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Tutorial-3The Cellular Concept-Traffic and System
Capacity-2-(cont.)
Fundamentals ofCellular and Wireless Networks
Lecture ID: ET- IDA-113/114
20.05.2012 , v05
Prof. W. Adibfolieq.drwPage : N Cellular & Wireless
NetworksTechnical University of BraunschweigIDA: Institute of
Computer and Network EngineeringProblem 3.1:Consider a cellular
system for which:An average call holding time H=2 minutes and
average call rate =2 calls/hour per user.Suppose AMPS cellular
system with a total of 395 traffic channels and 7-cell reuse
systemis used. Assuming Erlang B distribution and a designed
blocking probability not more than 1% is required.
Find the number of users in each cell and the number of
performed calls per hour in each cellRepeat (a) employing 120
sectoringRepeat (a) employing 60 sectoring
(Rap. Example 3.9 Ed. 2002)
bfolieq.drwPage : N Cellular & Wireless NetworksTechnical
University of BraunschweigIDA: Institute of Computer and Network
EngineeringSolution 3.1:(a)Traffic Intensity for each user: Au = H
= (2/60) x 2 = 0.006 Erlangs/user.Number of simultaneous users per
cell is:395 (voice channels) 56.42 = 57 channels 7
Cells/cluster
Given C=57, B=1% A = 44.2 Erlangs (From Erlang B Table).
Total number of users per cell:U= (A/Au)=(44.2/0.006) 669.7 =
670 users/cell.
No. of calls = 670 x 2 calls/hour = 1,340 calls/hour.
(b)For 120 sectoring: the number of simultaneous users per
sector is:57 channels = 19 channels 3
Given C=19, B=1% A = 11.2 Erlangs (From Table).
bfolieq.drwPage : N Cellular & Wireless NetworksTechnical
University of BraunschweigIDA: Institute of Computer and Network
EngineeringTotal number of users per sector:Usec=
(A/Au)=(11.2/0.006) 169.7 = 170 users/sector.
Total number of users/cell: U = 3 x 170 = 510 users/cell.
No. of calls = 510 x 2 calls/hour = 1,020 calls/hour.
(c)For 60 sectoring: the number of simultaneous users per sector
is:57 channels 9.5 = 10 channels 6
Given C=10, B=1% A = 4.46 Erlangs (From Table).Total number of
users per sector:Usec= (A/Au)=(4.46/0.006) 67.57 = 67
users/sector.
Total number of users/cell: U = 6 x 67 = 402 users/cell.
No. of calls/hour = 402 x 2 calls/hour = 804 calls/hour.
bfolieq.drwPage : N Cellular & Wireless NetworksTechnical
University of BraunschweigIDA: Institute of Computer and Network
Engineering
bfolieq.drwPage : N Cellular & Wireless NetworksTechnical
University of BraunschweigIDA: Institute of Computer and Network
Engineering
213Lees Microcell Zone Concept Large central sender is replaced
by 3 or more low power senders (coverage radius is retained) 3
zones act as receivers but only the best receiving zone sites sends
When the mobile moves, the zone may change but the channel remains
(no handover is necessary) Co-channel interference is small and N=3
can be used instead of N=7. Thus the capacity is increased by the
factor 7/3 = 2.33
135 each(Controls all 3 zones)bfolieq.drwPage : N Cellular &
Wireless NetworksTechnical University of BraunschweigIDA: Institute
of Computer and Network EngineeringChannel Planning for Wireless
SystemsAllocated frequency Typically 5% of the channels are used
for control, mostly 1 control channel/cell Rest channels for
payload (voice, data, ...)1 2 B kHz/channel3 4 5 6 7 8 9 10
kf1f2Total badwidth= f2 f1Total number of channels k = f2 f1/
BB1112... 1 4 7 10 2 5 8 11 3 6 912Frequency distribution in
adjacent cellsChannel spacingExample: 3B channel spacing within the
cell Channel assignment Strategies:1. Fixed channel assignment
strategy2. Dynamic channel assignment strategy (read Ch 2.3 in
textbook) c1 c2c3 bfolieq.drwPage : N Cellular & Wireless
NetworksTechnical University of BraunschweigIDA: Institute of
Computer and Network EngineeringProblem 3.2:Sketch the fixed
channel allocation in AMPS (Analog FDMA) and IS-136 (digital
FDMA/TDMA)Cellular systemFor A cellular cluster size of N=7
Solution: Both systems use 12.5 MHz bandwidth with 30 kHz per
channelA total of 416 channels are available21 are used for control
and 395 for voice communicationIn AMPS every channel carries one
voice call in IS-136 every channel carries 3 calls in TDMAWe have
395 channels per cluster and N=7 cells/cluster. Number of
channels/cell=395/7=56.42, therefore 56 or 57 channels/cell are
used.
Cell 1 has channels: ( 1, 8, ..... , 393), ch. number=(1 + 7. t
), where t = 0 to 56 (57 channels) Cell 2 has channels: ( 2, 9,
..... , 394), ch. number=(2 + 7. t ), where t = 0 to 56 (57
channels)Cell 3 has channels: ( 3, 10, .... , 395), ch. number=(3 +
7. t ), where t = 0 to 56 (57 channels) Cell 4 has channels: ( 4,
11, .... , 389), ch. number=(4 + 7. t ), where t = 0 to 55 (56
channels)Cell 5 has channels: ( 5, 12, .... , 390), ch. number=(5 +
7. t ), where t = 0 to 55 (56 channels) Cell 6 has channels: ( 6,
13, .... , 391), ch. number=(6 + 7. t ), where t = 0 to 55 (56
channels)Cell 7 has channels: ( 7, 14, .... , 392), ch. Number= (7
+ 7. t ), where t = 0 to 55 (56 channels) Total sum= 395
channelsFixed channel spacing within a cell is 7example 5.17 in the
Book: principles of Wireless Networks, by K. Pahlavan and P.
Krishnamurthy
(corrected)1234567{1,8,15,22..}{7,14,21,28..}bfolieq.drwPage : N
Cellular & Wireless NetworksTechnical University of
BraunschweigIDA: Institute of Computer and Network
EngineeringProblem 3.3:Sketch the fixed channel allocation in GSM
using 125 channels each 200 KHz in FDMA mode (total bandwidth for
one way is 25 MHz). Every channel carries 8 voice channels in TDMA
mode.
A typical cluster size of N=4 is used
Solution:
A total of 124 channels are availablefor voice communication and
1 channel for control.
For A cellular cluster size of N=4
Cell 1 has channels: ( 1, 5, ..... , 120)Cell 2 has channels: (
2, 6, ..... , 121)Cell 3 has channels: ( 3, 7, ..... , 122)Cell 4
has channels: ( 4, 8, ..... , 123)
Fixed channel spacing within a cell is 4
example 5.16 from the Book: principles of Wireless Networks, by
K. Pahlavan and P. Krishnamurthy)12341234123431
channels/cellbfolieq.drwPage : N Cellular & Wireless
NetworksTechnical University of BraunschweigIDA: Institute of
Computer and Network Engineering
