1. International Review on Computers and Software (I.RE.CO.S.), Vol. 8, N. 1
ISSN 1828-6003 January 2013
Manuscript received and revised December 2012, accepted January 2013 Copyright © 2013 Praise Worthy Prize S.r.l. - All rights reserved
115
A Study on the Effect of Different Velocities
on the Handover Delay in WiMAX Systems
Elmabruk S. Elgembari, Kamaruzzaman B. Seman
Abstract – Mobile WiMAX is a wireless networking system based on the IEEE 802.16e standard.
Currently, mobile WiMAX has a long handover delay that contributes to the overall end-to-end
communication delay. Since the data transmission should be paused during the hard handover
process, it causes handover delay in mobile communication. The handover delay makes severe
degradation in system performance when implemented in real-time applications such as IPTV and
VoIP. However, serving a large number of Mobile Stations (MS) in practice requires an efficient
handover scheme which guarantees lower level of the handover delay, particularly within the
mobility in the coverage area. Many factors are affecting the performance of the handover delay.
In this paper, the study has been done on location management area based multimedia and
multicast/broadcast handover and the modifying different velocity levels of Mobile WiMAX, by
comparing the number of Cells and the size in the location area have shown how all these
parameters within the simulation logarithm can affect the handover delay. Copyright © 2013
Praise Worthy Prize S.r.l. - All rights reserved.
Keywords: Mobile WiMAX, Handover, Handover Delay, Velocity, Packet Loss, Target BS,
Multimedia, Multicast
I. Introduction
Wireless access networks can be divided into micro,
macro, and pico cellular system as in [1], we are
assuming that the configuration of the networks has been
moving from all different aspects of cell size of Location
Management Areas, with the mobile WiMAX velocity,
where these cases will show within the algorithm
simulation processing. As the MBS infrastructure is
aimed at providing the multimedia streaming and despite
mobility with mobile WiMAX, it generally depends on
hard handover which will break call connections to the
serving BS before making a new connections to the
target BS.
This means the packets which are sent from the
current BS to the target BS within the handover
processing action in most cases will not be received, this
is called "services disruption” and this services disruption
causes loss in packet data which will effects the quality
of service. It is one of the reasons behind increasing the
delay in the handover processing therefore; the handover
delay in MBS should be minimized to enhance handover.
II. Background
The multimedia multicast services standard defines an
MBS zone [2], which is a group of adjacent BSs
transmitting the same MBS content of data traffic
streams. In case of the handover between BSs in the
same MBS zone, the handover delay is minimized
because the packets of the same MBS content can be
received from the target BS right after completing a link-
level handover. On the contrary, the handover among
BSs crossing the boundary between different MBS zones
requires not only link-level handover signaling but also
MBS-related signaling, which will take considerable
time. So updating the locations of the Mobile WiMAX
will influence the bandwidth of the handover link
channel, it will waste the link capacity of the air interface
In this paper we studied the handover delay with
modifying algorithm to reducing the delay within
focusing on different mobility velocities of the Mobile
WiMAX, comparing with the converge area size of
LMAs. This paper is structured as follows: the MBS
handover, the WiMAX system architecture and the
handover mechanism in the location management area
based on MBS has been described in section II.I, while
section III coverers the analytical model, the numerical
results and discussion has been presented in section IV,
with the conclusion in section V.
III. Related Work
The architecture of the Mobile WiMAX system is
based on the following entities: mobile station (MS),
access service network (ASN), and connectivity service
network (CSN) [3]. The BS performs radio-related
functions, which is located in the ASN. The CSN
provides IP connectivity services to MSs and performs
administrative functions such as authentication,
authorization, and accounting (AAA), and admission
TM
PDF Editor

2. Elmabruk Salem M. Elgembari, Kamaruzzaman B. Seman
Copyright © 2013 Praise Worthy Prize S.r.l. - All rights reserved International Review on Computers and Software, Vol. 8, N. 1
116
control for WiMAX operators. To provide MBS, a new
functional entity, multicast and broadcast service
controller (MBSC), is introduced, which is typically
multicast connection established between the MSs and
the MBSC.
The MBSC performs service provisioning and
delivery functions for MBS and serves as an entry point
for multimedia contents providers. That is, when a
multimedia stream is ready, the MBSC initiates the
corresponding MBS session by performing resource
reservation for data path and then forwards the
multimedia stream over the WiMAX network. The
handover delay of an MBS session includes two types of
delay: 1) the delay due to the link level messages during
the IEEE 802.16e handover; and 2) the delay due to the
MBS signaling messages.
The former occurs whenever an MS with an ongoing
MBS session switches to the new BS. Fig. 1(a) depicts
how the MBS signaling messages are exchanged after the
MAC layer handover.
As IEEE 802.16 is connection oriented, every
connection between a BS and an MS has its own
connection identifier (CID). To facilitate MBS, all BSs in
the same MBS zone have the same multicast connection
identifier (MCID) and the same security key for MBS
data packets.
In other words, whenever an MS moves from one
MBS zone to another (i.e., inter-MBS zone handover), a
new connection is needed, which is triggered by MBS
join, Step 2.
Fig. 1(a). Inter-MBS Zone handover
Fig. 1(b). Inter-MBS Zone handover
In Fig. 1(a), after the MBS authorization procedure
(Step 3) is done, the resource reservation (Step 4),
security key exchange (Step 5), and multicast distribution
tree update (Step 6) for the new connection will be
performed.
On the other hand, if the MS moves from one BS to
another within the same MBS zone (i.e., intra-MBS zone
handover), no further processing is required except for
the IEEE 802.16e MAC-layer handover (Step 1), as
shown in Fig. 1(b).
In case of the inter-MBS zone handover, the multicast
distribution tree update (Step 6) may not be necessary,
depending on the existence of users of the same MBS
session in the target MBS zone. MBS zones in which
MBS users currently reside are called active MBS zones,
whereas others in which no users for the MBS session
reside are called inactive MBS zones. If an MS enters a
new MBS zone which is inactive, the MS will be the first
user in the MBS zone.
Then, the signaling messages of Steps 4-6 should be
exchanged with all the other BSs in the MBS zone as
well as the target BS. On the other hand, if the target
MBS zone is active (i.e., there is already an MBS user
receiving the same multicast packets).
IV. Analytical Model
In [4] the location management area (LMA)-based on
multimedia multicast/broadcast services handover in
WiMAX systems, where an MBS zone is partitioned into
multiple LMAs, then packets are transmitted only to the
LMAs with MBS users.
The LMA based MBS handover evaluated in terms of
the service disruption time of an MBS session due to
handovers and its bandwidth usage considering the user
distribution and MBS session popularity. We assumed
that the paging area and the wireless cells are square-
shaped where there are n cell in a paging area.
The perimeter of a cell is l where the perimeter of the
paging are denoted as L, is L = lξ݊, mobile nodes move
at an average velocity of v in directions that are
uniformly distributed over [0, 2ʌ], and are uniformly
distributed with density p the cell boundary crossing rate
rc is:
‫ݎ‬௖ ൌ
‫݈ݒ݌‬
ߨ
(1)
MS Serving
BS
Target
BS
MBSC AAA
1. 802.16e
MACͲ
layer
2. Trigger MBS 3. MBS
Authorization
Response
Request
DSA Ͳ REQ
DSA Ͳ RSP
DSA Ͳ ACK Response
4. Resource
Reservation
PKM Ͳ RSP
Key Delivery
5. Security
6. Multicast
Distribution
Tree UpdateResponse
Response
MBS Data Transmission
MS
Serving
BS
Target
BS
MBSC AAA
1. 802.16e
MACͲ
layer
MBS Data Transmission
TM
PDF Editor

3. Elmabruk Salem M. Elgembari, Kamaruzzaman B. Seman
Copyright © 2013 Praise Worthy Prize S.r.l. - All rights reserved International Review on Computers and Software, Vol. 8, N. 1
117
where rc is the cell crossing rate (mobiles/s), p is the
mobile destiny (mobile/m2
); v is the moving velocity
(m/s); and l is the cell perimeter (m). Mobile devices
move across a boundary in two directions.
For evaluation purposes, however, only one direction
needs to be considered. The paging area boundary
crossing rate rp is:
‫ݎ‬௣ ൌ
‫ܮݒ݌‬
ߨ
(2)
One of the drawbacks of the fluid flow mobility model
used in the analysis is that mobile nodes are assumed to
move at constant fixed rate. The mobility model used in
the simulation supports a wide range of mobility
behavior; the mobility model is based on the random
waypoint algorithm [1]. A mobile node picks a random
location in the simulation area as the destination and
moves towards the locations as the speed chosen
uniformly between 0 and the maximum speed. When a
mobile node reaches the destination point, it stops for the
duration of pause time and picks another destination, and
speed and move again.
This cycle is repeated for the duration of the
simulation, when the pause time is set to simulation
duration time, the mobile node remains stationary. As the
pause time decreases so does the movement of the
mobile node. Continuous movement corresponds to a
pause time of 0. Node mobility movement patterns are
generated as in [5].
If the disruption time in multi broadcasting zone when
Z1 and Z2 are the numbers of inter-MBS zone handovers
to inactive MBS zones and to active MBS zones,
respectively; in addition, Z3 be the number of intra-
MBS zone handovers ,then, E [Z] = E [Z1] + E [Z2] and E
[C] = E[Z] + E[Z3].
The average service disruption time for an i-th popular
session in MZ can be obtained from
TMZ,i = E[Z1,i] · DZ1 + E[Z2,i] · DZ2 + E[Z3,i] · DZ3 (3)
where DZ1, DZ2, and DZ3 are unit handover delays of the
inter-MBS zone to an inactive MBS zone.
Let L1 and L2 be the numbers of inter-LMA handovers
to inactive LMAs and to active LMAs without changing
MBS zones, respectively. L3 is the number of intra-LMA
handovers. Since both the inter-LMA handovers and
intra- LMA handovers belong to the intra-MBS zone
handovers, so then E[Z3] = E[L1]+E[L2]+E[L3]. From (3),
the average service disruption time for an i-th popular
session in LMA can be expressed as:
TLMA,i = E[Z1,i] DZ1 + E[Z2,i] DZ2 + E[L1,i] DL1+
+E[L2,i] DL2 + E[L3,i] · DL3
(4)
where DL1, DL2, and DL3 are unit handover delays of the
inter-LMA handover to an inactive LMA, inter-LMA
handover to an active LMA, and intra-LMA handover,
respectively. Recall that L is the random variable for the
number of LMA crossings, which is equal to
E[Z]+E[L1]+E[L2]. By similar derivations in (4) and (5),
the LMA crossing probability per session PL is given by
ఒ೗
ఒ೗శഊೞ
. In addition, the probability mass function of L can
be obtained from Pr (L = n) = ܲ௅
௡
(1 í PL). Then, the
average number of LMA crossings is given by E[L] =
σ ݊Ǥ ܲ௅
௡
൉ ሺͳ െ ‫ܮ‬ሻ’
௡ୀ଴ =
ఒ೗
ఒೞ
.Since E[L1]+E[L2] = E[L]
í E[Z], the average number of inter-LMA handovers
without changing MBS zones is given by E[L] í E[Z] =
ሺఒ೗ି ఒ೥ሻ
ఒೞ
. On the other hand, the probability that there is no
user for session i in an LMA with area Al is p (0, i, Al)
=.݁ିఒ೔஺೗ . Finally, E[L1,i], E[L2,i], and E[L3,i] are derived
as follows:
‫ܧ‬ൣ‫ܮ‬ଵǡ௜൧ ൌ ሺ‫ܧ‬ሾ‫ܮ‬ሿ െ ‫ܧ‬ሾܼሿሻ ȉ ൫ͳ െ ‫݌‬ሺͲǡ ݅ǡ ‫ܣ‬௟ሻ൯ ൌ
ൌ
ሺߣ௟ െ ߣ௭ሻ
ߣ௦
݁ିఒ೔஺೗
(5)
‫ܧ‬ൣ‫ܮ‬ଶǡ௜൧ ൌ ሺ‫ܧ‬ሾ‫ܮ‬ሿ െ ‫ܧ‬ሾܼሿሻǤ ൫ͳ െ ‫݌‬ሺͲǡ ݅ǡ ‫ܣ‬௟ሻ൯ ൌ
ൌ
ሺߣ௟ െ ߣ௭ሻ
ߣ௦
൫ͳ െ ݁ିఒ೔஺೗൯
(6)
‫ܧ‬ൣ‫ܮ‬ଷǡ௜൧ ൌ
ሺߣ௟ െ ߣ௭ሻ
ߣ௦
(7)
Using (3), (4) (5), (6) and (7) we have:
‫ܦ‬௅ெ஺ǡ௜ ൌ
ߣ௭
ߣ௦
ቈ
݁ିఒ೔஺೥ ȉ ‫ܦ‬௓ଵ ൅
൅ ൫ͳ െ ݁ିఒ೔஺೥ ൯ ȉ ‫ܦ‬௓ଶ
቉ ൅
൅
ሺߣ௟ െ ߣ௭ሻ
ߣ௦
ቈ
݁ିఒ೔஺೗ ȉ ‫ܦ‬௅ଵ ൅
൅ ൫ͳ െ ݁ିఒ೔஺೗ ൯ ȉ ‫ܦ‬௅ଶ
቉
ሺߣ௟ െ ߣ௭ሻ
ߣ௦
ȉ ‫ܦ‬௅ଷ
(8)
V. Numerical Results and Discussion
In [6], we assumed that Tho is 50ms and all processing
delays are set to 1 ms which is typically in the literature
Fig. 2, shows the relationship between the perimeter
of the cell site and the velocity of the Mobile WiMAX so
L is running in different perimeters, it started from 100
until 300 with respect to the velocity where the speed
was 60 km/h.
The Disruption time is reduced when the cell site
becomes large, so the bandwidth of air interface within
the handover processing has no much traffic to receive,
beside the operations of location update will take long
time compared to the smaller cell site handover, which
will be busy of a high traffic crossing the boundary of
location management area.
Fig. 3 shows that when increasing the velocity of the
Mobile WiMAX with respect to the perimeter of the cell
into location management area which is fixed, the
disruption time will slightly increase at the point where
the size of the cell is really bigger.
The point where the size of the cell is really big as the
movement of the Mobile WiMAX with increasing in the
TM
PDF Editor

4. Elmabruk Salem M. Elgembari, Kamaruzzaman B. Seman
Copyright © 2013 Praise Worthy Prize S.r.l. - All rights reserved International Review on Computers and Software, Vol. 8, N. 1
118
velocity will affect the traffic data reception to the target
BSs, it will be busy with the processing of location
management updating and paging if the intra handover
is considered, although the handover delay is done, but it
is noted that the handover delay between (90 - 100 km) it
has lower disruption time compared to other velocities.
On the contrary in Fig. 4, shows that the cell site
location management area are less by four times, and by
following the same scenario the disruption was
increasing in parallel with the velocity increasing.
Fig. 2. Effect of the Cell Perimeter on the Handover
Fig. 3. Effect of the Velocity of M. WiMAX (NL=NZ=16,l = 4000)
Fig. 4. Effect of the Velocity of M.WiMAX ( NL=NZ=16, l = 1000)
Fig. 5, shows the number of location area to the
disruption time, so when the location areas is low with a
fixed the Mobile WiMAX velocity, the delay becomes so
high for a considerably small value of L; this is a worse
case, on the contrary Fig. 6 shows that the delay is better
if the location area has a larger L so the signaling traffic
will not have much effect on the location management
procedures within the handover procedure.
Fig. 5. .Effect of the NL ( l = 1000m, v =60 km/h)
Fig. 6. Effect NL ( l = 4000m, v =60 km/h)
VI. Conclusion
Worldwide Interoperability for Microwave Access
(WiMAX) deployment is growing at a rapid pace. Since
Mobile WiMAX has the key advantage of serving large
coverage areas per base station, it has become a popular
emerging technology for handling mobile clients. With
high demands on the data transactions among all
categories of the clients , and where the high
technologies support different elements of the
infrastructures of the WiMAX systems still the handover
delay play one of the big challenging keys in the
development WiMAX services, therefore the mobility ,
Mobile speed, location management schemes ,and cell
size of the coverage area are taking a highly attentions
from the researchers to come out with a significant
solution for the handover delay reduction in the paper
conclusion the results shown that the velocity has a clear
significant effect on the handover delay comparing to the
coverage area, so when the mobility of Mobile WiMAX
TM
PDF Editor

5. Elmabruk Salem M. Elgembari, Kamaruzzaman B. Seman
Copyright © 2013 Praise Worthy Prize S.r.l. - All rights reserved International Review on Computers and Software, Vol. 8, N. 1
119
in the high speed most of the time the handover delay be
less if the coverage area has a large size of cells with
respect the broadcasting BS when it is into the same
zone, so reducing location management signaling
procedure such as updating and paging minimize the
handover delay.
Also with increasing the size of location areas and
multimedia zones, it’s led the system to reduce the
handover delay even the mobile WiMAX speed is
limited. So in this case there is no waste of the handover
channels bandwidth, the results shown that with the
average velocity between 90 and 100 km/h the system
can achieve significant handover delay reduction, with
addressed cretin parameters values.
References
[1] X. Zhang, J. G. Castellanos, and A. T. Campbell, P-MIP: Paging
Extensions for Mobile IP, Mobile Networks and Applications
(MONET), vol. 7, no. 2, pp. 127–141, 2002.
[2] IEEE Std 802.16e-2005, IEEE Standard for Local and
metropolitan area networks, Part 16: Air Interface for Fixed and
Mobile Broadband Wireless Access Systems Amendment 2:
Physical and Medium Access Control Layers for Combined Fixed
and Mobile Operation in Licensed Bands, 2005.
[3] Gray, Doug, Mobile WiMAX–Part II: A Comparative Analysis,
WiMAX Forum, 2006.
[4] J.H. Lee,T. Kwon, Y. Choi, S. Pack, Location Management Area
Based MBS Handover in Mobile WiMAX Systems., 3rd
International Conference on Communication Systems Software
and Middleware and Workshops, 2008. PP 341 - 348, 2008.
[5] Y. Xiao, Y. Pan, and J. Li, Design and Analysis of Location
Management for 3G Cellular Networks, IEEE Transactions on
Parallel and Distributed Systems, vol. 15, no. 4, pp. 339–349,
2004.
[6] W. Wang, and I. F. Akylidiz, A Cost-Efficient Signaling Protocol
for Mobility Application Part (MAP) in IMT-2000 Systems, in
Proc. ACM Mobicom 2001, pp. 345–355, 2001.
Authors’ information
Faculty of Science Technology, USIM, Malaysia.
Elmabruk S. Elgembari, received his Master
degree, Faculty of Engineering, UPM
University Malaysia in 2003. Currently he is
doing PhD research in the Faculty of Science
and Technology in Universiti Sains Islam
Malaysia, the research focus on the handover
delay in the broadband networks
E-mail: gembari@hotmail.com
Kamaruzzaman B. Seman received the B.E.
degree in engineering from UNIVERSITI
TEKNOLOGI MALAYSIA(UTM), and the
Ms.c degree in telecommunication from
UNIVERSITY OF ESSEX , United kingdom
(UK), he received the PhD in Broadband
Communication from UNIVERSITY OF
STRATHCLYDE, United kingdom (UK).he
supervised of several PhD theses in various research themes of
telecommunications and computer science such as networking, image
processing, security network, application and modeling designs,…etc.
Currently he is in faculty of Science and Technology, Universiti Sains
Islam Malaysia.
E-mail: drKzaman@usim.edu.my
TM
PDF Editor