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University of Cyprus
Department of
Computer Science
EPL476: Tutorials* onWireless Computer
Networks Tutorial 3Cellular concept
Pavlos Antoniou
Fall 2011
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University of Cyprus
possible radio coverage of the cell
idealized shape of the cell: hexagonalcell
segmentation of the area into cells
GSM: cellular network
use of several carrier frequencies
not the same frequency in adjoining cells
cell sizes vary from some 100 m up to 35 km depending on
user
density, geography, transceiver power etc. hexagonal shape of
cells is idealized (cells overlap, shapes depend on
geography)
if a mobile user changes cells
handover of the connection to the neighbor cell
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University of CyprusThe Cellular Concept
Cluster of N=7 cells
Cells
Frequency reuse pattern
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University of CyprusFrequency reuse
D = minimum distance betweencenters of cells that use the
same frequency band (channels)
R = radius of celld = distance between centers of
adjacent cells
N = number of cells in a cluster(repetitious pattern)
K = total number of frequencies
(channels) allotted for the system.
Frequencies (channels) for each
cell = K / N
R
d
Clusters of N=7 cells
D
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University of Cyprus3-cell reuse pattern (i=1,j=1)
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University of Cyprus4-cell reuse pattern (i=2,j=0)
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University of Cyprus7-cell reuse pattern (i=2,j=1)
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University of Cyprus19-cell reuse example (i=3,j=2)
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University of Cyprus
Consider a cell that has L potential of customers(L mobile
units) and that is able to handle N
simultaneous users
If L
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University of Cyprus
Blocking System What is the degree of blocking?
What is the probability the call is blocked?
What is the capacity (N) is needed to achieve a certain
upper bound on the probability of blocking
A=hA = traffic intensity (erlangs)
= the mean rate of calls attempt per unit time (calls/sec)h =
the mean holding time per successful call (secs, mins)
Traffic Engineering
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University of Cyprus
A=h h=N
A=NA = is the average number of channels required = the mean
rate of calls attempt per unit time
h = the mean holding time per successful call = is server
utilization
N = channel capacity (number of servers or channels)
required
Traffic Engineering
Example:
Calling rate: 20 calls/min
Average holding time: 3mins
A = h =60 erlangs
If we want to have 0.5 server utilization
=> we expect a cell with a capacity of 120 channels
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University of CyprusWS Chapter 10, Exercise 10.1
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University of CyprusTable needed for Exercise 10.8
