11

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:

22

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.

33

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