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A Vision on Services and Architectures for 4GSimone Frattasi, Frank H.P. Fitzek, Anelia Mitseva, Ramjee Prasad

Center for TeleInFrastruktur (CTIF), Aalborg University, Niels Jernes Vej 12, 9220, Aalborg, Denmark{sf |ff |mitseva|prasad}@kom.aau.dk

Abstract— In this paper we will motivate the cellular con-trolled short-range communication for cooperative services in 4Gwireless networks. Without going into the technical details, weadvocate by means of very illustrative scenarios, that cooperationof users and their terminals better services can be achieved atlower prices. This new step in technology comes in combinationwith a social aspects of cooperation between customers.

Index Terms— 4G, Cellular network, Convergence, Cooper-ation, Heterogeneity, Personalization, Power consumption, Ser-vices, Short-range communication, Spectrum efficiency

I. I NTRODUCTION

The major reason for the ”failure” of theThird Generationof Mobile Communication Systems(3G) has been the tremen-dous worldwide downturn in the economy that lead to a star-vation of new investments and hence to delays in technologicaldevelopment, service roll out, etc. In some countries with highpenetration of mobile services, this was also combined with areward policy for releasing the spectrum usage rights that didnot favor the investments in IMT-2000 infrastructure. However,besides the difficulties and the technological limitations of3G [1], the evolution from 2G towards 3G has not brought anysubstantial new service for the customer, leaving the businessmodel largely unchanged [2]. The well known services plussome additional ones are provided, but they may not be enoughto encourage the customers to change their equipment. Thelack of innovative and appealing services was encounteredtoo late by the3G Partnership Project(3GPP). In the lateststandards, an attempt was made to incorporate some advancedservices into the 3GPP architecture such as theMultimediaBroadcast and Multicast Service Center(MBMS) in combi-nation with theIP Multimedia System(IMS). Nevertheless,these smaller improvements were made without the possibilityto adjust the access technology properly. Finally, anothermotivation of the limited success of 3G can be identified inthe different cultural and social backgrounds where the newsystem has been deployed. 3G has been more accepted inAsian countries than in Europe. In Japan, the teenagers sharevideos and books on their mobile phones in public places,whereas in Europe they experience the same exchange indoor,in their own rooms with their own TV-sets or computers.As a consequence, we derive that the acceptance of a newtechnology is not only dependant upon the mere technologicalinnovation, but also upon the cultural and social setting inwhich the new technology is being implemented.

The limitations and difficulties of 3G previously outlinedand the emergence of new mobile broadband technologieson the market have brought researchers and industries to athroughout reflection on theFourth Generation(4G). Basi-cally, many prophetic visions have appeared in literature [3]

presenting forthcoming generation as the ultimate boundaryof the wireless mobile communication without any limit inits potential, but practically not giving any designing rule andthus any definition of it. Recently, a first attempt has beendone within the framework of theJoint Advanced DevelopmentEnabling 4G(JADE) project1 in [4] and [5], where a pragmaticmethodology, centered on a user-centric approach, leads to thedefinition of the key features and the technological step-upof 4G. This methodology answers critically to the MAGICview of NTT DoCoMo [7] as well as to the somehow cloudyone of the EC of connecting ’everything with everything’ [8]:the technological possibilities of using the heterogeneity ofterminals and networks are tremendous if – and only if – theymeet the needs of the customers. It is hence strictly orientedtowards a use of the technology for better life conditionsand fair societies, where the inner logic of the technologicalevolution is coordinated with the societal evolution.

In line with [4] and [5], JADE envisions that 4G will bea convergence platform that will provide clear advantagesin terms of bandwidth, coverage, power consumption andspectrum usage, thus also offering a variety of new hetero-geneous services (from pop-up advertisements to location-based and interactive or on-demand ones – so called IPdatacasting). Though the core is still cellular, the systemarchitecture will be predominantly extended to short-rangecommunication systems, where the users may also cooperatein a completelydistributedor cellular-controlled fashion [6].Indeed, the concept of node cooperation introduces a newform of diversity where the terminals are less susceptible tothe channel variations and shadowing effects. This results inan increased reliability of the communication, leading bothto the extension of the coverage and the minimization ofthe power consumption, thus prolonging the battery life ofthe terminals. Furthermore, cooperative transmission strategiesmay also increase the end-to-end capacity and hence thespectral efficiency of the system.

The rest of the paper is structured as follows: Section IIdescribes the new system architecture; Section IV introducesa potential cooperative service; Section V discusses the socialimpact related to the proposed framework. Finally, the con-cluding remarks are given in Section VI.

II. SYSTEM ARCHITECTURE

The overall target is a cellular system that also supportsshort-range communications among the terminals. The ra-tionale for introducing short-range communication is mainly

1The JADE project is a cooperation between SAMSUNG Korea and theCenter for TeleInFrastruktur(CTIF).

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due to two arguments: (1) the need to supportpeer-to-peer(P2P) high-speed wireless links between the terminals and(2) to enhance the communication between a terminal andtheBase Station(BS) by fostering cooperative communicationprotocols among spatially proximate devices.

III. C OOPERATIVECOMMUNICATION

Recently, much research effort has been put to understandand utilize the benefit of cooperative behavior in wirelessnetworks [9]. The cooperation is expected to achieve highlink reliability, large coverage, high spectral efficiency and lesspower consumption of terminals through the use of exclusivecooperative stations (e.g., relay stations deployed by opera-tors) or short-range communications among different mobileterminals. In order to achieve these goals, the work is mostlyfocused on the design of different cooperative mechanisms inthe lower layers of the protocol stack, i.e.,Physical (PHY)andMedium Access Control(MAC) layers.

A. PHY Layer

The research in PHY-layer cooperation is in a mere infancy,but it has already promised a great potential. Cooperativediversity protocols exploiting the feature of wireless broadcastmedium have shown potential to achieve similar effect toconventionalMultiple Input Multiple Output(MIMO) trans-missions. However, theoretical analysis of capacity increasebrought by cooperative behavior has been the main topic inthe literature [10], and there have been few works on practicalprotocol designs to achieve the high diversity gain.

B. MAC Layer

An important issue to be addressed is the formation of thecooperating group for different targets (coverage enhancement,less power consumption, etc.), taking account of the inter-terminal channel conditions and the spatial distribution of theterminals. The design of protocols such as radio resourcemanagement and handoff has to be also addressed to coor-dinate transmissions between short-range links (links withincooperative groups) and long-range link (links between BSand terminals) so that the most appropriate links can be usedby terminals with the least interference conditions.

IV. POTENTIAL COOPERATIVESERVICES

A. Cooperative service support by customer diversity

As shown in Figure 1, we assume a certain number ofWireless Stations(WSs) in the range of the sameBase Station(BS), served by the same multicast service flow. In caseonly one terminal out of the group has received the overallinformation, we propose to perform the needed retransmissionslocally.

The terminals in the same multicast group are in physicalproximity, such that they can communicate with each otherusing high-speed wireless links. Due to the multi-user diver-sity, there is a high probability that at least one of them willreceive the downlink multicast packet correctly; that terminal

Fig. 1. Cooperative video service support by customer diversity.

may hence become leader –Cluster Head(CH)2 – and take theresponsibility, if needed, to retransmit the data packet locallyby using links with high data rate. In addition, it should alsoacknowledge the reception of the downlink packet towards theBS.

Contrarily to ad-hoc networks where the scope is to achievea better routing and the retransmissions are performed at the IPlayer, the novelty of the proposed service is to provide a moreefficient retransmission scheme and an increasedQuality ofService(QoS) to the users in the same group through an actionat theData Link Control(DLC) or Physical(PHY) layer. Anexplicative example of local retransmissions is shown in Figure2 and Figure 3.

Fig. 2. Example of percentage of data correctly received by each user withindifferent groups.

Local retransmissions within the same short-range grouphave the following advantages:

• Retransmitted packets from neighboring terminals will betransmitted at a lower power level than it would be doneby the BS, thus leading to a lower interference for parallelongoing communications.

• Retransmissions can be performed by exploiting the unli-censed band, thus providing the service at a lower price.

2Note that in this paper we do not take into consideration any specificalgorithm for the clusters’ formation, but we suppose that they have alreadybeen formed.

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Fig. 3. Example of ’triangular’ retransmissions.

• The BS can reserve some licensed band for the retrans-missions in each group. As an example, in Figure 4 acommon spectrum is used by the BS to convey multicastservices to the terminals in both groups. If a retrans-mission for Packet 1 is requested in Group A while aretransmission for Packet 2 is requested in Group B,different retransmissions can be performed at the sametime. In case of retransmissions performed by the BS,instead, the same amount of spectrum would have beenused for twice much time.

Fig. 4. Example of splitting the spectrum for common service support andlocal retransmissions for two different groups.

Note that the retransmissions performed by the BS maybe not totally avoided as all the group members may havenot received the overall information. Thereby, the number ofretransmissions performed by the BS depends on the numberof users belonging to the same group:

R = f(1

GS) (1)

whereRandGSare respectively the amount of retransmissionsand the group size. Therefore, as a consequence of Equation1, the proposed service infrastructure allows an adaptiveregulation of the redundancy in dependency of the group size.

B. Increasing the quality of service due to customer accumu-lation

As shown in Figure 5, we assume a finite number ofterminals in the range of the same BS served by the same

video flow – as an example, we suppose a video streamingencoded by using theMultiple Description Coding(MDC).In order to increase the quality of the video, we proposethat the BS transmits disjunctive descriptors to the differentmembers of the group. Therefore, even if the higher data ratecannot be processed by one terminal alone over the cellular airinterface, different terminals will receive different descriptorsand repeat/forward them over the short-range air interface,thus having more bandwidth available. As a consequence, theincreasing QoS will be dependant on the number of usersbelonging to the same group:

QoS = f(GS) (2)

whereGS is the group size.

Fig. 5. Increasing video quality due to customer accumulation.

The proposed service infrastructure hence induces the usersto form cooperative groups in order to achieve the commonbenefit of an enhanced quality of service. Figure 6 shows themessage sequence chart for a new user joining the group.

Fig. 6. Message sequence chart for a new user joining the group.

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Although we referred to a video streaming the same frame-work may be applied to any other type of service.

V. THE SOCIAL DIMENSION OF COOPERATIVESERVICES

This section gives an insight on the potential social impactof the proposed services. The latter are mainly based uponthree fundamental phenomena of social order:

1) Group building.Social groups on different levels (suchas teenage groups, organized groups of football players,loosely organized groups of neighbors, which are rela-tive stable over the time, or loosely organized and onlyfor a short time stable internet groups) are the interme-diaries in societies. Groups differ concerning what theyhave in common: spatial proximity (neighbors), interests(internet groups, business groups), age (teenage groups)and so forth. They are more or less durable over thetime and more or less organized. Although the serviceprovision is performed at the technical level, on thesocial level new groups might be established to lowerthe costs and offer a better quality of the services.

2) Network. The proposed cooperative services make in-telligent use of a decentralized network of terminals.As Manuel Castells outlined [15], fuzzy, spontaneousnetworks become more and more important. In the pro-posed services, instead of acting strictly hierarchically,the necessary but limited hierarchy is evolving out ofthe given situation. The decision concerning themaster-terminal is drawn on the background of technical meansand conditions seamless to the users. Customers will usethis service according to the resulting performance and ifthey trust in the capability of the network of terminalsto define a master-terminal that will be really able tocoordinate. This type of network could be coinedsitu-ational hierarchyand indicates the increasing relevanceof new types of time-limited and functional networks.

3) Cooperation/sharing.The cooperation in question couldbe clarified by taken into account how it works in thesociety. Cooperation is usually defined as a coordinatedeffort to reach mutual goals. The different reasons atthe base of this coordination are: traditions and habits,emotions (like compassion) or instrumental rational con-siderations (like efficiency, utility) or more normative ra-tional considerations (what one ought to do according agiven social or moral norm). It depends very much uponthe context and the behavioral setting as well as uponthe motivation in the background and thus in the stabilityof the cooperation. Although the common sense makesus believe that the best motivation for cooperation is apersonal good outcome or result, the concept of the self-interested actor that tries to maximize his own interestsand profits is not always valid. In the cooperative useof the mobile phone, for example, the rational interestof lowering costs and receiving a better quality of theservices lies clearly in the realm of maximizing theprofit. Nevertheless, also to become member of a groupand to share not only material but symbolic resources(e.g., joint values, prestige, friendship, etc.), could be

a strong motivation for utilizing the proposed services.Indeed, we can imagine groups that would like to makeclever use of them in order to watch videos or shareother files that are usually more expensive. Therefore,ad-hoc communities based on agreements about what towatch together are then possible to set up. These serviceshence increase the cooperative behavior and empowersthe consumer to make clever use of them. In general,the possibility for customers to deal in a creative mannerwith the technical possibilities is of great importance forthe services’ acceptance. In a way, the user terminal isnot any more a bare medium to transfer information,but a social medium that helps to build groups andfriendships.

Some researchers and mobile phone enthusiasts put highhopes in the possibilities of enhancing the cooperative behav-ior and the resource sharing by mean of technological settingslike ad-hoc networking. Howard Rheingold, who introducedin the beginning of the 90s thevirtual community, reflectsin his latest book [16] about the cooperational forces thatmobile phones –smart mobs, as he calls them – providefor modern societies. Beyond some more utopian visionsabout wearable computers in clothes and a world of thingsthat offers information about itself (the chocolate bar tellingyou its amount of calories aloud), Rheingold outlines thepossibilities for modern societies to enhance social integrationand solidarity with technological means.

Social integration, or more specific, some trust in the oper-ators is necessary for the proposed cooperative services. Thecustomer should be informed about the technical possibilitiesand services that enhance the use of his device. Transparencyof the technology that is not directly visible on the level ofthe user interface is not only important to give customers thechance for creating their own use pattern and for active groupbuilding, but also for ensuring the value of security and trust.Data security is a sensitive feature in all networks withinthe fields of communications technology. Operators have toensure that no unwanted data transfer arises with the proposedservices.

VI. CONCLUSIONS

In this paper we have highlighted the need of cellular con-trolled short range communication for 4G wireless networks.As traditional service provision in a peer to peer fashion willresult in unacceptable costs for the customers, the cooperationof terminal groups seems to be a feasible way out of thistechnology trap. Besides the technological challenges, thiswill also have an impact on the social behavior of customersgrouping for better services reception.

VII. A CKNOWLEDGEMENTS

This work has been supported by Samsung Electronics, Co.,LTD, Korea.

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