International Journal of Engineering Trends and Technology (IJETT) – Volume 11 Number 9 - May 2014
Simulation Based Analysis of Vertical Handover Between
WiFi and WiMAX Networks using NS2
Prof. S.S. Patil2
Miss. Minal J.Patil 1
PG Student, Dept. of Electronics, T.K.I.E.T
Warananagar, India 1
Abstract :Next generation heterogeneous wireless networks offer the
end users with assurance of QoS inside each access network as well
as during vertical handoff between them. For guaranteed QoS, the
vertical handoff algorithm must be QoS aware, which cannot be
achieved with the use of traditional RSS as the vertical handoff .
Hence it propose a vertical handoff algorithm which uses received
SINR from various access networks as the handoff criteria. This
algorithm consider the combined effects of SINR from different
access networks with SINR value from one network being
converted to equivalent SINR value to the target network.
Associate professor, Dept. of Electronics, T.K.I.E.T
Warananagar, India 2
aims to connect devices such as Personal Computers, PDAs,
laptops, printers.
Infrastructure mode :
A QoS based vertical handover mechanism between
WiMAX and WiFi networks is proposed by applying the Signal to
Interference and Noise Ratio SINR. The performance of the
proposed SINR and RSS based vertical handover algorithm have
been evaluated in terms of the maximum throughput.
Keywords - component; SINR; MIH; vertical handover ; WiMAX ;
WiFi.
I INTRODUCTION
Future network devices will need to roam seamlessly
across heterogeneous access technologies such as 802.l1,
WiMAX ,CDMA, and GSM, between wired networks such
as xDSL and cable, as well as between packet switched and
circuit switched(PSTN) networks[1-2].
The ability to change access link for better QoS in
different wireless communication networks is known as
seamless vertical handover [3]. To achieve this, the Media
Independant Handover (MIH) IEEE 802.21 standard has been
proposed to permit the exchange of entities to different access
networks and assists the handover decisions by defining the set
of functional components [4].
II. WIFI AND WIMAX NETWORKS
Wireless Fidelity (WiFi) is a wireless local area network
over limited range. It is known also under IEEE 802.11, and
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Fig 1: WiFi Infrastructure Mode
In infrastructure mode, each station computer (STA )
connects to an access point via a wireless link. The set-up
formed by the access point and the stations located within its
coverage area are called the basic service set, or BSS. Each BSS
is identified by a BSSID, a 6-byte (48-bite) identifier.
I t is possible to link several access points together using
a connection called a distribution system (DS ) in order to form
an extended service set or ESS. An ESS is identified with an
ESSID (Extended Service Set Identifier), a 32-character
identifier which acts as its name on the network.
When a roaming user goes from one BSS to another while
moving within the ESS, Access points communicate with one
another using a distribution system in order to trade information
about the stations and, if necessary, to transmit data from mobile
stations. This feature which lets stations move "transparently"
from one access point to another is called roaming.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 11 Number 9 - May 2014
Ad hoc mode :
In ad hoc mode, wireless client machines connect
to one another in order to forma peer-to-peer network, i.e. a
network in which every machine acts as both a client and an
access point at the same time. The set-up formed by the stations
is called the independent basic service set, or IBSS . [5]
WiMAX (Worldwide Interoperability for Microwave Access)
is a connection-oriented wide area network . It supports high
bandwidth and hundreds of users per channel at speeds similar to
currently seen for DSL, Cable or a T1 connection; Promises to
provide a range of 30 miles as an alternative to wired broadband
like cable and DSL. Use point-to-multipoint (P2MP) architecture.
It is designed for delivering broadband seamless quality
multimedia services to the end users. WiMAX combines the
familiarity of Wi-Fi with the mobility of cellular that will deliver
personal mobilebroadband that moves .
A WiMAX base-station which is similar to a cellular
tower, except that it can cover of almost of 3,000 square miles .
The mobile WiMAX standard, IEEE 802.16e, is a worldwide
broadband wireless standard that covers fixed, portable and
mobile deployments which is based on an IP service model [6] .
The simplified illustration of IP-based WiMAX network
architecture can be logically divided into three parts:
Fig 2: Adhoc mode
An IBSS is a wireless network which has at least two
stations and uses no access point. The IBSS therefore forms a
temporary network which lets people in the same room exchange
data. It is identified by an SSID, just like an ESS in
infrastructure mode.
In an ad
hoc network, the range of the independent BSS is determined by
each station's range. Unlike infrastructure mode, ad hoc mode
has no distribution system that can send data frames from one
station to another.[5]
Wimax Networks :
WiMAX (Worldwide Interoperability for Microwave Access)
is a connection-oriented wide area network . It supports high
bandwidth and hundreds of users per channel at speeds similar to
currently seen for DSL, Cable or a T1 connection; Promises to
provide a range of 30 miles as an alternative to wired broadband
like cable and DSL
(1) Base Station
(2) Access Service Network, comprising of one or more
BS and ASN gateways which forms the radio access
network
(3)Connectivity Service Network, which provides IP
connectivity to the IP core network functionality.
III.VERTICAL HANDOVER
A. Handover Management Process
Handover management process in a mobility scenario is the
procedure to maintain continuous connection in active mobile
terminal while moving from one access link (base station or
access router) to another. Handover management process has
been described in several works [7-9] which involve three
phases as shown in Figure 4:
Network
Discovery
Handover
Decision
Handover
Triggering
Fig 4 : Handover Management Process
Fig 3 : WiMax Network Architecture
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Network Discovery - This is the process where a MT searches
for reachable wireless networks. A MT with multiple interfaces
must activate the interfaces to receive service advertisements,
which are broadcasted by different wireless technologies.
The simplest way to discover reachable wireless
networks is to always keep all interfaces on. However, keeping
an interface active all the time consumes the battery power even
without receiving or sending any packets. The interface may be
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International Journal of Engineering Trends and Technology (IJETT) – Volume 11 Number 9 - May 2014
activated periodically to receive service advertisements. The
activating frequency directly affects the system discovery time.
Handover Decision - Handover decision is the ability to decide
when to perform the handover and to which access network to
handover. A decision for vertical handover may depend on
several issues relating to the network to which the mobile node
is already connected and to the one that it is going to handover.
For example, the decision to perform mobile-controlled
handovers may be made by a vertical handover agent, sitting in
the mobile device based on policies such as network bandwidth,
load, coverage, cost, security, QoS, or even user preferences.
Handover Triggering - Handover triggering requires the actual
transfer of data packets to a new wireless link in order to reroute a mobile user’s connection path to the new path. It
requires the network to transfer routing information about the
mobile user to the new access router for the proper
forwarding of packets.Transfer of packets to a new wireless
link . However, if context transfer delay is so large as to have
the same effect of complete re-establishment, or large enough
to increase the overall handover call dropping rate, the
advantages of context transfer are lost. Thus, a mechanism to
allow for inter-network and/or inter-service-provider
agreements to support fast inter-system handovers . VHD
algorithms help mobile terminals to choose the best network to
connect to among all the available candidates. [10]
1) Received signal strength (RSS) is used to measure the service
quality . RSS reading is directly related to the distance from the
MT to its point of attachment[l1].
2) Network connection time indicates the length of time that a
user connected to an access point or base station. proper
moment is essenial to initiate a quality of service handover [12].
3) Available bandwidth indicates the available data resources
and is a measure of traffic conditions in the network.SINR is
related to available bandwidth algorithms [13]
4)Power consumption refers to MT's battery level,which is
important when handover to another network that consumes
lower power [14].
5) Monetary cost: some algorithms take into consideration the
charging policies for different networks in making their
handover decisio[15]
6)Security: Integrity or confidentiality are
considered as
critical issue in some applications,where the VHD may be
chosen to a higher level of data security.
7)User preferences: a special user requirement or preference
could be the issue that decide t initiate the handover [16].
B. Vertical Handover Decision Algorithms
Vertical Handover Decision (VHD) Algorithms Several
algorithms have been proposed in the research literature for use
in the vertical handover decision (VHD) as shown in Figure .
Brief description of each algorithm is as follows:
Vertical
handover
decision
algorithm
Many VHD algorithms depending on the signal strength
recieved by the mobile terminal, where handover decisions are
made by comparing the received signal strength with the preset
threshold values. These algorithms which use signal strength as
their basic handover decision indicator are called Received
Signal Strength (RSS) algorithms.
However, the data rate achieved by a mobile terminal is
related to its Signal to Interference and Noise Ratio (SINR), as
well as the distance between Base Station (BS) or Access Point
(AP) to the mobile terminal. RSS-based VHD occurs when the
mobile terminal recieving power approaches the threshold value
regardless of the QoS needed, thus rendering RSS-based VHD
not to support user's QoS requirement. On the other hand, SINRbased VHD supports multimedia QoS requirement depending on
the achievable data rate which leads to seamless vertical
handover.
Fig 5 : Parameters used for VHD decision
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International Journal of Engineering Trends and Technology (IJETT) – Volume 11 Number 9 - May 2014
C. MIH overview
Fig 6 : MIH Architecture
The 802.21 add-on module contains an implementation of
the Media Independent Handover Function (MIHF) based
on draft 3 of IEEE 802.21 specification. An overview of the
MIHF interaction with the different components of the
mobile node (MN) is shown.
The MIHF and MIH Users are implemented as Agents. An
Agent is a class defined in ns-2, extended by NIST, that
allows communication with both the lower layers (i.e., MAC)
and the higher layers (i.e., MIH Users), providing the
mapping between the media independent interface service
access point (MIH_SAP) and (MIH_LINK_SAP and mediaspecific primitive.
MIH Users make use of the functionalities provided by
the MIHF in order to optimize the HO process. MIH Users
typically will send commands to the MIHF and receive
events or a message can be sent to the source node to inform
it of the new address or interface to use. The Handover class
provides a template for HO modules and computes a new
address after a successful HO.[17] The Interface
Management class (IFMNGMT) provides flow management
functions which facilitate the HO module in Neighbor
Discovery (ND) agent when a new prefix is detected or when
it expires.
IV. SINR BASED VERTICAL HANDOVER
STRATEGY
In this paper, a SINR based scenario similar to that proposed
by Kemeng et al [20] is proposed instead of RSS as the
handover criteria for WIFI and WiMAX integration network.
The Shannon capacity determines the maximum
achievable data rate for a given Signal to Interference and
Noise Ratio SINR and carrier bandwidth as:
• R is the maximum achievable data rate
• W represents the bandwidth of the carrier
• y is the received SINR at a MT· r is the gap in decibel
between channel capacity and uncoded QAM, minus the gain
caused by coding.
Let RBs be the maximum data rate from WiMAX base
station, RAP be the maximum data rate from WIFI access
point.
Shannon formula becomes:
Rbs =Wbslog 2(1+ γbs\ Гbs)
Rap=Waplog 2(1+ γap\ Гap)
National Institute of Standards and Technology (NIST) has
modified the network simulator NS-2 version 2.29 [18] to
implement the Media Independent Handover (MIH). The
modified NS-2.29 version [19] consisted of MIH Function
(MIHF) implementation based on the IEEE 802.21
specifications.
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Where, Y BS and YAP represent the recelvmg SINR from
WiMAX and WIFI respectively. By letting RBs = RAP. we
can find the relationship between required Y BS and YAP
incase of MT
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International Journal of Engineering Trends and Technology (IJETT) – Volume 11 Number 9 - May 2014
receiving the same data rate from WiMAX and WIFI :
The SINR-based VHD algorithm becomes applicable
by having the relationship between the receiving SINR and
the maximum data rate from both WiMAX and WIFI. Y BS
which represent the SINR received from WiMAX has been
converted to an equivalent YAP required to achieve the same
data rate in WIFI [20].
The future work may involve the implementation of
multiple MAC support in a single wireless node thereby
supporting heterogeneous handover. This will involve
making changes to the node structure in NS2 and other
related files so that a single wireless node can support
multiple MACs and multiple PHYs.
SINR
3
RSS 90
2.5
RSS 85
RSS 80
2
1.5
1
0.5
0
100
200
300
400
Data rate(kbps)
Fig 8: System throughput vs Data rate
VI. REFERENCES
Fig 7 : Equivalent SINR based model
With the combined effects of both SINR being
considered, handover is initiated while the user is getting
equivalent SINR from another access network. It means that
given the receiver end SINR measurements of both WIFI and
WiMAX channel, the handover mechanism now has the
knowledge of the estimated maximum possible receiving data
rates a user can get from either WIFI or WiMAX at the same
time within the handover zone, where both WIFI and
WiMAX signal are available.
We compare our SINR based vertical handover
algorithm with the RSS based vertical handover algorithm in
terms of the maximum downlink throughputs the user can
achieve while traveling through the integrated network.
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V. CONCLUSION AND FUTURE WORK
In this paper, we have proposed an SINR-based Media
Independent Handover mechanism with QoS support for
coexist heterogeneous WiMAX and WIFI networks. Besides
supporting QoS for different traffic flow, the proposed VHD
will also promote maximum achievable data rate. . The
performance of the proposed SINR based vertical handover
algorithm and RSS based vertical handover algorithm have
been evaluated in terms of the maximum downlink
throughputs.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 11 Number 9 - May 2014
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