4th genration moibile communication

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The Overview of the 4th

Generation Mobile

Communication System

Toshio Miki, Tomoyuki Ohya, Hitoshi Yoshino and Narumi Umeda NTT DoCoMo Inc., Wireless Labs.

3-5 Hikari-no-oka, Yokosuka-shi, Kanagawa, 239-8536 Japan

{ mikito, ooyat, yoshinoh, umedan}@nttdocomo.co.jp

Abstract — In order to satisfy the expectation of the users to have

more advanced wireless access even in the mobile environments,

research and development efforts for realizing the Fourth-

Generation (4G) mobile communication system has been

discussed. This paper outlines the requirements for the system,

technical challenges to be solved, and finally describes the

activities related to the standardization of the 4G mobilecommunication system..

4G mobile communication system; standardization

I. I NTRODUCTION

The users of the Third-Generation (3G) InternationalMobile Telecommunications-2000 (IMT-2000) [1] mobilecommunication services, which was launched in October 2001,has already reached about 34 million subscribers in Japan. Thesystem provides a variety of advanced multimedia servicessuch as video communications and high speed internet access.It is expected that this will lead to the mobile communicationmore important to our daily lives and will expand the role as alifestyle basis in the next ten years. It is also expected that such

an era requires a more advanced wireless communicationssystem, such as the Fourth-Generation (4G) mobilecommunication system, which far surpasses the capability of the existing IMT-2000 as shown in Figure 1. The development

process of the new mobile systems consists of developing therequirements, providing solutions satisfies the requirements,showing evidences for each technology to satisfy therequirements, as well as building international consensusthrough the standardization activities. In this article, wedescribe a basic approach to the technical issues and system

configuration involved in achieving the capability and performance required of the 4G system. We also describe thetrends in standardization concerning mobile communicationsystems.

II. SYSTEM OBJECTIVES

A.

Applications for 4G systemsThe improvements in media communication quality have

been one of the most perceptible advancements and only the perceptible advancements noted by the customers. For example,the size and resolution of LCD (Liquid Crystal Display)screens, the number of pixels in built-in camera, and the widevariety of ringer tones have been key to the popularity of mobile handsets. However, current mobile terminals still havemuch room in terms of improving communication reality. Theultimate objective of enhanced-reality media communicationsis to provide a transparent environment that is indistinguishablefrom face-to-face communications.

The applications, which require more advanced wirelesscapabilities, are discussed in [2]. In the article, three maindirections for enhancing media communication reality, that is3D audio communications, 3D visual communications and

biological information communications, as shown in Figure 2,were analyzed, and as a conclusion, it is expected that thefuture customers will be able to full use of 1 Mbit/s to 100

Biological info.Communications

Alter- ego

Tactilesense

3D Visual

Communications

3D Audio

Communications

Biological info.Communications

Alter- ego

Tactilesense

3D Visual

Communications

3D Audio

Communications

Figure 2. Three Main Targets for Enhanced-Reality Communications

2G 3G 4G

Mobile Ubiquitous

i-mode, SMSFOMA

Mobile

MultimediaMobile Internet

E-mail

Web

browsingVideo mail

Visual phone

TV conferencePersonalized communications

Reality communications

Broadband &

Ubiquitous

Generation

Media

Services

Digital Cellular

Internet High speed access

ATM Network

Ultra high speed access

Ubiquitous access

1990’s 2000’s 2010’s

Figure 1 Evolution of the Mobile Communications Systems

0-7803-9282-5/05/$20.00 ©2005 IEEE ICICS 2005

W2A.4

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Mbit/s under the end-to-end latency of 5 msec to 50 msec as

shown in Table I. This seems a reasonable motivation for discussing the necessity of the new mobile systems.

B. Requirements for 4G system

1) Broadband Wireless AccessThe traffic carried by mobile communication systems until

today was mainly for voice communications. The Second-Generation (2G) system, the Personal Digital Cellular (PDC)

system, introduced the i-mode services, which enabled theInternet access, electronic commerce and e-mail from mobileterminals, and mainly used for the text-based datacommunications. The IMT-2000 system offers high bit ratetransmission service from 64 kbit/s to 384 kbit/s, and it isexpected that the proportion of the amount of data traffic to thevoice traffic would continue to increase. Moreover, the rising

popularity of broadband services such as Asymmetric DigitalSubscriber Line (ADSL) and optical fiber access systems andoffice or home LANs is likely to lead to a demand for comparable services in the mobile communication environment.

2) Low Cost To make broadband services available to the user to

exchange various kinds of information, it is necessary to lower charges dramatically in order to keep the cost at or below thecost of existing service. The IMT-2000 system aimed at lower

bit cost and economical charge rates, however for the 4Gsystem, a broadband channel and an even lower bit cost are

both required.

3) Wide Area CoverageOne feature of mobile communications is that it is available

for use anytime and anywhere. That advantage is important for future mobile communication as well. In particular, it isimportant to maintain the service area in which the terminals of the new system can be used during the transition from theexisting system to a new system. It can be assumed thatterminals that have relatively large display screens, such asPersonal Digital Assistants (PDAs) or personal computers areused indoors rather than outdoors. Accordingly, better coverageof indoor service areas is needed.

4) Capable for Wide Variety of ServicesMobile communication is for various types of users. In the

future, we expect to make the advanced system performanceand functionality to introduce a variety of services not only theordinary telephone service but to transfer information about thefive sensual modes. Those services must be made easier for anyone to use.

C. Design Objectives

Considering that the video communications and datacommunications will be the main features, the 4G system must

provide even higher transmission rate and higher capacity thanIMT-2000. Also, considering that the video transmissionquality in current broadcasting is achieved by the transmissionrate of several megabits per second, the LAN transmission ratesare from 10 Mbit/s to 100 Mbit/s, and the rate of ADSL isseveral megabits per second, the design objective is a transfer rate of about 100 Mbit/s for the outdoor mobile environment

and gigabit class rates for indoors. It will not be possible toaccommodate future mobile communication traffic unless atransmission capacity of at least ten times that IMT-2000 doesattain as shown in Figure 4. To ensure throughput for communication between terminals and achieve highly real-timecommunication, it is necessary to realize the low transfer delaytime of 50 ms and even lower, and low connection set up delaytime of 500 ms or less. Also, assuming that the future serviceswill be based on IP (Internet Protocol) networks, the efficient

TABLE I R EQUIREMENTS FOR FUTURE NETWORKS (TENTATIVE) [1]

<10Mbps (Robotic I/F)

< 1Gbps (Virtual avatar)

< 100Mbps (Alter-ego

existence)

•Alter-ego robot<1sec< 10ms

< 30ms

< 5ms (Small and

known jitter)

Tele-existence

N/A

N/A

<1sec

<1sec

Connection

Latency

•Five sense sensors<50ms< 1MbpsFive senses

communications

•3D sound field control

•High efficiency loud

speakers

<50ms< 1 MbpsSpeech/

3D Audio

•Eyeglass display

•3D and multimodal UI

<< 50ms

Should be

predictable

< 1MbpsEnhanced

Reality

•Real time hologram<50ms10Mbps (2D video) ~

30Gbps (3D video)

Video/

3D video

Terminal capabilitiesDelayTransmission

speed

Media

<10Mbps (Robotic I/F)

< 1Gbps (Virtual avatar)

< 100Mbps (Alter-ego

existence)

•Alter-ego robot<1sec< 10ms

< 30ms

< 5ms (Small and

known jitter)

Tele-existence

N/A

N/A

<1sec

<1sec

Connection

Latency

•Five sense sensors<50ms< 1MbpsFive senses

communications

•3D sound field control

•High efficiency loud

speakers

<50ms< 1 MbpsSpeech/

3D Audio

•Eyeglass display

•3D and multimodal UI

<< 50ms

Should be

predictable

< 1MbpsEnhanced

Reality

•Real time hologram<50ms10Mbps (2D video) ~

30Gbps (3D video)

Video/

3D video

Terminal capabilitiesDelayTransmission

speed

Media

3G Systems beyond 3G

Cost

1/10 to 1/100 per bit

New service platform,which enables;- rapid deployment of new

services- easy development of new

services

Data rate：384kbps

Peak bit rate:100Mbps with high mobility1 Gbps in Hot-spots

System capacity

10 times higher

ATM（convergence of circuit- and packet-switched traffic）IP-based packet in 3.5G

All - IP-Can handle packet withvarious QoS requirements

Capability

Performanceimprovements

New capabilities

Mobility ：uniformcontrol

System controlaccording to mobility（the amount of control

signals reduced to1/10）

Transport：

Seamless networking amongdifferent radio access

techniques

Transmission delay Less than 50ms

For thedevelopment of

new services

Improvement

of basic systemperformance

Reduce of NW

costs

Figure 3 Requirements for 4G system

D a t a

s p e e d

[ b

p s ]

92 00

2G & 2.5G

2M

2M

Peak

3Gaverage

MAX sepc.

2ndG band (800MHz PDC)

3rdG band (2GHz)

95 05

384k

2.4k

PDC

9.6k

PDC

28.8k

PDC

Packet

32k

PHS

PHS

2ndG band (1.9GHz PHS)

-- Break Break - - throughthrough in Radio Interfaces is needed,in Radio Interfaces is needed,- Longer period of migrationLonger period of migration from IMT from IMT - - 2000 to2000 to

systems beyond IMT systems beyond IMT - - 2000 is forecasted,2000 is forecasted,- Inter Inter - - work work would be a solutionwould be a solution

10

４G

2005 in Urbanarea

Need deployment

to accommodate

increasing traffic

Break

through W-CDMA

10M

1M

100k

10k

1k

100M

1G

64k

Breakthrough

100M – 1G

Approx.

14M

Super3G

Reduced delay

IP commonalityHSDPA

Figure 4 Evolution in Data Transmission Rate

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transmission of IP packets between wireless terminals is also a

necessity. While increased capacity is also effective inlowering bit cost, the cost per bit must be reduced to from 1/10to 1/100 of the current levels by reduction of infrastructureequipment costs, operation costs and construction costs as well(Figure 3).

The design objectives described above aim at services thathave higher performance than existing services, yet are easy touse. It is necessary to pioneer new markets, making use of thecapabilities and performance of the 4G system such asintegration with indoor wireless LAN and wired systems, andthe implementation of a mechanism for introducing newservices in a short time, etc.

III.

APPROACH TO 4G SYSTEM CONFIGURATION

A. Technical Challenges

1) Technology for Implementing High-capacity and High-

rate TransmissionIMT-2000, which employs Wideband Code Division

Multiple Access (W-CDMA), achieves a transmission rate of 2Mbit/s with 5 MHz frequency bandwidth. Furthermore,technology for transmission at about 10 Mbit/s with the same

frequency bandwidth using multi-level adaptive modulationand demodulation is under development [3]. To achieve ratesthat are several times to several tens of times higher than that, itrequires a new transmission systems that are suited to high-ratetransmission.

One of the candidate technologies that satisfies therequirements is Variable Spreading Factor OrthogonalFrequency and Code Division Multiplexing (VSF-OFCDM) [4],

which is based on multi-career CDMA technologies with thevariable spreading factor scheme for increasing the systemcapacity shown in Figure 5. The biggest advantage of the VSF-OFCDM is its flexibility in the spreading factor. When it isapplied to isolated hot spots, we can achieve its highestcapacity by choosing a spreading factor of one to be compatiblewith conventional OFDM. On the other hand, it works as akind of CDMA with a spreading factor higher than one under multi-cell environments to enable the same frequency reuse.Then, a single air interface of VSF-OFCDM realizescapabilities of OFDM and CDMA in an adaptive manner according to environments. It was reported that success in 1Gbps real-time packet in-lab transmission experiments incombination with MIMO technology was confirmed in Aug.

2004 [5], and also reported that the success of 1 Gbps real-time packet field transmission experiment was confirmed in June2005 [6].

2) Technologies for Cost ReductionThe use of higher frequency band to achieve higher

transmission rate with conventional system configurationtechnology generally reduces the radius of the cell that one

base station can cover. To retain the original coverage area,more base stations are required and network cost is increased.To avert that problem, it is necessary to expand cell radii bymeans of higher performance radio transmission and circuittechnology, such as improved modulation/demodulationtechniques that can cope with low S/N, the use of adaptive

array antennas, and low noise receivers. There is also a need tostudy diversified entrance links that connect base stations to the backbone network, autonomous base station control technologyand multi-hop radio connection technology that employssimple relay stations, for further reduction in the costs of system construction and operation.

3) System Interconnection Technology Based on IP

Networking When a new system is first introduced, it is generally

difficult to fulfill the service area to the extent of the existingsystem. However, by implementing a terminal that has thecapabilities of both the new system and the existing system, itis possible to cover both areas. Also, giving consideration tointernational roaming, a terminal that can be configured towork with multiple systems based on Software Defined Radio(SDR) technology is an effective way to cope with periods of system introduction and operating frequency bands that differ from country to country and region to region. Furthermore,future mobile communication services will be provided withinterconnection and integrated with heterogeneous accesstechnologies, including wired and indoor area, access based onIP networks. Accordingly, interconnection and handover

Isolated cell

Variable

SpreadingFactor

= 1

Capacity

Freq.

Time > 1

Freq.

Time

Maximizing capacity in an isolatedcell environment, e.g. hot spot

⇒No spectrum spreading in Frequency Domain- Spreading Factor = 1, compatible with conventional OFDM

#3

#6

#2

#5

#4

#7

#1

Reuse of the same frequency

System bandwidth

Freq.

Code #1

Code #2

Code#N

Maximizing its capacity in multi-cell e nvironments⇒Spectrum Spreading in Frequency Domain

- Spreading Factor > 1

Freq.

System bandwidth

Multi-cell

Capacity

Scramble code unique to each cell

Figure 5 Variable Spreading Factor Orthogonal Frequency and Code DivisionMultiplexing (VSF-OFCDM)

Base Station Equipment Mobile Equip.on vehicle

Sector#1

Sector#2

NTTKinugasabuilding

（別館）

SectorKinugasa

NTT Yokosukabranch

buildingMacro Diversity among

multiple cells- Hand-over tests

Macro Diversity amongmultipesectors-Hand-over tests

Basic Radio Access Tests;Downlink: VSF-OFCDM

Uplink: VSCRF-CDMA- Test on targeted throughput

Downlink : More than 100Mbps，Uplink: more than 20 Mbps

- Coverage aspects testsFeasibility tests on key tech nologies inTransmission and MAC layersPropagation measuring campaign

Field trials of broadband mobileaccess in Yokosuka-city, Japan

Figure 6 Field Experiment for VSF-OFDM

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schedule for functional extension according to the ITU-R vision recommendation.

V. CONCLUSION

This paper reported the 4G system objectives including potential applications and system requirements, technicalchallenges, and related standardization activities. Through thediscussion, it has been revealed that the major feature of the 4G

system capability should be its ultra high speed IP packettransmission with reduced delay to meet a variety of requirements derived from the two-way enhanced realitycommunications such as 3D-audio, 3D-video, and biologicalinformation media world.

It was also described that our technical challenges in radiocommunication fields are likely to provide breakthroughcandidates to realize the above features. The local andinternational standardization activities indicate a global strongsupport toward this 4G direction.

ACKNOWLEDGEMENT

We would like to give our thanks to all the fellows in NTTDoCoMo Wireless Labs and Multimedia Labs for their fruitfulsuggestions and discussions.

R EFERENCES

[1] http://www.itu.int/home/imt.html

[2] T. Ohya and T. Miki, “Enhanced Reality Multimendia Communicationsfor 4G Mobile Networks,” The First International Conference onMultimedia Services Access Networks (MSAN) 2005, Olrand, U.S.A.,June 2005.

[3] F. Adachi and M Uesugi, “Latest Trends in CDMA Technology,” IEICEJournal. Vol. 86, No.2, pp. 96-102, 2003

[4] M. Sawahashi, S. Abeta, H. Atarashi, K. Higuchi, M. Tanno and T. Ihara,

“Broadband Packet Wireless Access,” NTT DoCoMo Technical Journal,Vol. 11, No. 2, Jul., 2003.

[5] http://www.nttdocomo.com/presscenter/pressreleases/press/pressrelease.html?param[no]=512

[6] http://www.nttdocomo.com/presscenter/pressreleases/press/pressrelease.html?param[no]=564

[7] ITU-R Recommendation M.1645, “Framework and overall objectives of the future development of IMT-2000 and systems beyond IMT-2000,”2003.

[8] C. Cooke, “Systems beyond IMT-2000,” ITU-R SG8 Seminar, 9thSeptember, 2004

[9] http://www.soumu.go.jp/joho_tsusin/policyreports/joho_tsusin/bunkakai/abstract.pdf (in Japanese)

[10] http://www.mitf.org/index_e.html

[11] http://www.mitf.org/public_e/archives/Flying_Carpet_Ver200.pdf

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4th genration moibile communication

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