Performance evaluation of the mobility management towards 4 g wireless netwo

International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 –
6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 5, September – October (2013), © IAEME
1
PERFORMANCE EVALUATION OF THE MOBILITY MANAGEMENT
TOWARDS 4G WIRELESS NETWORKS
Yang Jie
School of Information Technology,
Wuhan University of Technology, Wuhan, China
Dheyaa Jasim Kadhim
Electrical Engineering Department,
University of Baghdad, Iraq, Baghdad
ABSTRACT
The next generation of 4G wireless communication networks is supposed as a communication
of different wireless access technologies (vertical communication) permitting the user with the best
anywhere, anytime connection and developing the system resource utilization. So mobility
management is crucial to ubiquitous computing and requires network management operations to
avoid service degradation through this networks heterogeneity. Both location management and
handoff management constitute mobility management. Handoff management is one of the mobility
management components; it maintains mobile network’s connections active while roaming or
switching into a new area. The location management is a tracking process for the active mobile
during his roaming without a call. In this work the performance of mobility management is evaluated
during handoff and location management processes.
Keywords: 4G Wireless Network, Mobility Management, Handoff Process and Location
Management.
1. INTRODUCTION
The grouping of different wireless communication technologies toward 4G wireless networks
should face some expected challenges before realistic practice implementation. One of the major
challenges is the mobile station mobility managing among different wireless technologies in order to
keep the mobile station connected to the best available wireless network. To merge these vertical
wireless networks in one network as an underlay network that can submit a better service at lower
cost to the user, as well as improve the overall networks resource utilization. However, achieving
INTERNATIONAL JOURNAL OF ELECTRONICS AND
COMMUNICATION ENGINEERING & TECHNOLOGY (IJECET)
ISSN 0976 – 6464(Print)
ISSN 0976 – 6472(Online)
Volume 4, Issue 5, September – October, 2013, pp. 01-10
© IAEME: www.iaeme.com/ijecet.asp
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2
these two goals needs a well-designed mobility management system that can achieve the tradeoff
between efficient resource utilization and mobile station comprehended QoS [1][2].
Mobility management includes two parts, handoff and location management. When a mobile
station moving across the boundary of two neighbor cells, the MSC prepares a new two channels in
the new cell to conserve the call from dropping, this operation is called a Handoff Management
(HM). The location management (LM) is tracking the active mobile station (powered on MS) during
his roaming without a call. While the location of a MS must be known exactly during a call, LM
usually means how to track an active mobile station between two consecutive phone calls [3][4].
The most important issues in mobility management are seamless roaming (integration among
different 4G wireless networks, QoS assurance, operational costs supported features and a good
utilizing of the wireless links (utilizing the wireless links represented by occupying the control
channels in the paging and location update operations) [5]. Furthermore, vertical handoffs between
radio access networks using different technologies require additional delay for reconnecting the
mobile terminal to the new wireless access network, which may cause packet losses and degrade the
QoS for real-time traffic [6]. The occupancy of bandwidth, all computational processes in
infrastructure of the network, power consumption in MS, and power consumption in the network are
form the cost and all of this is a financial cost. Therefore the cost reduction is a very important issue
in LM [7].
The objectives of this paper are to focus on handoff management HM, which is an important
component of mobility management, and is crucial in enabling seamless mobility across
heterogeneous network infrastructures. Also focusing on location management LM with all location
management schemes especially paging operation schemes and location update schemes. In order to
satisfy seamless mobility a vertical handoff proposed by [8] is considered with some modification
using Relative Received Signal (RSS). In order to keep mobile station's location tracking, a proposed
location management scheme is submitted, where for each mobile station subscriber we divide his
movement pattern into sub-routines depending on randomness in movement during his day's hours.
This approach uses a data base to predict the future location of a mobile host based on the history of
movement pattern of a mobile host. Simulation is also carried out for different movement patterns
(i.e. regular, uniform, random) to predict the future location of a mobile host.
2. MOBILITY MANAGEMENT
Seamless roaming or mobility is crucial to ubiquitous computing and requires network
management operations to avoid service degradation. Both location management and handoff
management constitute mobility management as shown in Figure (1) below. Location management
involves two processes. The first process is called location registration, or location update, in which
the MT periodically informs the network of its current location, which leads the network to
authenticate the user and update its location profile in a database [9]. The second process related to
location management is called paging. The handoff management is one of the major functions under
mobility management that embraces several aspects of user mobility and mobility support procedures
for wireless networks. Handoff management includes wireless terminal handoff management
considerations within one network called horizontal handoff and handoff management across
different wireless networks which could be based on different wireless access technologies termed
vertical handoff [10].

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Figure 1. Mobility Management System
Mobility management generally deals with automatic roaming, authentication, and
intersystem handoff. Automatic roaming includes a set of network functions that allow a subscriber
to obtain service outside the home service provider area. These functions are automatic and do not
require special subscriber actions. The automatic roaming functions are divided into:
•Mobile station (MS) service qualification
•MS location management
•MS state management
•Home location register (HLR), and VLR fault recovery
The authentication process requires that end users of the system are authenticated; i.e., the
identity of each subscriber is verified.
Many researchers propose different mobility models, some of the mobility models are usually
used to describe the mobility of an individual subscriber and other models describe the aggregate
pattern of all subscribers. In [11] the author used Fluid Flow model to model the mobility of
vehicular MS. It requires a continuous movement with infrequent speed and direction changes. In
[12], the author used the discrete Random Walk, in this model the author assumed the time is slotted,
and the subscriber can make at most one move during a time slot. In [13] the author proposes another
model where the current move depends on the previous move, this model called Markov Walk.
There are many other mobility models like Cell Residence Time based, Gauss- Markov, Normal
Walk, Shortest Path, and Activity Based. For simplicity, and because of these models not required in
this thesis, be satisfied by listing them only. Figure (2) illustrates all mobility models [14].
Figure 2. Mobility Models

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3. HANDOFF MANAGEMENT SYSTEM
Handoff management is one of the mobility management components; it maintains mobile
network connections active while roaming or switching into a new area. Depending on the type of
attachment, the handoff can be classified into two types: horizontal handoff and vertical handoff. In
the horizontal handoff, the MS will not change the technology deployed for its connection even when
moving from one point of attachment to another. However, in the vertical handoff, the MS will
change the technology when handing off and when moving from one point of attachment to another.
The handoff process is divided into three phases [15]: Network Discovery, Handoff Decision and
Handoff Implementation. Periodically the system monitors for a better network which the mobile
terminal can be handed off. The handoff considerations include several different criteria depending
on the algorithms and the goals set for handoff.
3.1 Proposed Handoff Scheme
Received signal strength (RSS) is the most widely used criterion to evaluate the performance
of Handoff management in the 4G wireless networks because it is easy to measure and is directly
relevant to the service quality. There is a close relationship between the RSS readings and the
distance between the mobile terminal and its point of attachment. The majority of existing horizontal
handover algorithms use RSS as the main decision criterion, and RSS is an important criterion for
vertical handoff decision.
Since 4G heterogeneous networks will operate in an environment of multiple standards and
networks, transfer of packets to a new wireless link will also involve transfer of additional contextual
information in order to enable the mobile node to move through different networks, while
maintaining its data flows.
The proposed vertical handoff scheme will help mobile terminals to choose the best network to
connect to among all the available candidates. Here, the focus is only on the research efforts and
recent developments on improving the efficiency of vertical handoff decision process.
3.2 Proposed Handoff Scheme Procedure
The following steps show the procedure proposed to deal with the handoff scheme for
different wireless networks using RSS as a performance criterion:
Step 1:
RSS measurement: Equation (1) is used to monitor;
RSS=P-L-10*n*Log (d)-f (µ, α) (1)
Where: P is the transmitted power, L is a constant power loss, n is the path loss exponent, and d is
the distance of the MS from the access point.
Step 2: RSS average has been calculated using simple average function;
RSSavg.=1/N∑RSS (2)
Where N is the averaging window.
Step 3:
The slop estimation has been calculated and as follows;
S[k]=( RSSavg[k2]- RSSavg[k1])/(k2-k1) (3)
Where k1 and k2 are different distance values.

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Step 4:
The life time estimation in any wireless network can be calculated as;
EL[k]=(RSSavg[k]-ґ)/S[k] (4)
Where Ґ is the threshold value in this wireless network.
Step 5:
The plot of RSS versus distance (k) is as shown in Figure (3) below;
Figure 3. RSS vs. Distance (k)
As it clear when the distance increase the RSS decrease until reaches the minimum value of
attenuation.
Step 6:
Plot the number of expected handoffs according to distance as shown in Figure (4) below;
Figure 4. RSS and No. of Handoffs vs. Distance (k)
Where the green curve represents number of handoffs while the blue curve represents RSS curve.

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Step 7:
Plot the number of handoffs with respect to the velocity of the mobile station as shown in Figure (5)
below;
Figure 5. Number of Handoffs vs. Velocity of MS
According to the result plot we see that: As the velocity increased, the number of handoff will
also increase. This scenario happened because of the tendency of fast mobile user to leave the
coverage area is high compared to slow mobile user. Therefore, the number of handoff is increasing
with respect to the velocity of the mobile user.
Step 8:
Plot the life time to initiate the handoff according to the velocity of the mobile station as shown in
Figure (6) below. From this figure we can notice that as the velocity increased, the starting time for
the handoff process would be faster. This is due to the tendency of the mobile user to move out from
the coverage area is increasing.
Figure 6. Handoff Initiated Time vs. Velocity of MS

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4. LOCATION MANAGEMENT SYSTEM
With the growing of 4G wireless networks, the need for new services will grow also. Voice
call, internet service, multimedia transfer (picture and video), video conference, and other service, all
of that is needed to transfer a huge amount of data every second. The track of MS must be known by
the network to continually serve that MS by delivering his new calls. To keep the network knowing
the MS location at any time, two basic operations can perform that, paging and location update
operations. There is a tradeoff between location update and paging, when the MS is never making
location update, the cost of location update will be minimized, but we must search all cells to find a
MS, the paging cost will be of maximum value. For the inverse case where the MS make a location
update frequently, the network will know the MS at any time where he is, and there is no need to
paging for a MS, the cost of paging will at minimum while the location update will be of maximum
value. However, the total cost can be reduced or one cost can be reduced by putting a band on the
other cost [16].
4.1 Paging Operation
The first operation (paging) is accomplished by the cellular network, when an incoming call
arrives for a MS, the cellular network will page the MS in a number of cells to find out the cell in
which the mobile station is located so the incoming call can be routed to the corresponding base
station. The numbers of paged cells depending on how the location update is performed, and Figure
(7) explicate different paging schemes [14].
Figure 7. Paging Schemes
4.2 Location Update Operation
The second operation (location update) is performed by the MS, it informs the network with
his resent location and this operation can perform in many schemes, Figure (8) explicates location
update schemes [14]. The location update operation can be classified as global or local, a location
update scheme is local when the MS allowed to decide when and where it make location update, and
called global if all MSs at the same set of cells generate the location update. Also, this operation can
be classified as static and dynamic, it will be static when a predetermined set of cells allowed to MS
to generate location update in it regardless of its mobility, and it will be dynamic when the MS can
generate location update in any cell depending on its mobility.

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Figure 8. Location Update Schemes
4.3 Proposed Location Update Scheme
The proposed location update scheme predicts the future location of a mobile host based on
the history of its movement pattern. Movement pattern (Pn) is the history of movement of a mobile
host recorded for a period of time (Tn) where n is the number of regular time intervals at which the
mobile host movements are recorded. The time interval can be minutes, hours, days, etc. The
movement pattern Pn can be represented by a data at regular time interval, t1, t2 ...tn.
Let the movement pattern Pn={p1, p2, ...,pn} be recorded for a mobile station, where Pi indicates the
movement of a mobile host during time ti, and we define the movement in terms of direction and
distance travelled by a mobile station during the time interval ti. Then Pi is represented by a pair
(di,dsi). Where di is the possible direction in which a mobile host moves at ith
time interval. For
example, if we consider four possible directions, North, East, South and West, of movement of a
mobile station, then di={North, East, South, West}. If a mobile host moves towards North direction
at ith
time interval, then di = North. And dsi is the distance travelled by a mobile host at ith
time
interval. Here, the distance travelled may be number of cells, kilometers, meters, etc.
For example, if a mobile movement pattern is recorded for three time intervals (n=3) with direction
of movements, North, East, East and the distance travelled is 2, 1, and 3 units, then the movement
pattern is, P3={p1, p2, p3}={(d1, ds1), (d2, ds2), (d3, ds3)}={(North, 2), (East, 1),(East, 3)}. Note that we
divided the service area into four location area with each contain eight cells.
The Procedure of our proposed location update scheme as follows:
Step 1:
For the example above, the proposed scheme is assumed that there is a user's database which stored
the last four movement cells of the user and then takes the four values.
Step 2:
Next, the time will calculate and depended on it, the proposed scheme will go to the appropriate
database.

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Step 3:
a. If the time is between (7 A.M -3 P.M) then the program will go to the work database and then go
the next step.
b. If the time is between (4 P.M -6 P.M) then the program will go to the road database and then go
the next step.
c. If the time is between (7 P.M -6 A.M) then the program will go to the home database and then go
the next step.
Step 4:
The proposed scheme will compare the last four movement cells for the user with the patterns that
stored in the appropriate database that will selected from the previous step.
a. If the match is done then the predicted cell, location area, movement direction and distance will
be obtained.
b. If the match is not occur then the scheme will propose that the prediction movement cell for the
user is known, so the four movement cells getting from the user database with the given
prediction movement will make new record added to the appropriate database that will selected
before.
c. Then the user database will then update with the last four movement cells (taking into account the
prediction movement as the last movement).
5. CONCLUSIONS
In this work, the mobility management is enhanced into its two directions, handoff
management and location management. From the above simulation results for the proposed handoff
scheme, it could be concluded that algorithm using lifetime (i.e. using the equation of delay), gives
better results compared with the results using RSS. Also these simulation results show that as the
velocity increased, the number of handoff will also increase. This scenario happened because of the
tendency of fast mobile user to leave the coverage area is high compared to slow mobile user.
Therefore, the number of handoff is increasing with respect to the velocity of the mobile user.
On the other side, we propose a prediction-based location management in a mobile network. This
approach uses a data base to predict the future location of a mobile host based on the history of
movement pattern of a mobile host. Multiple move prediction is designed for predicting the future
location of a mobile host. The performance of the method has been verified for prediction accuracy
by considering different movement patterns of a mobile host.
6. REFERENCES
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