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INVITED PAPER

IETE Technical Review

Vol 23, No 4, July
-
August 2006, pp 253
-
265

Fourth Generation (4g) Networks:

Roadmap
-

Migration to the Future


SAYAN KUMAR RAY

Department of Computer science & engineering, Heritage Institute of technology

Kolkata 7001
07, India.

email:
raysk@rediffmail.com

and


ITI SAHA MISTA

ETCE Department, Jadavpur university, Kolkata 700 032, India.

email:
itimisra@cal.vsnl.net.in

The mobile
communication generations has traversed a long way through different phases of evolution since its birth early in the 1970s.
the steady global boom in the number of mobile users each year has periodically spurned the development of more and more
sophistica
ted technologies trying to strike the right chord primarily in terms of provision of seamless global roaming, quality service
s and

high data rate. today numerous different generation technologies with their individual pros and cons are existing globally. t
he coming era
of 4g systems is foreseeing a potential smooth merger of all these heterogeneous technologies with a natural progression to s
upport
seamless cost
-
effective high data rate global roaming, efficient personalized services, typical user
-
centric i
ntegrated service model, high
Qos and overall stable system performance. However, every step in such technological advancements presents huge research
challenges. this article aims to focus upon some of these potential challenges along with different propo
sed feasible and non
-
feasible
solutions in the areas of mobile terminals and users, mobile services, mobile and wireless access networks, and communication
, in order
to give an indepth view of the next
-
generation communication systems.

1.INTRODUCTION

IMAGI
NE

a situation where while traveling in a vehicle in a
large metropolis with a small handheld wireless device, a
person can seamlessly visualize the entire environment ahead
(like buildings, streets, highways, and shopping malls) and, at
the same time can
track other vehicles that may come in his
way to avoid any accidents. Era of next generation of intelligent
wireless systems ahead, effectively termed as 4G, is slowly
taking shape to make such highly intelligent, user
-
focused
personalized service like vir
tual navigation a reality. Different
industry and research organizations worldwide like NTT
DoCoMo, QualComm, Nokia, Ericsson, Motorola, Alcatel,
WWRF, ITU, IEEE, Mobile VCE and 4GW
-
PCC, to name a few,
are all set to make 4G wireless systems hit the commer
cial
market by 2010.

___________________________________

Paper No 36
-
C; Copyright © 2006 by the IETE..



Network systems evolution starting way back at 1970 when the
design of the analog
-
voice
-
oriented First Generation (1G)
systems began. The transition t
o digital voice and data
-
oriented
Second Generation (2G) systems in 1991 marked the beginning
of a multi
-
service platform from the previous mono
-
service era.
Low bit
-
rate data and mono
-
media systems like GSM,
cdmaOne, IS
-
95 and TDMA are still existing in m
ultiple global
locations. The 2.5G systems (like GPRS), an interim step
between 2G and 3G, provided enhanced channel capacity,
higher data rate and throughput and optimized packet
-
data
transmission enhancing Internet access from different wireless
devices.

The commercialized transition to 3G systems in 2002
marked the beginning of a truly multimedia era [1] where more
person
-
to
-
machine interactions than person
-
to
-
person
interactions are prevalent. Core packet networked systems like
cdma2000 and WCDMA provid
e higher channel capacity,
broadband data up to 2 Mbps, high speed multimedia
transmission and global roaming across a cellular network.


241


254

IETE TECHNICAL REVIEW, Vol 23, No 4, 2006



This era marked the beginning of full
-
fledged huge revenue
g
enerating multimedia Internet applications and e
-
commerce.

However, with the huge worldwide increase in the number of
mobile users each day and with emerging demands like totally
user
-
centric services, high speed streaming Internet multimedia
services (tel
emedicine, tele
-
geoprocessing, virtual navigation
and VoIP), seamless global roaming with ubiquitous coverage
and unhampered QoS support, 3G systems have started
showing their limitations with bandwidth availability, spectrum
allocation, air interference s
tandards and lack of seamless
transport mechanisms between different networks. Moreover,
different short range communication systems like WLAN,
Bluetooth and HIPERLAN as well as broadcast communication
systems with different features spanned during this ti
me each
with its own merits and demerits targeting different types of
users and different service types [2] making the situation more
complicated for 3G systems.

b. Migration to the Future

These limitations and drawbacks have generated the
requirement for
an universal framework encompassing all the
existing heterogeneous wired and wireless systems in use. This
IPv6
-
based potential 4G framework, commonly described as
MAGIC [3] (Mobile multimedia, Anytime anywhere access,
Global mobility support, Integrated w
ireless solution and
Customized personal service), would be highly



dynamic and significantly handle the limitations of 3G systems.
So, consolidated solutions that can seamlessly operate on the
multiple, diverse networks migrating to the 4G environment
fu
lfilling the plethora of nextgeneration dream visualizations on
implementing a transparent open wireless architecture (OWA),
should be imperatively designed. This obviously invites new
challenges on every step and researchers worldwide face an
uphill task
of designing suitable solutions. Figure 1, shows such
a 4G vision.

This paper is divided into four sections: introduction, overview of
the potential research challenges, highlighted research
challenges and conclusions. We have identified a whole lot of
pro
bable 4G research challenges and have grouped them under

four research areas: mobile terminals and users, mobile and
wireless access networks, mobile services, and communication
challenges.

2.OVERVIEW OF THE POTENTIAL RESEARCH
CHALLENGES

The different pot
ential challenges are summarized in Table 1.
Section 3 discusses in details on few of the highlighted research
challenge areas.
Table 2 represents the abbreviation used in
this article.




Fig 1 4G

vision 2010




255

RAY & MISRA : 4G NETWORKS

TABLE 1 Summary of the different 4G research challenges





Aim



Vitally important challenges and
problems

Mobile Terminals and Users









Multistandard/Multimode User Terminals



A single wireless us
er terminal should be
designed, which can automatically operate
in different heterogeneous access
networks.



Problems related to high cost,
limitations in terminal size, high power
consumption, high circuit complexity,
and unimproved analog
-
to
-
digital
con
verter (ADC) performance in
software defined radio (SDR)
-
based
implementations.

The different software downloading
schemes related to reconfigurable
terminals have got their own problems.

Automatic Network Tracking and Selection



A roaming user in a hete
rogeneous
environment should be able to auto
-

matically track and select the available
underlying wireless network. In each
communication session for a particular
service the most appropriate underlying
network should be chosen.



The different software do
wnloading
schemes related to reconfigurable
terminals have got their own problems.

Mobile Services









Personal and Session

Mobility



Provision of personalized services through
different personalized operating
environments to the same address.



Con
fusions regarding the choice of
either MIP or SIP as the core protocol
and also whether the ideal framework
be Network layer
-
based or Application
layer
-
based.

Streaming multimedia based services:



To provide very high speed (streaming)
video applications

ensuring high QoS and
bandwidth usability.



UDP suffers from acute congestion
related problems, so TCP is gaining
importance as the ideal transport layer
protocol for video streaming.
Opportunistic scheduling based video
streaming needs more attention.

Multioperator
-
oriented intelligent billing
system



Users subscribing to multiple service
operators for multiple different services
should ideally be charged a single bill
covering all the different billing schemes
involved.
Users need not worry about the
different billing schemes.



Designing new packet
-
switched
oriented billing and accounting policies
for 4G users. From customers and
operators points of view handling
issues like QoS dependant charging,
real
-
time billing information support,
interworking p
repaid systems support
and billing support to diverse service
accesses as well as cost calculation
flexibility, IP traffic billing support,
instant discontinuation of service if any
fraud is detected and correct
maintenance of customer’s profile, are
瑨e⁲
eal⁰roblems.

Mobile and Wireless Access Networks









Seamless Terminal Mobility management



Users should be able to roam freely and
seamlessly across the various global
geographic locations.
Location and
handoff managements should be done
properly.



Maintaining high data rate, best
possible QoS, reducing packet loss and
signaling overhead are the primary
challenges. The system throughput
should be increased with low handover
latency. In location management,
issues like optimally handling diverse
us
er calling and mobile patterns, and
better inter
-
network location
coordination should be handled
properly.
In handover




256

IETE TECHNICAL REVIEW, Vol 23, No 4, 2006

TABLE 1 (Contd...)





Aim



Vitally important challenges and
problems

Mobile Term
inals and Users
















management, challenges like reducing
call droppings and disruptions, reducing
handover time, and optimizing effective
call completion time need more
attention.

Integration and Interoperability of diverse
networks



Seamless

integration and interworking of
the multiple heterogeneous existing and
new wireless access technologies to
provide unhampered connectivity, fully
broadband access, unhampered global

roaming, perfect QoS and user controlled
services.



Problems owing to d
iverse nature of the
constituent access technologies in
terms of varying bit rates, bandwidth
allocation, channel characteristics,
fault
-
tolerance levels and handoff
management mechanisms are the key
ones.

QoS Maintenance



Unaffected QoS should be provid
ed
between the end users and end
-
to
-
end
services.



Significant overhead problems still
persist in different QoS schemes like
traffic control, dynamic resource
reservation and QoS renegotiation.
Ideal mixing of packet level and non
-
packetlevel QoS mechanis
ms should
be done.

Dependability



To ensure fully fault
-
tolerant and
survivable 4G systems.



Ideal fault discovery, notification service
& recovery schemes should be
designed to minimize failures and their
potential impacts on any level of the
hierarchi
cal topologies of the 4G

networks.

Security aspects



Stronger end
-
to
-
end security services are
needed to get credentials of the
communicating parties (residing in
different environment) authenticated
without even knowing each other.



Stronger levels of
protection is needed
against eavesdropping, malicious calls,
and service denials.
Adaptive and
lightweight security mechanisms should
be implemented.

Routing



To implement intelligent packet and call

routing techniques enhancing system
performance.



Low
est Power Consumption and best
QoS are the key attributes to be
addressed while defining a “best path”
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Communication Challenges









Enhancing spectrum eff
iciency and
channel capacity along with ubiquitous
coverage.



To enhance spectral efficiency and
channel capacity with wide area coverage
providing cost
-
effective very high data
rate.
Increasing bandwidth usability and
minimizing multi
-
path effects.



Han
dling the different drawbacks
related to Orthogonal Frequency
Division Multiplexing (OFDM)
-
based air
interfaces, Ultra
-
Wideband (UWB) radio
transmission technology (UWBRT) and
smart antenna technology.




257

RAY & MISRA : 4G NETWORKS


3.HIGHLIGHTED RESEARCH CHALLENGES

Due to space limitation, we have focused our detailed
discussions on five most important research challenge areas. A
bunch of important proposed potential solutions to those
chal
lenge areas are discussed and new as well as less
accessed challenges demanding further research attentions are
pointed out under sub
-
sections 3 (A), (B) and (C).

A. Mobile Terminals and Users

A.1. Automatic Network tracking and selection

Multiple heteroge
neous wired and wireless networks each
having own its unique features and offering unique services
constitute the 4G environment. For efficient seamless global
roaming across the 4G OWA, users with multimode terminals
should be



automatically able to trac
k and select a particular target wireless
system supposedly the most appropriate one in a specific
location offering the needed service. Choosing the best suitable
network is required to optimize the system performance, QoS,
resources accessibility, costs
and service capabilities in that
particular session [2,3]. Suppose an user visits a shopping
center in the city where the wireless access network is WLAN or
WLL to get some vegetables Automatically his reconfigurable
terminal tracks and connects to the ava
ilable local high
-
speed
wireless access system. Afterwards, when the user is driving
across a highway, say, his same terminal again selects and
automatically switches to the appropriate wireless mobile
network, say GPRS or CDMA2000. However in this entire
network selection mechanism transparent to the end users, the
mobile terminal plays a significant role.




258

IETE TECHNICAL REVIEW, Vol 23, No 4, 2006



Based on user preferences (user decides the location to visit
and services to accept at any partic
ular time) the algorithms on
the mobile terminals detect and select the most suitable
underlying access network that provide better link layer
connectivity at that particular location and reconfigures itself as
per the chosen network’s needs and regulation
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(i)

Reconfiguration over the air:

In this a dedic
ated channel
bridges between user terminal and base station facilitating
information exchange and error
-
free downloading of the
requested software module. However this approach suffers from
the problems of handling the varying bandwidth requirements
over n
arrow
-
band channels and also of realistically allocating a
dedicated physical channel for downloading.
(ii
)
Reconfiguration using advanced SIm Cards:

Here based on
the prior stored information regarding the reconfigurable
software modules on the smart card
s, downloading and
configuring of the appropriate services on the terminals take
place on insertion of the cards on the terminals. However this
approach is mostly suitable for stand
-
alone terminals.



(iii)

Internet Download
:

Here software modules download
ed
from Internet by means of a modem, a PC and a terminal are
reconfigured on the user’s terminal.
(iv)

Over
-
the
-
air (OTA)
download [7]:

In this approach multimode user terminals
constantly monitor the predefined broadcasting global pilot and

download chan
nel (GPDCH) and, on detection of any available
network, the terminals decide whether to switch or not. This
approach suffers from slow speed of GPDCH and long
downloading time.

Possible Research Directions: Automatic network tracking and
selection in the 4
G context is a primary research challenge. The
idea of seamless global roaming is much dependent on this.
Needs are there in framing out an universally accepted network
tracking and selecting solution, which on the basis of optimal
resource usage, QoS requ
irements and user preferences would
select the most appropriate available network. In this regard
problems discussed during the different downloading schemes
should be taken care of. However, it’s a big challenge to gather
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b. Mobile Services

b.1. Personal and Session Mobility

In 4
G eras it is critical to ensure that users get convenient
access to the services needed at any given situation. In this
context user mobility has become an important aspect in the
design of next
-
generation wireless communication systems.
Researchers have f
ocused on three such mobility
-
related
research areas: terminal mobility deals with mobility of users
having a single device (discussed under sub
-
section 3.C.1),
session mobility deals with user in a PAN having multiple
personal devices to provide a live se
ssion and personal mobility
concentrates on provision of personalized operating
environments for users along with user movements [2]. In
personal mobility a service required by the user will be
instantaneously delivered irrespective of the user’s location,

device and deviceocationIpe牡瑯爯p牯vide爠domain⁡ndⰠ瑹pe
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瑥牭inal movements.



259

RAY & MISRA : 4G NETWORKS



Current State of

Research:

Insignificant volume of research
works related to personal mobility frameworks for 4G systems
have taken place till date. In this respect, two mobile agent
-
based personal mobility frameworks need mentioning. These
agents bridge the users and the

Internet. The first of these
integrated personal mobility architectures proposed by Thai et al
[9], uses mobile agents and signaling protocols to facilitate
significant optional usage of the communication channels. This
improves the system usability and a
llows accessibility of
required services anytime globally. However though integrating
personal communication and personalized operating
environment, this framework suffers from considerable cost
overhead. The second framework facilitates users providing
as
sistance in browsing, accessing emails, accessing files and in
FTP related mechanisms [10]. Some researches on Session
Initiation Protocol (SIP)
-
based frameworks supporting both
personal and session mobility by augmented signaling
mechanisms are also being

carried out.

Possible Research Directions:

Both personal and session
mobility have drawn limited research attentions until now and
much needed to be done. The whole gamut of works done till
date towards a complete solution between the heterogeneous
nature

of the 4G systems and the personal and session mobility

management issues is yet to achieve any significant break
through.



Major confusions regarding the choice of Mobile IP (MIP) or SIP
as the core protocol and whether the ideal framework should be
Net
work Layerbased or Application Layer
-
based in case of
personal and session mobility still persist with each having its
own pros and cons.

b.2. Streaming Multimedia Based Services:

4G wireless multimedia communication aims at efficient
transmission of strea
ming data for video applications such as
telemedicine, multimedia video conferencin, 3D virtual reality,
virtual navigation, which account for large portion of future traffic,
and needs overcoming the constraints like scarce system
resources, high QoS and
bandwidth requirements, variations in
delays and packet loses [11]. Bursting and streaming video
services are the two types of video services to have gained
popularity in 4G systems. However, while memory requirement
for bursting is much large, streaming l
acks in bandwidth
usability. So implementation of new streaming video application
schemes making optimum use of the available bandwidth in
limited available memory is the research activity of the future.
Choice of appropriate protocols is important in this

context. UDP
and TCP are the two important transport layer protocols for
video streaming. However UDP suffers from acute congestion
related problems (like congestion collap and unfair bandwidth
allocation), which may be more conveniently handled by the
TC
P.


Fig 2 (a) User is confused with the underlying technology to choose; (b) Multimode terminal helps him to automatically track
and select the available
technology appropriate for his service


260

RAY & MISRA : 4G NETWORKS



Current State of Research: In this respect, an efficient scheme
facilitating video streaming at very high data rate has shown that
significant improvement in cellular capacity and video quality can
be achieved for closed
-
l
oop rate controlled encoded video [12] in

a cellular Multi
-
Code CDMA (MC
-
CDMA) wireless system using
TCP as the transport layer protocol and simultaneous MAC
Packet Transmission (SMPT) techniques. For open
-
loop
encoded video, however, this scheme failed to

prove its
suitability. Achieving high performance gain is an important for
streaming video applications. Use of opportunistic scheduling
techniques proved fruitful in this regard. Reference [11]
considers both channel variation and burstiness of video tra
ffic
and shows that significant performance gain for streaming video
applications is still achievable. Very high quality web service,
achievable through the use of Java
-
based i
-
mode and i
-
appli
programs, are suitable for e
-
commerce and mobile banking
appli
cations.

Possible Research Directions: Work done till date on
opportunistic scheduling based video streaming over wireless
networks is negligible and needs significant research attention.
More TCP friendly video streaming schemes over wireless
networks are

desirable to make TCP an automatic choice as the
transport layer protocol over UDP because with enhanced
streaming video applications all set to flood the coming
generation of wireless networks UDP may lead to the instability
of the Internet [12]. On anot
her front, proper management of
bandwidth and efficient schemes for providing quality QoS
between the end
-
systems are two very important criteria for
quality multimedia services. Issues like proper traffic control,
admission control and QoS signalling sche
mes require more
attention in this regard.

C. Mobile and Wireless Access Networks

C.1. Seamless terminal mobility management


Users should be able to roam freely and seamlessly across the
geographic boundaries of different 4G constituent networks
maintaini
ng high data rate, best possible QoS and satisfactory
connectivity with the application servers. Multimode terminals
capable of automatically tracking and selecting the appropriate
available underlying network play an important role in this
context. Ample
research activities in this field have taken place
with prime concerns about reducing packet loss, signaling
overhead and handover latency



apart from increasing the throughput. IPv6, providing link
-
layer
independent mobility management solutions, is unan
imously
accepted as the prime backbone of the future 4G core network.
Further protocol advancements in this context have implemented
Mobile IPv6 (MIPv6) and Hierarchical Mobile IPV6 (HMIPv6).
Effect of other protocols like Location Independent Network
Arch
itecture for IPv6 (LIN6), Transmission Control Protocol
(TCP), User Datagram Protocol (UDP), Stream Control
Transmission Protocol (SCTP), Datagram Congestion Control
Protocol (DCCP), Multiple Address Service for Transport
(MAST), Session Initiation Protoco
l (SIP) and Dynamic Domain
Name System (DDNS) at the different layers are also being
studied [13] in depth. Slow increase in the number of effective
Personal Area Networks (PANs) have urged more research
activities in tackling issues related to mobility ma
nagement of
roaming networks [14]. In this paper we have focused our
discussions on location management and handoff management
scenarios as the primary challenges related to seamless global
terminal mobility.

C.1.1. Location Management

The process of track
ing and maintaining the exact whereabouts
of wireless terminals by the underlying system for possible
connections when powered
-
on, powered
-
off or on the move is
location management, which is a two phase technique. Location
tracking deals with tracking the
exact location of the terminals
and location information storage [15] then maintains other
location information like QoS capabilities, authentication and
traffic. Roaming through diversified range of networks have
given rise to the need for efficient and i
ntegrated location
management schemes.

Current State of Research:

Till date many effective location
management schemes have been proposed. An integrated
location management architecture for inter
-
network roaming is
discussed in [15]. Here the underlying ne
tworks can coordinate
amongst themselves, track whether terminals are located within
coverage and thus route incoming packets/calls meant for
individual terminal. Though ubiquitous coverage and high
dependability are the biggest advantages here, yet this s
cheme
may suffer from enhanced cost of complicated programmable
devices and intelligent hardware. Location of the coordinating
servers in the underlying networks also play an important role in
handling the location management problems. Proposed location
ma
nagement architectures may be centralized, distributed or
hybrid depending on whether all the underlying coordinating
sub
-
networks are centrallymanaged (entire system’s location
managemen琠




261

RAY & MISRA : 4G NETWORKS



decisions are coordinated by

a central server) or individually
-
managed (each sub
-
network manage its own decision) or part
centrally part individuallymanaged (location management
decisions jointly taken by central server and individual networks).
Though the centralized scenario seems
optimal but it needs
close inter sub
-
network coordination and chances of signaling
bottlenecks are always there. The second approach has the
disadvantage of higher update cost but has much less paging
overhead than the third.

Possible Research Directions:
Research analysis has shown
that nearly all the proposed Transport layer protocols for
wireless mobility management like TCP, UDP, SCTP and DCCP
have proved ineffective in handling problems related to location
management. However, nearly all Network layer
and higher
layer protocols [13] supports efficient location management
features and might play fruitful roles in future location information
management researches on issues like location estimation,
location prediction and location privacy. Other related c
hallenges
which needs attention are provision of better location
coordination among the different diverse sub
-
networks, and
optimally matching call to mobility ratio and location update rate.
Lastly, special mentioning is required about the challenges
rela
ted to managing the location of future mobile software
modules that will play an important role in the next generation
network era.

C.1.2. Handoff management

Efficient handoff or handover management is another primary
area of concern for maintaining global

mobility. While roaming,
smooth handover of the mobile terminals is necessary for
seamlessly maintaining the ongoing communication.
Advancements in the various protocols designed play a prime
role in this context. Though MIPv6 was designed as the future
s
tandard mobility protocol it suffers from drawbacks like high
packet loss, increased system load, high handover latency [2]
and signaling scalability mainly due to absence of location
management hierarchy, absence of paging support and wastage
of mobile no
de’s battery power. HMIPV6 promoted by the
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Fig 3 Vertical and horizontal handover of a mobile terminal [2]

However, unlike horizontal handovers, dealing with vertical
handover mechanisms is much complicated. References [5] and
[17] describes effect
ive 4G vertical handover management
architectures, which reduces unnecessary handover attempts
and simplifies the signaling effect.

Possible Research Directions: Much scope for further significant
research in developing a globally accepted handover
managem
ent framework for 4G systems is there. Though
several solutions combining Mobile IP with routing at lower layer
are proposed to significantly manage handover related
difficulties for different networks but plethora of challenges still
exist in every aspect
. Like designing of new handover decision
policies and algorithms relating to soft, hard and hybrid
handovers and efficient handover selection policies for optimal
cross
-
layer performance in multiradio environments, to name a
few.




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IETE TECHNICAL
REVIEW, Vol 23, No 4, 2006



Problems relatingto reducing handover delays and QoS
variability in heterogeneous systems need the developments of
enhanced priority based algorithms and locationaware adaptive
application techniques. Another ongoing research
area is to
finding out whether Virtual Connectivity Manager may emerge as
a better option than Mobile IP in terms of Internet mobility in
future. However it would take considerable amount of time
before a significant handover managing framework could be
su
ccessfully devised.

C.2. Integration and Interoperability of diverse networks:

4G systems intend to facilitate the seamless integration and
interoperation of a broad range of existing systems like satellite
broadband, 3G systems, WLL, fixed wireless access

systems,
WLAN, PAN, ad
-
hoc systems, WiMAX and the new truly
broadband wireless access technologies with IP as the
infrastructure backbone. Such an open wireless architecture
intending to provide unhampered connectivity, fully broadband
access, unhampered
global roaming, global Internet/ data/voice,
perfect QoS and user controlled services is really difficult to
achieve owing to diverse nature of the constituent access
technologies in terms of varying bit rates, bandwidth allocation,
channel characteristics
, fault
-
tolerance levels and handoff
management mechanisms.
Figure 4 [19] shows the probable 4G
interworking approach.



Current State of Research:

A plethora of global diversified
research activities exists, which examined how and to what
extent the seaml
ess merger of the diversified access networks
should be carried on. The merged Ipv6
-
based cooperative,
heterogeneous infrastructure would allow users with multimode
terminals to roam globally, accessing any service anywhere
without the QoS getting affected
. In reference [18] Varsney and
Jain have discussed three such probable merged architectures
(shown in Fig 5 [18]). In the first integrated framework multimode
devices access the diverse services offered by the different
underlying networks. This architect
ure provides better call
completion and area coverage but is not cost
-
effective. The
second integrated framework is overlay network
-
based where
the different universal access points (UAPs) in the overlay
network select the available appropriate underlying
network for
the user. This architecture is complex but supports better billing
and subscription. The third architectural framework uses
common access protocol and hence is less complicated but is
feasible only in case of wireless ATMs. Researchers have
poi
nted out that the extent to which an integration should be
carried out depends on whether it is possible to integrate the
subsystems within the existing standards or it needs
modifications. General trend of integration and interoperation
-
oriented researche
s have identified loose coupling, tight
coupling and very tight coupling as the three potential integration
or coupling schemes for hot
-
spot extensions (like WLAN) to 3G
networks .
Loose coupling provides authenticated billing but
poor



263

RAY & MISRA : 4G NETWORKS



seamless connectivity and QoS support, tight coupling supports
efficient vertical handoffs but is complicated as well as delay
prone and the much complicated very tight coupling
architecture
can efficiently provide radio resource measurement (RRM) and
better QoS support. In this context, diversity of research
activities studying the different potential integration and
interoperation techniques of WLAN and 3G networks have taken
pl
ace. References [20
-
24] discusses effective integration
techniques between WLAN and UMTS/GPRS/WWAN each with
its own pros and cons improving the overall system
performance. The ambient networks proposed by Niebart et al
[25] is another multi
-
operator contr
olled, flexible, multinetwork
integration technique facilitating rich end
-
toend QoS support. An
unique convergence framework of TV broadcast and mobile
cellular technologies really enriching the 4G Information Society
is described in reference [26].

Possib
le Research Directions: Despite all these fruitful research
efforts there is still a long way to go before an universally
accepted, completely transparent, user
-
focused, cooperative
public
-
private wireless broadband communication framework
can be designed,

which will provide seamless, ubiquitous



coverage to the public network using multiple different private
systems [27]. This envisioned IPv6 based completely packet
-
switched framework should be dynamically layered and
reconfigurable as well as dynamically

self
-
organized and
cooperative in terms of network operations, control, maintenance
and reuse of independent modularized functional network blocks
[28]. Research on these aspects are currently channelized to
diversified directions. Several research groups

worldwide like
IETF, IEEE, 3GPP and 3GPP2, WiMAX Forum to name a few
are competing against each other to provide fast, easy and cost
effective interoperable solutions between the different existing
standards. Huge research advancements are carried out eac
h
day in terms of designing more enriched integrated WiFi
-
3G
cellular networks, WiFi
-
WiMAX networks, 3G
-
WiMax networks
and WiFi
-
Distributed Wireless Communication Systems (DWCS)
[29]. As a result each day different products with different
embedded features

compliant with the different technologies are

flocking the global market but wait is still on for truly 4G devices
that would be universally compliant with all the different existing
technologies.


Fig 5 Possible 4G wireless architectures [18]


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IETE TECHNICAL REVIEW, Vol 23, No 4, 2006


4. CONCLUSION

With the plethora of promising features 4G is truly moving
towards getting universally accepted as the ideal next
generation communication s
ystem. 4G is visualized as a
conglomeration of different heterogeneous access technologies.
With this view, this article discussed the probable research
challenges under the different headings of mobile terminals and
users, mobile services, mobile and wire
less access networks,
and communication challenges along with their proposed
potential solutions. While some of these challenges like
multimode user terminals, automatic network selection,
seamless mobility management and smooth interworking of
different h
eterogeneous access networks have drawn much
research attentions, others like routing, protocol requirements,
services and the different communication
-
related challenges
demand much more research enhancements. The article also
identified the different unac
cessed or less accessed research
topics, which need significant contributions for the 4G visions to
come true by 2010.

ACKNOWLEDGEMENT

The author Iti Saha Misra is thankful to AICTE, India for the
financial support of this research under CAYT.

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AUTHOR

Iti Saha misra

is presently holding the
post of Reader in the Department of
Electronics and Telecommunication
Engineering
, Jadavpur University,
Kolkata, India. She received her BTech
degree in Radio Physics and Electronics
from Calcutta University (1989) and
Masters in Telecommunication
Engineering from Jadavpur University
(1991), Kolkata. She completed PhD in
Engineering in

the field of Microstrip Antennas from Jadavpur
University (1996). Her current research interests are in the areas
of Mobility Management Network Architecture and protocols,
Integration Architecture of WLAN and 3G Networks, Location
Management for Cellular

Wireless Networks. Her other research
activities are related to Microstrip. Antennas, Design
Optimization of Wire Antennas using Numerical Techniques. Dr
Saha Misra has authored several journal and International
Conference papers. She is the recipient of
the prestigious
Career award for Young teachers by All India Council for
Technical Education (AICTE) for the financial year 2003
-
2004.

*

*

*



Sayan Kumar Ray

is currently a PhD scholar in the Network
Research Group in

Department of Computer Science and
Software Engineering in the University of Canterbury,
Christchurch, New Zealand. He completed his BE from Gulbarga
University, Karnataka in Computer Science and Engineering in
1999 and MTech from University of Calcutta i
n Computer
Science and Engineering in 2002. He has worked in multiple
software companies after BE and prior to MTech served as
Lecturer in couple of reputed engineering colleges (Narula
Institute of Technology
-

2002 to 2003 and Heritage Institute of
Techn
ology
-

2003 to 2006) in Calcutta in the Dept of Computer
Science and Engineering. His research interests is in the area of
4G networks.

*

*

*


http://folk.uio.no/paalee