4G Wireless Systems

4G Wireless Systems

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4G Wireless Systems
Table of contents

Chapter 1 Introduction 7

Chapter 2 Service Evolution 13

2.1 Dimensioning Targets 14
2.2 Dimensioning Objectives 15
2.3 Multi-technology Approach 15
Chapter 3 The User-centric system 17
3.1 Key Features of 4G 18
3.1.1 User Friendliness and User Personalization 18
3.1.2 Terminal Heterogeneity and Network 19
Heterogeneity
Chapter 4 The Real Technical Step-Up of 4G 22
4.1 “Integration” of Heterogeneous Systems 23
4.2 System Design Rules 24
4.3 Provisioning of Heterogeneous Services 25
4.4 Multimode/Reconfigurable and Interworking 27
Devices

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Chapter 5 Key 4G Technologies 30

5.1 OFDMA 31
5.2 Software-defined Ratio 32
5.3 Multiple input Multiple output 32
5.5 Caching and Pico cells 33
5.6 Coverage 33

Chapter 6 Conclusion 36

Appendices 37
Bibliography 37
List of Figures 38
Glossary 39

Abstract
The ever-increasing growth of user demand, the limitations of the third generation
of wireless mobile communication systems and the emergence of new mobile broadband
technologies on the market have brought researchers and industries to a thorough
reflection on the fourth generation. Many prophetic visions have appeared in the
literature presenting 4G as the ultimate boundary of wireless mobile communication
without any limit to its potential, but in practical terms not giving any design rules and
thus any definition of it.

The evolution from 3G to 4G will be driven by services that offer better quality
(e.g. video and sound) thanks to greater bandwidth, more sophistication in the association
of a large quantity of information, and improved personalization. Convergence with other
network (enterprise, fixed) services will come about through the high session data rate. It

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will require an always-on connection and a revenue model based on a fixed monthly fee.
The impact on network capacity is expected to be significant. Machine-to-machine
transmission will involve two basic equipment types: sensors (which measure
parameters) and tags (which are generally read/write equipment). It is expected that users
will require high data rates, similar to those on fixed networks, for data and streaming
applications. Mobile terminal usage (laptops, Personal digital assistants, and handhelds)
is expected to grow rapidly as they become more user friendly. Fluid high quality video
and network reactivity are important user requirements. Key infrastructure design
requirements include: fast response, high session rate, high capacity, low user charges,
rapid return on investment for operators, investment that is in line with the growth in
demand, and simple autonomous terminals.

Chapter 1 Introduction

1 Introduction

The Second Generation of Mobile Communication Systems (2G) was a huge

success story because of its revolutionary technology and the services brought to its
customers. Besides high quality speech service, global mobility was a strong reason for
buying 2G terminals. The Third Generation (3G) has been started in some parts of the
world, but the success story of 2G is hard to be repeated . One reason is that the evolution
from 2G towards 3G has not brought any qualitatively new service for the customer,
leaving the business model largely unchanged. The well known services plus some

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additional ones are provided, which may not be enough to encourage the customers to
change their equipment.
The lack of innovative services was encountered too late by the 3G Partnership
Project (3GPP). In the latest documents, an attempt was made to incorporate some
advanced services into the 3GPP architecture such as the Multimedia Broadcast and
Multicast Service Center (MBMS) in combination with the IP Multimedia System (IMS).
However, these smaller corrections were made without the possibility to adjust the access
technology properly .
The upcoming Fourth Generation (4G) is projected to solve still-remaining
problems of the previous generation and to provide a convergence platform for a wide
variety of new services, from high-quality voice to high-definition video, through high-
data-rate wireless channels. Various visions of 4G have emerged recently among the
telecommunication industries, the universities and the research institutes all over the
world .

There has been tremendous interest recently in the Fourth Generation (4G)
mobile communication technologies on the worldwide basis. Research and development
on 4G technologies mainly focus on two directions: Open Wireless Architecture (OWA),
and Cost-effective and spectrum-efficient high-speed wireless transmission. It is well
predicted that the business of 4G industries will be over $800 billion by the year 2020,
and therefore major developed countries have already spent huge R&D funds on this
emerging communication technology.
In Europe, the European Commission (EC) envisions that 4G will ensure
seamless service provisioning across a multitude of wireless systems and networks, from
private to public, from indoor to wide area, and provide an optimum delivery via the most
appropriate (i.e., efficient) network available. From the service point of view, it foresees
that 4G will be mainly focused on personalized services . In Asia, the Japanese operator
NTT DoCoMo has introduced the concept of MAGIC for defining 4G: Mobile
multimedia; anytime, anywhere, anyone; Global mobility support; integrated wireless
solution; and Customized personal service, which mostly focuses on public systems and

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treats 4G as the extension of 3G cellular service. This view is referred to as the linear 4G
vision and, in essence, focuses on a future 4G network that will generally have a cellular
structure and will provide very high data rates (exceeding 100 Mb/s). In general, the latter
is also the main tendency in China and South Korea . Nevertheless, even if 4G is named
as the successor of the previous generations, the future is not limited to cellular systems
and 4G should not be seen exclusively as a linear extension of 3G.
India aims to leapfrog to 4G (fourth-generation) wireless technologies, skipping
3G technologies as it has not been found to be cost-effective. Even if 4G is named as the
successor of previous Wireless communication generations, it is not limited to cellular
systems, therefore has not to be exclusively understood as a linear extension of 3G.
Figure1 shows the shift in paradigm.
There is clearly a need for a methodological change in the design of 4G. Indeed,
in order to boost innovation and define and solve relevant technical problems, the system-
level perspective has to be envisioned and understood with a broader view, taking the
user as its departing point. This user-centric approach can result in a beneficial method
for identifying innovation topics at ‘all’ the different protocol layers and avoiding a
potential mismatch in terms of service provisioning and user expectations. A new user-
centric methodology that considers users as the cornerstone in the design of 4G and
identifies their functional needs and expectations, reflecting and illustrating them in
everyday life situations is needed. In this way, fundamental user scenarios that implicitly
reveal the key features of 4G, which are then expressed explicitly in a new framework —
the “user-centric” system — that describes the various level of interdependency among
them. This approach consequently contributes to the identification of the real technical
step-up of 4G with respect to 3G and thus to a less prophetic and more pragmatic
definition of the forthcoming technology.

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Figure 1 Evolution from 2G to 4G[i]

While 2G was focused on full coverage for cellular systems offering only one
technology and 3G provides its services only in dedicated areas and introduces the
concept of vertical handover through the coupling with Wireless Local Area Network
(WLAN) systems, 4G will be a convergence platform extended to all the network layers.
Moreover, in order to boost the innovation and define and solve relevant technical
problems, it has to be envisioned and understood the system level at a broader view,
taking primarily into account the user. This approach can result in a beneficial method for
identifying innovation topics at all the different protocol layers. There is clearly a need
for a methodological change in the design of the next wireless communication generation
The design should be more user-centric to avoid potential “flop” of the system.
Finally, it is also worth to highlight that the forthcoming technology should be as less
dependent as possible from any geographical matter, addressing very different markets,
such as Europe, Asia, and America.

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Chapter 2 Service Evolution

2.1 Dimensioning Targets
2.2 Dimensioning Objectives
2.3 Multi-technology Approach

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2 Service Evolution

The evolution from 3G to 4G will be driven by services that offer better quality
(e.g. video and sound) thanks to greater bandwidth, more sophistication in the association
of a large quantity of information, and improved personalization. Convergence with other
network (enterprise, fixed) services will come about through the high session data rate. It
will require an always-on connection and a revenue model based on a fixed monthly fee.
The impact on network capacity is expected to be significant. Machine-to-machine
transmission will involve two basic equipment types: sensors (which measure
parameters) and tags (which are generally read/write equipment). It is expected that users
will require high data rates, similar to those on fixed networks, for data and streaming
applications[iv].
Mobile terminal usage (laptops, Personal digital assistants, handhelds) is expected
to grow rapidly as they become more user friendly. Fluid high quality video and network
reactivity are important user requirements. Key infrastructure design requirements
include: fast response, high session rate, high capacity, low user charges, rapid return on
investment for operators, investment that is in line with the growth in demand, and simple
autonomous terminals.
The infrastructure will be much more distributed than in current deployments,
facilitating the introduction of a new source of local traffic: machine-to-machine. Figure
2 shows one vision of how services are likely to evolve; most such visions are similar.

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Figure 2 Service Evolution Vision

2.1 Dimensioning targets

A simple calculation illustrates the order of magnitude. The design target in terms
of Radio performance is to achieve a scalable capacity from 50 to 500bit/s/Hz/khz
(including capacity for indoor use), as shown in Figure3. As a comparison, the expected
best performance of 3G is around 10 bit/s/Hz/km2 using High Speed Downlink Packet
Access (HSDPA), Multiple-Input Multiple-Output (MIMO), etc. No current technology is
capable of such performance[iv].

Figure 3 Dimensioning Examples

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2.2 Dimensioning objectives

Based on various traffic analyses, the Wireless World Initiative (WWI) has issued
target air interface performance figures. A consensus has been reached around peak rates
of 100 Mbit/s in mobile situations and 1 Gbit/s in nomadic and pedestrian situations, at
least as targets. So far, in a 10 MHz spectrum, a carrier rate of 20 Mbit/s has been
achieved when the user is moving at high speed, and 40 Mbit/s in nomadic use. These
values will double when MIMO is introduced. Clearly, the bitrate should be associated
with an amount of spectrum. For mobile use, a good target is a network performance of 5
bit/s/Hz, rising to 8 bit/s/Hz in nomadic use.

2.3 Multi-technology Approach

Many technologies are competing on the road to 4G, as can be seen in Figure 4.
Three paths are possible, even if they are more or less specialized. The first is the 3G-
centric path, in which Code Division Multiple Access (CDMA) will be progressively
pushed to the point at which terminal manufacturers will give up. When this point is
reached, another technology will be needed to realize the required increases in capacity
and data rates.

The second path is the radio LAN one. Widespread deployment of WiFi is
expected to start in 2005 for PCs, laptops and PDAs. In enterprises, voice may start to be
carried by Voice over Wireless LAN (VoWLAN). However, it is not clear what the next
successful technology will be. Reaching a consensus on a 200 Mbit/s (and more)
technology will be a lengthy task, with too many proprietary solutions on offer.

A third path is IEEE 802.16e and 802.20, which are simpler than 3G for the
equivalent performance. A core network evolution towards a broadband Next Generation
Network (NGN) will facilitate the introduction of new access network technologies
through standard access gateways, based on ETSI-TISPAN, ITU-T, 3GPP, China
Communication Standards Association (CCSA) and other standards. How can an operator

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provide a large number of users with high session data rates using its existing
infrastructure? At least two technologies are needed. The first (called “parent coverage”)
is dedicated to large coverage and real-time services. Legacy technologies, such as
2G/3G and their evolutions will be complemented by WiFi and WiMAX. A second set of
technologies is needed to increase capacity, and can be designed without any constraints
on coverage continuity. This is known as pico-cell coverage. Only the use of both
technologies can achieve both targets (Figure 4). Handover between parent coverage and
pico cell coverage is different from a classical roaming process, but similar to classical
handover. Parent coverage can also be used as a back-up when service delivery in the
pico cell becomes too difficult.

Figure 4 Multiple Overlay Architecture[iv]

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Chapter 3 The User-centric system

3.1 Key Features of 4G
3.1.1 User Friendliness and User Personalization
3.1.2 Terminal Heterogeneity and Network
Heterogeneity

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3 The User-Centric System

In this section, I list and describe all the key features derived from the previous
user scenarios. Inspired by the Helioscentric Copernican theory[i], the user is located in
the center of the system and the different key features defining 4G rotate around him on
orbits with a distance dependent on a user-sensitive scale.

3.1 Key Features of 4G

3.1.1 User Friendliness and User Personalization

In order to encourage people to move towards a new technology, which is a

process that usually takes a long time and a great deal of effort from the operators’ side, a
combination of user friendliness and user personalization appears to be the winning
concept. User friendliness exemplifies and minimizes the interaction between
applications and users thanks to a well designed transparency that allows the users and
the terminals to naturally interact (e.g., the integration of new speech interfaces is a great
step for achieving this goal). For instance, consider a scenario A, where even before
leaving home to reach the place of a work appointment, users would like to receive
information about train/subway schedules, door-to-door delays, and so forth, as well as
more personalized information, such as knowing how long it takes to walking to be on
schedule in order to eventually wait for the next train. According to the users’ decisions,
their time-plan must consequently be scheduled in the most efficient way. During their
stay on the train, users would like to download e-mails, listen to radio, watch TV, and so

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on. Finally, before they get off the last planned train, the most time-saving exit and way
to reach their final destination must be known and available in multimedia format.
User personalization refers to the way users can configure the operational mode of
their device and preselect the content of the services chosen according to their
preferences. Since every new technology is designed keeping in mind the principal aim to
penetrate the mass market and to have a strongly impact on people’s lifestyles, the new
concepts introduced by 4G are based on the assumption that each user wants to be
considered as a distinct, valued customer who demands special treatment for his or her
exclusive needs. Therefore, in order to embrace a large spectrum of customers, user
personalization must be provided with high granularity, so that the huge amount of
information is filtered according to the users’ choices. This can be illustrated in scenario
where users can receive targeted pop-up advertisements. The combination between user
personalization and user friendliness provides users with easy management of the overall
features of their devices and maximum exploitation of all the possible applications, thus
conferring the right value to their expense.

3.1.2 Terminal Heterogeneity and Network Heterogeneity

In order to be a step ahead of 3G, 4G must not only provide higher data rates but
also a clear and tangible advantage in people’s everyday life. Therefore, we believe that
the success of 4G will consist of a combination of terminal heterogeneity and network
heterogeneity. Terminal heterogeneity refers to the different types of terminals in terms of
display size, energy consumption, portability/weight, complexity, and so forth (Figure5).
Network heterogeneity is related to the increasing heterogeneity of wireless networks due
to the proliferation in the number of access technologies available (e.g., UMTS, WiMAX,
Wi-Fi, Bluetooth). These heterogeneous wireless access networks typically differ in terms
of coverage, data rate, latency, and loss rate. Therefore, each of them is practically
designed to support a different set of specific services and devices. As explained below,
4G will encompass various types of terminals, which may have to provide common
services independently of their capabilities. Therefore, tailoring content for end-user
devices will be necessary in order to optimize the service presentation.

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Furthermore, the capabilities of the terminal in use will determine whether or not
new services are to be provisioned, so as to offer the best enjoyment to the user and
prevent declining interest and elimination of a service offering. This concept is referred to
as service personalization. It implicitly constrains the number of access technologies
supportable by the user’s personal device. However, this limitation may be solved in the
following ways:

Figure 5 Heterogeneous Terminals

3.1.2.1 By the development of devices with “evolutionary design.”

A naive example can clarify this concept: in the case where a user has a watch-
phone on which he would like to see a football match, simply by pressing a button on the
watch’s side, a self extracting monitor with a larger display can emerge. Therefore,
having the most adaptable device in terms of design can provide customers with the most
complete application package, thus maximizing the number of services supported[i].

3.1.2.2 By mean of a “personalization transfer.”

An example can clarify this concept: in the case where the user has a watch-phone
on which he would like to see a video, he does not need to possess larger display
terminals, as all the publicly available terminals can be borrowed for the displaying time.
Therefore, the advantage for the customers is to buy a device on which they have the

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potential to get the right presentation for each service, freeing it from its intrinsic
restrictions. Furthermore, in a private environment, users can optimize the service
presentation as they wish, thus exploiting the multiple terminals they have at disposal.

The several levels of dependency highlighted by the “user centric” system

definitely stress the fact that it is not feasible to design 4G starting from the access
technology in order to satisfy the user’s requirements. A contextual and a strong
preliminary consideration of the user are a more relevant and appropriate approach to the
design.

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Chapter4 The Real Technical Step-Up of 4G

4.1 “Integration” of Heterogeneous Systems
4.2 System Design Rules
4.3 Provisioning of Heterogeneous Services
4.4 Multimode/Reconfigurable and Interworking Devices

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4 The Real Technical Step-Up of 4G

4.1 “Integration” of Heterogeneous Systems

The real technical step-up of 4G with respect to 3G can be summarized with the
word integration — seamless integration of already existing and new networks, services,
and terminals, in order to satisfy ever-increasing user demands.

Figure 6. Heterogeneous Networks

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4.2 System Design Rules

Regardless of the actual technology, the forthcoming generation will be able to
allow complete interoperability among heterogeneous networks and associated
technologies, thus providing clear advantages in terms of:

4.2.1 Coverage.
In Fig. 5, the shift in paradigm is shown: while 2G was focused on full coverage
for cellular systems offering only one technology and 3G provides its services only in
dedicated areas and introduces the concept of vertical handover through the coupling with
wireless local area network (WLAN) systems,4G will be a convergence platform
extended to all the network layers. Hence, the user will be connected almost anywhere
thanks to widespread coverage due to the exploitation of the various networks available.
In particular, service provision will be granted with at least the same level of quality of
service (QoS) when passing from one network’s support to that of another one.

4.2.2 Bandwidth.
Resource sharing among the various networks available will smooth the problem
related to the spectrum limitations relative to 3G.

4.2.3 Power consumption.

Battery drain is a chronic problem of wireless devices and battery technology is
not progressing at an appropriate pace. For example, 2G mobile phones were shipped out
with one battery, whereas 3G ones are shipped out with two batteries. Therefore, if we
follow this 3G rule, power consumption will increase proportionally to more advanced
services.

For example, a cellular system that also supports short-range communications

among the terminals can achieve the goals outlined above. The rationale for introducing
short-range communications is mainly due to the need to support peer-to-peer (P2P) high-
speed wireless links between mobile stations (MSs) and to enhance the communication

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between an MS and the base station (BS) by fostering cooperative communication

protocols among spatially proximate devices. This communication enhancement
primarily refers to higher link reliability, larger coverage, higher spectral efficiency, and
lower power consumption due to the use of exclusive cooperative stations (e.g., relay
stations (RSs) deployed by operators) or short-range communications among different
MSs. Indeed, the concept of cooperation introduces a new form of diversity where
terminals are less susceptible to channel variations and shadowing effects. This results in
an improvement of the reliability of the communication and the extension of the
coverage. Furthermore, whereas in voice networks the resources are dedicated separately
for each user, in cellular-controlled short-range data networks it is possible to group users
in clusters and gain the following advantages:

 Only the cluster head (CH) needs to have a dedicated channel to the BS, while the
other MSs can communicate using unlicensed bands; thus, more bandwidth is not
required. The CH selection is an important issue that should take into account, among
other factors, the channel conditions of the short-range links (RS-MS and MS-MS)
and the long-range ones (BS-MS), the available rate, the speed, the location, the
computational power, and the residual energy of the MSs.
 Due to the short range of the transmissions performed by the MSs to the CH, it is
possible to reduce their power consumption and hence prolong their battery life.

4.3 Provisioning of Heterogeneous Services

Services are heterogeneous in nature (e.g., different types of services such as
audio, video, pop-up advertisements, etc.), quality, and accessibility. In fact, at a certain
time and place, the quality of and the accessibility to a service may not be the same due
to the intrinsic heterogeneity of the network. For instance, users in proximity to the
shopping mall but outside the coverage of a WLAN can still receive pop-up
advertisements by exploiting a possible multihop ad hoc network in their surroundings.
Therefore, thanks to the dynamics of the network environment (in which the number of
users, terminals, topology, etc. can change), 4G maximizes the probability to provide

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users with the requested connectivity. Therefore, contrary to the previous generations, the
services provided in 4G will depend on the time, place, terminal, and user:

S2G ~ const, (3)

S3G ~ f (place), (4)
S4G ~ f(time, place, terminal, user), (5)
where the service provisioning depends on terminal and user because of terminal
heterogeneity and service personalization, and user personalization, respectively.
Apart from some soft additional emerging services (e.g., fast Internet connection,
pop-up advertisements, etc.), there is still a lack of really new and distinct services that
will enable new applications with tangible benefits for their users. Therefore, we envision
that the real advantage in terms of services that 4G will bring will be based on the
integration of technologies designed to match the needs of different market segments:

 Short-range wireless technologies, such as Wi-Fi and Bluetooth, will enable machine-
to-machine (M2M) communications, where users sign up online on the waiting list,
which sends them back the approximate waiting time, where they can transfer content
to a publicly available larger display. In particular, from the sociological point of
view, in the latter case the private and public spheres are definitely mixed. This
recombination can result in the enhancement of public access such that the access to
displays will be as common as the access to public telephone booths is nowadays.
Short-range wireless technologies also open the possibility to cooperative
communication strategies, which can provide better services at lower costs, thus
maximizing the users’ profit. In this way, they increase the social cooperative
behavior and empower the consumer to make clever use of it. Hence, the user’s
personal device is no longer a mere medium for transferring information, but a social
medium that helps to build groups and friendships.
 Since 3G networks are not able to deliver multicast services efficiently or at a decent
level of quality, the synergy of Universal Mobile Telecommunication System
(UMTS) and digital audio/video broadcasting (DAB/DVB) will open the possibility
to provide to mobile users interactive or on demand services — so called TP data

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casting — and audio and video streaming in a much more efficient way than using the
point-to-point switch network .
 The embedding in the user terminal of a Global Positioning System (GPS) receiver
will offer the essential feature of location-awareness that is necessary to provide users
with the most comprehensive and extensive level of information, thus bringing about
real revolution in terms of personalized services. The user terminal can hence
provide not only location based information, such as maps and directions to follow to
reach a specific place, but also useful information relevant in time and space, such as
pop-up advertisements concerning offers in shops nearby. However, GPS technology
can only support outdoor localization. Indoor localization, which is important in order
to provide, for instance, the guided tour in a museum, requires the cooperation of
short-range wireless technologies.
Finally, it is worth highlighting that although users are attracted by high data
rates, they would certainly be even more attracted by useful services exploiting high data
rates. The support of imaging and video as well as high-quality audio gives service
providers (SPs) a myriad of possibilities for developing appealing applications. These
features, blended with the support of high data rates, result in a particularly attractive
combination. Indeed, in addition to an explosive increase in data traffic, we can expect
changes on the typically assumed downlink-uplink traffic imbalance. Data transfer in the
uplink direction is expected to increase considerably and, as a result of these trends, the
mobile user will ultimately become a content provider (CP). In future wireless networks,
the CP concept will broaden to encompass not only the conventional small- or middle-
size business-oriented service companies, but also any single or group of users. Mobile
CPs will open up a new chapter in service provision.

4.4 Multimode/Reconfigurable and Interworking Devices

As illustrated in Fig. 5, 4G is characterized by the support of heterogeneous terminals,
ranging from pen-phones to cars. However, due to its wide acceptance and usage in the
past ten years, the mobile phone is still expected to be on the next “edge of the wave” of
the mass market. Indeed, while the penetration of other devices will occupy a restricted

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niche role in the market (e.g., personal digital assistants (PDAs), watch phones, and pen-
phones will continue to be restricted to an elite group of tech-savvy people), the mobile
phone will still have no competitor in the near future, due to its size and weight, which
guarantee high portability. Moreover, due to the casual and informal feeling it gives,
people will pay more attention to the pop-up advertisements/news/events they receive on
it than on any other device.

Looking at the latest releases of mobile phones, the actual tendency is to use a
General Packet Radio System (GPRS) platform and provide users with the most complete
range of applications possible, trying to continually include new additional features (e.g.,
digital camera recorder, etc.). On the other hand, the emerging UIMTS phones essentially
provide the possibility to support the mobile video communication. However, the real
enhancement that 3G brings to our everyday life is not really clear. This new application
cannot necessarily be considered as the “killer application,” as the quality of the video is
low and it is practically limited to a semi-static situation that implies a complete
concentration of users during the conversation (e.g., it is obviously not practical to watch
a mobile phone while walking in the street), restricting the field of action and raising
secondary problems, such as safety issues (e.g., for the driver and pedestrians while
driving, etc.). Since 4G is based on the integration of heterogeneous systems, the future
trend of wireless devices will move toward:

4.4.1 Multimode/reconfigurable devices.

The user terminal is able to access the core network by choosing one of the
several access networks available and to initiate the handoff between them without the
need for network modification or interworking devices. This leads to the integration of
different access technologies in the same device (multimodality) or to the use of the
software-defined radio (SDR) (reconfigurability) . For example, whereas the integration
of Bluetooth in the user terminal will enable a personalization-transfer service, a built-in
GPS receiver will allow users to utilize their personal devices as navigators just by
plugging them in their cars and thus even lighten the number of needed devices.

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However, the reconfigurability of the user terminal could be a key aspect that would
make the future 4G technology as highly adaptable as possible to the various worldwide
markets.

4.4.2 Exploitation of Interworking devices.

In order to reduce the hardware embedded in the user terminal and the software
complexity, the use of interworking devices is exploited. For example, this is the case of
an integrated access point (AP) performing the interworking between a wireless
metropolitan area network (WMAN) technology and a WLAN technology, such as
WiMAX and Wi-Fi, respectively: the WMAN is considered as the backbone and the
WLAN as the distribution network; therefore, instead of integrating both technologies,
the user terminal will only incorporate the Wi-Fi card. The price to be paid for this relief
is hence an increased system (infrastructure) complexity.

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Chapter5 Key 4G Technologies

5.1 OFDMA
5.2 Software-defined Ratio
5.3 Multiple input Multiple output
5.4 Caching and Pico cells
5.5 Coverage

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5 Key 4G Technologies

Some of the key technologies required for 4G are briefly described below:

5.1 OFDMA
Orthogonal Frequency Division Multiplexing (OFDM) not only provides clear
advantages for physical layer performance, but also a framework for improving layer 2
performance by proposing an additional degree of freedom. Using ODFM, it is possible
to exploit the time domain, the space domain, the frequency domain and even the code
domain to optimize radio channel usage. It ensures very robust transmission in multi-path
environments with reduced receiver complexity.

Figure 7 OFDM Principles[i]

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As shown in Figure 7, the signal is split into orthogonal subcarriers, on each of

which the signal is “narrowband” (a few kHz) and therefore immune to multi-path
effects, provided a guard interval is inserted between each OFDM symbol. OFDM also
provides a frequency diversity gain, improving the physical layer performance. It is also
compatible with other enhancement technologies, such as smart antennas and MIMO.

5.2 Software defined radio

Software Defined Radio (SDR) benefits from today’s high processing power to
develop multi-band, multi-standard base stations and terminals. Although in future the
terminals will adapt the air interface to the available radio access technology, at present
this is done by the infrastructure. Several infrastructure gains are expected from SDR. For
example, to increase network capacity at a specific time (e.g. during a sports event), an
operator will reconfigure its network adding several modems at a given Base Transceiver
Station (BTS). SDR makes this reconfiguration easy. In the context of 4G systems, SDR
will become an enabler for the aggregation of multi-standard pico/micro cells. For a
manufacturer, this can be a powerful aid to providing multi-standard, multi-band
equipment with reduced development effort and costs through simultaneous multi-
channel processing.

5.3 Multiple-input multiple-output

MIMO uses signal multiplexing between multiple transmitting antennas (space
multiplex) and time or frequency. It is well suited to OFDM, as it is possible to process
independent time symbols as soon as the OFDM waveform is correctly designed for the
channel. This aspect of OFDM greatly simplifies processing. The signal transmitted by m
antennas is received by n antennas. Processing of the received signals may deliver
several performance improvements: range, quality of received signal and spectrum
efficiency. In principle, MIMO is more efficient when many multiple path signals are
received. The performance in cellular deployments is still subject to research and
simulations. However, it is generally admitted that the gain in spectrum efficiency is
directly related to the minimum number of antennas in the link.

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5.4 Caching and Pico Cells

Memory in the network and terminals facilitates service delivery. In cellular
systems, this extends the capabilities of the MAC scheduler, as it facilitates the delivery
of real-time services. Resources can be assigned to data only when the radio conditions
are favorable. This method can double the capacity of a classical cellular system.
In pico cellular coverage, high data rate (non-real-time) services can be delivered
even when reception/transmission is interrupted for a few seconds. Consequently, the
coverage zone within which data can be received/transmitted can be designed with no
constraints other than limiting interference. Data delivery is preferred in places where the
bitrate is a maximum. Between these areas, the coverage is not used most of the time,
creating an apparent discontinuity. In these areas, content is sent to the terminal cache at
the high data rate and read at the service rate. Coverages are “discontinuous”. The
advantage of coverage, especially when designed with caching technology, is high
spectrum efficiency, high scalability (from 50 to 500 bit/s/Hz), high capacity and lower
cost.

5.5 Coverage
Coverage is achieved by adding new technologies (possibly in overlay mode) and
progressively enhancing density. Take a WiMAX deployment, for example: first the
parent coverage is deployed; it is then made denser by adding discontinuous pico cells,
after which the pico cell is made denser but still discontinuously.

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Figure 8 Pico cell network design[iv]

Finally the pico cell coverage is made continuous either by using MIMO or by
deploying another pico cell coverage in a different frequency band (see Figure 9). Parent
coverage performance may vary from 1 to 20 bit/s/Hz/km, while pico cell technology can
achieve from 100 to 500 bit/s/Hz/km, depending on the complexity of the terminal
hardware and software.
These performances only refer to outdoor coverage; not all the issues associated
with indoor coverage have yet been resolved. However, indoor coverage can be obtained
by:

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 Direct penetration; this is only possible in low frequency bands (significantly

below 1 GHz) and requires an excess of power, which may raise significant
interference issues.
 Indoor short range radio connected to the fixed network. Connection via a relay to
a pico cellular access point.

Figure 9 Example of deployment in dense traffic areas

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6 Conclusion

The provision of megabit/s data rates to thousands of radio and mobile terminals per
square kilometer presents several challenges. Some key technologies permit the
progressive introduction of such networks without jeopardizing existing investment.
Disruptive technologies are needed to achieve high capacity at low cost, but it can still be
done in a progressive manner. The key enablers are:

 Sufficient spectrum, with associated sharing mechanisms.

 Coverage with two technologies: parent (2G, 3G, WiMAX) for real-time delivery, and
discontinuous pico cell for high data rate delivery.
 Caching technology in the network and terminals.
 OFDM and MIMO.
 IP mobility.
 Multi-technology distributed architecture.
 Fixed-mobile convergence (for indoor service).
 Network selection mechanisms.
Many other features, such as robust transmission and cross-layer optimization, will
contribute to optimizing the performance, which can reach between 100 and 500
bit/s/Hz/km2. The distributed, full IP architecture can be deployed using two main
products: base stations and the associated controllers. Terminal complexity depends on
the number of technologies they can work with. The minimum number of technologies is
two: one for the radio coverage and one for short range use (e.g. PANs).

However, the presence of legacy networks will increase this to six or seven.

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7 Appendices

7.1 References : Journals and Magazines

i. Simone Frattasi, Hanane Fathi, Frank H.P Fitzek, and Ramjee Prasad, Aalborg
University, Marcos D. Katz, Samsung Electronics, “Defining 4G Technology from
the User’s Perspective”, published by IEEE Jan/Feb 2006

ii. “Third/fourth generation wireless networks”, proceeds of the IEEE conference

2001

iii. K.R.Santhi, G. Senthil Kumaran, “Migration to 4 G: Mobile IP based Solutions”,

published by IEEE 2006

iv. D. Rouffet, S. Kerboeuf, L. Cai, V. Capdevielle, “4G Mobile”, technical paper

published by Alcatel.

v. Linda Doyle, “Beyond 3G: 4G Based Mobile Networks”

7.2 References : Websites

vi. www.wikipedia.org

vii. www.alcatel.com

viii. www.ieee.org

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ix. www.eurotechnology.com

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7.3 List of Figures and Tables used

Fig.1 Evolution from 2G to 4G 10

Fig.2 Service Evolution Vision 14

Fig.3 Dimensioning Examples 14

Fig.4 Multiple Overlay Architecture 16

Fig.5 Heterogeneous Terminals 20

Fig.6 Heterogeneous Networks 23

Fig.7 OFDM Principles 31

Fig.8 Pico cell network Design 34

Fig.9 Example of deployment in dense traffic areas 35

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7.4 Glossary

Access Point(AP): An access point is a station that transmits and receives data
(sometimes referred to as a transceiver). An access point connects users to other users
within the network and also can serve as the point of interconnection between the WLAN
and a fixed wire network.

Bandwidth: Bandwidth is the width of the range (or band) of frequencies that an
electronic signal uses on a given transmission medium.

Broadband: Broadband refers to telecommunication in which a wide band of frequencies

is available to transmit information.

CDMA: CDMA is a form of multiplexing, which allows numerous signals to occupy a

single transmission channel, optimizing the use of available bandwidth. The technology is
used in ultra-high-frequency (UHF) cellular telephone systems in the 800-MHz and 1.9-
GHz bands.

Fourth Generation Mobile Systems: 4G is the short term for fourth-generation wireless,
the stage of broadband mobile communications that will supersede the third generation
(3G). While neither standards bodies nor carriers have concretely defined or agreed upon
what exactly 4G will be, it is expected that end-to-end IP and high-quality streaming
video will be among 4G's distinguishing features.

GSM: GSM digitizes and compresses data, then sends it down a channel with two other
streams of user data, each in its own time slot.

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IP: The Internet Protocol (IP) is the method or protocol by which data is sent from one
computer to another on the Internet.

MIMO: MIMO (multiple input, multiple output) is an antenna technology for wireless
communications in which multiple antennas are used at both the source (transmitter) and
the destination (receiver).

OFDM: Orthogonal frequency-division multiplexing (OFDM) is a method of digital

modulation in which a signal is split into several narrowband channels at different
frequencies.

Pico Cell: Very small cell in a mobile network for boosting capacity within buildings.

UMTS: UMTS (Universal Mobile Telecommunications Service) is a third-generation

(3G) broadband, packet-based transmission of text, digitized voice, video, and
multimedia at data rates up to 2 megabits per second (Mbps).

WiMAX: WiMAX (Worldwide Interoperability for Microwave Access) is a wireless

industry coalition whose members organized to advance IEEE 802.16 standards for
broadband wireless access ( BWA ) networks.

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