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

Fourth Generation (4g) Networks:

Roadmap- Migration to the Future


Department of Computer science & engineering, Heritage Institute of technology
Kolkata 700107, India.



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


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 sophisticated technologies trying to strike the right chord primarily in terms of provision of seamless global roaming, quality services and
high data rate. today numerous different generation technologies with their individual pros and cons are existing globally. the coming era of 4g systems is foreseeing a potential smooth merger of all these heterogeneous technologies with a natural progression to support seamless cost-effective high data rate global roaming, efficient personalized services, typical user-centric integrated 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 proposed 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.


IMAGINE 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 virtual 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 commercial 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 to 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 multiple 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 provide higher channel capacity, broadband data up to 2 Mbps, high speed multimedia transmission and global roaming across a cellular network.





This era marked the beginning of full-fledged huge revenue generating 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 (telemedicine, 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 standards 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 time 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 wireless 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 fulfilling 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 probable 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.


The different potential 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




TABLE 1 Summary of the different 4G research challenges





Vitally important challenges and problems

Mobile Terminals and Users





Multistandard/Multimode User Terminals


A single wireless user 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 converter (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 heterogeneous 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 downloading schemes related to reconfigurable terminals have got their own problems.

Mobile Services





Personal and Session


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


Confusions 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 prepaid 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 the real problems.

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 user calling and mobile patterns, and better inter-network location coordination should be handled properly. In handover




TABLE 1 (Contd...)





Vitally important challenges and problems

Mobile Terminals 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 diverse 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 provided 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 mechanisms should be done.



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 hierarchical topologies of the 4G

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.



To implement intelligent packet and call
routing techniques enhancing system performance.


Lowest Power Consumption and best QoS are the key attributes to be addressed while defining a “best path” routing technique. Efficient global and ad-hoc routing techniques, and semantic routing based content delivery techniques need to implemented. Mesh network routing techniques are also inadequately addressed.

Protocol Requirements


Unified networking protocol stack and vertical protocol integration mechanisms adapting to the 4G constituent networks requirements should be designed.


Efficient 4G mobile network and security protocols capable of dynamically adopting to variant channel conditions and security requirements should be implemented. New ad-hoc protocols for self-organization to be designed.

Communication Challenges





Enhancing spectrum efficiency 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.


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




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 challenge 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 heterogeneous 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 track 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 available 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.





Based on user preferences (user decides the location to visit and services to accept at any particular 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 regulations. Figure 2 shows how the promising 4G feature of automatic network tracking and selection will be fruitful to the users.

Current State of Research: The feature of on-the-fly automatic network tracking and selection is complicated in 4G environments due to its heterogeneous nature. In this context, one of the proposed solutions is Access Network Selection [3] where for each particular communication session the multimode terminal collects adequate information (like user subscription, supported service types, costs, QoS, bandwidth requirements, coverage and pricing policies) of the available underlying networks and stores them in the Service Platform (SP). The decision of which network to choose depends on the stored information. However limited availability or non-availability and inaccuracy in gathering the underlying network related information are the major drawbacks of this approach. Unlike this approach where user preferences on network selection is optional, the Adoptive Service Access Solution (ASAM) [4] significantly considers user preferences while selecting a particular access network. Reference [5] describes a call admission policy-based approach, which selects the least loaded available network in any particular situation. However this approach demands for more accurate load balancing approach. In spite of all these research activities in this domain, till date the

most successful approach is the use of software radio devices that scan the available networks and, after downloading the appropriate software(s) reconfigure themselves as per the selected network features. Different reconfiguration and downloading modes exist each having its own advantages and disadvantages. Few of them proposed in [6] are: (i) Reconfiguration over the air: In this a dedicated 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 narrow-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 cards, 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 downloaded 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 channel (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 4G 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 requirements 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 adequate knowledge of each network before any selection is made. To conclude in brief, future researches should focus on the problem areas related to: Discovering the available access networks and their respective points of presence (PoPs), selecting the proper authentication identifier for each PoPs and efficiently figuring out the best possible AAA routing and payload routing means for seamless exchange of the authentication conversation and payload packets between the endpoints.

b. Mobile Services

b.1. Personal and Session Mobility

In 4G 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 focused 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 session 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 device location, operator/provider domain and, type of network. So, unlike terminal mobility, session and personal mobility concentrate more on user movements rather than terminal movements.




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 allows 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 assistance 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 Network 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 streaming 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 lacks 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 TCP.

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




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-loop 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 traffic 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 applications.

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 another 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 schemes 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 maintaining 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 unanimously 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 Architecture 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 Protocol (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 management 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 tracking 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 integrated 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 networks 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 scheme 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 management architectures may be centralized, distributed or hybrid depending on whether all the underlying coordinating sub-networks are centrallymanaged (entire system’s location management





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 challenges 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 related 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 standard 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 node’s battery power. HMIPV6 promoted by the Internet Engineering Task Force (IETF) as a further advancement to MIPv6 has till now proved to be a promising technology for the next generation wireless networks efficiently tackling the MIPv6 drawbacks. However, effects of HMIPv6 on 4G security aspects (like AAA) and roaming PANs have not been studied in depth. Seamless handovers in a 4G scenario requires to handle challenges related to both intra-network inter-cellular (horizontal)

handover and inter-network inter-cellular (vertical) handover mechanisms and is thus complicated. Figure


3 [2] shows the concept of horizontal and vertical handover mechanisms of a mobile terminal. Problems like provision of enriched QoS support, reducing call droppings and disruptions, reducing handover time, ensuring correct handover completion time, and optimizing effective call completion time are tricky to handle and all the IP-based advanced protocols should be thoroughly ensured of meeting the challenges. Current State of Research: Global roaming with multimode terminals is supported by IPv6 for both intra and inter technology handover mechanisms. HMIPv6 also supports both type of handovers. It reduces overloading and improves the handover speed [13]. Fast Handovers for MIPv6 (FMIPv6) [16] is a new proposal trying to optimize MIPv6. It greatly reduces packet loss and handover time in both types of handover. The other network, transport and higher layer protocols (except DDNS) effectively supports handover mechanisms.

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 effective 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 management 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.





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 successfully 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 seamless 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 architecture 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 pointed 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 researches 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




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 place. 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 controlled, 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].

Possible 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 each 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]




With the plethora of promising features 4G is truly moving towards getting universally accepted as the ideal next generation communication system. 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 wireless 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 heterogeneous 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 unaccessed or less accessed research topics, which need significant contributions for the 4G visions to come true by 2010.


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


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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.

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

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