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The Cellular Concept The Cellular Concept System Design FundamentalsSystem Design Fundamentals
Wireless CommunicationsWireless CommunicationsPrinciples and PracticePrinciples and Practice
22ndnd EditionEditionT.S. T.S. RappaporRappapor
Chapter 3:Chapter 3:
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Adjacent channel interference: interference from adjacent in frequencyto the desired signal.– Imperfect receiver filters allow nearby frequencies to leak into thepassband– Performance degrade seriously due to near-far effect.
Adjacent channel interference
Adjacent channel interference can be minimized through carefulfiltering and channel assignment.• Keep the frequency separation between each channel in a given cell aslarge as possible• A channel separation greater than six is needed to bring the adjacentchannel interference to an acceptable level.
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The Cellular ConceptThe Cellular Concept
44
1919--cell reuse example (N=19)cell reuse example (N=19)
Figure 3.2Figure 3.2 Method of locating coMethod of locating co--channel cells in a cellular system. In this example, channel cells in a cellular system. In this example, NN = 19 (i.e., = 19 (i.e., II = 3, = 3, jj = 2). (Adapted from [Oet83] © IEEE.)= 2). (Adapted from [Oet83] © IEEE.)
55
Smaller N is greater capacitySmaller N is greater capacity
66
Handoffs Handoffs –– the basicsthe basics
77
Umbrella CellsUmbrella Cells
88
CoCo--channel cells for 7channel cells for 7--cell reusecell reuse
99
Cochannel Interference RatioCochannel Interference Ratio
∑=
= N1
1kkI
SIS
From Fig. 3.5From Fig. 3.5
2 2 ≤≤ n n ≥≥ 5 5 -- Path loss exponent depend upon the terrain environmentPath loss exponent depend upon the terrain environment
6q
)q(61
RDS
IS n
n6
1k
nk
==
= −
=
−
∑
nnn
n
)RD(2D2)RD(2R
IS
−−−
−
+++−=
nnn )1q(2q2)1q(21
IS
−−− +++−=
q q == 4.6 for a normal 74.6 for a normal 7--cell cellular Patterncell cellular Pattern
S/I = 54.3 or 17.3 dBS/I = 54.3 or 17.3 dB
Worst Case With Omni Directional AntennaWorst Case With Omni Directional Antenna
1010
Cells are split to add channelsCells are split to add channelsReceive power at the old and new cells:Receive power at the old and new cells:
Pr Pr ~~ PPtotoRR--nn
Pr Pr ~~ PPtn(tn(R/2)R/2)--nn
16PP 1t
2t =
1111
Cell Splitting increases capacityCell Splitting increases capacityExampleExample
RR
Original cell radiusR = 1 kmOriginal cell radiusR = 1 km
Micro cell radiusR = 0.5 kmMicro cell radiusR = 0.5 km
Each BS has NEach BS has Nbsbs=60 channels=60 channels
Number of channelsNumber of channels
a)a) Wihout microcelsWihout microcels5x60=300 ch.5x60=300 ch.
b) With lettered microcelsb) With lettered microcels(5+6)x60=660 ch.(5+6)x60=660 ch.
b) If orijinal BS replaced byb) If orijinal BS replaced bymicrocelsmicrocels(5+12)x60=1020 ch.(5+12)x60=1020 ch.
3 km3 km
1212
Sectoring improves S/ISectoring improves S/I
D+RD+R
DD
4444
4
0.7)(qq1
0.7R)(DDR
IS
−−−−
−
++=
++=4
4
4
0.7)(q0.7R)(DR
IS
+=+
= −
−
ThreeThree--Sector Case:Sector Case: SixSix--Sector Case:Sector Case:
285 or 24.5 dB 285 or 24.5 dB For q=4.6 , S/I = 785 or 29dBFor q=4.6 , S/I = 785 or 29dB
Worst case, without sectoringWorst case, without sectoring
nnn 1)2(q2q1)2(q1
IS
−−− +++−=
For q=4.6 , S/I =For q=4.6 , S/I =
For q=4.6, S/I = 54.3 or 17.3 dB For q=4.6, S/I = 54.3 or 17.3 dB
Penalty: İncreasing handPenalty: İncreasing hand--off; decreasing trunking efficiency.off; decreasing trunking efficiency.
1313
Sectoring improves S/ISectoring improves S/I
1414
InIn--building deployment is the building deployment is the next great growth phase next great growth phase
1515
The Zone Cell ConceptThe Zone Cell Concept
1616
Zone Cell ConceptZone Cell Concept
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