chapter1 cellular concepts
TRANSCRIPT
NCCU Wireless Comm. Lab.
Cellular Concepts
IntroductionFrequency reuseChannel assignment strategiesInterferenceImproving capacity in cellular system
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NCCU Wireless Comm. Lab.
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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NCCU Wireless Comm. Lab.
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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NCCU Wireless Comm. Lab.
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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NCCU Wireless Comm. Lab.
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 ++=•
NCCU Wireless Comm. Lab.
Co-Channel Cells
N=4 Q=D/R=4.6N=7
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NCCU Wireless Comm. Lab.
Co-Channel Cells
Q=D/R=6N=12
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NCCU Wireless Comm. Lab.
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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NCCU Wireless Comm. Lab.
Co-Channel Cells
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Illustration for the heuristic determination of the number of cells per cluster
NCCU Wireless Comm. Lab.
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
NCCU Wireless Comm. Lab.
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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NCCU Wireless Comm. Lab.
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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NCCU Wireless Comm. Lab.
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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NCCU Wireless Comm. Lab.
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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NCCU Wireless Comm. Lab.
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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NCCU Wireless Comm. Lab.
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
NCCU Wireless Comm. Lab.
Improving Capacity in Cellular System
Cell splitting
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A5
A4A1
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NCCU Wireless Comm. Lab.
Improving Capacity in Cellular System
Sectoring
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NCCU Wireless Comm. Lab.
Improving Capacity in Cellular System
A Novel Microcell Zone Concept
Tx/Rx
Tx/Rx
Tx/Rx
Microwaveor fiber opticlink
Zone
Sel
ecto
r
BaseStation
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NCCU Wireless Comm. Lab.
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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NCCU Wireless Comm. Lab.
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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NCCU Wireless Comm. Lab.
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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