M KhanEE, MAJUEE, MAJUEE, MAJUEE, MAJU
EE6733 Cellular Mobile CommunicationsWeek 3Week 3Week 3Week 3- ---4 ; Fall4 ; Fall4 ; Fall4 ; Fall - --- 2009200920092009Cellular Concept 32
When the transmit power of each BS is equaland the path loss exponent is the same
=
= 0
1
)(i
i
ni
n
D
R
I
S
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Simpler SIR
Considering only the first layer of interferingcells & if all these BS are equidistant
Dr. Noor M KhanDr. Noor M KhanDr. Noor M KhanDr. Noor M KhanEE, MAJUEE, MAJUEE, MAJUEE, MAJU
EE6733 Cellular Mobile CommunicationsWeek 3Week 3Week 3Week 3- ---4 ; Fall4 ; Fall4 ; Fall4 ; Fall - --- 2009200920092009Cellular Concept 33
i0 - number of neighboring/interfering co-channel cells
00 ii I ==
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Interference LimitationExample
i0 =6 number of co-channel cells N =7 n = 2
Dr. Noor M KhanDr. Noor M KhanDr. Noor M KhanDr. Noor M KhanEE, MAJUEE, MAJUEE, MAJUEE, MAJUEE6733 Cellular Mobile Communications
Week 3Week 3Week 3Week 3- ---4 ; Fall4 ; Fall4 ; Fall4 ; Fall - --- 2009200920092009Cellular Concept 34
Considering only the first layer of interferingcells & if all these BS are equidistant
26 I ==
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1 6
2 12
Dr. Noor M KhanDr. Noor M KhanDr. Noor M KhanDr. Noor M KhanEE, MAJUEE, MAJUEE, MAJUEE, MAJUEE6733 Cellular Mobile Communications
Week 3Week 3Week 3Week 3- ---4 ; Fall4 ; Fall4 ; Fall4 ; Fall - --- 2009200920092009Cellular Concept 35
3 18
k 6k
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Interference Limitation
n
=
= 0
1
)(i
i
ni
n
D
R I S
N kR D K 31
0 !1!
]0Pr[ C
k
k C
C
k A
C AC A
Adelay
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Grade of Service for DelayedCalls
]Pr[ t delayGOS >=
Dr. Noor M KhanDr. Noor M KhanDr. Noor M KhanDr. Noor M KhanEE, MAJUEE, MAJUEE, MAJUEE, MAJU
EE6733 Cellular Mobile CommunicationsWeek 3Week 3Week 3Week 3- ---4 ; Fall4 ; Fall4 ; Fall4 ; Fall - --- 2009200920092009Cellular Concept 48
( ) H
t AC
edelay
>= ]0Pr[
]0|Pr[]0Pr[ >>>= delayt delaydelay
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Average Delay in a QueuedSystem
The average delay D for all calls in a queuedsystem is: H
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EE6733 Cellular Mobile CommunicationsWeek 3Week 3Week 3Week 3- ---4 ; Fall4 ; Fall4 ; Fall4 ; Fall - --- 2009200920092009Cellular Concept 49
Where the average delay in the queue is H/(C-A) H average duration of a call
C number of channels A total offered traffic
AC