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Improvements to Seamless Vertical
Handover between Mobile WiMAX,Wi-Fi and
3GPP through MIH
Omar Khattab and Omar Alani
School of Computing, Science & Engineering
The University of Salford
Greater Manchester- M5 4WT,UK
Abstract— In the ubiquitous networks, The Next Generation
Wireless Systems (NGWS) allow the co-existence of different
wireless technologies such as GSM (Global System for mobile
Communication), Wireless Fidelity (WiFi), Worldwide
Interoperability for Microwave Access (WiMAX), Universal Mobile
Telecommunications System (UMTS) and Long Term Evolution
(LTE). One of the challenging issues in NGWS is seamless Vertical
Handover (VHO) during the mobility between these technologies;
therefore the telecommunication operators will be required to
develop a strategy for interoperability of these different types of
existing networks to get the best connection anywhere anytime.
To achieve this, in this article we proposed a new approach that
based on approaches proposed in the literature, our new
proposed approach provides better performance, less complexity
and more exhaustive for enhancing VHO.
Keywords-component; Vertical Handover (VHO), Radio Access
Technologies (RATs), MIH (Media Independent Handover),
ANDSF (Access Network Discovery and Selection Function).
I. INTRODUCTION
With the advancement of wireless communication and
computer technologies, mobile communication has been
providing more versatile, portable and affordable networks
services than ever. Therefore, the number of users of mobile
communication networks has increased rapidly as an example;
it has been reported that number of pages viewed on the
mobile Web browser Opera increased from 1.8 billion pages in
January 2008 to 23 billion pages in January 2010 [1] and there
is a growing demand for services over broadband wireless
networks [2]. This fact means that heterogeneous environment
of wireless systems such as Wireless Fidelity (WiFi), Universal
Mobile Telecommunications System (UMTS), Worldwide
Interoperability for Microwave Access (WiMAX) and Long
Term Evolution (LTE) will coexist providing mobile user with
roaming capability across different networks. To fulfill these
requirements of seamless Vertical handover (VHO) two
mechanisms were produced independently by IEEE and 3GPP
[3] namely Media Independent Handover (MIH) and Access
Network Discovery and Selection Function (ANDSF),
respectively. Each of them enables a seamless VHO between
the different types of technologies (3GPP, non-3GPP) such as,
UMTS, WLAN, WiMAX, and LTE. However within MIH “The
actual algorithms to be implemented are left to the designers”
[4] also there is inconsistency in its operation, hence it needs
some improvements [2]. In this paper we propose a new
approach to improve VHO in heterogeneous networks
environment. The rest of the paper is organized as follows:
section II presents VHO procedure, in section III we present
previous work related to the Vertical Handover (VHO)
procedure. In section IV we present our suggested approach
and finally, conclusion and future work in section V.
II. VERTICAL HANDOVER PROCEDURE
The handover is a mechanism which allows the mobile
users to continue their ongoing sessions when moving within
the same RAT coverage areas or traversing different RATs,
named Horizontal Handover (HHO) and VHO, respectively.
In the literature most of the research papers divide VHO into
three phases; Collecting Information, Decision and Execution
[5], [6] as described below.
A. Handover Collecting Information
In this Phase, all the required information for VHO decision
is gathered. Some of criteria related with the user preferences
(such as cost, security), network (such as latency, coverage)
and terminal (such as battery, velocity).
B. Handover Decision
In this Phase, select the best RAT based on aforementioned
information and informs the handover execution about that.
C. Handover Execution
In this Phase, the active session for the user will be
maintained and continued on the new RAT after that the
resources of old RAT is released eventually.
ISBN: 978-1-902560-26-7 © 2012 PGNet
The key of VHO management procedure is Access
Network Selection (ANS) in the decision phase. Though there
are many proposals introduced by researchers about ANS “the
proposed ANS schemes lack unity, while a number of issues
still need to be resolved” such as ANS problems as a result of
different goals between user's perspective (user centric) and
operator's perspective (network centric) and on the other hand
“VHO management is an active area of research” [7].
One challenge of wireless network integration is the
ubiquitous wireless access abilities which provide the
seamlessly automatic VHO for any moving devices in the
heterogeneous networks combining different access
technologies. Especially the users are increasingly demanding
services regardless the technological constraints which is
associated with this heterogeneous networks. To fulfill these
requirements of seamless VHO two mechanisms have been
produced independently by IEEE and 3GPP defined MIH and
ANDSF, respectively. Each of them enabling a seamless VHO
between the different types of technologies (3GPP, non-
3GPP), Refer to Figure1.
III. RELATED RESEARCH OVERVIEW
There are many researches which have been conducted
recently about the integration of RATs to enhance the VHO
procedure [3, 8, 9]. In [8], new logical entity was introduced in
target network named Forward Authentication Function (FAF)
for two reasons, First, to enable the transmission form WiMAX
to 3GPP (Authentication), Second, to avoid direct link
between 3GPP and WiMAX, i.e., “avoid the WiMAX access
scheduling measurement opportunities to the UE in order to
measure neighbor 3GPP sites”. This approach does not
consider two vital things in the VHO procedure, First, the
source network is not informed by User Equipment (UE) about
it’s moving to the target network which results in Packet
losses. Second, it lacks a releasing procedure for the resources
already in use in the network. This is depicted in Figure2.
In [9], new logical entity was introduced named Data
Forwarding Function (DFF) to solve the problems that were
raised in [8]. This is depicted in Figure3.
In [3], it was demonstrates that due to the combination
between MIH and NADSF there is no need for FAF and DFF
to be exist, beside, the UE obtains operator’s policies from the
ANDSF which has the role of selecting the target network. This
is depicted in Figure4.
IV. OUR PROPOSED APPROACH
Some of the presented approaches such as [3] and [8] have
not provided any evaluations or validations about their works.
The approach in [3] was to improve VHO process by
combining MIH and ANDSF. We studied this approach and
present new approach that can provide better performance, less
complexity and more exhaustive compared to the approach in
[3]. Table1 shows the comparison between the approach in [3]
Figure 2: Seamless single-radio handover from mobile WiMAX to 3GPP
access [8]
Figure1: Various RATs integration supported by MIH/ANDSF
and our approach for enhancing VHO. Our approach consists
of a procedure which is implemented by an algorithm and will
provide the following:
1. Gives details on how to deal with cases like, if the
VHO will initiate imperatively due to Radio Signal
Strength (RSS) or/and alternatively due to the user
preferences such as low cost, low latency, etc. taking
into account the high priority to execute imperative
session. This is depicted in Figure5.
2. VHO algorithm based on our approach which
achieves less failure of connection due to using the
optimum RATs (list of priorities) procedure. When the
first of choice form the list RATs priorities could not
be satisfied with available resources the Admission
Control (AC) will automatically move to another RAT
in the list and to look for satisfying requirements of
another RAT and so on. This is depicted in Figure6.
3. No need to combine between NADSF and MIH as in
[3] by assigning the rules and preferences operator
form Point of Service (PoS) in the destination
network.
4. Use single solution instead of dual radio solution as
which was suggested in [8], [9] it can eliminate the
Radio Frequency (RF) coexistence issues.
5. Dynamic Host Configuration Protocol (DHCP) server
to distribute the Care of Address (CoA) to mitigate the
load on PoS.
A. OUR PROPOSED PROCEDURE
We describe our Procedure through the VHO phases;
Initiation, decision and execution as depicted in Figure5. Three
VHO scenarios are considered to be in the source network and
destination network: UMTS to Wi-Fi, Wi-Fi to WiMAX and
WiMAX to UMTS.
Initiation Phase
In this phase, while the UE is connected to the source
network the VHO will trigger imperatively e.g. RSS or/and
alternatively based on the user preferences such as low cost,
low latency, etc.
Decision Phase
In this phase, As a result of triggering, Media Independent
Information Service (MIIS) Request/Response Available RATs
message will be responsible to pass Available RATs to UE, the
UE will select optimum RATs based on low data Rate, low
coverage, low latency, low cost, good RSS, etc (list of
priorities). When the first choice form the list of RATs
priorities could not be satisfied with available resources the AC
will automatically move to another RAT in the list and to look
for satisfying requirements of another RAT and so on, once
RAT of resources is available, selected RAT based on rules and
preferences of operators by PoS in the destination network.
Finally, the source network will be informed to start buffering
the data wherever is in the source network or in Correspondent
Node (CN).
Execution Phase
In this phase, The UE will be received optimum RAT to
start its authentication with the target network and obtain CoA
from DHCP. After that update/Acknowledge binding message
notifies Home Agent (HA) about new CoA to starting
send/receive data buffering and continuing the session within
target network. Finally, after the completion of sending the
buffered data the resources is released by MIH.
B. OUR PROPOSED ALGORITHM
The algorithm to implement our proposed procedure will
defines type of VHO imperative and alternative. Imperative
session will be high priority. For example, if there are two
VHO sessions at the same time, one due to user Profile and the
other due to RSS going down, the first session will execute
(high priority) and the second session if there is no any
imperative session under process, otherwise it has to wait in
queue. In the imperative case, optimum of RATS (list of
priorities) will be selected. When the first choice form the list
of RATs priorities could not be satisfied with Sufficient of
Resource (SoR) the AC will automatically move to another
RAT in the list and to look for satisfying requirements of
another RAT and so on until finding available resources,
otherwise the session is rejected. Finally, selected RAT based
on rules and preferences of operators by PoS in the destination
network. In the alternative case, the session will take the same
path of imperative session if it is due to user profile otherwise
there is no need to list of priorities step because the RAT
selected on behalf of user selection therefore the session will
be rejected from the first time when SoR are not available for
user selection session. This is depicted in Figure6.
V. CONCLUSION
In this paper we proposed our VHO approach based on the
approaches that have been studied in the literature with better
performance, less complexity and more exhaustive for
enhancing VHO procedure and VHO algorithm compared with
similar approaches in the literature. The proposed VHO
procedure primarily based on MIH to execute it as depicted in
Figure5. However it introduced the definition of VHO type and
giving priority to imperative sessions over alternative sessions.
Also it achieves less failure of connection due to using the
optimum RATs (list of priorities) as depicted in Figure6. In
future work we plan to execute the proposed VHO algorithm
by considering different scenarios in order to evaluate the
performance of our approach.
Approach Complexity Performance
For Resource Availability
Check
Exhaustive Power
Consumption
Implementation
In [3] High due to:
1. Combination between MIH and ANDSF in order to get operator’s
policies form ANDSF.
2. Eliminates of the data loss during VHO by MIH in
combination with IETF definition
of PMIPv6 and 3GPP standard. 3. Release the resources by MIH.
No selection Criteria
indicated.
VHO algorithm not
provided.
Dual Radio
Solution.
NO.
Our approach Less due to:
1. MIH in order to get operator’s
policies from PoS in the destination network (without combination with
ANDSF). 2. MIP, improve on it by buffering
data early and MIP HA will be
collocated in MIIS [10]. 3. Release the resources by MIH.
(No Change).
High due to:
1. Using the optimum RATs
to achieve less failure connection.
2. DHCP server to distribute CoA.
VHO algorithm
provided which supports
both types, imperative and alternative.
Single Radio
Solution.
In progress,
Figure5, Figure6.
Figure3: Signalling flow of the improved VHO from mobile WiMAX to 3GPP UTRAN [9]
Figure4: Handover Process with MIH and ANDSF development [3]
Table1: Comparison between approach in [3] and our approach for enhancing VHO
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Figure5: Our proposed procedure Figure6: Our proposed algorithm
