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Evolution towards Fourth Generation

Mobile Multimedia Communication

Carlos Rodrguez Casal(1,2)

, Frits Schoute(1,3),

Ramjee Prasad(1)

(1) Delft University of Technology P.O.Box 5031 Delft, The Netherlands

Tel: +34.15.278.35.44 Fax: +34.15.278.18.43

carlos@ frits@ ramjee@mmc.et.tudelft.nl

(2) Universidad Pblica de Navarra, Campus Arrosada s/n Pamplona, Spain

(3) Philips Business Communications P.O.Box 32 Hilversum, The Netherlands

Abstract.

In this paper a view of the European developmentsin the field of wireless broadband multimedia

communications is given following two lines: on one sideevolution in Second and Third Generation of mobilecommunications; on the other side evolution of multimedia

data communications. This two evolutions will merge into anew concept of communications: the Mobile BroadbandSystems, or fourth generation of Mobile Multimedia

Communications.

Within this context, a multi-disciplinary project isbeing developed at Delft University of Technology. The

MMC (Mobile Multimedia Communications) project.MMC holds a combination of: promising applications,novel user-interfaces, compression, protocols geared to the

mobile user and transmission techniques that give abundantbandwidth to the user.

1. Cellular Evolution.

The First Generation Cellular Systems wereimplemented in early eighties. They used direct analog

voice modulation and were based on a cellular architecture.Transmission rates where around 2.4 kbps and there weredifferent systems working at different countries.

The Second Generation Cellular Systems weredesigned as the technical evolution of microelectronics

enabled use of full digital communication over the radiochannel with portable devices. From Europe the standardGSM (Global System for Mobile communications) has

emerged as an European standard and it has became themain mobile system all around the world providing servicesto 70 million users in Europe, and over 100 million users

word wide not only in Europe but in 110 countries with

over 200 networks all over the word.

The unprecedented growth of world-wide mobileand wireless markets, coupled with advances incommunications technology and the accelerateddevelopment of services taking place in fixed networks,point now to two possibilities: GSM evolution and the

introduction of a Third Generation Mobile CommunicationSystem.

1.1. GSM Evolution.

The initial transmission rate of GSM systems is9.6 kilobits per second (kbps) with a possible increase to14.4 kbps by changing the error protection coding.

High Speed Circuit Switched Data (HSCSD)allows the combination of multiple time slots and offers araw data rate of up to 64kbps (38.4 kbps user data rate).This high-speed data functionality is available in GSMnetworks without any base station hardware modifications,

only the software upgrade is needed [1].Next step will go up to 164 kbps by using packet

switched resource allocation; this means that resources areallocated only when data are to be sent or received. This

technique is known as General Packet Radio Service(GPRS), also known as GSM2+. Although this may appearto be a perfect evolution from GSM, it is not as it is not

possible to "commute" between high speed circuit switcheddata and general packet radio service, because each of them

requiring a priori a dedicated specialised radio [2].An improvement upon the former system is

Enhanced Data rate for GSM Evolution, (EDGE), also

known as Evolved GSM. EDGE technology is designed tobe introduced in existing digital networks such as GSM andthe North American Digital Advanced Mobile Phone

Service (D-AMPS). It is based on a higher level modulationand allows transmission at data rates of 384 kbps [3].

This evolution is shown in figure 1.

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Figure 1: Cellular Systems Evolution

1.2. Mobile Systems Convergence:Third Generation.

Nowadays mobile communication systems can bedefined in 5 groups: cordless, cellular, satellite, paging andprivate mobile radio systems. These mobile communication

systems will all be included at a common system: the

Universal Mobile Telecommunications System, (UMTS).While the 1st and 2nd generation cellular systems

were all deployed at 1 GHz spectrum domain with someextensions to higher frequencies as the earlier allocationsbecome congested. Radio regulation authorities did

allocate new spectrum for mobile use in the 2 GHz area.Initial transmission will be at 2GHz with a rate of

2Mbps in low mobility conditions, independently of the

environment. This rate will be only between 144 and 384kbps for wide area services. 144 kbps Is the minimumachievable user bit rate in any mobility condition and theUMTS system will have to support user speed up to 500km/h [4]. There will be available up to 10 Mbps for local

area mobility services by 2.005, but only in a provisionalway. The final extension, everywhere, will be available by2.010.

2. Multimedia Data Communication.

Multimedia communication points out a

communication with multiple ways of presenting theinformation, as a combination of text, data, graphics,animation, images, sound, speech and still or moving video.

Interesting characteristics added to multimedia

communication definition, are the media flexibility fordifferent applications and the possibility of interaction

between the communication subjects.

Concurrently to the mobile telephony change,local area networks are also changing to make it possible to

distribute all wireless services to the users. This will evolvethe local area networks (LAN's) towards wireless local areanetworks (WLANs) that will provide multimedia services.

The European Telecommunication Standards Institute(ETSI) supports projects, as the Broadband Radio Access

Networks (BRAN) project, in order to developHIPERLAN2, (HIgh PErformance Radio Local Area

Network.) to be used as next generation of WLAN.

Some other dimensions as HomeRF or Bluetoothare being developed in wireless communications.

HomeRF: the Home Radio Frequency WorkingGroup (HRFWG) [5] was formed in March 1998 to lookfor a specification for wireless digital communication

between PCs and consumer electronic devices anywhere inand around the home. This new communication system willprovide flexibility and mobility and will enable

interoperability between many different consumerelectronic devices from different manufacturers. A newprotocol is being developed, it is called the Shared Wireless

Access Protocol (SWAP). The system is designed to carryboth voice and data traffic and to interoperate with thePublic Switched Telephone Network and the Internet. It

operates in the 2.4 GHz band and uses a digital frequencyhopping (FH) spread spectrum (SS) radio. It supports both aTime Division Multiple Access (TDMA) service to

provide delivery of interactive voice and other time-criticalservices, and a Carrier Sense Multiple Access / CollisionAvoidance (CSMA/CA) service for delivery of high-speed

packet data. The system data rate will be 1 or 2 Mbps and

use 2 or 4 FSK modulation (Frequency Shift Keying) and itwill support up to 127 devices per network.

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Bluetooth technology will allow the replacement

of the many proprietary cables that connect one device toanother with one universal short-range radio link.Bluetooth, "A Global Specification for Wireless

Connectivity" [6], will replace the cable used today toconnect printers, desktops, fax machines, cellular phones,

laptops, keyboards, joysticks and virtually any other digitaldevice. Bluetooth radios will operate in the unlicensedIndustrial Scientific Medical (ISM) band at 2.45 GHz. (thisfrequency is available all over the world) with a gross datarate of 1 Megabit per second (Mbps). Spectrum spreading isaccomplished by frequency hopping in 79 hops displacedby 1MHz, starting at 2.402 GHz and stopping at 2.480

GHz.

Multimedia data communication and mobile

telephony are evolving simultaneously. Future systems willmake use of both technologies and a new concept forcommunications will become a reality. This future

communication system is the so-called "Mobile MultimediaCommunication". Systems convergence towards MobileMultimedia Communication is shown in figure 2.

3. Towards a Fourth Generation ?

Only if the third generation becomes a success

there will be other future generations. The successfulintroduction of third generation mobile systems is criticallydependent on the matching of the offered services to the

user needs (applications), and on cost-effective provision ofthose services.

Between 1992 and 1995 there was a project on theEuropean Community that was called Mobile Broadband

System, MBS [7]. It was part of the second part of theRACE program (Research and development in AdvancedCommunications in Europe). It was a project, but also theMobile Broadband Systems concept was born there,targeting future outdoor, cellular scenarios with high

mobility and high data rates, as to carry Mobile MultimediaCommunications. These systems will be the fourth mobilegeneration. No standardisation activity has so far been

foreseen, although the European RadiocommunicationsOffice, ERO, has already considered the spectrum needs ofthis new service [8].

4. MMC Project:

For fourth generation mobile telecommunicationsystems, innovative concepts are needed that may not befound by evolutionary enhancements to existing systems,the approach taken at the Mobile Multimedia

Communication project of the Delft University ofTechnology is to form a multi-disciplinary team in whichuser aspects get as much attention as the technological

challenges. This MMC project has five research lines,some of their achieved results are here presented.

4.1. Applications: Work Coordination.

Multimedia was seen as most suitable for non-

standard work situations, i.e. those situations where theprofessional runs into a complex problem that cannot besolved by known procedures and for which the professional

lacks some expertise. These situations are typically found inemergency services, medical assistance and disastermanagement.

Two field studies have been performed so far:ambulance services and the repair and maintenance ofphoto-copying machines. During field observations themobile workers and related actors were followed in theirdaily work. All actions and conversations were written

down. Based on the field studies, scenarios are build toenvision the role of different kinds of support for the dailywork practice of ambulance and copier services. Theseespecially concern the remote support through mobile

communication via different modalities (speech/audio/video) and ways of interaction (synchronous/asynchronous) [9].

4.2. User Interface and Transparency.

Communication from one office to another isrelatively straightforward with today's technology.However when one of the parties wishing to communicateis based outside, problems of remoteness and insufficientinfrastructure can limit the effectiveness of their

communications.

UMTSUniversal Mobile Telecommunication System

Cellular

Cordless

PMR Systems

Satellite

Paging

MBSMobile Broadband Systems

MOBILE TELEPHONY

MULTIMEDIA DATACOMMUNICATION

HIPERLAN

HomeRF

Bluetooth

MobileMultimediaCommunication

Figure 2: Mobile and Multimedia convergence.

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The emergence of wearable computers offers a

potential method of improving this situation particularlywhen a visual link is provided by a mobile videotransmission system.

The wearable equipment that is proposed at theMMC project is a head mounted display. Head mounted

displays can be used to present visual informationtransparent as to the environment, (presentingtransparent information means taking characteristics ofbackground visual information and characteristicsreceived at the head mounted displays into account).

This transparency problem had to be solved as

the visual information could not be projected in just anypart of the field of view [10].

4.3 Compression.

Most compression methods perform well on atransmission channel with a very low bit error rate, but

many of them break down on a wireless channel whereerrors are more rule than exception. Very-low bit ratecompression should not be the prime objective, since theemphasis is on sufficient quality in order to performtasks which depend strongly on the context. Thereforethat reducing the bit rate is important, but not the most

important objective in wireless communication. It ismore important to make the compression (incollaboration with the transmission system) as robust as

possible against the errors that are typical for thewireless channel, possibly with the help of the video-analysis tools that are also being used for MPEG-4

multimedia applications.

Research has been carried out in two areas forsource coding and two techniques have been proposed:

H.263 For mobile video communication.

This technique proposed in the MMC project isbased on the high compression recommendation by theInternational Telecommunication Union (ITU) H.263.

The basic configuration of the video source codingconsists of two parts: the reference frame, with respect towhich the differential frames are coded, and the

possibility to force intra coding of the macro blocks thathave been detected as corrupted [11].

Compression of the Shapes of Video Objects.Errors will occur during the transmission, so

the compression has to be error-robust. A technique for

contour coding combining polar coordinates and DiscreteCosine Transform (DCT) has been proposed [12].

4.4. Transmission Protocols.

In all OSI layers measures are taken to deal withthe adverse conditions of the wireless channel. It is hard

to maintain the OSI ideal according to which the higherlayers need not know by which method the lower layers

provide a service to them. Transmission errors can be

countered by Forward Error Correction (FEC) andAutomatic Repeat reQuest (ARQ) at the link layer, butthis has consequences for the delay and throughput

performance that is experienced by the higher layers.The answer found in the MMC project is a hierarchical

protocol structure that provides different Qualities ofService (QoS) to the various traffic streams in mobilemultimedia communication.

The hierarchy is realised with a hybridTDM/FDM (Time Division Multiplexing / FrequencyDivision Multiplexing) technique in which frames (thelargest unit of data) are subsequently composed of

packets, fragments and Radio Data Units (RDUs). Thehierarchical approach allows for easy future expansion,both in terms of the allocated bandwidth and

technological advances in modulation and coding [13].

Further steps have been taken to complete the

system for communication by developing a method tocombine data from multiple receivers in a virtual cellularnetwork (VCN). A virtual cellular network uses a virtual

cell architecture, defined as an area of a predeterminedsize and formed virtually around a mobile station. Thebasic idea is that one mobile is heard by multiple base

stations and viceversa, multiple base stations can senddata to one mobile. It is shown that virtual cell conceptgreatly enhances the quality of transmission [14].

The MMC-project proposes a virtual cellularnetwork for the links between base stations and mobile

users. This implies that at every instant each active

mobile station is in contact with multiple base stations.A testbed for high speed cellular networks is being

developed. The testbed consists of an RF front-end thatoperates in the 2.4GHz band, and a low-powerprocessing unit. Data rates are up to 25Mbit/s, with

higher rates attainable by placing multiple units inparallel.

4.5. Broadband Radio Transmission.

Future demands for mobile communicationsystems will be dominated by the heterogeneity of

broadband services which are to be supplied in indoorsand outdoor environments, simultaneously, with varyingdegrees of mobility. Because these heterogeneous

telecommunication services get more sophisticated andbecause the introduction of multimedia, the amount ofinformation being exchanged increases. More

information means higher data rates in order to meet thechallenges of the information society. In the context ofmobile services one of the constraints in realising the

needs of the information society is the availability offrequency spectrum. The scarcity of spectrum and thenew technical possibilities in recent years have drawn

attention all over the world to the millimetre band. In the

MMC project, transmission is located at the V band(from 40 to 75 GHz), centered at 60 GHz. Measurements

have been developed, new techniques for measurements

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have been proposed, measurements have been carried out

and channel simulators have been built [15].

The Chosen modulation scheme has been

Orthogonal Frequency Division Multiplex (OFDM), thismodulation is specifically able to cope with the problems

of the multipath reception. Current research on OFDMcovers the development of advanced synchronisationalgorithms and the influence of non-linear poweramplification.

5. Conclusions.

Mobile communications are evolving fast.

While data rate is growing, different services are beingintegrated and multimedia based services are shown tobe the next step to be taken.

For fourth generation mobile

telecommunication systems, innovative concepts are

needed that may not be found by evolutionaryenhancements to existing systems. The approach taken at

the Mobile Multimedia Communication project of theDelft University of Technology is to form a multi-disciplinary team in which user aspects get as muchattention as the technological challenges.Within the project, an experimentation platform has been

developed, and multimedia services has been tested inworking and emergency situations. To provideinformation to the user, different interfaces are being

analysed. A Head Mounted Display is the solutionproposed by the MMC members. Regarding Videocompression has in consideration that frequency errorswill happen due to the wireless channel where the

transmission takes place. Virtual Cell architecture andprotocols specially designed to cope with the mobileenvironment are presented in combination withOrthogonal Frequency Division Multiplexing asmodulation technique.

References.

[1] www.gsmdata.com

[2] http://www.cs.hut.fi/~hhk/GPRS

[3] "Vision for the evolution from GSM to UMTS"

GSM MoU Association 1998, TG.13http://www.gsmworld.com/3g/index.html

[4] GSM MoU Association Permanent ReferenceDocument, TG 32, April 98. "UMTS RadioRequirements" at :

http://www.gsmdata.com/artholley.htm

[5] http://www.homerf.org

[6] http://www.bluetooth.com

[7] http://www.comnets.rwth-aachen.de/report96/node211.html#

[8] Mobile Broadband Systems, Final Report, EROJuly 1.997. www.ero.dk

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[15] D. M. D. Matic, H.Harada and R. Prasad,"Indoor and outdoor frequency measurements

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