Capacity utilization and admission control in the downlinkof WMAX

International Review on Computers and Software (I.RE.CO.S), Vol. 5, N. 2 March 2010.
Manuscript received and revised February 2010, accepted March 2010 Copyright © 2010 Praise Worthy Prize S.r.l. - All
rights reserved
CAPACITY UTILIZATION AND ADMISSION CONTROL IN THE
DOWNLINK OF MOBILE WIMAX
D. S. Shu’aibu, S. K. Syed-Yusof and N. Fisal
Abstract – WiMAX is a broadband wireless technology that uses base station like the present
GSM. WiMAX offers services to different traffic classes with different quality of services
requirements. Unlike GSM, five different traffics were identified in WiMAX in which all
subscribers can be in any of the traffics. These traffics are either constant bit rate application or
variable bit rate. In this paper, we present a call admission control that divides the total
bandwidth capacity (bit rate) of the down link in to constant bit rate traffics and variable bit rate
traffics within the base station coverage and those out of coverage area through the relay
station. The relay station is assumed to decode and forward. Eight different traffics were
randomly deployed a number of times, in to the sector of the cell of the base station and the relay
station. The traffics were admitted based on their signal to noise ratio (SNR), bit rate and
availability of the bandwidth on the down link sub-frame. The results showed that the propose
admission policy utilizes the capacity more efficiently and the bandwidth is well managed
compare to the conventional policy in WiMAX system.
Keywords: admission control, bandwidth management, blockage, Data rate, policy, QoS,
rejection, andTraffics.
Nomenclature
BE Best effort
UGS Unsolicited Grand Service
rtPs Real time polling service
nrtPs None real time polling service
ertPs Extended real time polling service
cbr Constant bit rate
vbr Variable bit rate
QoS Quality of service
SNR Signal to noise ratio
cbr Constant bit rate
vbr variable bit rate
J Total data rate capacity
nslot Total no of down link slots
nsubch Total no of downlink sub-channels
nDLOFDMA Total OFDMA symbol in the downlink
DLsub Total number of downlink subcarriers
ncs no. of subcarriers per sub-channels
nif no. of information bits per subcarrier
Cr coding rate
M number of symbols
fD frame duration
nf no of frame per second
TDcbr Total capacity of cbr for base station
TDvbr Total capacity of vbr for base station
TDrly Total capacity of Relay station
TDrly(cbr), TDrly(vbr) cbr and vbr capacity in relay station
I. Introduction
WiMAX is the next-generation of the wireless
broadband technology designed to enable pervasive,
high-speed mobile internet access to a very large
coverage area. WiMAX has the solution of the problems
of non-coverage area in the rural community [1]. It has
radius coverage of several kilometers at data rate of
about 75Mbps [1], [2]. WiMAX provides service to
many devices like notebook personal computer; handset,
Smartphone and some consumers’ electronics such as
gaming devices, cameras, camcorder, and music player.
It is the first of all IP mobile internet solution enabling
efficient and scalable networks for data, video and voice
[3]. It is the only wireless MAN that operates at scalable
bandwidth, different mode of access (OFDM and
OFDMA) and also it uses different value of cyclic prefix
[1], [4], [5], [6], [7]. It supports QoS on the wireless
domain and interfaces for ATM, IP, E1/T1 and
Ethernet. Due to its functionality, it supports several
broadband services like voice over IP and video on
demand [2].
WiMAX forum in [1] has identified and classified the
traffics expected in WiMAX in to five categories. These
are;- Unsolicited grand service (UGS), Real time polling
service (rtPs), non-real time polling service (nrtPs), best

Copyright © 2007 Praise Worthy Prize S.r.l. - All rights reserved International Review on Computers and Software, Vol. 5, N. 2
effort (BE) and extended real time polling service
(ertps). These traffics are randomly deployed into the
coverage area of WiMAX and request for entry in to the
network. There is a need to have proper and efficient
policy on how these traffics can be admitted in to the
network. Admission control can be consider as one of
such policy which is a trade of whether to optimize the
revenue or to satisfied the subscribers’ requirements.
A lot of researches were conducted in the area of
admission control of wireless and wire communication
system. In [8] admission policy was considered to be
optimization problems in which utility and fairness
constrained greedy revenue algorithm was used, the
problem here is that there is no demarcation between the
constant bit rate application and variable bit rate
application, thus the bandwidth is not properly
optimized because a lot of variable bit rate applications
will consumed the bandwidth as such the revenue may
not be optimized. In [9] adaptive power allocation was
combine with work in [8] and the same policy was
implemented. In [10] possibility of providing access to
the base station (BS) by applying ad-hoc network to
extend the service to subscribers outside the BS coverage
with other mobile station in the relay coverage area was
considered. Giving admission by ad-hoc network does
not grantee good quality of service.
Admission control for multimedia application in
cellular networks using semi Markov decision model
was used in [11], the target was to get optimal policy
that seeks to optimized blocking probability but in the
same paper it was started that optimal policy cannot be
implemented in a real system. Admission control for
MPEG-4 videoconference traffics was considered in [12]
over next generation cellular wireless network a good
quality of services was grantee to all videoconference
users, what happen if other traffics joint the network? In
[13] admission control was investigated when it comes
to hand-over from one base station to the target base
station by adaptively adjusting the guard channel of the
target BS this may not work well with some traffic.
None real time traffic bandwidth was adaptively reduce
by using fuzzy logic in [14] the problem with this is that
if the channel changes, the nrtps traffic may eventually
be blocked. A parameter call load factor was used to
estimate the network congestion in [15], every time
there is request for entry in to the network the parameter
is calculated and then compare with a certain threshold
value before admission this is additional over head.
In this paper, admission control in downlink of mobile
WiMAX (IEEE802.16e) is considered by divide the total
bandwidth into constant bit rate & variable bit rate
applications through base station and those traffics at the
extended coverage area of base station, which are also
constant bit rate & variable bit rate applications. The
traffics applications have four access zones depending
on where the traffic is and its type. The rest of the report
is organized in the following format; section II deals
with the traffics in mobile WiMAX, proposed admission
control policy in section III, simulation results was in
section IV, the report is concluded in V.
II. TRAFFICS IN MOBILE WIMAX
The traffic classes in mobile WiMAX are classified in to
five categories, as showing in Table 1, quality of service
required by each of this traffic is indicated on the same
table 1.
TABLE I
WIMAX APPLICATION CLASSES
Application
Bandwidth
guideline
Latency Jitter
guideline
Multiplayer
interactive
gaming
50-85 kbps <150ms <100ms
VoIP & Video
Conference 4-384 kbps <150m <50msec
Streaming
Media
5kbps – 2Mbps N/A <100ms
Web Browsing
and Instant
message
10kbps – 2Mbps N/A N/A
Media content
downloads
>2Mbps N/A N/A
The following 8 specific traffics were extracted from [1]
for the purpose of this work. Table 2 gives the specific
traffic type extracted from [1] except for relay station
which was assumed
TABLE 2
TRAFFIC LOAD USED IN THE DOWNLINK SUB-FRAME
Traffic /
Application
Bandwidth
Requirement
Service Application
Type
Traffic 1
Multiplayer
interactive
gaming
60 kbps rtPs vbr
Traffic 2 Web
Browsing 100 kbps BE vbr
Traffic 3 Video
Conference
384 kbps rtPs vbr
Traffic 4
Streaming
media
2000kbps rtPs vbr
Traffic 5
Music / Speech
Traffic 6
Instant message
Traffic 7
Media content
downloads
128kbps
10kbps
nrtPs vbr
BE vbr

Traffic 8
VoIP
Traffic 9
Relay station
(vbr)
Traffic 10
Relay station
(cbr)
2000kbps
22.8kbps
>200kbps
22.8kbps
nrtPs vbr
UGS/ertPs cbr
rtPs/nrtPs/BE vbr
UGS/ertPs cbr
The traffics in table 2 above were randomly deployed
into the coverage area of the base station, and relay
station. The relay station is modeled to give a maximum
bandwidth of 200kbps per vbr application traffic;. The
bit rate for each variable bit rate application was chosen
gives the required quality of service. A typical business-
quality videoconference runs at 384kbps can deliver TV-
quality video at 25 to 30 frames per second. For music/
speech to have CD quality it is subjective but 128kbps
MP3 is sufficient [1]. A cbr with 22.8Kbps can give
audio quality like GSM [1].
II.1 Downlink Data Rate
The frame of WiMAX is divided in to the uplink and
the downlink, with 5ms duration. When using time
division duplex (TDD) the frame is divided along the
time axis. A total of 47 OFDMA symbols are available
on the frame. It’s divided into n & 47-n where n is total
number of OFDMA symbol in the uplink and 47-n is for
the downlink [1]. The downlink data rate is computed
once the frame size, and other parameters on the frame,
modulation and coding rate are known [16] the formulae
is;
ymbolno_OFDMA_s
bitsformation_
*
_
_ in
periodsymbol
ssubcarrierdata
J 
(1)
Where J, is the physical data rate capacity in bits per
second. The data subcarriers depend on the bandwidth
and the FFT size. The information bits depend on the
type of modulation used and the coding rate [16], [17].
WiMAX uses 4-different types of modulation BPSK,
QPSK, 16-QAM and 64-QAM, BPSK is used in mobile
WiMAX for control message transmission. To assign a
particular types of modulation, SNR is used as given in
[2], [5] as shown in table 3.
TABLE 3
REQUIRED SNR AT THE RECEIVER FOR EACH
MODULATION SCHEME
Modulation
Scheme CODING RATE SNR (dB)
BPSK ½ 6.4
QPSK ½ 9.4
QPSK ¾ 11.2
16-QAM ½ 16.4
16-QAM ¾ 18.2
64-QAM
64-QAM
2/3
¾
22.7
24.4
In some case when the signal to noise ratio is very
good a coding rate of 5/6 of 64-QAM can be use [6], [7].
The receiver (ss) always feedback the channel state
information to the base station via pilot subcarriers, this
help the base station to determine the type of modulation
scheme to be assign to the receiver. Mobile WiMAX use
OFDMA access mode where by the minimum resource
that can be allocated to any subscriber station (ss) is a
slot [1]. Figure 1gives the existing frame structure [1]
and the DL burst for different traffic users. The users are
randomly assigned to a slot without considering the type
of traffics. Figure 2 gives the propose frame structure in
which similar traffics are confine in one segment.
Figure 1 Existing frame structure

Figure 2 Propose frame structure
II.2 Data Rate Modeling
In mobile WiMAX, the frame has different types of
permutation, the partial usage sub channelization
(PUSC), full usage sub channelization (FUSC), tile
usage sub channelization (TUSC) and the Band
Adaptive modulation and coding Band AMC. The total
physical downlink data rate depends on the type of
permutation. In this paper PUSC was use as the
permutation for all subcarriers in the downlink whereby
a slot is defined as two OFDMA symbol by one sub-
channel. The total downlink rate capacity is derived as
follows;-
Let be the total number of slot in the downlink
sub-frame.
2
* _ OFDMADLsubch
slot
nn
n  (2)
Where subchn is total number of sub-channel and
OFDMADLn _ is number of OFDMA symbols in the
downlink, hence the total down link
subcarriers )( subDL is computed as
csslotsub nnDL *
(3)
csn is the number of subcarriers per subchannel. The
total information bits carried by each subcarriers is
given by ifn with coding rate rC
)(log* 2 Mcn rif 
(4)
M is the number of symbols. If Df is the frame duration
and fn is the number of frames per second then,
D
f
f
n
1

(5)
Hence substitute (2,3,4 and 5) in to (1) we have the total
downlink physical data rate capacity as,
fifsub nnDLJ **
(6)
This total capacity in the propose admission control is
subdivide as follows;-
Let cbrTD be the total bit rate capacity allocated to
constant bit rate application through base station, as
shown in figure 2 with red
JxTDcbr *
(7)
For variable bit rate application, let the total allocation
capacity be vbrTD as shown in figure 2 blue area hence
JyTDvbr *
(8)
Then the relay station capacity allocated is given by,
JzTDrly *
(9)
Such that   1)( zyx
x, y and z are fraction of the total capacity
The relay capacity is subdivided among the
traffics applications as in the propose policy as follows;
rlycbrrly TDxTD *1)( 
(10)
Where )(cbrrlyTD is capacity allocated to constant bit
rate application through relay station as shown shaded
white and the last compartment is given by
rlycbrrly TDyTD *1)( 
(11)
Is the capacity allocation for variable bit rate in relay
station as shown shaded with yellow color.
Provided that   1)11( yx
The total downlink rate capacity is then formulated as
optimization problem using equation 7, 8 and 9 the total
downlink bit rate is formulated in (12) to maximize the
number of users.
)max(
111
 

N
i
rly
N
i
vbr
N
i
cbr TDTDTDJ
(12)
where N is the respective number of traffics (users) in
each partition. Equation (12) is further expanded to
include equations 10 & 11 actual traffics and other
control variable as follows

).....
.............max(
1
)(
1
)(
1 1

 

 


N
i
vbrrly
N
i
cbrrly
N
i
N
i
vbrcbr
TDtpTDp
TDtpTDpJ


(13)
Where p is admission matrix indicator which shows that
traffic is admitted or not, the matrix p is given by
whether the traffic is
within the base station or relay station. If =0 the
traffic is within the base station coverage, otherwise is at
relay station coverage. U is a traffic matrix, this indicate
type of traffic been admitted µ5)T
µ1 is for cbr at base station, µ4 is for vbr at relay station.
Seven different traffics types in vbr are used so matrix t
is use to identify the exact traffic. Hence matrix t has
seven elements
this
matrix indicate one out of traffic class from the seven
traffic with variable bit rate. For example if p =( 1 0 0 0
0) and µ=(1 0 0 0 0)T
, it means that a traffic has been
admitted within the base station coverage and the traffic
is cbr application. But for variable traffic matrix t must
be define, as example if p = (0 0 0 1 1), µ= (0 0 0 1 0)T
and t = (0 0 1 0 0 0 0) this means a vbr application has
been admitted through relay station and the application
is videoconference.
III Admission Control Policy
In the propose admission control policy, we made the
following assumptions (i) No provision for handover
traffics (ii) the life time of a traffic admitted is long
enough and (iii) the base station can provide enough
power to all admitted traffics. The propose policy is on
the physical layer of mobile WiMAX.
1 Let Pj be the total capacity of the downlink.
2 Let Px, Py, Pz and Pi represent four different capacity
of pj such that
2.1 px+py+pz+pi ≤ pj
2.2 let x, y z and i be the four traffic type
2.3 Deploy traffics randomly
If traffic is x type
Allocate x in Px such that
∑n
x=1 Px ≤ TDcbr
Elseif traffic is y type
Allocate y in py such that
∑n
y=1 Py ≤ TDvbr
ElseIf traffic is z type
Allocate z in pz such that
∑n
z=1 Pz ≤ TDrly(cbr)
ElseIf traffic is i type
Allocate i in pi such that
∑n
i=1 Pi ≤ TDrly(vbr)
Else
Reject the traffic
End
IV Simulation and Analysis of the Results
The program was run for 30, 50, 100, and 150 traffics
several times. Table 4 gives the simulation parameters
used.
TABLE 4
SIMULATION PARAMETERS OF THE DOWNLINK SUB-FRAME
Parameters Settings
FFT Size
512
Bandwidth
5MHz
DL / UL ratio 35 / 12
No. of DL
Subchannels
15
Data
Subcarriers
Frame duration
Frame
modulation
Scheme
Total DL
Capacity
Modulation
Scheme for the
360
5mS
64-QAM 5/6 Coding rate
12.8Mbs
QPSK, 16-QAM &
64-QAM
The program was run while were randomly deployed
and requesting for entry in to the network with random
SNR through base station and the extended coverage of
relay station. The propose admission policy was used
based on the propose policy and existing policy to admit
a traffic. If the capacity allocated to given section in the
propose policy cannot accommodate a particular traffic
request the traffic is rejected and wait for the next traffic
with less capacity requirement in term of bandwidth.
Figure 3, 5, 7 & 9 shows the results of comparison
between the propose system policy in which the total
capacity is divided into four and the existing one in
which the whole capacity is used without division for 30,
50, 100 & 150 traffic users. Figure 5, 7 & 9 shows that
the propose policy outperformed the existing one in term
of number of blockage as shown. Figure 4, 6, 8 & 10
shows the performance of various traffics in their
respective segments for 30, 50, 100 & 150 users in the
propose admission policy. Figure 11 & 12 gives the
statistical data for the number of admitted traffics and
number of rejected / blockage traffics for 30, 50, 100 &
150 users on both policies. It can be seen that the

propose admission policy performed better than the
existing one.
0 5 10 15 20 25 30
0
2
4
6
8
10
12
14
x 10
6
no of traffics
capacityinbps
graph for 30 random traffics for two the policies
Propose policy
Existing policy
Figure 3 traffics shown across the two
policies for 30 traffics
0 5 10 15
0
1
2
3
4
5
6
7
8
9
x 10
6
no of traffics
Capacityinbps
graph for 30 random traffics
vbr at base station
cbr at base station
vbr relaystation
cbr relay station
Figure 4, traffics across the 4 sections
for 30 traffic users
0 5 10 15 20 25 30 35
0
2
4
6
8
10
12
14
x 10
6
no of traffics
Capacityinbps
graph for 50 random traffics for the two policies
Propose policy
Existing policy
Figure 5 traffics shown across the two policies
for 50 traffic users
0 5 10 15 20
0
1
2
3
4
5
6
7
8
9
x 10
6
no of traffics
Capacityinbps
graph for 50 random Traffic
vbr at base station
cbr at base station
vbr relay station
cbr relay station
Figure 6, traffics across the 4 sections for 50
traffic users
0 10 20 30 40 50
0
2
4
6
8
10
12
14
x 10
6
no of traffics
Capacityinbps
Propose policy
Existing policy

Figure 7 traffics shown across the two
policies for 100 users
0 5 10 15 20 25 30
0
1
2
3
4
5
6
7
8
9
x 10
6
no of traffics
Capacityinbps
vbr at the base station
cbr at the base station
vbr relay station
cbr relay station
Figure 8, traffics across the 4 sections for
100 users
0 10 20 30 40 50 60
0
2
4
6
8
10
12
14
x 10
6
no of traffics
Capacityinbps
Propose policy
Existing policy
Figure 9 traffics shown across the two policies
for 150 users
0 5 10 15 20 25 30 35 40
0
1
2
3
4
5
6
7
8
9
x 10
6
no of traffics
capacityinbps
vbr at base station
cbr at base station
vbr relay station
cbr relay station
Figure 10, Traffics across 4 sections for 150
users
1 2 3 4
0
10
20
30
40
50
60
70
80
90
100
Simulation of 4 scenario
NumberofadmittedTraffics
Using existing policy
Using Propose policy
Figure 11, Statistic of admitted traffics in
the two policies
1 2 3 4
0
20
40
60
80
100
120
Simulation 4 Scenario
Numberofblockedtraffics
Using existing policy
Using Propose policy
Figure 12, Statistic of number of blockage
traffics in the two policies

V Conclusions
In this paper a propose system policy of admission
control is presented, the proposed system performed
better than the existing system policy in term of number
of blockage and capacity utilization. The propose system
ensure that it can provide a quality of service in terms of
bit rate requirements for each traffics. The propose
system has a better bandwidth management because the
number of traffics admitted is higher compare to the
number of traffics in the existing one when the same
traffics are randomly deployed. The propose scheme
consider only one QoS parameter in WiMAX which is
the bandwidth. We also make assumption that there is
no hand over traffics from neighboring base station and
all the traffics pass through the admission control.
Acknowledgment
The authors would like to thank all those who
contributed toward making this research successful. Also,
we would like to thanks to all the reviewers for their
insightful comment. This work was sponsored by the
research management unit, Universiti Teknologi
Malaysia.
References
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Dahiru Sani Shuaibu received his B.Eng and
M.Eng from Bayero University Kano Nigeria
in the year 1999 and 2005 respectively. He has
been working with Bayero University since
2001 as a lecture. He is currently doing his
Ph.D at Universiti Teknologi Malaysia in
Telamatic research group. He is a member of
Nigerian Society of Engineers and a member
Council for the Regulation of Registered Engineers in Nigeria (COREN).
His research interest are radio resource managements and OFDMA based
system
Sharifah Kamilah Bnt Syed Yusof received
BSc (cum laude) in Electrical Engineering from
Geoge Washington University USA in 1988
and obtained her MEE and Ph.D in 1994 and
2006 respectively from universiti Tecknologi
Malaysia. She is currently working as a Senior
lecturer with the department of Radio
Communication, Faculty of Electrical
Engineering Universiti Teknologi Malaysia. Her research interest includes
OFDMA based system, Software define Radio and Cognitive radio.
Norsheila Fisal received her B.Sc. in Electronic
Communication from the University of Salford,
Manchester, U.K. in 1984. M.Sc. degree in
Telecommunication Technology, and PhD
degree in Data Communication from the
University of Aston, Birmingham, U.K. in 1986
and 1993, respectively. Currently, she is a
Professor with the Faculty of Electrical
Engineering, University Technology Malaysia and Director of Telematic
Research Group (TRG) Laboratory.
Her Professional Affiliations are with Member of Institute Electrical and
Electronic Engineers (IEEE), Member of Malaysian National
Confederation of Computers (MNCC), Member of Institute For
Information Processing (IFIP) and Member of Board of Engineer
Malaysia.

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