International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 3, Issue 2, February 2014
ISSN 2319 - 4847
Handoff Algorithms based on RSSI and Fuzzy
Approach: A Survey
Pooja Dhand1, Sumit Mittal2
1
Research Scholar, MMU, Mullana
2
Professor, MMU, Mullana
Abstract
Wireless networks are standing at threshold of 5G which will revolutionize the world with its new facets. With the proliferation of
4G and 5G, efforts are being made to focus on user centric approach, high reliability, more security and low latency. With an aim
of connecting the world through World Wide Wireless Web (WWWW) and providing customers with best Quality of Service (QoS)
and Quality of Experience (QoE), 5G will soon be a part of our daily life. These upcoming networks are based on the integration
of heterogeneous networks to satisfy user demands for seamless mobility. For the mobile users, during handoff its mobile terminal
terminal switches between different networks either due to technical or performance issues. We have categorized the handoff
strategies into seven groups which will offer a researcher with an insight of efficient handoff management schemes. A detailed
classification is presented about handoff types on the basis of four categories. This paper also focuses on active research
initiatives and future work in the area of handoff in Next Generation Heterogeneous Networks and reveals few challenges which
still exist and hinder in providing seamless services during mobility.
Keywords: Vertical Handoff (VHO), Next Generation Heterogeneous Networks (NGHNs), Mobile Station (MS), Base
Station (BS), Quality of Service (QoS).
1. INTRODUCTION
Growth and Development in the field of technology has engrossed a lot of attention in the current scenario. From the
epoch of traditional telephone systems to smart handheld devices, there is a considerable increase in the number of
mobile users. With this, the needs and requirements are also escalating which are putting immense pressure on the
wireless technology to raise its potency day by day [ADE2011][AHA2013].
Many wireless technologies exist today, that can satisfy customer by providing competent QoS. These wireless networks
act as complementary to each but integration of these different networks will endow a customer with better grade of
service and a boost in QoE. To make this vision of ‘Constantly Connected’ a reality, next generation heterogeneous
networks are at peak.
Next generation heterogeneous networks which mainly comprises of 4G and 5G has envisioned providing mobility across
different types of wireless and mobile networks with guaranteed QoS and imperceptible to users. Global connectivity has
attracted many researchers to this field of handoffs to provide Constant Connectivity. Heterogeneous networks differ in
their capabilities, services and scale, therefore, to handle handoff mechanism becomes more complex. It involves the
integration of different access networks technologies that differ in reliability, bandwidth or cost but intelligent enough to
connect the entire world without limits [MKA2008]. In such framework in which a mobile user is roaming across
heterogeneous networks and switching from one network to another, mobility management becomes critical concern. This
switching between diverse networks for seamless approach is called handover and mobile station (MS), in such
environment switches from one AP to another either belonging to same network or different Network.
Section 2 gives a detailed analysis of the various handoff types on the basis of four categories. Section 3 provides
performance metrics whose value is to be measured during the handoff process to check the efficiency of the algorithm.
Section 4 focuses on the various handoff strategies which are classified in seven categories. Section 5 gives a tabular
comparison of various handoff strategies and Section 6 focus on still remaining issues and challenges to be taken care of.
2. HANDOFF TYPES
Vertical Handoff is switching between heterogeneous networks. These VHOs are required to maintain the continuity and
quality of the current session while the MS moves between different wireless access technologies. Usually, these types are
recognized by the type of architecture or technology they use as expressed in Figure 1.
Handoff can be classified on following factors such as
1. Access technology of the access network
2. Protocol layers involved [JAS2010]
3. Type of technology that the network supports, signaling process and the number of active connections
4. Type of initiating and assisting entities [NEK2006]
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Volume 3, Issue 2, February 2014
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1. On the basis of access technology:- Handoffs can be classified as follows:a. Horizontal handoff or intra-technology handoff refers to handoff between Base Station (BS)'s using the same type
of network interface. This is found in homogeneous circuit-switched cellular systems such as GSM and CDMA
networks.
b. Vertical handover or inter-technology handover occurs between two networks based on different access
technologies. It is further categorized as:
i. Upward vertical handover occurs from a BS/AP with smaller radio coverage to a BS/AP with wider coverage.
ii. Downward vertical handover occurs in the reverse direction to an upward vertical handover.
Apart from handover for radio link quality reasons, vertical handover can be initiated for optimizing service quality
for wireless data services. In this context, vertical handover has to deal with the heterogeneities existing in the
interconnected wireless networks [ESN2008] [ASG2009] and classified as follows:
Table 1. Types of Handover
During an imperative handover, the mobile node changes its point of attachment because of the technical issues like weak
signal from the current network. These issues can be received signal strength indicator (RSSI), Signal –to-noise
interference (SINR), coverage offered by the new network. These handovers are called so because there may be a severe
loss of performance or loss of connection if they are not performed. These may further be classified into reactive
handovers or proactive handovers. In case of the reactive handovers, as the user moves around, the Mobile Terminal
(MT) reacts to the information provided by its network interface regarding changes in the network availability. A reactive
handover may either be anticipated handover or unanticipated handover. An anticipated handover is the one in which
there are alternative base stations to which the MT can handover whereas in unanticipated handover the current network
signal is fading and the mobile node has no point of attachment to which it can handover. So, the MT is forced to
provisionally shut down its continuing connections and only recommence them when a new network point of attachment
is set up [MAI2013].
An alternative vertical handoff occurs in order to provide the users with better performance rather than the technical
issues [ABH2012]. Alternative handoff considers several network parameters such as available bandwidth, supported
velocity and cost of the network along with the device parameters such as QoS (Quality of Service) desired by the
application and user preference. The handover procedure can be characterized as hard handover or soft handover. Hard
handover also referred as a break-before-make (BBM) handover which occurs when the MT is connected to only one
point of attachment at a time i.e. the MT will break the old connection before making the new connection [LYB2000].
Therefore, the MT cannot communicate with the old and new access point simultaneously. On the other hand, soft
handover also referred as a make-before-break (MBB) handover which occurs when the MT is connected to two points of
attachment for a while. Thus, the MT can communicate simultaneously with the old access point as well as the new one.
2. On the basis of protocol layers:- According to the protocol based, handoff can be classified as
1. Layer 2 handoff
2. Layer 3 handoff
3. Cross layer handoff
A layer 2 handover (Datalink Layer Handoff) occurs when a mobile station signals begin decreasing and to enjoy
continuation of services, it changes its association from one access point to another within the same subnet. Based on
handoff initiation parameters such as RSSI, data rate and SINR (Signal to Interference ratio), BSC can take decision of
handing over the control to scanned Access Point. It also involves releasing the association with the previous connected
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Volume 3, Issue 2, February 2014
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access point and building a new connection with the new access. This type of handoff is limited to same subnet and all
connections are updated within the same local loop. So it does not require any help from higher layers for making any
decision. But if they are on different subnets then Layer 2 is helpless in executing it alone, hence higher layers are required.
required. Network layer contributes in handling vertical handoff which occurs among different subnets. In this MSC or
other higher authorities are involved for executing handoff. But horizontal handoff can take place without layer 3
involvement but vertical handoff requires both layer 2 and layer 3 to work in coordinating manner to complete the handover
handover procedure successfully.
The cross-layer protocols are more common for handoff management. These protocols aim to achieve network layer handoff
with the help of communication and signaling from the link layer. By receiving and analyzing, in advance, the signal
strength reports and the information regarding the direction of movement of the mobile node from the link layer, the system
gets ready for a network layer handoff so that packet loss is minimized and latency is reduced [JAS2010].
3. On the basis of technology, signaling process and active connections:- On this basis handoff is classified as
1. Hard handoff
2. Soft handoff
3. Softer handoff
Hard handoff occurs when the connection with the current base station is released first and then the new association is done
with the scanned and selected base station. Due to this, there is slight delay and service interruption when the handoff
occurs affecting the quality of service. Hard handoff is used by GSM (TDMA) and GPRS (FDMA). It can be further
divided into two categories:
1. Inter frequency handoff: In this the carrier frequency of the new base station is different from the old base station.
2. Intra frequency handoff: The carrier frequency of the new base station is same as the previous base station.
While in soft handoff connection with neighboring base station is established first and then the connection with the old
base station is relinquished. Soft handoff is used by the systems using Code Division Multiple Access (CDMA) e.g HSUPA
and Wideband CDMA (WCDMA). Soft handoff is superior to hard handoff and offers Fast Base Station Selection (FBSS).
During FBSS, each MS maintains a set of BSs called active set in which BSs are added when the signal strength is above
the set threshold and detached from the list when it drops below threshold value. But MS communicates with single base
station at one time referred to as anchor Base station.
Softer Handoff is a case of soft handoff but with a very minor difference. In this, mobile station is currently in connection
with two different sectors of the same cell. This is case when handoff occurs between the sectors of the same cell.
4. Type of initiating and assisting entities:- The handover process can also be categorized according to initiating network
entity, assisting network entity or the network entity controlling the handover process [NEK2006]. Based on the entity
initiating, the handover process may be classified as –
1. Mobile-Initiated-Handover (MIHO) or
2. Network-Initiated-Handover (NIHO).
In MIHO, the MS makes the initial decision to perform the handover process and in NIHO, the radio access network
makes the initiation of the handover process.
Handover may also be classified according to the entity in control of the handover process –
1. Network Controlled Handover (NCHO) or
2. Mobile Controlled Handover (MCHO).
In NCHO, the primary control of the handover is with the network and in MCHO, the MS has the primary control of the
handover process. Since the handover decision needs some sort of measurements, information about when and where to
perform handover in NCHO, the network does all the measurements and in MCHO, the MS must take its own
measurement and make the handover decision on its own.
In Mobile-Assisted-Handover (MAHO), the information and measurements from the MS are used by the network to make
the decision. Whereas, in a Network-Assisted-Handover (NAHO), the network collected information is used by the MS in
a handover decision [ARE2007].
3. HANDOFF METRICS
Handoff metrics can be classified into two categories depending upon how network administrator looks at it. First those
metrics which are responsible for handover due to technical reasons like RSSI, SINR. Secondly, those metrics which relate
to the quality of signal which if starts diminishing, chances of handoff start increasing. So, handoff initialization lays down
the foundation for the complete handoff process. It is essential to study few parameters to realize the need for handoff. A
check is required as the mobile station moves away from the base station. If the handoff is to be triggered on the basis of the
technical issue, then it can be network controlled or mobile assisted network controlled. And if the reason for handoff is a
performance issue, then control is given in the hand of a user to trigger a handoff. So depending upon the situation, a
handoff strategy is chosen. It’s not necessary that it must be always a mobile controlled or network controlled. But yes, both
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together make a better solution. Few important metrics are as [ABH2011]:
Table 2. Types of handoff on the basis of initiating and assisting entities
Handoff metrics to be analysed for handoff Handover metrics measured during handover
Initialization and decision making process to check the handover algorithm performance








RSSI
SINR
BER
Distance
Velocity
Network Coverage
Delay
Power Consumption








Load
Jitter
Bandwidth
Cost
Security
Jitter
History
Direction






Handover delay
Handover Call blocking
New Call Blocking
Outage Probability
Number of Handovers
Number of Packet Losses
4. HANDOVER METHODS AND STRATEGIES
No doubt with the increase in use of communication system, there is a race between new methods being proposed and
discovered to remove problems associated with wireless communication like latency, bandwidth, reliability etc. In this
section, existing handoff methods and algorithms have been elaborated based on techniques like soft computing, neighbor
graphs, selective caching etc. The section is concluded with the findings from the existing work and what new is being
added to the proposed method which makes it unique from the existing work. The literature surveyed is divided into
following categories as shown in Figure 1.
Figure 1. Different Handoff Strategies
5. Parameter Based Algorithms
In RSS based algorithms, signal strength of the current network to which the mobile station is attached is measured and is
compared with the RSSI value of the scanned networks for handover. Many models like Free space model, Propagation
model, Hata Okumara model gave a direct equation for calculating the value of RSSI. So many researchers because of its
user friendly nature and availability of the resources required for RSSI calculations consider this parameter. Conventional
methods used only RSSI to initiate handover but later on this metric was combined with many other parameters to
enhance the performance evaluation. Main issues which led to the addition of more parameters to RSSI are like corner
effect, ping-pong problem and multipath fading which led to unnecessary handoffs, call failure and forced termination
during the handoff process [MKA2008] [MCN2004]. Various RSS based algorithms are classified into following
categories [NEK2006]:1. RSS+Threshold
2. RSS+Hystersesis
3. RSS+Threshold+hysteresis
4. RSS+Dwell Timer
5. RSS+adaptive threshold
6. RSS+adaptive hysteresis
By considering RSSI as a most critical parameter for vertical handoff, [SBJ2013] has adopted mathematical
model based VHO prediction approach comprising a well defined objective function considering RSS, UE
velocity, load and cost per user bandwidth. The system performance can be enhanced according to the
user preferences by adjusting the weights in the defined objective function. Due to the high bandwidth
and ease of networking we consider the wireless access standards: Wi-Fi and Wimax. The propagation
propagation model considered in this paper is Jake’s model. The algorithm is simulated in MATLAB and
the performance of the network is evaluated in terms of user velocity and handover numbers.
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In [AHZ 2006] authors focused on signal threshold adaptation strategy to evaluate the performance of Vertical
Handover algorithm (VHO) named an adaptive lifetime-based VHO (ALIVE-HO) algorithm. It uses multiple
parameters such as handoff latency, application QoS and delay tolerance with RSSI as the prime factor.
Application-based signal strength threshold (ASST) choice can be optimized based on multiple criteria such as
handoff signaling, user available bandwidth and packet delay. Since the ASST can be adaptable according to
the access network values hence it may play a significant role in next generation networks. Previous studies
focussed on fixed values of threshold and hysteresis but recent work has made use of adaptive threshold and
adaptive hysteresis to reduce the ping-pong effect. Work by [AHI2011] has taken dynamic dwell timer which is
set to higher values for slow moving mobile stations and vice-versa. This helped to determine the appropriate timing
for Handoff initiation and ensured minimum latency during handoff from cellular to WiFi networks. Also it lowers the
handoff failure probability and the number of unnecessary handoffs.
[LTN2005] used packet success rate instead of RSSI to improve the QoS in handoff process. The author set the priority of
a handoff request based on its current packet success rate (PSR), its degradation rate and the minimum PSR requirement
of its service class and author considered multimedia communication networks to reduce the handoff call dropping
probability under resource-limited condition. Very less researchers have taken packet success rate as the only criteria to
judge the QoS of a handover. In many other cases this parameter is combined with other parameters using fuzzy logic as
in [JYA2013] to gave better results.
In [MLA2012] authors have removed ping pong effect by building an intelligent network selection algorithm by
combining two strategies: Analytic Network Process (ANP) and the technique for order preference by similarity to an
ideal solution (TOPSIS) method. This algorithm tries to remove limitations of ranking abnormality and the ping-pong
effect.
6. Fuzzy based algorithms
In [SDH2010] [SDH2011] [SDH2012], author have used MADM approaches such as Analytic Hierarchy Process (AHP)
to assign weights to different parameters taken to solve the network selection problem. Various network metrics
considered are- Received Signal Strength (RSS), initial delay for connection establishment, network traffic load and
bandwidth offered, service context like usage cost, user contexts like type of application and terminal context like speed of
the vehicle are considered as different attributes. The details of the parameters taken in this paper are given in Table 3.
[KRA2011] presented an access network selection mechanism for multihomed mobile terminals that enable users to
dynamically choose access network based on a set of QoS parameters during handoff. The input parameters used are
available bandwidth, end-to-end Delay, Jitter, Packet Loss, Cost and security of the network and Wi-Fi, WiMax and
CDMA networks as the alternatives.
[MOL2012] proposed a new approach for network selection decision based on Saaty’s Fuzzy Analytical Hierarchy Process
(FAHP) and the Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS). The FAHP method is used
to find out a weight for each criterion and the TOPSIS method is applied to rank the alternatives i.e. various networks.
The proposed approach takes into consideration a new criterion namely history. The use of this attribute helps to deal
with the ping-pong effect by reducing the number of handoffs.
[LEC2012] proposed a novel method based on mahalanobis distance which takes into consideration the correlation with
different criteria and also aims to choose the optimal network while ensuring no ranking abnormality and reducing the
number of handoffs. Simulation results are shown to illustrate the effectiveness of this novel method based on
mahalanobis distance. Results show that the method is able to deal with ranking abnormality problem better than all
decision algorithms such as SAW, MEW etc.
[MOL2013] proposed a novel ranking algorithm, which combines multi-attribute decision making (MADM) and
Mahalanobis distance. Firstly, a classification method is applied to build a classes which having the homogeneous
criteria. Afterwards, the Fuzzy AHP, MADM method is applied to determine weights of inter-classes and intra-classes.
Finally, Mahalanobis distance is used to rank the alternatives. [DPU2006] proposed a simulation solution based on fuzzy
logic to control the handoff decisions and in order to study the behaviour of the fuzzy controllers. The performance of the
fuzzy controller versus traditional methods was compared resulting in an improvement of the average Received Signal
Strength (RSS) due to the fuzzy design of the thresholds and hysteresis margins.
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[YCH2009] presented a novel handoff selection algorithm based on hierarchy analysis and fuzzy evaluation, which was
applied to solve the access network selection problem in the heterogeneous wireless network. Hierarchy analysis can
effectively estimate the weights of evaluation factors. The evaluation matrix was built by analysing the fuzzy evaluation
model, in which RSS is introduced as a dynamic parameter.
[ASD2010] proposed a Fuzzy logic-based Hand-off Decision (FHD) approach for wireless networks. The parameters
included Received Signal Strength Indicator and the relative direction of a Mobile Node toward an access point, which
were considered as inputs to the fuzzy logic system in order to facilitate the handoff decision process for switching to the
best preferable access point. To achieve a fair comparison with a standard handoff procedure, author has implemented a
fuzzy logic-based hand-off decision approach in Omnet++.
[CCK2010] proposed a fuzzy logic-based handoff decision algorithm for optimizing the performance of wireless
networks. The parameters input to the system are data rate, received signal strength indicator (RSSI) and mobile speed for
handoff initialization phase. The system also takes interference rate as input to the system. Simulation results show that
the proposed decision algorithm is better and successful in determining the most appropriate network under different
dynamic working conditions.
[FKA2012] proposed a vertical handover technique based on fuzzy logic. In this, the author has assigned weights to the
handoff performance metrics and defined the scale and range for different networks taken.
[PTK2013] proposed a fuzzy rule based decision mechanism considering user preference, available bandwidth, received
signal strength, network coverage area and QoS values. The proposed algorithm has much more desirable performance
and is more reasonable in selecting the target network, compared with the traditional method. This algorithm decreases
the number of unnecessary handoffs which can effectively reduce ping-pong effect on the basis of ensuring network
performance.
[DCS2011] has designed and implemented a Fuzzy Logic based Handoff controller on an FPGA. The proposed system
can be reconfigured and additional features can be incorporated with increasing need of the end users and thus providing
better quality of service by adding additional parameters.
[AAA2012] reviewed various applications of the core soft computing methodologies in mobile and wireless
communications. The advantages of using soft computing include robustness, cost effectiveness and simplicity. Though
the application areas can be broadly classified into optimization, uncertainty management and prediction, combining soft
computing techniques had shown to effectively solve problems that cut across these boundaries. Genetic algorithm has
been shown to be very useful in optimization problems such as network design, antenna design and resource allocation.
[AFC2013] proposed a new approach to perform vertical handoff using fuzzy logic and neural networks considering
congestion as the primary criterion in making handoff decisions. The proposed approach works with reduced handoff
latency and also the network experiences increased bandwidth availability than the pure fuzzy logic and neural networks
based systems.
[TTH2013] used fuzzy logic to enhance the intelligence of the handoff decision engine. An adaptive traffic dependent
fuzzy-based handoff decision system (ATD-HDS) was presented. The results showed that the proposed ATD-HDS
significantly improves the decision quality and algorithm execution time as compared to a monolithic fuzzy-based
handoff decision system.
[SUM2013] presented an intelligent adaptive and user-centric network selection algorithm which uses Sugeno fuzzy
inference system (FIS) to decide when to perform handoff. Artificial Neuro-Fuzzy is used to rank different wireless
networks for VHO based on set of parameters along with user preferences on a mobile device.
[PDH2013] proposed an intelligent handoff algorithm based on fuzzy logic. A handoff algorithm termed as Fuzzy
controller for Handoff Optimization (FCHO) is introduced based upon fuzzy logic. Traditional algorithms for handoff
using fixed values of parameters can perform well only in specific environment but FCHO exploits attractive features of
several existing algorithms, and adds more capabilities to provide adaptation to the dynamic environment.
[CAM2013] has given a new intelligent Vertical Handoff (VHO) that uses Fuzzy Logic to estimate the necessity of
handoff and to find the new point of attachment of AP. Depending upon the traffic type, different Fuzzy Logic Controllers
(FLC) are used for each traffic to improve the overall performance of proposed system. To assign weights to each
parameter in heterogeneous environments, a Fuzzy Multi-attribute Decision Making (MADM) access network selection
function is used.
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6.1 Comparison on Various Fuzzy Based Algorithms
The comparison in this paper is given in two ways:
1. On the basis of the objectives achieved by the algorithm Table 3.
2. On the basis of parameters referred as in Table 4.
Table 3. Comparison of Fuzzy based handoff algorithms
S.No.
Papers
studied
1.
[SDH2010]
2.
[SDH2011]
3.
Method Used
Tools used
Analytical
hierarchy
process
FAHP
Matlab
[MOL2012]
6.
[LEC2012]
7.
[MOL2013]
8.
[YCH2009]
10.
12.
13.
[FKA2012]
[PTK2013]
14.
[DCS2011]
16.
[AFC2013]
17.
19.
[SUM2013]
[PDH2013]
20.
×
×


×
×
×


×
×
×
Only
background
class studied
×

×
×

×
×
×
×

×
×
×

×
×

×
×
Matlab
Matlab
Oment++
-Matlab
-Opnet Simulation
tool
- AHP
- TOPSIS
- SEW
- Fuzzy logic
Matlab toolRUNE

×
×
×

×
×
×
×
×


×
×

×
×
×


×
×

×

- Fuzzy logic
Matlab
Fuzzy Logic
Matlab
- Fuzzy Logic
Matlab

×
×
Fuzzy Logic
Matlab
×
×
- Sugeno Fis
- ANFIS
Fuzzy Logic
Matlab
×
×
×

Matlab



×
×
×
[TTH2013]
18.
×
-
×

Java
Fuzzy Logic

×
×
AHP
[CCK2010]



Matlab/Simulink
[ASD2010]
11.


×
Matlab
- AHP
- Fuzzy logic
Fuzzy Logic


×
×
×

×
[DPU2006]
9.


FAHP
- FAHP
- Topsis
- FAHP
- Mahalanobis
distance
- AHP
- Mahalanobis
distance
- Fuzzy logic
Fuzzy Logic

Delay
reduced
[KRA2011]
5.
Different
traffic
classes
considered
Corner
effect
removed
[SDH2012]
4.
Computational
Overhead
reduced
PingPong
effect
removed
Fuzzy Logic
[CAM2013]
Simulink model
of Matlab
7. Issues and Challenges for Next Generation Heterogeneous Networks
Handoff initialization and network selection are important phases and performed well to ensure ideal QoS and QoE to
customers. Traditional methods were good in their own times because at that time mobile and internet technology was not
so widespread. So as the technology is advancing from 1G towards 5G, issues and challenges are also accelerating.
Customer demands are increasing which are putting pressure on the mobile companies for better services day by day. The
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next generation of wireless communications networks promises mobility in providing continuous and seamless services to
the users. Future wireless networks will be based on heterogeneous access technologies and must be able to support
features such as inter-carrier handoff, personal mobility and location management for a heterogeneous network.
Researchers are doing much work in handoff decision phase so emphasis must be laid down in initialization and
authentication phase in order to obtain better output.
1. Better QoS and QoE: Today along with QoS, focus is on QoE. No doubt next-generation wireless networks promises
for better and guaranteed QoS to mobile terminals but do they promise for better grade for QoE to customers by offering
solutions for reducing delay and providing timely service delivery.
2. Use of Smart phones: The type of technology available in Smart phones today allows user to communicate with
heterogeneous networks. This terminal provides information like its position (direction) in order to provide better
services and assist in handoff. This will also put strong emphasis on the concept of mobile assisted traditional algorithms
were mostly based on parameters like RSSI or SINR but mobile node conditions were not realized. But today a researcher
can get detailed information about the mobile node through metrics like history, velocity and direction.
3. Cross-Layer based algorithms: Process of handoff is not one layer work. It makes use of physical layer to collect the
values, Datalink layer to perform horizontal handoff, network layer to perform vertical handoff and application layer
which consist of some important protocols. Therefore design an algorithm based on efficient cross-layer-based approaches
will help in efficient mobility management.
4. Requirement of a prerequisite evaluation module: The requirement of the handoff for uninterrupted services should be
foreseen. It is not always preferred that handoff should be avoided but in some cases it must be favoured to decrease call
blocking probability. To achieve this, an efficient need evaluation module to ensure whether a handoff is actually
required. And this could be possible only after rigorous study of few important handoff initialization parameters.
5. Range of heterogeneous networks: Many researchers are using same scale for measuring the range for heterogeneous
networks which is not possible. For example, network coverage of UMTS is 50km and WiMax is 7 km.
6. Providing consistent and seamless connectivity: Both vertical and horizontal handoffs are critical for 4G and are
required to maintain uninterrupted connectivity. It is easy to provide and maintain connection in homogenous
environment but in heterogeneous, complexity increases and variety of networks intensify the problem.
7. Use of fixed threshold and fixed hysteresis: Conventional algorithms were using fixed value of threshold and hysteresis
but how could be this possible if we are using different type of applications. The need of the hour is that the handoff
algorithm must be adaptive according to the type of application and input parameters.
8. Other Criticalities: However well is the design of the mobility management schemes, still many issues like security,
cost, fault-tolerance, routing are still in picture. As we are moving towards 4G and 5G, user centric approach is coming
into focus.
Table 4: Parameters used in fuzzy based algorithms
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6. Conclusion and future Work
Next Generation Heterogeneous Networks aims at providing consistent level of connectivity and connection quality to all
connected users. The advent and necessity of such systems and the issues like limited bandwidth, low reliability has
generated the interest of the researchers into various fields of the mobility management in heterogeneous networks. Our
future work will focus on following objectives. First of all, there are number of metrics which are to be considered for
taking a decision for handoff. Therefore, a thorough study is performed, taken from existing state-of- the-art research papers
and standards, and the key parameters are isolated and clearly identified. The proposed system aims to help designers decide
a proper set of handoff performance metrics that are required to access the software early in process thereby reducing
complexity and improving the continuing capability of the design. Secondly, this work aims at designing an intelligent and
optimal vertical handoff initialization and decision making algorithm to avoid excessive handoffs because unnecessary
handoffs lead to problems like degradation of communication quality , wastage of channel bandwidth, packet loss,
increasing system load, etc. Thirdly, this work will emphasize and consider different types of applications or services such
as voice, data and multimedia applications which require different levels of data rate, network coverage and reliability.
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AUTHOR
Pooja Dhand has done M.Tech. in Computer Science and Engineering from Maharishi Markandeshwar
University, Mullana, Ambala. She is pursuing Ph.D in Computer Science & Applications from Maharishi
Markandeshwar University, Mullana, Ambala. She is working as the Assistant Professor, Computer Science in
Apeejay College of Fine Arts, Jalandhar. She has published his research works in several well renowned
conferences and journals. Her research interests and contributions are related to field of Wireless communication.
Dr. Sumit Mittal received his Ph.D degree & Master’s degree from Department of Computer Science &
Applications, Kurukshetra University, Kurukshetra. Presently, he is working as Professor, M.M. Institute of
Computer Technology & Business Management, M.M. University, Mullana, Ambala, Haryana, India. He is a
life member of Computer Society of India. He is also a member of various academics bodies of M.M.
University, Mullana. He has more than 25 publications in International / National Journals and Conferences. His research
area includes Simulation and Modeling, Operating System, Computer Architecture, Wireless communication and
Distributed Environments.
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