INTERNATIONAL WORKSHOP ON CONVERGENT TECHNOLOGIES (IWCT) 2005
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Abstract—This paper explores the next generation of mobile communication system from different perspectives. A user-centric approach to 4G is considered. We envision 4G as a convergence platform where wide-area (cellular) technology, wireless metropolitan area network (WMAN) and wireless local area network (WLAN) will coexist and complete. Legacy systems, their evolution as well as newly developed access techniques are all embraced by the 4G network. We then discuss 4G enabling technologies as well as identify design challenges that research and development community is likely to encounter.
I.
I NTRODUCTION
T he deployment of IMT-2000 (International Mobile
Telecommunications-2000) networks has already started in several countries. In addition to voice and text messaging, users today can experience basic multimedia services, though system capabilities and services need to be greatly enhanced in order to fully exploit all the potential of advanced multimedia systems. Already at this 3G introductory stage, efforts are being put at a global scale to envision, define and develop the successor mobile communication system. Systems beyond IMT-2000 are commonly referred to as the “Fourth Generation” or “4G” in short. Preliminary explorations around the world coincide to show that countless useful and interesting services and applications could be developed under the assumption that ubiquitous and high-speed wireless access are available. The opposite is also true: Future users will be appealed by rich-content based services that pervasively interact with the environment. Thus, it appears that one of the main driving forces for 4G development is the unrelenting demand for higher data throughputs in virtually every possible scenario.
The key players in this multi-year development process are, without a doubt, terminal and infrastructure equipment manufacturers, though, more than ever, academia, operators, service providers, regulatory bodies and governmental agencies play a vital role in supporting the development. Manufactures should develop technically sound solutions, capable to fulfill the expectations of users and operators. This is not a trivial task as key players must find a good balance between achieving a mutually convenient technical consensus, interpreting market needs and, at same time, imposing industry views. At the end of the developing chain and conveying the voices of the involved parties, pre-standardization bodies have a fundamental harmonizing role, as they serve not only as the melting pots of visions but also as the forefront stage for technical debate.
Considering the complex interaction among the aforementioned players and taking into account that these diverse contributors do not necessarily share the same interests, goals and time plans, no one would be surprised to realize that finding a universal definition of 4G is a very elusive task, even after several years of activities and countless attempts in the literature.
The current 4G development efforts can be regarded as the preceding stage of the upcoming 4G standardization process, hence the importance of these activities. The main official guideline is the ITU-R Framework Recommendation
M.1645 [1], which delineates the research goals for system capabilities. As of today, despite huge efforts being put by the involved parties and even with some common understanding on the definition and goals of 4G, there are clear indications that technology-wise, the 4G arena is fragmented. Indeed, worldwide 4G development is following several paths with target solutions that can be complementary (co-existing) as well as mutually exclusive
(competing). Evolution is an important component of the development, in especial, taking into account the integration and further enhancement of legacy systems. In addition,

INTERNATIONAL WORKSHOP ON CONVERGENT TECHNOLOGIES (IWCT) 2005 development of novel approaches might be required to cope with some of the stringent requirements.
II.
A U SER -C ENTRIC A PPROACH TO 4G
Unlike previous generations, the research community has early recognized the key role of the user when developing future 4G systems. Putting the user in the center of the development aims to guarantee a long-lasting, sound and profitable future for 4G, as more than ever we need to know what are the needs and expectation of the users before embarking to develop technical solutions. Technology should be the response to the user needs, and not the other way around. As the starting point, a user-centric approach should consider the user as a) an isolated individual with personal and (somewhat) unique needs, b) a member of a distinctive group with some common characteristic and c) a infinitesimal constituent part of society. These different approaches should give us some hints on the user needs and expectations as well as on the scenarios that are most likely to become popular. In each possible scenario then we would have to develop services and applications aiming to appeal future users. Some work has already been done in identifying scenarios and developing services, particularly in the
Wireless World Research Forum (WWRF) [4], Mobile IT
Forum (mITF) [5] and also in [10, 11]. Several user trends have been recognized:
Users are avid consumers of information. Accessing information and knowledge is always valued by users.
Information comes in many forms, multimedia formats becoming the de facto presentation style.
Pervasive connectivity: Ubiquity of services increases drastically the value of the information.
Personalization of devices and services: Personal preferences and the uniqueness of each user should be taken into account to allow differentiation of users.
Simplicity: User friendliness is highly valued. Natural, transparent, intuitive and minimal interaction between man and machine will make the gap between people and technology closer.
Core life values more and more appreciated: Health, closer circles (family, friends), security and environmental values.
Interaction with other users (from the same group or not) becomes more tangible, e.g., enabling cooperative communications.
High data rates alone do not appeal users, there should be matching services/applications.
Various promising 4G scenarios have been identified. They include typical everyday life situations with potential to unlock user needs for connectivity and bandwidth. Typical mobile scenarios are: E-commerce, business/work, private life (home/free-time), vehicular, public places, entertainment, education, health-care, travel, etc. Services are seen as the key link to success in any telecommunication business. Several service concepts have been developed around user scenarios, trying to match user values and expectations. Examples are:
Personal manager/assistant (finance, health security, information, etc.).
Home manager/assistant (control, comfort, security, maintenance, etc.).
News/weather report delivery.
Travel agent/mobile tourist guide.
Mobile gaming.
Mobile shopping.
Positioning-related services (tightly complementing the above mentioned services)
Etc.
As a summary, and in order to better appreciate the wider range of services possibilities that 4G will bring, we can state that [11]
Service
2G
~ constant (1)
Service
3G
~ f(place) (2)
Service
4G
~ f(place, time, terminal, user). (3)
In a few years it is expected that the number of worldwide subscribers will exceed 40% of the world population.
Competition has significantly contributed to the global massification of the mobile phone. The already huge mobile subscriber base today is a clear indication of the existing potential for an explosive growth in traffic. People using wireline broadband internet are likely to expect similar degrees of data connectivity “on the move”, with comparable degrees of quality. If user expectations for new, useful and exciting mobile services and applications are matched by the industry with capable and appealing terminals, and supporting networks, one can anticipate a future with even higher numbers of subscribers as well as steep increase in the amount of data traffic. The share of data communications from the overall traffic becomes more important.
Revenue-wise, it is expected that by year 2010 more than
75% of the operators’ incomes come from data traffic. Users expect more dynamic, continuing stream of new applications, capabilities and services. These services and applications will exploit not only the fact that terminals will support high data rates, but also they will fully take advantage of other capabilities, as connectivity to different access networks or peer terminals, multiple air interfaces on board allowing simultaneous access, positioning, higher processing power of terminals, etc. The above growth figures, though impressive, only account for the subscribers, mostly representatives of the so-called man-to-man communications. It is expected that 4G will become a fertile playground for further developments targeting also man-to-machine and machine-to-machine communications.
Then, even conservative predictions estimate that the total number of wireless transceivers worldwide could easily exceed ten- or even hundred-fold that amount of subscribers.

INTERNATIONAL WORKSHOP ON CONVERGENT TECHNOLOGIES (IWCT) 2005
III.
D EFINING 4G
We start this section by referring to the ITU-R
Recommendation M.1645 [2], which states that future wireless communications systems could be realized by functional fusion of existing, enhanced and newly developed elements of current 3G systems, nomadic wireless access systems and other wireless systems with high commonality and seamless inter-working. Though the term 4G is widely used, it is not endorsed by all involved parties. In particular, the ITU refers to “beyond IMT-2000” in lieu of 4G. We can see that a paradigm shift may be needed to define future wireless communications. Indeed, previous and current generations (1G-3G) refer mainly to cellular systems while future systems (4G) encompass several access approaches, mainly cellular (wide-access) and nomadic (local-access).
The ITU definition is generous and flexible, truly allowing legacy systems (2G and 3G), their evolutionary development as well as new systems to coexist, each being a component part of a highly heterogeneous network, the 4G network.
Backward compatibility and interoperability are key characteristics of 4G. We can expect that the 4G arena will be highly competitive as telecom (mobile) and IT (wireless) communication industry will contend to attain an important share of the business.
In Figure 1 the 4G domain is depicted as a conjunction of two well-known mobile (wide-area coverage, cellular) and nomadic (local-area coverage, short-range) developments, corresponding to the upper and lower portions of figure, respectively. Cellular mobile communications have enjoyed a steady growth in terms of achievable throughputs. Every generation of cellular systems (1G, 2G, 3G) offered marked improvements with respect to its preceding one. The same applies with the nomadic (local-area) access, characterized by low-mobility and moderate-to-high data rates. The transitional period between 3G and 4G is sometimes known as Beyond 3G (B3G), where further enhancements are expected. It is expected that local-access systems will tend to acquire more characteristics of wide-area systems, for instance higher mobility, seamless coverage, better use and reuse of radio resources, voice/data/multimedia capabilities, etc. Conversely, it is expected that wide-area cellular systems will tend to become closer to their nomadic counterparts in terms of supporting high data throughputs.
The most critical feature of 4G is the simultaneous support of high data rates with moderate-to-high mobility. This may pose challenges to the designers of future systems as new
(revolutionary) technologies may have to be developed.
Telecommunication manufacturers (the mobile sector) tend to focus on the cellular components of 4G, including both, an
evolutionary path aiming to further enhance the current mobile systems, as well as an innovative path, concentrating in developing new technical solutions. These approaches correspond to the upper right corner of Figure 1 (path 1).
Equally, IT companies (the wireless sector), with background business in local access systems are more inclined to see 4G as enhanced extensions of current short-range communication systems (lower right corner in
Figure 1, path 2). In addition to the cellular and WLAN paths there is a third development also aiming 4G, namely through enhancements having wireless Metropolitan Area
Network (WMAN) as a starting point (path 3 in Fig. 1). In terms of data throughput, mobility and coverage WMANs represent a mid-way point between local- and wide-area approaches.
Academia, regulatory bodies and other parties with less economic ties to the wireless business tend to favor a more unified and balanced vision of 4G and its constituent technologies.
4G can be approached from the network coverage standpoint, by looking at how different wireless services are provided at different geographical scales, as depicted in
Figure 2 [10]. We start first with of the tenets mostly associated with 4G that is “Being Always Connected,
Everywhere, Anytime”. Fulfilling such a simple principle demands unprecedented efforts to the designers of future wireless communication systems. Indeed, the apparent simplicity and transparency enjoyed by users of future 4G systems has an enormous price to be paid by manufacturers, research community and standardization bodies. Their goal is to make appear a network of highly eclectic networks as a single, simple and everywhere reaching network. Figure 2 shows the network hierarchy, starting with a distribution
layer at the largest scale. This layer provides large geographical coverage with full mobility, though links may convey a chunk of composite information rather than signals from individual subscribers, for instance broadcast services such as DAB and DVB. Next in the hierarchy is the cellular
layer, with typical macro-cells of up to a few tens of kilometers. This network also provides full coverage, full mobility but now connections are intended to cater individual users directly. Global roaming is an essential component of 2G cellular systems, e.g., GSM. Note that the cellular layer encompasses both macro and micro cells. The
metropolitan layer or network, of which IEEE 802.16 [12],
HyperMAN [13] and Korean WiBro [14] are typical examples, provides urban coverage with a range of a few kilometers at the most, with moderate mobility and moderate data speed capabilities. In a further smaller scale and moving to the local-area layer, e.g., indoor networks or short-range communications, the network provides here access in a pico-cell, typically not larger than a few hundred meters, to fulfill the high capacity needs of hot-spots.
Nomadic (local) mobility is supported as well as global roaming. 3G makes use of the cellular layer (typically micro-cells) in combination of hot-spots (WLAN), through vertical handovers, to provide coverage in dedicated areas.
The next in the wireless network hierarchy is reserved for the personal area network (PAN), very-short range communication links (typically 10 m or less) in the immediate vicinity of the user. Within this layer we can also enclose body area networks (BAN), and some other

INTERNATIONAL WORKSHOP ON CONVERGENT TECHNOLOGIES (IWCT) 2005 sub-meter wireless short-range access (e.g., RFID, NFC).
Going back to the paradigm of a pervasive 4G wireless network, in order to effectively have an unlimited reach while being able to support a variety of data rates, 4G would have to embrace all the described network layers or, in other words, 4G could be defined as a convergence platform taking in and working across BAN, PAN, LAN, MAN,
cellular and distribution networks. Figure 2 depicts another shift in paradigm in mobile communications: While 2G was focused on full coverage for cellular systems based on one technology and 3G provides its services only in dedicated areas and introduces the concept of vertical handover through the coupling with WLAN systems, 4G is envisaged as a convergence platform extended to all the network layers.
A concurrent vision of 4G, often identified as the
European vision, supports the integrative role of 4G as a convergence platform of several networks. This approach leads us to consider 4G as a network consisting of
heterogeneous networks and heterogeneous terminals. The integration of such an eclectic system is achieved at an IP networking layer, where the role of IP is paramount to enable a seamless network operation. An all-IP network
(access + core) is the most straightforward and effective way to integrate all the possible different networks constituting
High mobility
(Low data rate)
4G. A linear vision of 4G also exists, with focus on linear extensions of current (3G) technologies aiming at high data rates. This vision, to some extent prevalent in Asia, is limited to highlight the high speed capabilities of future wireless communication systems.
Regardless differences in approaching 4G, developing parties tend to agree on several of the key characteristics of such systems. The features are listed next:
Achievable data rates: 100 Mbps (wide coverage), 1 Gbps
(local area). These are design targets and represent cell overall throughput.
Networking: All-IP network (access and core networks).
Ubiquitous, mobile, seamless communications.
Shorter latency.
Connection delay < 500 ms
Transmission delay < 50 ms
Cost per bit significantly lower, 1/10-1/100 lower than that of 3G.
Lower infrastructure cost, 1/10 lower than that of 3G.
Plug & Access network architecture.
Enabling person-to-person, person-to-machine and machine-to-machine communications.
Technical capabilities defined after new services and applications are identified. Services and applications fully exploiting the technical capabilities of the system. higher data rates, multimedia services
B3G voice, mobility, roaming, simple data communications high data rates, better capacity, coverage,
QoS
3G
2G
WCDMA
EV-DV
GSM
GPRS
1
Wide-access
(cellular) IS-95
IS-136
EDGE
CDMA1x
HSDPA
000000000000000000
000000000000000000
000000000000000000
3
4G
IEEE 802.16e
Wi-Fi
Wi-MAX
IEEE 802.11
Local-access
(nomadic)
IEEE 802.16
W-PAN
2
Bluetooth UWB limited mobility, indoor operation, hot-spots, data oriented continuous service
(handoffs) high-speed dat, voice, moderate mobility and coverage, multimedia services
B3G
Approach through evolution
Low mobility
(High data rate)
Approach through new technologies
2005 2010 time
Fig. 1. Approaching 4G through convergence of cellular, nomadic (WLAN) and metropolitan (WMAN) paths.

INTERNATIONAL WORKSHOP ON CONVERGENT TECHNOLOGIES (IWCT) 2005
WAN
MAN
LAN
PAN
Networks Shell
Distribution Network
(e.g., DAB, DVB)
Cellular Network
(e.g., GSM)
Metropolitan Network
(e.g., 802.16, HiperMAN, WiBro)
Hot Spot
(e.g., 802.11, HiperLAN/2)
Personal Network
(e.g., Bluetooth, HiperPAN)
Fixed (Wired) Network
(e.g., xDSL, CATV)
Network Layers Stack
5 technique for 4G, being OFDM (Orthogonal Frequency
Division Multiplexing) the main proponent technique. OFDM was original proposed for single users but extensions to multi-users, e.g., OFDMA, support multiple access. Usually
OFDM is combined with other access techniques, typically
CDMA and TDMA, to allow, among others, more flexibility in multi-user scenarios. Multicarrier CDMA (MC-CDMA) is another access technique with great potential. OFDM and
CDMA are robust against multipath fading, which is a primary requirement for high data rate wireless access techniques.
Overlapping orthogonal carriers OFDM results in a spectrally efficient technique. Each carrier conveys lower-data rate bits of a high-rate information stream, hence it can cope better with the ISI problem encountered in multipath channels. The delay-spread tolerance and good utilization of the spectrum has put OFDM techniques in a rather dominant position within future communications. OFDM, on the other hand has strict time and frequency synchronization requirements and is prone to the Peak-to-Average Power Ratio (PAPR) problem.
2G
3G
G
Distribution Layer
Cellular Layer (Macro Cells)
Cellular Layer (Micro Cells)
Metropolitan Network Layer
Hot Spot Layer
Fixed (Wired) Layer
Vertical Handover
4G
Fig. 2. Approaching 4G from the network coverage standpoint.
NABLING
T
ECHNOLOGIES
Several key 4G technologies have been already identified and discussed in the literature. In this section we will briefly discuss some promising techniques that are likely to take significant roles in future mobile communication systems. The following list is by no means exhaustive, and it intends to serve as an initial pointer.
A.
IV.
Personal Network Layer
Network Layers Coverage
E
Modulation/Access Techniques
Multicarrier modulation has been identified as a key
B.
Non-Conventional Access Architectures
Wide- and local-coverage are the two most distinctive 4G access components. It is expected that the requirement for higher data throughputs and support of high number of users will result in a shift to higher and less congested frequency bands, e.g., 5 GHz band and wider bandwidths (20-100 MHz).
In cellular access this would mean that the link budget would be seriously degraded and unreasonable high power should be used to compensate for the higher attenuation occurring at this frequency band. This could easily exceed the regulation for power emission from base stations, and also it could dramatically reduce (the already challenged) battery life in terminals. Other than conventional access architectures for wide-area access are being considered to cope with this problem. Multi-hop cellular, and particularly two-hop approaches appear to be an effective solution to the problem of achieving wide coverage and high data throughput. By using relaying (repeating) stations the equivalent distance between base station and mobile station is reduced. Efficient use of radio resources can be also attained since some resources can be reused in different hops. In principle the relay stations can be
fixed, this is called infrastructure-based relaying, or mobile, that is ad hoc relaying. In the distributed radio access approach a base station has under its control a number of remote access sites, each with its own antenna(s) and covering a small area.
The small-size cells covering a large cell reduce the distance between the mobile terminal and its most suitable (e.g., closest) access point. The base station is connected to the remote radio access sites by using optical fiber or radio links. Distributed radio access is a cost effective approach to scalable networks.
In local-area access also several architectures can be used in addition to the single-hop cellular access approach. Several ad

INTERNATIONAL WORKSHOP ON CONVERGENT TECHNOLOGIES (IWCT) 2005 6 hoc access concepts have shown their potential for short-range communications, including multi-hop, peer-to-peer and higher the modulation rate and code rate combination, and vice versa. Clearly, AMC is more effective in packet networks.
cooperative communications. Collaboration among users (or nodes) aims to benefit either a single user or several (all) collaborating users. Through cooperation (at intra- and/or inter-layer level) the data throughput can be increased and
AMC is a closed-loop approach as the transmitted needs to know the channel state information for selecting the modulation/coding pair. Conventional wireless services were mostly for constant rate applications, such as voice transmission. To combat channel fading, communication signal quality can be enhanced. Moreover, power efficiency can be boosted, which is paramount to increase battery life in terminals. systems were usually designed to maximize time diversity, e.g., combination of interleaving and coding, for better bit error rate performance. Present and future wireless systems, including
C.
Multiantenna techniques are regarded as one of the most
D.
Multiple Antenna Techniques
Adaptive Modulation and Coding
4G, target packet data, and thus, are usually designed to maximize throughput for a given battery energy budget, while allowing certain delay. Then, the power/rate needs to be controlled according to channel fading conditions. important enabling technologies for 4G. In principle no other technique will allow us to achieve easily high spectral efficiency as by using multiple antennas. By exploiting these techniques we can increase achievable data throughput,
4G. In order for the receiver to separate and decode the parallel
E.
Software Defined Radio improve link quality, extend cell coverage and increase
Since different air interfaces will be used in 4G, Software network capacity. Three approaches can be used, namely
Defined Radio (SDR) appears to be a cost-effective solution to
diversity, beamforming (smart antennas) and spatial
multiplexing. Diversity techniques require widely separated antenna elements (typ. several wavelengths at least). Actual linear increase in capacity by exploiting parallel transmission uses a flexible architecture which allows the air interface to be reconfigured. This allows multi-standard air interface separation depends on the type of channel. Directional channels (narrow angular spread) require large separation and number of element of the array. Spatial multiplexing offers a operation with a common hardware platform, opening the door for forward compatibility. Furthermore SDR is one enabler for vice versa. Diversity techniques exploit the fact that associated channels fade independently, while diversity domains can be statistics) is not affected. The array gain is proportional to the cooperative networks. Ideally, and in its broadest sense, SDR allows on-the-fly modifications of the RF front-ends, baseband space, time, frequency and polarization. Diversity gain will improve the average SNR. In beamforming signals are beamforming the variability of the signal (e.g., fading processing and even the MAC layer of the terminal aiming to realize a particular air interface, by reconfiguring the system. coherently combined (either in reception or transmission) as to enhance the array response into preferred directions. Nulls can transmitter/receiver. Unlike with diversity, by using
The degree of flexibility brought by real-time reconfigurability opens up a new world of possibilities for users, operators and also be spatially controlled. Beamforming allows establishing services providers, and terminal manufacturers. Users can of directional links. Beamforming assumes that the channel or direction of arrival (DoA) are known to the establish connection in any network, allowing simple local and global roaming. Users could be also benefited from the low cost terminals that this technology would eventually bring. As new advanced services are introduced, software modifications can catch up with the possibly new requirements. Hardware and software updates could be easily and wirelessly carried out by the user or operators. Manufacturers can also take advantage of of different information from different antennas. This is implement several access approaches into one terminal. SDR
SDR as large volumes of terminals with identical hardware essential for attaining the high spectral efficiencies required by
(and less number of components) would have to be produced.
Even upgrades or changes in the terminals can be simply streams it is assumed that the signal propagates in a rich carried out. Also operators and service providers could exploit scattering channel and the number of receive antennas at least this flexibility to better match their operation and services to equal to number of transmit antennas. The term MIMO the user demands.
(Multiple Input Multiple Output) refers in principle to any technique exploiting multiple antennas at receiver and transmitter, though sometimes allusion to spatial multiplexing is meant.
F.
Other Key Technology for 4G
There are several other technologies that can be thought as essential for 4G. These include:
Adaptive Modulation and Coding (AMC) is a form of link adaptation which is used in response to the changing characteristics of the radio channel. AMC jointly selects the most appropriate modulation and coding scheme according to the channel conditions. The better the radio conditions, the
Ultra-Wide Band (UWB) techniques for short-range communications.
Optical wireless techniques for short-range communications.
Techniques for seamless vertical and horizontal handovers.
Cross-layer design and optimization.

INTERNATIONAL WORKSHOP ON CONVERGENT TECHNOLOGIES (IWCT) 2005 7
Advanced radio resource management. Multidimensional scheduling (time, frequency, space).
Techniques for reducing the PAPR problem typical of multicarrier systems
Advanced channel coding techniques (turbo codes, LDPC codes, etc.).
Sensor networks
Network security.
Battery technology.
Etc. these increasing power drain from battery. “Always being connected”, advocated loudly as one of the most appealing features of 4G can be interpreted also as “always being drained”. The obvious “wireless” or “mobile” condition of a terminal is ultimately dictated by the battery simply because the terminal operates wirelessly as long as its battery will allow it.
Unfortunately and despite huge research efforts, progress in battery development advances slowly in comparison with advances in microelectronics and communications. Fuel cell technology, offering energy densities of three-to-ten times
IV.
C HALLENGES
Introducing a new system always involves risks. 4G is not the exception, even when considering that it will integrate also eyes of the user) could result in a colossal task, in particular if
RF integration seems to be one critical challenge, in particular if the current tendency of integrating multiple legacy systems. Integration in 4G means having different networks, different terminals and different services working network into a single, simple and monolithic network (in the functions in the terminals continues. We can assume a multi-standard terminal supporting wide-area and local-access together seamlessly. It is precisely the integrative capability of
4G one of the crucial challenges, as access solutions for
(horizontal/vertical) handovers. Turning a very heterogeneous with different air interfaces, and also having very short-range connectivity (e.g., Bluetooth, RFID), FM radio receiver and TV different 4G scenarios are being developed independently by different parties. Seamless operation is one of the pillars of 4G, receiver (terrestrial/satellite) and a GPS receiver. In principle every air interface or receiver uses a different frequency.
Though all these services will not be used simultaneously a few could be switched on in certain applications. Terminal design could become the bottleneck for the development of multi-standard multi-featured terminals as radio frequency the integration aspects are left for the final phase of the 4G interference between different transceivers could have development, after different access techniques are developed.
The risk is not only in the integration of access technologies but higher than those of current batteries, is promising, but still far from mature. detrimental effects on the performance, in particular taking into account the physical limitations of having receivers and also in their adoption. Indeed, not all proponent solutions being transmitters enclosed in a very small volume. Methods for currently developed are complementary; many of them interference management and control should be carefully compete with each other. applied at the design. Note that several antennas would be needed onboard, including antenna arrays. The latter would
A radical change in the design rules might be needed in have to be distributed in the terminal plane to maximize order to cope with other of the key design challenges of 4G: The antenna element separation. Effective placing of antennas in ever increasing power consumption. Going from 2G to 3G have future terminals would be a challenge. shown a steep increase in power consumption, fact that could be attributed to the new multimedia capabilities, including the
Based on estimations of traffic and subscriber growth as well support of much higher data rates. Content-rich services tend to as taking into account that proposed new multimedia-based increase power consumption and 4G will not be the exception, services will require considerably higher bandwidths, it is unless some measures are taken. Advanced ad hoc networking expected that future 4G systems will need a much broader based on multi-hop or cooperative techniques can significantly bandwidth that current systems and hence, it seems inevitable improve power efficiency and thus, they could help us to reduce that new bands will be allocated. Spectrum in the 1-2 GHz band the consumption. However there are other factors that appears to be already congested and it is expected a shift inherently increase power consumption. High-speed processors towards higher frequencies, being 5-6 GHz a candidate band are needed for fast wideband data processing, having this a with good possibilities. Spectrum is a challenge confronted by direct impact in power consumption. Furthermore, multiple the research and development community engaged with 4G. antennas will play a fundamental role at the terminal side in
More precisely, the lack of knowledge on the frequency order to achieve high data rates and guarantee an acceptable allocations for 4G complicates the design of future systems. In quality of service. This means that the terminals will integrate a number of transceivers, typically two, three, four or even more. computational power to process more frames per second. All fact, it is tricky to design wireless communication systems without knowing the target frequency band, available
Also to consider, rich-content multimedia means a shift towards high-definition imaging services, implying in turn higher pixels count, improved contrast and more bandwidths, etc. This difficulty is more evident when taking into account that multiple antennas are one of the main building blocks of 4G, and knowledge of channel behavior is crucial in order to devise effective algorithms. ITU-R is

INTERNATIONAL WORKSHOP ON CONVERGENT TECHNOLOGIES (IWCT) 2005 8 responsible to identify and investigate prospective bands to then make a recommendation. The World Radio Conference
(WRC) is expected to make some decisions on the frequency bands for 4G in 2007.
4G can be seen as a common, flexible and scalable converging platform. Equivalently, 4G can be understood as
will be a heterogeneous network serving heterogeneous terminals and supporting heterogeneous services, but appearing to the user as a simple and single homogeneous network. Several enabling technologies as well as some of the challenges that 4G designers are likely to encounter were also discussed. mosaic of complementary scenarios and associated access REFERENCES technologies. For each scenario there could be more than one proponent access solution. Regional schedules to adopt 4G appear to differ considerably, with Asia aiming to introduce 4G already by 2010, and Europe taking a slower pace. Integrating several access technologies, complementary and competing, to realize a harmonious network would be one of the greatest initial challenges of 4G.
IV.
C ONCLUSION
This paper discussed 4G from a user-centric perspective. A logical way to initially approach 4G starts from the users’ needs and expectations. Identifying promising scenarios, services and applications is the next step. The 4G technology solutions should come as a response of the user requirements extracted form the initial analysis. There are different ways to define 4G, the integrative approach sees 4G as a convergence platform of several complementary access technologies, covering the
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[10] Simone Frattasi, Hanane Fathi, Frank Fitzek, Marcos Katz, Ramjee Prasad,
“A Pragmatic Methodology to Design 4G: From the User to the Technology, whole range of mobility and data transfer capabilities, and Fourth International Conference on Networking (ICN’05), Reunion Island, embracing legacy systems, their evolution as well as making ample room for new access technologies. This
April 17-21, 2005.
[11] Simone Frattasi, Hanane Fathi, Frank Fitzek, Ramjee Prasad, "4G: A
User-Centric System", Kluwer – Wireless Personal Communications Journal all-encompassing definition emerges a universal, flexible and open, and is in sharp contrast with the approach considering
4G only as a new very high-speed air interface. A 4G network
(WPC) – Advances in Wireless Communications: Enabling Technologies for
4G. In press, 2005.
[12] “IEEE 802.16”, www.ieee802.org/16/.
[13] “HiperMAN”, http://portal.etsi.org/Portal_Common/home.asp.
[14] “An Introduction to WiBro”, Available at www.itu.int/ITU-D/imt-2000/ documents/Busan/Session3_Yoon.pdf.