tt seminar report

8/7/2019 tt seminar report

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Abstract

Today, mobile communications play a central role in the voice/data network

arena. With the deployment of mass scale 3G just around the corner, new

directions are already being researched.

The 4G mobile technology -convergence of wireless mobile and wireless access,

will definitely drive this growth.The advent of 4G wireless systems has created

many research opportunities. The expectations from 4G are high in terms of data

rates, spectral efficiency, mobility and integration. Orthogonal Frequency Division

Multiplexing (OFDM) is proving to be a possible multiple access technology to be

used in 4G.


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CONTENTS

1.Introduction2.Histroy3.Objectives of 4G4.Developments5.Key 4G Technologies6.Advantages7.Conclusion8.References


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INTRODUCTION

A descendant to 2G and 3G aiming to provide the very high data

transfer rates. This technology can provide very speedy wireless

internet access to not only stationary users but also to the mobile

users. This technology is expected to trounce the deficiencies of 3G

technology in terms of speed and quality. 4G can be best described in

one word MAGIC, which stands for Mobile multimedia Anytime

Anywhere Global mobility support, integrated wireless and

personalized services

In telephony, 4G is the fourth generation of cellular wireless standards.

It is a successor to 3G and 2G families of standards. A 4G system is

expected to provide a comprehensive and secure all-IP based solution

where facilities such as ultra-broadband (giga-bit speed such as 100+

MiB/s) Internet access, IP telephony, gaming services, and streamed

multimedia may be provided to users.

Pre-4G technologies such as mobile WiMAX and first-release 3G Long

term evolution (LTE) have been available on the market since 2006 and

2009 respectively, and are often branded as 4G. Current versions of

these technologies do not fulfill the ITU-R requirements of data rates

approximately up to 1 Gbit/s for 4G systems.

In all suggestions for 4G, the CDMA spread spectrum radio technology

used in 3G systems and IS-95 is abandoned and replaced by frequency-

domain equalization schemes, for example multi-carrier transmission

such as OFDMA. This is combined with MIMO (Multiple In Multiple

Out), e.g., multiple antennas, dynamic channel allocation and channel-

dependent scheduling.


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HISTORY

The history and evolution of mobile service from the 1G (first

generation) to fourth generation are discussed in this section. Table 1

presents a short history of mobile telephone technologies. This process

began with the designs in the 1970s that have become known as 1G.

The earliest systems were implemented based on analog technology

and the basic cellular structure of mobile communication. Many

fundamental problems were solved by these early systems.

Numerous incompatible analog systems were placed in service around

the world during the 1980s.The 2G (second generation) systems

designed in the 1980s were still used mainly for voice applications but

were based on digital technology, including digital signal processing

techniques. These 2G systems provided circuit-switched data

communication services at a low speed. The competitive rush to design

and implement digital systems led again to a variety of different and

incompatible standards such as GSM (global system mobile), mainly inEurope; TDMA (time division multiple access) (IS-54/IS-136) in the U.S.;

PDC (personal digital cellular) in Japan; and CDMA (code division

multiple access) (IS-95), another U.S. system. These systems operate

nationwide or internationally and are today's mainstream systems,

although the data rate for users in these system is very limited. During

the 1990s, two organizations worked to define the next, or 3G, mobile

system, which would eliminate previous incompatibilities and become a

truly global system. The 3G system would have higher quality voice

channels, as well as broadband data capabilities, up to 2 Mbps.

Unfortunately, the two groups could not reconcile their differences,

and this decade will see the introduction of two mobile standards for

3G. In addition, China is on the verge of implementing a third 3G


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system.An interim step is being taken between 2G and 3G, the 2.5G. It

is basically an enhancement of the two major 2G technologies to

provide increased capacity on the 2G RF (radio frequency) channels and

to introduce higher throughput for data service, up to 384 kbps. A very

important aspect of 2.5G is that the data channels are optimized for

packet data, which introduces access to the Internet from mobile

devices, whether telephone, PDA (personal digital assistant), or laptop.

However, the demand for higher access speed multimedia

communication in today's society, which greatly depends on computer

communication in digital format, seems unlimited. According to the

historical indication of a generation revolution occurring once a decade,

the present appears to be the right time to begin the research on a 4G

mobile communication system.

Wireless System Evolution

Short History of Mobile Telephone Technologies


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Legend:

AMPS = advanced mobile phone service

CDMA = code division multiple access

EDGE = enhanced data for global evolution

FDMA = frequency division multiple access

GPRS = general packet radio system

GSM = global system for mobile

NMT = Nordic mobile telephone

PDC = personal digital cellular

PSTN = pubic switched telephone network

TACS = total access communications system

TDMA = time division multiple access

WCDMA = wideband CDMA

First generation: Almost all of the systems from this generation were

analog systems where voice was considered to be the main traffic.

These systems could often be listened to by third parties. Some of the

standards are NMT, AMPS, Hicap, CDPD, Mobitex, DataTac, TACS and

ETACS.

Second generation: All the standards belonging to this generation are

commercial centric and they are digital in form. Around 60% of thecurrent market is dominated by European standards. The second

generation standards are GSM, iDEN, D-AMPS, IS-95, PDC, CSD, PHS,

GPRS, HSCSD, and WiDEN.


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Third generation: To meet the growing demands in network capacity,

rates required for high speed data transfer and multimedia

applications, 3G standards started evolving. The systems in this

standard are essentially a linear enhancement of2G systems. They are

based on two parallel backbone infrastructures, one consisting of

circuit switched nodes, and one of packet oriented nodes. The ITU

defines a specific set of air interface technologies as third generation,

as part of the IMT-2000 initiative. Currently, transition is happening

from 2G to 3G systems. As a part of this transition, numerous

technologies are being standardized.

Fourth generation: According to the 4G working groups, the

infrastructure and the terminals of 4G will have almost all the standards

from 2G to 4G implemented. Although legacy systems are in place to

adopt existing users, the infrastructure for 4G will be only packet-based

(all-IP). Some proposals suggest having an open platform where the

new innovations and evolutions can fit. The technologies which are

being considered as pre-4G are the following: WiMax, WiBro, iBurst,

3GPP Long Term Evolution and 3GPP2 Ultra Mobile Broadband.


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OBJECTIVES OF 4G

4G is being developed to accommodate the quality of service (QoS) and

rate requirements set by forthcoming applications like wirelessbroadband access, Multimedia Messaging Service (MMS), video chat,

mobile TV, HDTV content, Digital Video Broadcasting (DVB), minimal

service like voice and data, and other streaming services for "anytime-

anywhere". The 4G working group has defined the following as

objectives of the 4G wireless communication standard:

y A spectrally efficient system (in bits/s/Hz and bits/s/Hz/site),y High network capacity: more simultaneous users per cell,y A nominal data rate of 100 Mbit/s while the client physicallymoves at high speeds relative to the station, and 1 Gbit/s while

client and station are in relatively fixed positions as defined by the

ITU-R,

y A data rate of at least 100 Mbit/s between any two points in theworld,

y Smooth handoff across heterogeneous networks,y Seamless connectivity and global roaming across multiple

networks,y High quality of service for next generation multimedia support

(real time audio, high speed data, HDTV video content, mobile TV,

etc)

y Interoperability with existing wireless standards,andy An all IP, packet switched network.

In summary, the 4G system should dynamically share and utilise

network resources to meet the minimal requirements of all the 4G

enabled users.


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DEVELOPMENTS

The Japanese company NTT DoCoMo has been testing a 4G

communication systemprototype with 4x4 M

I

MO called VS

F-OFC

DM at100 Mbit/s while moving, and 1 Gbit/swhile stationary. NTT DoCoMo

recently reached 5 Gbit/s with 12x12 MIMO while moving at 10

km/h,and is planning on releasing the first commercial network in 2010.

Digiweb, an Irish fixed and wireless broadband company, has

announced that they have received a mobile communications license

from the Irish Telecoms regulator, ComReg.This service will be issued

the mobile code 088 in Ireland and will be used for the provisionof 4GMobile communications.

Pervasive networks are an amorphous and at present entirely

hypothetical conceptwhere the user can be simultaneously connected

to several wireless access technologies and can seamlessly move

between them. These access technologies can be Wi-Fi, UMTS, EDGE,

or any other future access technology. Included in this concept is also

smart-radio (also known as cognitive radio technology) to efficientlymanage spectrum use and transmission power as well as the use of

mesh routing protocols to create a pervasive network.

Sprint plans to launch 4G services in trial markets by the end of 2007

with plans to deploy a network that reaches as many as 100 million

people in 2008.... and has announcedWiMax service called Xohm.

Tested in Chicago, this speed was clocked at 100 Mbit/s.

Verizon Wireless announced on September 20, 2007 that it plans a joint

effort with the Vodafone Group to transition its networks to the 4G

standard LTE. The time of this transitionhas yet to be announced.


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The German WiMAX operator Deutsche Breitband Dienste (DBD) has

launched WiMAX services (DSLonair) in Magdeburg and Dessau. The

subscribers are offered a tariff plan costing 9.95 euros per month

offering 2 Mbit/s download / 300 kbit/s upload connectionspeeds and

1.5 GB monthly traffic. The subscribers are also charged a 16.99 euro

one-time fee and 69.90 euro for the equipment and installation. DBD

received additional nationallicenses for WiMAX in December 2006 and

have already launched the services in Berlin,Leipzig and Dresden.

American WiMAX services provider Clearwire made its debut on

Nasdaq in New York on March 8, 2007. The IPO was underwritten by

Merrill Lynch, Morgan Stanley and JPMorgan. Clearwire sold 24 million

shares at a price of $25 per share. This adds $600 million in cash to

Clearwire, and gives the company a market valuation of just over $3.9

billion.


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KEY 4G TECHNOLOGIES

Access schemes

As the wireless standards evolved, the access techniques used alsoexhibited increase in efficiency, capacity and scalability. The first

generation wireless standards used plain TDMA and FDMA. In the

wireless channels, TDMA proved to be less efficient in handling the high

data rate channels as it requires large guard periods to alleviate the

multipath impact. Similarly, FDMA consumed more bandwidth for

guard to avoid inter carrier interference. So in second generation

systems, one set of standard used the combination of FDMA andTDMA

and the other set introduced a new access scheme called CDMA. Usage

ofCDMAincreased the system capacity and also placed a soft limit on it

rather than the hard limit. Data rate is also increased as this access

scheme is efficient enough to handle the multipath channel. This

enabled the third generation systems to used CDMA as the access

scheme IS- 2000, UMTS, HSXPA, 1xEV-DO, TD-CDMA and TD-SCDMA.

The only issue with CDMA is that it suffers from poor spectrum

flexibility and scalability.

Recently, new access schemes like Orthogonal FDMA (OFDMA), Single

Carrier FDMA (SC-FDMA), Interleaved FDMA and Multi-carrier code

division multiple access (MC-CDMA) are gaining more importance for

the next generation systems. WiMax is usingOFDMA in the downlink

and in the uplink. For the next generation UMTS, OFDMA is being

considered for the downlink. By contrast, IFDMA is being considered for

the uplink since OFDMA contributes more to the PAPR related issuesand results in nonlinear operation of amplifiers. IFDMA provides less

power fluctuation and thus avoids amplifier issues.Similarly, MC-CDMA

is in the proposal for the IEEE 802.20 standard. These access schemes


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offer the same efficiencies as older technologies like CDMA. Apart from

this, scalability andhigher data rates can be achieved.

The other important advantage of the above mentioned access

techniques is that they require less complexity for equalization at the

receiver. This is an added advantage especially in the MIMO

environments since the spatial multiplexing transmission of MIMO

systems inherently requires high complexity equalization at the

receiver.

In addition to improvements in these multiplexing systems, improved

modulation techniques are being used. Whereas earlier standards

largely used Phase-shift keying, moreefficient systems such as 64QAM

are being proposed for use with the 3GPP Long Term Evolution

standards.

OFDMA: Orthogonal Frequency Division Multiple Access

Orthogonal Frequency-Division Multiple Access (OFDMA) is a multi-user

version of the popular Orthogonal frequency-division multiplexing(OFDM) digital modulation scheme. Multiple access is achieved in

OFDMA by assigning subsets of subcarriers to individualusers as shown

in the figure below. This allows simultaneous low data rate

transmission from several users.

Based on feedback information about the channel conditions, adaptive

user-to subcarrier assignment can be achieved. If the assignment is

done sufficiently fast, this further improves the OFDM robustness tofast fading and narrow-band cochannel interference, and makes it

possible to achieve even better system spectral efficiency.


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Different number of sub-carriers can be assigned to different users, in

view to support differentiated Quality ofService (QoS), i.e. to control

the data rate and error probabilityindividually for each user.

OFDMA resembles code division multiple access (CDMA) spread

spectrum, whereusers can achieve different data rates by assigning a

different code spreading factor or a different number of spreading

codes to each user.

OFDMA can also be seen as an alternative to combining OFDM with

time division multiple access (TDMA) or time-domain statistical

multiplexing, i.e. packet modecommunication. Low-data-rate users can

send continuously with low transmission power instead of using a

"pulsed" high-power carrier. Constant delay, and shorter delay, can be

achieved.

However, OFDMA can also be described as a combination of frequency

domain and time domain multiple access, where the resources are

partitioned in the time-frequency space, and slots are assigned along

the OFDM symbol index as well as OFDM sub-carrier index.

OFDMA is considered as highly suitable for broadband wireless

networks, due to advantages including scalability and MIMO-

friendliness, and ability to take advantage of channel frequency

selectivity.

Claimed OFDMA Advantages

y Flexibility of deployment across various frequency bands withlittle needed modification to the air interface.

y Averaging interferences from neighboring cells, by using differentbasic carrier permutations between users in different cells.


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and link reliability or diversity (reduced fading). Because of these

properties, MIMO is a current theme of international wireless research.

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MIMO can be sub-divided into three main categories, precoding, spatial

multiplexing,or SM, and diversity coding.

Precoding is multi-layer beamforming in a narrow sense or all spatial

processing at the transmitter in a wide-sense. In (single-layer)

beamforming, the same signal is emitted from each of the transmit

antennas with appropriate phase (and sometimes gain) weightingsuchthat the signal power is maximized at the receiver input. The benefits of

beamforming are to increase the signal gain from constructive

combining and to reduce the multipathfading effect. In the absence of

scattering, beamforming results in a well defined directional pattern,

but in typical cellular conventional beams are not a good analogy.

When the receiver has multiple antennas, the transmit beamforming

cannot simultaneously maximize the signal level at all of the receive

antenna and precoding is used. Note that precoding requires

knowledge of the channel state information (CSI) at the transmitter.

Spatial multiplexing requires MIMO antenna configuration. In spatial

multiplexing, ahigh rate signal is split into multiple lower rate streams

and each stream is transmitted from adifferent transmit antenna in the

same frequency channel. If these signals arrive at thereceiver antenna

array with sufficiently different spatial signatures, the receiver can

separate these streams, creating parallel channels for free. Spatial

multiplexing is a very powerful technique for increasing channel

capacity at higher Signal to Noise Ratio (SNR). Themaximum number of

spatial streams is limited by the lesser in the number of antennas at the


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transmitter or receiver. Spatial multiplexing can be used with or

without transmit channelknowledge.

Diversity coding techniques are used when there is no channel

knowledge at the transmitter. In diversity methods a single stream

(unlike multiple streams in spatialmultiplexing) is transmitted, but the

signal is coded using techniques called space-timecoding. The signal is

emitted from each of the transmit antennas using certain principles of

full or near orthogonal coding. Diversity exploits the independent

fading in the multipleantenna links to enhance signal diversity. Because

there is no channel knowledge, there is nobeamforming or array gain

from diversity coding.

Spatial multiplexing can also be combined with precoding when the

channel is knownat the transmitter or combined with diversity coding

when decoding reliability is in trade-off.


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ADVANTAGES

1.VIRTUAL PRESENCE: This means that 4G provides user services atall times, even if the user is off-site.2.VIRTUAL NAVIGATION: 4G provides users with virtual navigationthrough which a user can access a database of the streets,

buildings etc.

3.TELE-GEOPROCESSING APPLICATIONS: This is a combination ofGIS(Geographical Information System) and GPS (Global

Positioning System) in which a user can get the location by

querying.

4.TELE-MEDICINE AND EDUCATION: 4G will support remote healthmonitoring of patients. For people who are interested in life longeducation, 4G provides a good opportunity.

5.CRISIS MANAGEMENT: Natural disasters can cause break down incommunication systems. In todays world it might take days or 7

weeks to restore the system. But in 4G it is expected to restore

such crisis issues in a few hours.

6.MULTIMEDIA VIDEO SERVICESy4G wireless systems are expected to deliver efficient

multimedia services at very highdata rates.

yBasically there are two types of video services: bursting andstreaming video services.

yStreaming is performed when a user requires real-time videoservices, in which the server delivers data continuously at a

playback rate.

yBursting is basically file downloading using a buffer and this isdone at the highest data rate taking advantage of the wholeavailable bandwidth.


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CONCLUSION

As the history of mobile communications shows,attempts have been

made to reduce a number of technologies to a single global standard.Projected 4G systems offer this promise of a standard that can be

embraced worldwide through its key concept of integration. Future

wireless networks will need to support diverse IP multimedia

applications to allow sharing of resources among multiple users. There

must be a low complexity of implementation and an efficient means of

negotiation between the end users and the wireless infrastructure. The

fourth generation promises to fulfill the goal of PCC (personal

computing and communication)a vision that affordably provides highdata rates everywhere over a wireless network.

4G is expected to be launched by 2010 and the world is looking forward

for the most intelligent technology that would connect the entire globe.


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REFERENCES

y B.G.Evans and K.Baughan Visions of 4G,ELECTRONICS AND COMMUNICATION JOURNAL

DECEMBER2000,pp.293-303

y Glenford Mapp,Frank Stajano, and Andy Hopper,Autonomic System for Mobility Support in 4G

Networks IEEE Journal vol 23,no.12,December

2005,pp.

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