TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to a method and a system for handover in a telecommunication
system and more particularly to a vertical handover method for implementing handoff among
heterogeneous wireless networks and a system thereof.
BACKGROUND AND THE PRIOR ART
Vertical handoff decision in a heterogeneous wireless network environment is very complex and
involves a tradeoff among many handoff metrics including QoS requirements, network conditions,
system performance, mobile terminal conditions, power requirements, application types, user
preferences, and pricing details. Among the various applications, those involving real- time video are
more delay sensitive than non-real time services such as file downloads. In these kinds of
applications, it is likely that numerous types of access networks will coexist to support wireless
services with different QoS requirements.
According to 3GPP, "IMT -2000 QoS classes", TSG-SA #17 Meeting September 2002, different
applications have different QoS requirements. Moreover, battery power consumption in mobile
devices is an important attribute that needs to be considered while making a handoff decision.
Various vertical handover mechanisms have been proposed in the past including the following: SAW
(Simple Additive Weighted), TOPSIS (Technique for Order Preference by Similarity to Ideal
Situation), and MEW (Multiplicative Exponential Weighted).
IEEE 802.21 is responsible for enabling handover and interoperability between heterogeneous
network types including both 802 and non-802 networks. It provides information required for
providing handover to and from a range of networks including cellular, GSM, GPRS, WiFi, and
Bluetooth. The network handover enabling function is a part of the media independent handover
(MM) function. The MIH function consists of 3 elements, the event service, command service and
information service as given in Fig. 1. Fig. 1(a) explains the reference model of MIH function and
Fig. 1(b) represents the multiple access network reference model. MIH function provides convergence
of link-layer state information from multiple heterogeneous access technologies into a unified
presentation to the upper layers of the mobility management protocol stack. The MIH_SAP allows
access from the upper layers, MIH_NMS_SAP allows for management, and MIH_LrNK_SAP is a
generalization, each access network has preexisting SAPs for such access. Each or any number of the
access networks will interface directly with the MIH function using their own SAPs. A sample
primitive for each of the service access points from MIH standard is given in Fig. 2. Similar kind of

standard is proposed from the 3GPP as generic access network (3GPP TS 43.318), where GAN
(generic access network) supports two modes of operation GAN A/Gb mode, and GAN Iu mode. A
typical call flow during circuit switched handover from GERAN to GAN is explained in Fig. 3.
QoS information about the available networks within the range of the current network interface of a
mobile node is obtained periodically by using the IEEE 802.21 /GAN standard. This information is
utilized by our proposed FUZZY-TOP vertical handover decision mechanism. Internet Engineering
Task Force IP Performance Metrics Working Group has standardized procedures for performance
metrics such as available bandwidth and average delay for Internet services. After the handoff
decision is taken, handoff is executed using mobility management protocols, e.g., the Host Identity
Protocol (HIP).
From the survey on 3GPP heterogeneous networks as provided in Aleksandar Damnjanovic, Juan
Montojo, Yongbin Wei, Tingfang Ji, Tao Luo, Madhavan Vajapeyam, Taesang Yoo, Osok Song,
And Durga Malladi, "A Survey On 3gpp Heterogeneous Networks "JJEEE Transactions On
Wireless Communications, Vol. 18, Issue: 3, Pages: 10-21, June 2011, it is concluded that macro
node deployment, cell range expansion enabled through resource partitioning, and the interference
cancellation receiver at the user equipments (UE), enables one to exploit the full potential of
heterogeneous deployments.
Jun-pyo Hong, and Wan Choi, "Dynamically Reconfigurable Relay Communications With
Multiple Radio Access Technologies", IEEE Transactions On Vehicular Technology, Vol. 59,
No. 9, November 2010 propose a opportunistic communication system using multiple radio access
techniques (RATs) in heterogeneous networks, which ultimately improves the performance in terms
of diversity gain, stability, throughput, transmit energy, load balancing, and average packet arrival
rate regardless of the distance between the source and destination nodes. Reserving resources prior to
the actual vertical handoff is a difficult task in heterogeneous wireless networks, just as the exact
handoff initiation time is difficult to predict.
In this regard, Kibria M. Rubaiyat., Jamalipour Abbas., and Mirchandani Vinod., "A Location
Aware Three-Step Vertical handoff Scheme for 4G/B3G Networks", IEEE Globecom, pages:
2752 - 2756, 2005, propose a periodical three-step vertical handoff prediction algorithm embedded
within the mobile terminal, including (i) location management, (ii) enhanced access network selection
process to initiate handover in an overlapped cell structure, and (iii) prediction algorithm to initiate
handoff to a neighboring network. Vertical handover in heterogeneous networks poses a challenge for
seamless access for real time services, such as Mobile IPTV due to the large handover delay and
packet loss.
To solve those issues, Qi Qi, Yufei Cao, Tonghong Li, Xiaomin Zhu, and Jingyu Wang, "Soft
Handover Mechanism Based on RTP Parallel Transmission for Mobile IPTV Services", IEEE

Transactions on Consumer Electronics, Vol. 56, No. 4, November 2010, propose a new soft
handover algorithm based on the IPTV server and the consumer electronic devices where the
proposed parallel soft handover technique transmits the RTP packets efficiently by using parallel
transmission, ultimately providing efficient bandwidth utilizations. The handoff decision generally
depends on various parameters including available bandwidth, bit error rate, jitter, average battery
lifetime, access cost, transmit power, and end-to-end delay.
In Smaoui, I., Zarai, F., and Kamoun, L., "Vertical Handoff Management for Next Generation
Heterogeneous Networks", in Proc. IEEE CCC, 2007, the authors propose a new handoff scheme
for reducing handoff delay using the concepts of received signal strength (RSS) and threshold
management.
Considering reduction of total interference in CDMA, a vertical handoff decision algorithm among
the CDMA networks and Wireless Local Area Networks (WLANs) is proposed in Shengdong, X.
and Meng, W., "Vertical Handoff Algorithm in Heterogeneous Networks for Reducing
Interference", Journal of Electronics (China), Vol.26, No.l, January 2009.
A combination of some of the criteria like bandwidth, RSSI, and delay are also considered for making
a handoff decision as provided by Shenoy, N. and Mishra, S., "Vertical handoff and mobility
management for seamless integration of heterogeneous wireless access technologies" in
'Heterogeneous Wireless Access Networks: Architectures and Protocols' published by Springer
Verlag 2008.
In QingHe, "A Fuzzy Logic Based Vertical Handoff Decision Algorithm between WW AN and
WLAN", IEEE International Conference on Networking and Digital Society, vol. 2, pages: 561-
564,2010, authors propose a fuzzy logic based vertical handoff decision algorithm by considering the
RSS, available network bandwidth, monetary cost, and user preferences. Even though it reduces the
unnecessary handoffs and decreases the probability of call blocking and dropping, authors do not
consider the QoS requirements of the applications during handoff. Based on the on-off characteristics
of VoIP, the authors Hyun-Ho Choi, Ohyoung Song, Yeon-Kyung Park, and Jung-Ryun Lee,
"Performance Evaluation of Opportunistic Vertical Handover Considering On-Off
Characteristics of VoD? Traffic", IEEE Transactions On Vehicular Technology, Vol. 59, No. 6,
July 2010, proposed an opportunistic vertical handover scheme, which introduces a margin time
before the L2 handover procedure to align the service disruption time with the mutual silence period.
The proposed scheme can be extended to traffic whose transmission rate is not fixed but varies by
aligning the service disruption time. However the authors mainly concentrate on VoIP as the target
application.

Authors Amit Sehgal, and Rajeev Agrawal, "QoS Based Network Selection Scheme for 4G
Systems", IEEE Transactions on Consumer Electronics, Vol. 56, No. 2, May 2010, propose a
network selection algorithm that uses the distance function to generate an ordered list of various
available access networks. This ordering is done based on the multiple user preferences and level of
interest in a particular region. However, the proposed scheme using the distance function does not
incorporate any intelligence while making a decision.
A brief discussion regarding a multi attribute decision mechanism is presented and compared in
Lassoued Imed., Bonnin Jean-Marie., Hamouda Zied Ben., and Belghith Abdelfettah., "A
Methodology for Evaluating Vertical Handoff Decision Mechanisms", IEEE ICN, Page(s): 377 -
384, 2008, where, the authors propose a novel methodology for evaluating vertical handoff decision
mechanisms. This methodology takes into account the current context, different realistic user mobility
models, user preferences, applications requirements as well as wireless access technologies
specificities and QoS parameters.
US 2007/0091844 Al, April 2007, "Novel Vertical Handover Control Algorithm for WLAN and
UMTS", has proposed a method for making handover decisions between UMTS and WLAN systems.
In this method, signal strength is measured to estimate the throughput performance to create a
comparable SNR value. Here, in this method the handover threshold H is dynamically adjusted to
effectively control the handover trigger according to different applications. To reflect the benefit of
the vertical handover in various aspects, besides the effective SNR values, the algorithm needs to
consider dynamic thresholds and the associated timers to achieve the QoS requirements. Ping-pong
effect is avoided by setting trigger timers for both uplink and downlink. A two state model with state
probabilities and transitions are used as the analysis model for handover performance study in
integrated systems. However, this method does not consider the power consumption parameters and
QoS requirements of different kinds of applications, and the method uses a simple equation based
control mechanism instead of intelligent techniques.
US 2008/0101318 Al, May 2008, "Vertical Handover Composite Quality Measures", proposes a
method for plurality of composite quality measures based vertical handover mechanism. In this
method, composite quality measure of different radio interfaces are measured against a target quality
measure. This plurality of composite quality measures are compared to determine which of the
plurality of radio interfaces to utilize for a vertical handover. Measurements include at least one
measurement from the set consisting of signal strength, bit error rate, effective bandwidth, round trip
delay, and re-transmit rate. Different target quality measures are utilized for each of the plurality of
radio interfaces. Simple weighted measurements and summing the plurality of weighted normalized

measurements to form a composite quality measures lacks intelligence to make a decision of selecting
the best radio interface.
US 7096022 B2, November 2009, "System and Method for Supporting Quality of Service in Vertical
Handovers between Heterogeneous Networks", proposes a method to support vertical handover
between heterogeneous networks, where QoS properties can be accommodated by establishing
handover paths. In this method, several block units are utilized to handle the individual block units,
which make up the vertical handover procedure. However, due to the ignorance of the relationship
between each block, the QoS performance for different requirements can be degraded. As the real-
time services are more delay constrained, overhead due to the numerous blocks may degrade
performance of those services. This invention does not consider the power consumption parameters
and lacks intelligence.
US 7,653,392 B2, January 2010, "Methods and Systems for Heterogeneous Wireless Network
Discovery and Selection", methods and system is provided for a mobile client to discover and obtain
the parameters of heterogeneous wireless networks via a fuzzy logic based operation, within a
popularity of heterogeneous wireless networks. In this method a simple fuzzy logic based technique is
considered. Input selection parameters considered are: RSSI, power consumption, bandwidth, and
network availability where the network characteristics are compared with mobile client application
requirements to provide ordered list of preferred networks. This order list of preferred networks is
compared with user policies to select a new network. However, the method did not consider relation
among the QoS requirements (like delay, jitter, BER, and bandwidth) and different kinds of
applications. Moreover, simple fuzzy logic does not consider the relative importance among the
various QoS parameters.
US 7,907,569 B2, March 2011, "Media Independent Handover (MIH) terminal, MIH server, and
method of vertical handover by the terminal and the server", proposes a method of media independent
handover. This method includes a searching for a second communication network appropriate for a
requested vertical handover (VHO), and transmitting MIH terminal information to the second
communication network when the VHO is requested from a predetermined MIH terminal connected
to a first communication network. MIH server requests the MIH terminal to perform the VHO to the
second communication network. It also transmits the temporary channel information of the second
communication network to the MIH terminal from the second communication network, where a
temporary channel connection is established between the MIH terminal and the second
communication network. Here the MIH server detects a second communication network appropriate
for the MIH terminal, and performs the VHO after referring to the communication network
information included in the MIH_Handover_Initiate message, and examining availability of resource,

requested by the MIH terminal. But, MIH server needs the control over both the networks which is
difficult to manage as multiple networks are involved and latency can be increased that ultimately
degrades the QoS for real-time applications. However, in heterogeneous wireless access networks
only the mobile nodes have specific knowledge about the kind of interfaces they are equipped with;
so, the network dependency on the mobile node is high.
It should be noted that in the above prior art the fuzzy logic techniques always make a clear decision
among the input parameter values using a fuzzy rule base whereas TOPSIS maintains the relative
closeness to the ideal solution. A simple fuzzy logic based technique does not consider the relative
importance of the various parameters whereas the TOPSIS approach lacks intelligence in decision
making.
The present invention therefore proposes a novel FUZZY-TOP mechanism that uses the properties of
both fuzzy logic and TOPSIS. The FRB is used to evaluate the score value corresponding to the input
parameters. This score value is compared to the ideal solution to get the network to which handover is
to be carried out.
OBJECTS OF THE INVENTION
A basic object of the present invention is to overcome the disadvantages/drawbacks of the known art.
Another object of the present invention is to provide a vertical handover method for implementing
handoff among heterogeneous wireless networks and a system thereof.
Another object of the present invention is to provide a method of vertical handover integrating both
Fuzzy logic and TOPSIS technique.
Another object of the present invention is to incorporate energy awareness in vertical handover
decision method.
Yet another object of the present invention is to provide a simple application aware fuzzy rule set.
These and other advantages of the present invention will become readily apparent from the following
detailed description read in conjunction with the accompanying drawings.
SUMMARY OF THE INVENTION

The following presents a simplified summary of the invention in order to provide a basic
understanding of some aspects of the invention. This summary is not an extensive overview of the
present invention. It is not intended to identify the key/critical elements of the invention or to
delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a
simplified form as a prelude to a more detailed description of the invention presented later.
There is provided a method and system for handover in a telecommunication system
According to one embodiment of the present invention, there is provided a vertical handover method
for implementing handoff among heterogeneous wireless networks, said method comprising the steps
of obtaining periodically signal strength (RSSI) of current network to monitor the need to handover;
monitoring the signal strength of foreign network at mobile client when said signal strength of said
current network go below the handover threshold; obtaining information on QoS and energy
parameters of the available networks within a range of current network interface of a mobile node,
said information on QoS and energy parameters maintained in the information servers provided at
each network; processing said information using a FUZZY-TOP module, said module evaluating
handoff score value of network using a Fuzzy rule base system corresponding to said information
parameters, said information given to a fuzzzification module to convert to corresponding
membership values using membership functions, said membership values used for decision making to
give an output membership value, said output membership value converted to a crisp value using a
defuzzzification process, selecting a network using TOPSIS by comparing with said score value;
executing handoff using mobility management protocols to said selected network.
Other embodiment of the present invention provides system for vertical handover implementing
handoff among heterogeneous wireless network, said system comprising a terminal for obtaining
periodically the signal strength (RSSI) of current network to monitor the need to handover; a means at
mobile client to monitor signal strength of foreign network when said signal strength of said current
network go below the handover threshold; a means for obtaining information on QoS and energy
parameters of available networks within the range of current network interface of a mobile node; a
plurality of information servers provided at each network for maintaining said information on QoS
and energy parameters; a FUZZY- TOP module for processing said information, said module
evaluating handoff score value of network using a Fuzzy rule base system corresponding to said
information parameters; said Fuzzy top module further comprising a fuzzification module taking said
information for converting to membership values using membership functions, said membership

values used for decision making to give an output membership value, said output membership value
converted to a crisp value using the defuzzzification process, selecting a network using TOPSIS by
comparing with said score value and executing handoff using mobility management protocols to said
selected network.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
In the appended drawings:
Fig 1 illustrates the media independent handover and multiple access reference models.
Fig 2 illustrates the primitives for service access points in MIH.
Fig 3 illustrates GERAN to GAN CS (circuit switched) handover.
Fig 4 illustrates the FUZZY-TOP vertical handover.
Fig 5 illustrates a typical heterogeneous wireless network environment.
Fig 6 illustrates the Fuzzy rule base (FRB) technique.
Fig 7 illustrates the input and output membership functions.
Fig 8 illustrates the block diagram of the FUZZY-TOP handover decision mechanism.
Fig 9 illustrates the Average power consumption (mW) to average connection life-time (minutes) in
comparison with SAW (Simple Additive Weighted), TOPSIS (Techniques for Order Preference by
Similarity to Ideal Situations), MEW (Multiplicative Exponential Weighted), FUZZY, FUZZY-TOP
(FUZZY-TOPSIS).
Fig 10 illustrates Average Bit Error Rate to average connection life-time (minutes) in comparison
with SAW (Simple Additive Weighted), TOPSIS (Techniques for Order Preference by Similarity to
Ideal Situations), MEW (Multiplicative Exponential Weighted), FUZZY, FUZZY-TOP (FUZZY-
TOPSIS).

Fig 11 illustrates the Average Jitter (msec) to average connection life-time (minutes) in comparison
with SAW (Simple Additive Weighted), TOPSIS (Techniques for Order Preference by Similarity to
Ideal Situations), MEW (Multiplicative Exponential Weighted), FUZZY, FUZZY-TOP (FUZZY-
TOPSIS).
Fig 12 illustrates the Average end-to-end delay (msec) to average connection life-time (minutes) in
comparison with SAW (Simple Additive Weighted), TOPSIS (Techniques for Order Preference by
Similarity to Ideal Situations), MEW (Multiplicative Exponential Weighted), FUZZY, FUZZY-TOP
(FUZZY-TOPSIS).
Fig 13 illustrates the Average available bandwidth (kbps) to average connection life-time (minutes) in
comparison with SAW (Simple Additive Weighted), TOPSIS (Techniques for Order Preference by
Similarity to Ideal Situations), MEW (Multiplicative Exponential Weighted), FUZZY, FUZZY-TOP
(FUZZY-TOPSIS).
Fig 14 illustrates the Availability to average connection life-time (minutes) in comparison with SAW
(Simple Additive Weighted), TOPSIS (Techniques for Order Preference by Similarity to Ideal
Situations), MEW (Multiplicative Exponential Weighted), FUZZY, FUZZY-TOP (FUZZY-TOPSIS).
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The following drawings are illustrative of particular examples for enabling methods of the present
invention, are descriptive of some of the methods, and are not intended to limit the scope of the
invention. The drawings are not to scale (unless so stated) and are intended for use in conjunction
with the explanations in the following detailed description.
Reference is first invited to Fig 1 where (a) explains the reference model of MIH function and (b)
represents the multiple access network reference model. MIH function provides convergence of link-
layer state information from multiple heterogeneous access technologies into a unified presentation to
the upper layers of the mobility management protocol stack.
Fig. 2 shows primitives for service access points in MIH (IEEE 802.21). A sample primitive for each
of the service access points from MIH standard is given, typical call flow during circuit switched
handover from GERAN to GAN is explained.

Fig. 3 shows GERAN to GAN CS (circuit switched) Handover (Ref: 3GPP TS 43.318). A typical call
flow during circuit switched handover from GERAN to GAN is explained.
Fig. 4 shows different method steps for making FUZZY-TOP vertical handover. It shows the method
step of detecting available network till switching from current network to the best available network.
Fig. 5 shows a typical heterogeneous wireless network environment consisting of UMTS, GSM,
WLAN, and WiMAX networks. UMTS and GSM network are connected to the GPRS infrastructure
via MSC. This GRPS infrastructure consists of SGSN and GGSN gateway components. The SGSN is
responsible for mobility management and manages the end-user via the BSC/RNC into the radio
network.
Fig. 6 shows Operation of the fuzzy rule base system. A set of conditions are verified and if these are
true certain actions are taken. It shows different operations like Fuzzification, defuzzification and
provision for Handoff Score value of Network.
Fig. 7 shows the membership functions for different input parameters considered as triangular
functions with five different regions: very low, low, medium, high, and very high. It shows Input and
Output membership functions: (a) Bit Error Rate (b) Jitter (c) End-to-End Delay (d) Power
consumption (e) Bandwidth (f) Handoff score.
Fig. 8 shows the FUZZY-TOP method, first evaluates the actual score value of network parameters
and then compares the actual score value with the best score value of the network. It verifies the
relative closeness of actual score value of network to the best score value. Then, the best network is
selected based on the relative closeness. The selected candidate network is the one which is having a
score value closest to best score value of the network.
Fig. 9 shows Average power consumption obtained for all the traffic classes. Even though average
power consumption using FUZZY-TOP is more than the TOPSIS for conversational, the power
consumption values for other traffic classes like streaming, interactive, and background kind of
applications is less using the proposed technique.
Fig. 10 shows Average BER performance for FUZZY-TOP that is better compared to other
mechanisms. SAW, and MEW give nearly the same performance. SAW, and MEW give the poor
performance whereas FUZZY and TOPSIS give the moderate performance.

Fig. 11 shows Average Jitter performance obtained for both conversational and streaming kind of
applications. A similar interpretation, as explained for BER performance, is applied for average Jitter
performance. Even though TOPSIS gives better performance than SAW, MEW, and FUZZY, the
Jitter performance for FUZZY-TOP is even much better than TOPSIS.
Fig. 12 shows Average E2EDelay performance obtained. Average E2EDelay performance of SAW,
MEW, and FUZZY is poorer than TOPSIS and FUZZY-TOP. A similar interpretation is also applied
here as explained above in BER performance. However, the E2EDelay performance for TOPSIS is
better than FUZZY-TOP in interactive kind of applications.
Fig. 13 shows Average available bandwidth performance obtained. Average available bandwidth
performance using proposed FUZZY-TOP technique is worse than other vertical handoff algorithms.
However, it is better than the simple TOPSIS. Streaming applications need a more bandwidth
requirement, whereas background kind of applications need moderate level of bandwidth.
Fig. 14 shows Availability to average connection life-time (minutes) in comparison with SAW
(Simple Additive Weighted), TOPSIS (Techniques for Order Preference by Similarity to Ideal
Situations), MEW (Multiplicative Exponential Weighted), FUZZY, FUZZY-TOP (FUZZY-TOPSIS).
(a) Conversational and b) Interactive. For both conversational and Interactive applications it is
observed that the availability performance of TOPSIS and FUZZY-TOP are better than SAW, MEW,
and FUZZY. However, the availability performance of FUZZY-TOP in interactive applications is less
than TOPSIS.
The invented system is thus a system for vertical handover implementing handoff among
heterogeneous wireless network.
DETAILED DESCRIPTION OF THE INVENTION
Accordingly in the present invention a method for vertical handover in heterogeneous wireless
networks is provided with a novel FUZZY-TOP decision mechanism based on QoS (quality of
service), and energy parameters.
FUZZY-TOP is an intelligent handover mechanism that uses the properties of both FUZZY logic and
TOPSIS (Technique for Order Preference by Similarity to Ideal Situation). As mobile devices are very
energy constrained, power consumption at mobile client is considered in the decision making process.

Along with the energy parameter, the QoS parameter considered are: available bandwidth, end-to-end
delay (E2EDelay), jitter, and bit error rate (BER).
A non birth-death Markov chain with states corresponding to the available networks is used for
creating the heterogeneous simulation environment. Simulation results are provided to assess relative
performance of FUZZY-TOP technique with the existing vertical handover decision techniques. The
proposed FUZZY-TOP based decision mechanism performs better for different traffic classes as
supported by results in a subsequent section.
PROPOSED FUZZY-TOP VERTICAL HANDOVER DECISION MECHANISM:
Assuming the mobile client is able to access any and every network; and the mobile client has each
and every interface built-in a method for an intelligent handover decision mechanism among different
radio access networks follows as explained in flow chart in Fig. 4. Initially mobile client periodically
checks for the signal strength (RSSI) of current network to monitor the need to handover. When the
RSSI of mobile client is going below the handover threshold, the available networks are monitored at
the mobile client. In the second step, the QoS and energy parameters of the available networks is
obtained either using MIH or GAN or both based on the available network set. In the third step, the
best network is decided by using FUZZY-TOP vertical handoff mechanism based on application QoS
and energy requirements obtained in the second step. Finally, the mobile is switched to the best
network from the current network after making a decision; this may use any mobility management
protocol.
Fig. 5 explains a typical heterogeneous wireless network environment consisting of UMTS, GSM,
WLAN, and WiMAX networks. UMTS and GSM network are connected to the GPRS infrastructure
via MSC. This GRPS infrastructure consists of SGSN and GGSN gateway components. The SGSN is
responsible for mobility management and manages the end-user via the BSC/RNC into the radio
network. It maintains the connected user's context and integrates with other element such as the
HSS/HLR to manage allowed services and the GGSN to manage access to external IP networks. The
GGSN is the IP access point for mobile users to the wider internet, corporate VPN or other IP access
networks. Static information about the QoS and energy is maintained by the information servers
provided at each network. WLAN infrastructure provided by the operator can directly connect to the
GPRS infrastructure via WLAN gateways. WLAN networks can also connect to internet via a router.
WiMAX network is connected to the GPRS infrastructure via ASN-GW (which is not shown in fig).
A critical component of any mobile WiMAX network is the ASN Gateway, which aggregates
subscriber and control traffic from base stations within an access network.

The correspondent node can be the streaming server or it can be any other mobile device to which the
user is connected. Mobile client is also equipped with MIH client and generic access network support.
Mobile clients access the information about the network through media independent handover (IEEE
802.21) for non-3gpp networks and through generic access network controller for 3gpp based
networks. AAA server provides the authentication, authorization, and accounting functions.
While the mobile is moving, if it detects that the signal strength of current network is less than the
predetermined threshold value, it scans the available foreign network set. The mobile client needs to
obtain the information about the foreign networks via GANC or MIH. Then the information is
provided to the FUZZY-TOP module that resides in the mobile client. This module decides the best
network based on the information provided from the information servers. The information includes
the achievable QoS parameters and power consumption from the past knowledge. Then the mobile is
switched to the best network by using the mobility management protocols.
The proposed FUZZY-TOP based vertical handover mechanism uses the hybrid mechanism of fuzzy
logic and TOPSIS. The input QoS parameters considered are: the available bandwidth, End-to-End
Delay, Jitter, BER and an energy parameter reflecting the power consumption at the mobile client.
The Fuzzy Rule Base (FRB) system takes the input parameter values of network and evaluates the
handoff score value of network as shown in Fig .6. The input crisp values are first given to
fuzzification module where these input values are converted to membership values using membership
functions. These membership values are used for decision making to give an output membership
value. The output membership value is converted to a crisp value using the defuzzzification process.
One of the well known methods for defuzzzification is the Centriod method. In TOPSIS the selected
candidate network is the one which is the closest to the ideal solution and the farthest from the worst
case solution. The ideal solution is obtained by using the best values for each parameter.
The fuzzy logic techniques always make a clear decision among the input parameter values using a
fuzzy rule base whereas; TOPSIS maintains the relative closeness to the ideal solution. A simple
fuzzy logic based technique does not consider the relative importance of the various parameters
whereas the TOPSIS approach lacks intelligence in decision making.
This invention proposes a novel FUZZY-TOP mechanism which uses the properties of both fuzzy
logic and TOPSIS; the FRB is used to evaluate the score value corresponding to the input parameters.
This score value is compared to the ideal solution to get the network to which handover is to be
carried out.

The membership functions for different input parameters are considered as triangular functions with
five different regions: very low, low, medium, high, and very high as shown in Fig. 7(a)-(e). The
output membership function is also assumed to be a triangular function as shown in the Fig. 7(f). The
membership regions for BER is given in Fig. 7(a), where the membership regions are very low, low,
medium, high, and very high. Similarly for Jitter, E2EDelay, and Power consumption also considered
as shown in Fig 7(b)-(d). For Bandwidth we can usually say that 0 to 150 kbps is a very low
bandwidth region, low bandwidth is in 50-350, medium or enough bandwidth to be in the range of
150 to 750 kbps, high bandwidth region to be between 350 to 2000 kbps, and very high to be in the
range of 750-12000 kbps. These membership regions are described in Fig. 7(e). The output parameter
is a handoff score value as shown in Fig. 7(f). The handoff score value is assumed to be in range of 0
to 100.
The FUZZY-TOP method, depicted in Fig. 8, first evaluates the actual score value of network
parameters and then compares the actual score value with the best score value of the network. It
verifies the relative closeness of actual score value of network to the best score value. Then, the best
network is selected based on the relative closeness. The selected candidate network is the one which is
having a score value closest to best score value of the network.
As per the IMT2000 QoS Classes and*Requirements (3GPP- TS 23.107), various applications have
different QoS requirements as explained in Table-1 with linguistic terms. From this table, we can infer
that applications generating conversational traffic are mainly concerned with End-to-End delay and
Jitter. Streaming applications need less Jitter and more Bandwidth. Although Interactive and
Background applications are mainly concerned about BER, Interactive applications need the
E2EDelay to be less, whereas Background applications need at least a moderate bandwidth. So, with a
view to reduce the fuzzy rule set, only few parameter values, which are important for the applications,
are used to constitute the fuzzy rule base.
The fuzzy rules are made as per the requirements of 3GPP QoS classes and power requirements. A
total of 125 rules are made for each traffic class, corresponding to three input parameters and five
membership regions. Out of this, we show only 6 rules for each traffic class in Table-2 for the sake of
illustration. Operation of the fuzzy rule base system is shown in Fig. 6. A set of conditions are verified
and if these are true certain actions are taken. As the fuzzy rules are made based on the application
types, rules are reduced to 125 for each application, so typical memory requirement is in the order of
few kilobytes (50-100) which can be easily provided by the typical mobile handset. It is obvious that
even standard processors can work at very high speeds. For many applications even 8 bit processors

can perform the evaluation of a rule base in milliseconds. The output is a handoff score value, which
is generated with the help of a rule base and individual consequents of each rule. The output is in the
range of 0-100 with triangular membership functions having five regions as shown in Fig. 7(f). When
handoff is required, a mobile calculates the handoff score value for all available networks with a set of
input parameters by using the FUZZY-TOP scheme proposed above, and selects the best one.
The information about the QoS and energy consumption of networks is obtained to use as input to the
FUZZY-TOP vertical handoff module. This information is obtained from the information servers
provided at the network side. This information is obtained through MIH (media independent
handover) services from non-3 GPP networks and through GAN (Generic Access Network) from the
3GPP networks. This information server provides the static database from the past knowledge to
provide information about the estimated QoS and energy expenditure values, the FUZZY-TOP
vertical handoff module evaluates the handoff score values of network based on the information
provided from information servers and decides the best network from the available network set. This
FUZZY-TOP vertical handover decision mechanism uses the combined properties of both FUZZY
logic and TOPSIS (Techniques for Order Preferences by Similarity to the Ideal Solution). The
FUZZY-TOP uses the QoS and energy parameters of available networks and evaluates the handoff
score values using fuzzy rule base (FRB) technique. These handoff score values are compared to the
ideal solution of networks. The ideal solution of network is obtained by measuring the handoff score
value for best values of each parameter. The candidate network is selected as best network which is
closest to the ideal solution and farthest from worst case solution. The mobile is switched to the best
network from the current network using mobile IP protocols.
Validation results are provided for FUZZY-TOP algorithm with the existing vertical handover
decision mechanisms (i.e. SAW, TOPSIS, MEW, FUZZY LOGIC), where the proposed FUZZY-TOP
based decision mechanism performs better for different traffic classes.
Advantages:
i) QoS maintenance during handoff from one network to another network by considering different
kinds of applications.
ii) As mobile devices are more energy constrained, energy aware vertical handoff decision is more
appropriate for heterogeneous wireless networks, which is addressed in this invention.
iii) Method is implementable over the existing standards as the information is obtained through IEEE
802.21 and 3GPP GAN.
iv) Method can be easily incorporated into the existing telecom infrastructure without much change.

v) It is an intelligent handover decision mechanism.
vi) It is more efficient than existing vertical handover mechanism for both real-time and non real-time
applications.
Testing:
Referring to Fig. 5, a heterogeneous wireless network environment has been modeled and simulated
for vertical handoff using FUZZY-TOP decision mechanism. Testing and validation steps are
considered in the test of the proposed method.
A. Scenario of heterogeneous wireless networks.
i. The networks assumed to illustrate the proposed method are an UMTS network, a
GPRS network and a WLAN. The parameters assumed for these networks are as
specified in Table-3. Mobile is able to access the available network set in a
typical heterogeneous wireless network environment.
ii. We considered four traffic classes defined by 3GPP, which are conversational,
streaming, interactive and background. Each traffic class is associated with
different QoS parameters and energy parameter.
iii. The four traffic classes have different QoS requirements along with the
requirement of power consumption. So it is assigned with different weights
according to the importance of parameters in different traffic classes.
B. Model and parameters considered in simulation:
i. In simulation, we consider a non birth-death Markov chain where a state
corresponds to the available networks, including the unavailability of any
network, with connection lifetimes of all the states assumed to be independent
identically distributed (iid) random variables.
ii. In this model, we assume that a state corresponds to the set of networks available
at any instant of the time.

iii. State lifetimes are assumed to follow an exponential distribution with a mean X;
whereas within a state connections will follow an exponential distribution with a
mean u. State transitions are instantaneous and do not involve any delay.
iv. In each state, the best network is selected from the available networks and
connections are assigned to that network.
v. The connection life time of the mobile is assumed to follow an exponential
distribution, where average connection lifetime (u) is varied from 1 to 10 min.
vi. State changing time is also assumed to follow an exponential distribution with
mean equal to h (where i is 1 for UMTS, 2 for GPRS, 3 for WLAN). For UMTS
and GPRS networks, we use X\ = X2 - 4min. whereas for WLAN networks, we
useA,3 = lmin.
vii. We compare vertical handoff algorithms: SAW (Simple Additive Weight),
TOPSIS (Techniques for Order Preference by Similarity to Ideal Solution), MEW
(Multiplicative Exponent Weighting), and FUZZY algorithms with our proposed
FUZZY-TOP algorithm.
viii. The vertical handoff decision algorithms: SAW, MEW, and TOPSIS needs
Relative importance of each parameter which is usually given by the set of
weights Wj. The analytical hierarchical processing (AHP) method is used to
determine the weights by using the comparison between a pair metrics with 1-9
AHP scale. The weights are obtained as shown in Table-4.
C. Outcomes of results and discussion:
The simulation results obtained are plotted in Fig. 9 to Fig. 14, respectively for average power
consumption at mobile client, BER, Jitter, E2EDelay, average available bandwidth, and availability.
Average Power consumption, bandwidth and average E2EDelay values are obtained with 95%
confidence level where the margin of error is computed as 1.86. State '0' is assumed to be associated
with a bandwidth of zero, delay of 500 msec, BER, Jitter, and power consumption of zero values.
State changes evolve according to the Markov chain with the adaptive state transition matrix T. A
Mobile can be in any state as the state changes. In any state the best network is selected from the
available networks. The best network is decided based on handoff score values calculated for each

network. The handoff score value is calculated using various handoff decision algorithms. The
average connection lifetime is varied from 1 to 10 minute. Weighted moving average is used for
smoothing the curves with a period of 3. As the best network is selected from the networks available
in any state, average state lifetime is decided based on the network selected from the previous state.
For UMTS and GPRS networks, the state lifetime is assumed to be 4 minute, whereas for the WLAN,
the state lifetime is assumed to be 1 minute. In any state for each network the power consumption,
bandwidth, delay, jitter, and bit error rate values are assigned randomly from the specified values for
that network. The mean value is obtained by averaging over 10000 connections.
Average power consumption is obtained for all the traffic classes as shown in Fig. 9. Even though
average power consumption using FUZZY-TOP is more than the TOPSIS for conversational, the
power consumption values for other traffic classes like streaming, interactive, and background kind of
applications is less using the proposed technique. Data oriented applications are more energy prone
than simple voice calls due to the huge amount of traffic. The performance for SAW and MEW is
less compared to other algorithms due to the simple weighting mechanisms involved for making a
handoff decision. Whereas, TOPSIS gives a somewhat better performance because of relative measure
towards the best network value, but it is still less to utilize the energy efficiently. Simple fuzzy logic
technique is also not sufficient to make handoff decision due to the tradeoff among the various
parameters. So it is observed that FUZZY-TOP makes the handoff decision more efficiently than
other vertical handoff decision mechanisms.
As interactive and background kind of applications need less bit error rate, the average BER
performance is obtained for both kind of applications as shown in Fig. 10. Average BER performance
for FUZZY-TOP is better compared to other mechanisms. SAW, and MEW give nearly the same
performance. SAW, and MEW give the poor performance whereas FUZZY and TOPSIS give the
moderate performance. As SAW and MEW follows simple weighting mechanisms, those applications
give the poor performance. Even though FUZZY, and TOPSIS give moderate performance, those are
alone not sufficient to make decision due to their disadvantages as explained above. So, FUZZY-TOP,
which is a combined technique of FUZZY and TOPSIS, gives the better performance among all the
techniques.
Average Jitter performance is obtained for both conversational and streaming kind of applications as
shown in Fig. 11. A similar interpretation, as explained for BER performance, is applied for average
Jitter performance. Even though TOPSIS gives better performance than SAW, MEW, and FUZZY,
the Jitter performance for FUZZY-TOP is even much better than TOPSIS.
Average E2EDelay performance is obtained as shown in Fig. 12. Average E2EDelay performance of
SAW, MEW, and FUZZY is poorer than TOPSIS and FUZZY-TOP. A similar interpretation is also

applied here as explained above in BER performance. However, the E2EDelay performance for
TOPSIS is better than FUZZY-TOP in interactive kind of applications. Since, the interactive kinds of
applications need much importance in BER performance than the E2EDelay performance; tradeoff is
involved among the parameters in making a decision.
Average available bandwidth performance is also obtained as shown in Fig. 13. Average available
bandwidth performance using proposed FUZZY-TOP technique is worse than other vertical handoff
algorithms. However, it is better than the simple TOPSIS. Streaming applications need a more
bandwidth requirement, whereas background kind of applications need moderate level of bandwidth.
In literature, many of the schemes are proposed to address bandwidth allocation strategy and channel
resources issue of cellular network. One of the important schemes is Max-Min fair bandwidth
allocation algorithm. The bandwidth resources of the system are divided into two sets: the reserved
bandwidth, which is reserved for handoff call specially; the non-reserved bandwidth, which can be
used by new call and handoff call. When a new connecting request is sent to the network, the classes
of the service and its bandwidth set are transmitted to the network as well. The network assigns the
bandwidth as much as possible to accept the call.
As real-time applications need ubiquitous support in heterogeneous wireless network, availability of
network is an important performance measure during the vertical handoff. For conversational and
interactive traffic classes, average end-to-end delay and availability are obtained for various vertical
handoff algorithms as shown in Fig. 14: Availability is defined as the probability that the mobile is in
any state other than the state '0'. For both conversational and Interactive applications it is observed
that the availability performance of TOPSIS and FUZZY-TOP are better than SAW, MEW, and
FUZZY. However, the availability performance of FUZZY-TOP in interactive applications is less
than TOPSIS. In both these applications, it is observed that availability is always above eighty
percent.
From the results obtained using different vertical handoff techniques, it is concluded that the proposed
FUZZY-TOP technique gives better performance for different types of applications. The FUZZY-
TOP technique based on awareness of QoS requirements of the applications, and power requirements
make a clear decision regarding implementing handoff among the networks. The fuzzy membership
regions help in making a clear distinction among the parameter values of the networks and the fuzzy
rule base is used to compute the handoff score value. This handoff score value is used to measure the
relative closeness towards the best handoff score value of the network. The SAW, TOPSIS, and MEW
mechanisms follow simple additive or multiplicative approaches. These mechanisms require
information about the relative importance of each QoS parameters and power consumption values as
explained in Table-5. It is usually given by a set of weights. In these approaches the parameter values

of networks are weighted by these values. The analytical hierarchical processing (AHP) method is
used to determine the weights by using the comparison between a pair metrics with 1-9 AHP scale.
Table-1: QoS (Quality of Service) requirements and traffic classes where the QoS parameters:
BER, E2EDelay, Jitter, Bandwidth; and Traffic Classes: Conversational, Streaming,
Interactive, Background.

Table-3: Networks with their QoS and power consumption parameter values used for
illustrating the proposed mechanism where networks are UMTS, GPRS, and WLAN.

Table-4: QoS, and Power consumption values with their relative importance weights for
Conversational, Streaming, Interactive, and Background kind of traffics. These weights are
derived using AHP (Analytical Hierarchical Processing).

Although the embodiments herein are described with various specific embodiments, it will be obvious
for a person skilled in the art to practice the embodiments herein with modifications. However, all
such modifications are deemed to be within the scope of the claims.
It is also to be understood that the following claims are intended to cover all of the generic and
specific features of the embodiments described herein and all the statements of the scope of the
embodiments which as a matter of language might be said to fall there between.

WE CLAIM
1. A vertical handover method for implementing handoff among heterogeneous wireless
networks, said method comprising the steps of:
obtaining periodically signal strength (RSSI) of current network to monitor the need to
handover;
monitoring the signal strength of foreign network at mobile client when said signal strength of
said current network go below a predetermined handover threshold;
obtaining information on QoS and energy parameters of the available networks within a range
of current network interface of a mobile node, said information on QoS and energy
parameters maintained in the information servers provided at each network;
processing said information using a FUZZY-TOP module, said module evaluating handoff
score value of network using a Fuzzy rule base system corresponding to said information
parameters, said information given to a fuzzzification module to convert to corresponding
membership values using membership functions, said membership values used for decision
making to give an output membership value, said output membership value converted to a
crisp value using a defuzzzification process, selecting a network using TOPSIS by comparing
with said score value;
executing handoff using mobility management protocols to said selected network.
2. Method as claimed in claim 1 wherein mobile client monitor the signal strength of available
network through media independent handover for non-3 gpp networks and through generic
access network controller for 3gpp based networks.
3. Method as claimed in claim 1 wherein authentication, authorization and accounting functions
performed using AAA server.
4. Method as claimed in claim 1 wherein information on said foreign network is obtained
optionally through GANC or MIH.

5. Method as claimed in claim 1 wherein said information on QoS and energy parameters
comprising bandwidth, End to End delay, Jitter, BER and an energy parameter reflecting
power consumption at the mobile client are processed by said Fuzzy-Top module.
6. Method as claimed in claim 6 wherein said selected network is the one having a score value
closest to best score value of network.
7. A system for vertical handover implementing handoff among heterogeneous wireless
network, said system comprising:
a terminal for obtaining periodically the signal strength (RSSI) of current network to monitor
the need to handover;
means at mobile client to monitor signal strength of foreign network when said signal strength
of said current network go below the handover threshold;
means for obtaining information on QoS and energy parameters of available networks within
the range of current network interface of a mobile node;
a plurality of information servers provided at each network for maintaining said information
on QoS and energy parameters;
a FUZZY- TOP module for processing said information, said module evaluating handoff
score value of network using a Fuzzy rule base system corresponding to said information
parameters; said Fuzzy top module further comprising a fuzzification module taking said
information for converting to membership values using membership functions, said
membership values used for decision making to give an output membership value, said output
membership value converted to a crisp value using the defuzzzification process, selecting a
network using TOPSIS by comparing with said score value and executing handoff using
mobility management protocols to said selected network.
8. System as claimed in claim 7 wherein said mobile client monitor the signal strength of
available network through media independent handover for non 3gpp networks.

9. System as claimed in claim 8 further comprising a generic access network controller for 3gpp
based networks.
10. System as claimed in claim 1 further comprising a AAA server for performing
authentication, authorization and accounting functions.

11. System as claimed in claim 7 wherein information on said foreign network is obtained
optionally through GANC or MIH.
12. System as claimed in claim 7 wherein said Fuzzy-Top module process information on QoS
and energy parameters comprising bandwidth, End to End delay, Jitter, BER and an energy
parameter reflecting power consumption at the mobile client.
13. System as claimed in claim 7 wherein said selected network is the one having a score value
closest to best score value of network.
14. A system for vertical handover implementing handoff among heterogeneous wireless network
as herein described and illustrated with reference to accompanying drawings.
15. A vertical handover method for implementing handoff among heterogeneous wireless
network as herein described and illustrated with reference to accompanying drawings.

ABSTRACT

This invention relates generally to a method and system for handover in a telecommunication system
and more particularly to a vertical handover method for implementing handoff among heterogeneous
wireless networks and a system thereof. It provides a FUZZY- TOP module for processing said
information, said module evaluating handoff score value of network using a Fuzzy rule base system
corresponding to said information parameters; said Fuzzy top module further comprising a
fuzzification module taking said information for converting to membership values using membership
functions, said membership values used for decision making to give an output membership value, said
output membership value converted to a crisp value using the defuzzzification process, selecting a
network using TOPSIS by comparing with said score value and executing handoff using mobility
management protocols to said selected network.