In this paper we explore the principle of heterogeneous wireless networking and discuss the potential avenues towards the realization of the ubiquitous wireless communications. Specifically, we demonstrate that the heterogeneous network architecture, constituted by the fusion of the classic cellular and the ad hoc network topologies, inherits the vital complementary characteristics of both architectures, and thus has the potential of attaining the levels of performance and efficiency required by the future wireless communications

Akhtman, Jos

Hanzo, Lajos

English

Southampton (e-Prints Soton)

P O I N TO FV I E WHeterogeneous Networking:An Enabling Paradigm forUbiquitous WirelessCommunicationsBy JOS AKHTMANLAJOS HANZOSchool of ECSUniversity of Southampton, SO17 1BJ Southampton, U.K.It is a widely accepted notion that the long-term aim of the technologicalprogress in the field of wireless communications is constituted by theprovision of ubiquitous connectivity between individuals, as well as amultiplicity of existing and future pervasive devices which increasinglypermeate our environment.In this context the currently dominant cellular (a combination of metro-politan, local, and personal area networksVMANs, LANs, and PANs, respec-tively), as well as the emerging mobile ad hoc network (MANET) architecturesconstitute the two major contenders for the role of systemic paradigm, whichwould facilitate the realization of ubiquitous wireless networking. Thecorresponding literature offers an extensive body of theoretical as well asexperimental work [1]–[3] advocating the potential advantages of either of thetwo aforementioned approaches.Against this background, wewould like to maintain that in orderto achieve the required level of inte-gration, performance and efficiency,the future telecommunications tech-nology may have to infer cues fromthe structural characteristics of thehuman society itself. Correspond-ingly, in this paper we would like toconsider some of the relevant aspectsof the societal constitution, whichmay hold crucial clues to identifyingthe promising avenues towards fur-ther technological advancement.More specifically, in this paper weexploretheprincipleofheterogeneouswireless networking, constituted bythefusionofclassiccellularandadhocnetwork topologies. Specifically, wewould like to maintain, that the hete-rogeneous network inherits the vitalcomplementary characteristics ofboth aforementioned architectures,and thus has the potential of attainingthe levels of performance and effi-ciency required by the future wirelesscommunications.II. UBIQUITOUSWIRELESS NETWORKSA. The Heterogeneous Nature ofSocial OrganizationWe would like to identify twomajor complimentary ingredients in Digital Object Identifier: 10.1109/JPROC.2009.2037213Vol. 98, No. 2, February 2010 | Proceedings of the IEEE 135 0018-9219/$26.00 2010 IEEEAuthorized licensed use limited to: UNIVERSITY OF SOUTHAMPTON. Downloaded on February 1, 2010 at 13:22 from IEEE Xplore.  Restrictions apply. the composition of the modern soci-ety. On the one hand, the societalstructure is constituted by multiplelayers of large-scale infrastructure,which may be associated with thevarious facets of the human activities.Such infrastructure layers include, forexample, the transportation networkscomposed of multiple subnetworks,including land, sea, and air transpor-tation systems. Other examples ofsocietal infrastructure include theeducational system, healthcare sys-tem, legislative and jurisdictionalsystems, banking system, etc. Wemay safely establish that the foremostmerits of such systems lie in theirrobustness, reliability, and predict-ability. The deployment of suchsystems typically involves a top-downdesign methodology, systematic plan-ning, as well as a strictly hierarchicalapproach to their management andmaintenance. Ultimately, these sys-tems are typically governed by a set ofwell established and explicitly formu-lated rules.On the other hand, the humans o c i e t yi sa n i m a t e db yt h el a y e ro fpersonal ad hoc interactions amongindividuals. The nature of such inter-actions is decidedly different, andoften opposed to that, pertaining tothe interactions occurring within theinfrastructure layers. Specifically, theindividuals are capable of establishingtemporal ad hoc links with each other,depending on the specific context oftheir daily activities. Furthermore, incontrast to the infrastructure-boundinteractions, the interpersonal interac-tions rely on an implicit code of in-formal rules and behavioral practices.1In order to further emphasize thedistinctive, yet complementary rolesof the two aforementioned constitu-ents of the social organization, wew o u l dl i k et oi n v o k et h et e r m i n o l o g ydevised in [4], where we discuss theinherent dichotomy between the no-tions of system’s efficiency and itsefficacy. Specifically, in [4], we defineefficiency as the ratio between thequantities describing the desired andthe total outputs of some productivesystem. Subsequently, we define effi-cacy as the ratio between the attainedamount of the desired output andsome nominal amount, which thesystem considered was conceived toattain.For example, a conventional in-candescent light bulb is highly ineffi-cient, since most (about 90%) of itsoutput is constituted by heat, ratherthan the desirable product in the formof visible light. On the other hand, theconventional incandescent light bulbmay be categorized as highly effective,s i n c et h eo b j e c t i v eo fp r o v i d i n ga nadequate illumination using this devicemay be readily realized. In contrast, alight-emitting diode (LED) based light-ing system may exhibit a remarkablyhigh efficiency at low power levels,whereitsrelativeefficacyisinadequatelylow for most mainstream lightingapplications [5].For the sake of this discussion,therefore, we would like to conjec-ture that while the large-scale infra-structure layers of the social structurem a yb ed i r e c t l ya s s o c i a t e dw i t hi t sefficacy, it is the diversity, adaptabil-ity and the inherent flexibility of thead hoc personal interactions thatmake human society efficient.F u r -thermore, the intricate interplay be-tween these two constituents of thesocietal organization, and the ensuingbalance between society’s efficacyand its efficiency,d e t e r m i n e st h ea p -parent stability and the relative pros-perity of a developed contemporarysociety [6].Likewise, some of the major pro-blems, which our society is currentlyfacing, including the unsustainableexploitation of the natural resourcesmay be ultimately traces to our preoc-cupation with the collective and per-sonal efficacy, and the associatedexcessive reliance on the society’sinfrastructure, at the expense of theefficiency of our actions.In the following sections, wewould like to translate our observa-tions concerning the structural com-position of the human society into therealm of wireless communicationnetworks.B. Cellular Versus Ad HocL e tu sc o n s i d e rt h et w om a j o rnetworking paradigms, namely thecellular and the ad hoc networkarchitectures schematically portrayedin Fig. 1(a) and (b). Specifically, thecellular network architecture ofFig. 1(a) is characteristic of thecurrently prevalent multioperatorwireless communication networks[7]. The cellular topology exhibits astrictly hierarchical structure, wherethe single master node shown at thetop of Fig. 1(a) corresponds to thecentral authority, such as the FederalCommission of Communications(FCC) in the United States, or Ofcomin the U.K., which owns and regulatest h eu s a g eo ft h ee n a b l i n gr e s o u r c econstituted by the frequency spec-trum. The executive power within themultioperator cellular network is dis-tributed across multiple mutuallycompetitive commercial entities, typ-ically referred to as service providers,or wireless carriers, as indicated bythe distinctive branches in the net-work hierarchy of Fig. 1(a). Theseservice providers install, own, andoperate a proprietary infrastructure,which utilizes the allocated spectrumin order to generate value for thesubscribers and to maximize thecorresponding monetary revenue forthemselves.Relatively small fragments of thefrequency spectrum are licensed inthis context for the exclusive use by aspecific network operator. Impor-tantly, two subscribers of the sameoperator are not authorized to directlyutilize the spectrum without invokingthe operator’s infrastructure. In thecontext of the network topology ofFig. 1(a), this implies that no horizon-tal node-to-node interactions betweenthe bottom-level user nodes are possi-ble. In other words, no peer-to-peercooperation between the network1The social behavioral practices should notbe confused with the civil or criminal law,which is a set of explicit rules employed byjurisdictional system in order to resolve con-flicts whenever a satisfactory resolution may notbe achieved by the individuals themselves.Point of View136 Proceedings of the IEEE |V o l .9 8 ,N o .2 ,F eb r u a r y2 0 1 0Authorized licensed use limited to: UNIVERSITY OF SOUTHAMPTON. Downloaded on February 1, 2010 at 13:22 from IEEE Xplore.  Restrictions apply. subscribers is allowed. The resultantinfrastructure-based network archi-tecture exhibits the highly advanta-geous properties of centralized control,dependability and scalability.On the other hand, the MANETarchitecture schematically depictedin Fig. 1(b) potentially offers adramatically higher power efficiency,which is facilitated by the structuralflexibility and the ability to leverageshort-range ultra-low-power commu-nication links. The utilization of thead hoc networking has been success-fully demonstrated by, for example,the One Laptop Per Child (OLPC)project (laptop.org), which utilizesthe technology based on the IEEE802.11s standard [8].Importantly, a wireless ad hocnetwork relies on peer-to-peer coop-eration, where the mobile terminalsutilize peer terminals as relays inorder to gain access to the network’sinfrastructure. Clearly, the necessityof peer-to-peer cooperation suggests asuitable open access approach to spec-trum management [7], where a sub-stantial portion of the frequencyspectrum is made available to thenetwork’s end users, as opposed to thenetwork operators in the case of com-mercial cellular networks. Accord-ingly, the sharing of the resources, aswellasthe diverseconditionstypicallyencountered in wireless channelsimply a substantial level of control,including elements of resource man-agement,tobedelegatedtothemobileterminals. The resultant distributedcontrol and resource management ca-pabilities of the mobile terminals maybe intricately related to the concept ofcognitive radio [9].Subsequently, we would like tohypothesize that the heterogeneousnetwork constituted by the fusion ofthese two networking models mayinherent the advantageous propertiesof both architectures. The resultantheterogeneous radio access network(HRAN) is depicted in Fig. 1(c). Spe-cifically, the main role of thelarge-scale cellular infrastructure de-n o t e db yl a r g ec i r c l e si nF i g .1 ( c )i st oassure dependability, availability, andgenerally the efficacy of the network,while the complimentary layer ofad hoc connections may facilitate thedesirable flexibility and the associatedefficiency.I nt h en e x ts e c t i o n ,w ewould like to detail some of the dis-tinctive properties of the proposedheterogeneous networking paradigm.C. Heterogeneous RadioAccess NetworkFollowing the principles of het-erogeneous networking, a mobileterminal may choose among multipleavailable connectivity alternative, in-cluding infrastructure-based, as wellas cooperative multihop ad hoc links,based on the criteria of cost-efficiency[10] and suitability for the particularapplication scenario, while pursuingthe objective of dramatically improv-ing the cost- and energy-efficiency ofthe entire network. Specifically, wewould like to emphasize some of theimportant properties of the resultantHRAN of Fig. 1(c), which exhibits thecomplementary characteristics of theconstituent WLAN and MANET net-work layers.Topology: The HRAN architec-ture considered exhibits the structuralproperties of a scale-free network [6],[11]. In addition to the aforemen-tioned example of contemporary hu-man society, another prominentexample of such scale-free network isconstituted by the World Wide Web(WWW). Specifically, the WWW con-stitutes a virtual ad hoc network ofinterconnected multimedia docu-m e n t s ,w h i l er e l y i n go nt h ep h y s i c a linfrastructure formed by the globalInternet [11], which is comprised bya multiplicity of interconnectedinfrastructure-based networks of var-ious sizes, topologies and purposes.Scalability: Importantly, as op-posed to the infrastructureless ad hocnetwork discussed in [12], the hetero-geneous network architecture ofFig. 1(b) contains a relatively smallnumberofadhocnodespersinglenodeof the infrastructure, thus facilitatingthe seamless scalability of the cellulararchitecture,andavoidingtheper-nodecapacity degradation of the ad hocarchitecture potentially inflicted byexcessive relaying, as formulated bythe Gupta–Kumar law [12].Adaptability: As opposed to thecellular architecture of Fig. 1(a), theheterogeneous network of Fig. 1(b)exhibits the desirable properties ofadaptability and self-organization,where the average range of theFig. 1. Network architecture. (a) Cellular: scalable and highly dependable architecturedesigned to maximize efficacy. (b) Ad hoc: flexible, self-organizing architecture designed formaximum efficiency. (c) Heterogeneous: a fusion of cellular and ad hoc architectures,which inherits the advantages of both topologies, and thus attains the desired trade-offbetween efficacy and efficiency.Point of ViewVol. 98, No. 2, February 2010 | Proceedings of the IEEE 137Authorized licensed use limited to: UNIVERSITY OF SOUTHAMPTON. Downloaded on February 1, 2010 at 13:22 from IEEE Xplore.  Restrictions apply. communication links and their re-spective power efficiency is deter-mined by the density of the networkusers. Observe that in an adequatelydesigned HRAN, which employs anappropriate method of power control,spectrum sensing, and frequency re-use, the amount of the frequencyspectrum required is independent ofthe number of end users.Spectrum Management:T h er e -sultant heterogeneous networkingmodel is likely to require a combina-tion of licensed and unlicensed spec-trum access models reminiscent tothat existing today [7]. We would liketo hypothesize, however, that incontrast to the currently prevailingspectrum management policy, a sub-stantial increase in the amount ofspectrum allocated for the unlicensedaccess will be required in order tofacilitate an interference-free layer ofbroadband ad hoc connectivity.REFERENCES[1] K. Ozan and G. Ferrari, Ad Hoc WirelessNetworks: A Communication-TheoreticPerspective. New York: Wiley, 2006.[ 2 ]L .H a n z o ,J .B l o g h ,a n dS .N i ,3G, HSDPA,HSUPA and FDD Versus TDD Networking:Smart Antennas and Adaptive Modulation.New York: IEEE Press-Wiley, 2008.[ 3 ] J .A n d r e w s ,S .S h a k k o t t a i ,R .H e a t h ,N .J i n d a l ,M .H a e n g g i ,R .B e r r y ,D .G u o ,M. Neely, S. Weber, S. Jafar, and A. Yener,BRethinking information theory formobile ad hoc networks,’’ IEEE Commun.Mag., vol. 46, no. 12, pp. 94–101, Dec. 2008.[4] J. Akhtman and L. Hanzo, BEfficiency versusefficacy of wireless communicationsnetworks,’’ IEEE Commun. Mag.,2010.[5] R. Stevenson, BThe LED’s dark secret,’’IEEE Spectrum,v o l .4 6 ,n o .8 ,p p .2 6 – 3 1 ,Aug. 2009.[6] D. MacKenzie, BWhy the demise ofcivilization may be inevitable,’’ NewScientist, pp. 29–35, Apr. 2008.[7] G. Gow and R. Smith, Mobile andWireless Communications: An Introduction.New York: Open University Press/McGraw-Hill, 2005.[8] Draft Standard forInformation-Telecommunicationsand Information Exhange BetweenSystemsVLocal and Metropolitan AreaNetworksVPart 11: Wireless LAN MAC andPHY Specifications Amendment 10: MeshNetworking, IEEE Std., Mar. 2009.[9] K. Werbach. (2010, Feb.)Telecommunications: Network strategiesfor network industries? Social Sci. Res.Netw. [Online]. Available: http://ssrn.com/abstract=11000685[ 1 0 ] S .B a l u j a ,M .C h u ,a n dM .M a t s u n o ,‘‘Flexible Communication Systems andMethods,’’ Sep. 2008, Patent applicationno. A1,20080232574, filled by Google Inc.[11] A.-L. Baraba ´si and E. Bonabeau, BScale-freenetworks,’’ Sci. Amer.,v o l .2 8 8 ,n o .2 8 8 ,pp. 60–69, May 2003.[12] P. Gupta and P. Kumar, BThe capacity ofwireless networks,’’ IEEE Trans. Inf. Theory,vol. 46, no. 2, pp. 388–404, Mar. 2000.Point of View138 Proceedings of the IEEE |V o l .9 8 ,N o .2 ,F eb r u a r y2 0 1 0Authorized licensed use limited to: UNIVERSITY OF SOUTHAMPTON. Downloaded on February 1, 2010 at 13:22 from IEEE Xplore.  Restrictions apply. 

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Telecommunications: Network strategies for network industries?

Heterogeneous Networking: An Enabling Paradigm for Ubiquitous Wireless Communications

Heterogeneous Networking: An Enabling Paradigm for Ubiquitous Wireless Communications

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