Chapter1 Cellular Concepts

NCCU Wireless Comm. Lab.

Cellular Concepts

IntroductionFrequency reuseChannel assignment strategiesInterferenceImproving capacity in cellular system

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Introduction

The cellular concept was a major breakthrough in solving the problem of spectral congestion and user capacity.

It offered very high capacity in a limited spectrum allocation without any major technological changes.

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Frequency reuse

The use of radio channels on the same carrier frequency to cover different areas which are separated from one another by sufficient distance so that co-channel interference is not objectionable.

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Cluster

Consider a cellular system which has a total of S channels available and each cell is allocated a group of k channels(k <S).

S= k N

The N cells which collectively use the complete set of available frequencies is called a cluster.

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Co-Channel Cells

• Using “Shift parameters”(i,j) to lay out a cellular system.

•Move i cells along anychain of hexagons ; turn counter-clockwise 60 degree ; move j cells along thechain that lies on thisnewheading.

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22 jijiN ++=•


Co-Channel Cells

N=4 Q=D/R=4.6N=7

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Co-Channel Cells

Q=D/R=6N=12

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Co-Channel Cells

( ) ( )( ) ( )2121212

2

1212 vvvvuuuud −+−−+−=

31=R

2jij2iD ++=

22 jijiN ++=

NRD 3=

d12:distance between two point with coordinates(u1,v1)and(u2 ,v2)

060=α

∗∗ v,u :coordinates ofpoint P

∗u∗v

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Co-Channel Cells

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Illustration for the heuristic determination of the number of cells per cluster


Co-Channel Cells

Co-channel reuse ratio:

R: radius of the cellD: the distance to the center of the nearest co-

channel cellN: cluster size

NRDQ 3==

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Cluster Size (N) Co-channel Reuse Ratioi=1 , j=1 3 3

i=1 , j=2 7 4.58

i=2 , j=2 12 6

i=1 , j=3 13 6.24


Channel Assignment Strategies

Fixed channel assignment strategy

Each cell is allocated a predetermined set of voice channels.

Dynamic channel assignment strategy

Voice channels are not allocated to different cells permanently.

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Interference

Signal-to-interference ratio (S/I or SIR)

S: desired signal power: the number of co-channel interfering cells: the interference power caused by the ith interfering co-

channel base station

∑=

=

oi

iiI

SIS

1

oi

iI

•Co-channel interference

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Pr: average received powerPo: the power received at a close-in reference point do: distance from the transmitting antenna to the reference pointd : distance from the transmitting antenna to the considered receiver

n

oor d

dPP−

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛=

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛−=

oor d

dlog)dBm(P)dBm(P 10

Interference

Average received power Pr

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Interference

Di:the distance of the ith interference from the mobile

If all the interference base station are equidistant from the desired base station and if the distance is equal to the distance D

( )∑=

−

−

=oi

1i

ni

n

D

RIS

( )o

n

o

n

iN

iRD

IS 3

=⎟⎠⎞

⎜⎝⎛

=

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Interference--Example

Using co-channel reuse ratio Q

( ) ( ) ( ) ( ) 44444

4

DRDR50DR50DRD2R

IS

−−−−−

−

+++++−+−=

..

( ) ( )( )

( ) ( )( ) 442

44

42

44 1250

50501

1121

Q.Q.Q.Q

QQQI

S

+−

−+++

−

−++=

5649647 .IS,.QN ≈=→=For (17dB)

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Interference

Adjacent Channel Interference

---Interference resulting from signals which are adjacent in frequency to the desired signals.

---It can be minimized through careful filtering and channel assignments.

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NCCU Wireless Comm. Lab.1-17

Interference


Improving Capacity in Cellular System

Cell splitting

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A5

A4A1

A6



Sectoring

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A Novel Microcell Zone Concept

Tx/Rx

Tx/Rx

Tx/Rx

Microwaveor fiber opticlink

Zone

Sel

ecto

r

BaseStation

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Reference

W. C. Jack, ed., Microwave Mobile Communication, New York: John Wiley, 1974.“Telephone Service for St. Louis Vehicles,” Bell Laboratories Record, 24, No. 7 (July 1946), pp. 267-268.H. W. Nylund and R. M. Swanson, “Improved Mobile Dial Telephone System,” IEEE Trans. Veh. Commun., 1 1963, pp. 32-36.

“Communication Tomorrow: Who? What? Which? Where? Why? and How Much?” Communication; Part I (October1972), pp. 42-45; Part II (November 1972), pp. 20-23.

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Reference

“World Mobile Telecommunications,” Cambridge, Mass.: Arthur D. Little, 1974.

“A New Era in Mobile Communications,” Raymond Kraus, Consulting Communications Engineers, Inc., 1976.

“The U.S. Mobile Equipment Market,” Report No. 556, May 1978, Frost and Sullivan, Inc.Bell Laboratories, “High-Capacity Mobile Telephone System-Technical Report,” (December 1971), Submitted to the FCC.V. H. MacDonald, “AMPS: The Cellular Concept,”B.S.T.J., this issue, pp. 15-41.

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Reference

Bell Laboratories Report, 46, No. 6 (June 1965), page 210.G. C. DiPiazza, A. Plitkins, and G. I. Zysman, “AMPS: The Cellular Test Bed,” B.S.T.J., this issue, pp. 215-248.

D. L. Huff, “AMPS: The Developmental System,” B.S.T.J., this issue, pp. 249-269.

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Chapter1 Cellular Concepts

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