Over the past few years we have witnessed the pro-liferation of hi-tech mobile devices such as laptops,palm tops, mobile phones, pagers, etc. The need foreasy and spontaneous communications between suchdevices led to the development of a new class of wire-less mobile networks, with no fixed infrastructure orcontrol hub. These self-organizing networks, known as“ad hoc networks,” have recently attracted the attentionof researchers and industry, since they can be used insituations where either there is no wired or wireless in-frastructure present or, if present, it cannot be used be-cause of security, cost, or safety reasons (for example,earthquake disaster recovery, collaborative computingin the airports, etc.). These configurations will be part ofsystems beyond third generation, where different accessschemes will be integrated in a cooperative manner onan IP-based platform.

Ad hoc networks present challenging design prob-lems. However, they are becoming absolutely necessary,a natural byproduct of a society “in motion,” to ensurean end-to-end, high-quality provision of services what-ever the global fixed infrastructure (UMTS, IP). Rulesfor the interconnection of all these islands through a uni-fied infrastructure must be clearly formulated. The bridg-ing of these wireless LANs is mainly realized todaythrough ALL-IP infrastructure. Various schemes havebeen proposed for the design and evaluation of stand-alone ad hoc configurations and for Internet connectivity,with solutions ranging from wireless LAN extensions toBluetooth. Worldwide standardization activities havebeen underway and recommendations for several of thewireless protocols are already in place.

Two of the first widespread WLAN standards thatsupported ad hoc networking are IEEE’s 802.11 andETSI’s HIPERLAN. The version IEEE 802.11b, a re-vised 802.11 standard that offers greater speeds, cur-rently holds the greatest share in the WLAN market.However, the much-publicized 802.11a and HIPER-LAN/2 are about to alter the present balance. IEEE802.11a is based on the same paradigm as its predeces-sor (IEEE 802.11b), but offers greater speeds. HIPER-LAN/2 is a major departure/improvement over the orig-inal HIPERLAN. Specifically, besides the higher speed,

HIPERLAN/2 offers inherent QoS support and better in-tegration to infrastructure networks such as Ethernet,ATM, IP, and UMTS. On the other hand, multihop adhoc networking is no longer supported. Targeted at acompletely different market niche, Bluetooth devicesprovide the means for one’s personal devices to inter-connect into a PAN (personal area network). It’s worthmentioning that while IEEE 802.11b and Bluetooth areallocated in the ISM band, where uncontrollable coexis-tence issues with other systems may arise, IEEE 802.11aand HIPERLAN/2 use dedicated frequency bands in the5 GHz range and thus can provide services of control-lable quality.

Although much of the interest in this technology sofar has been from the military, the recent establishmentof the Internet Engineering Task Force (IETF), MobileAd Hoc Networks (MANET) Working group is a clearindication that many in this field envision that this tech-nology has commercial promise. The IETF society hasalso launched a dialog page to collect comments andproposals from the international society on this issue [1].In the United States, the MONARCH project is evaluat-ing a testbed implementation and is making tools and re-sults available to the public via the Internet [2]. Like-wise, in European Union IST research circles a WLANinterest group debates topics relevant to self-organizingnetworks [3]

New wireless gadgets are appearing daily on themarket. Almost every manufacturing company tries tocapture a share in this new networking environment. Forexample, in the wireless LAN card market we have: theLucent ORiNOCO PC Card, Nokia’s C110/C111 Wire-less LAN Card, Compaq’s WL110 Wireless PC Card,Intel’s PRO/Wireless 2011B LAN PC Card, Proxim,Inc.’s Harmony 802.11 PC card, etc. [4].

Academic research has also been extremely activein this field, as reflected by the numerous sessions dedi-cated to the topic at major international conferences(ACM/IEEE MobiHoc, Mobicom, IEEE Globecom,etc.). The number of special issues of scientific journalson this topic has literally mushroomed over the last cou-ple of years, for example, IEEE Trans on Selected Areasin Communications, IEEE Personal Communications

Guest Editorial: Ad Hoc Networking

International Journal of Wireless Information Networks, Vol. 9, No. 2, April 2002 (© 2002)

711068-9605/02/0400-0071/0 © 2002 Plenum Publishing Corporation

Magazine, International Journal on Wireless Informa-tion Networks,etc.

The basic concept of ad hoc networking finds itsorigins in the DARPA packet radio network project inthe early 1970’s. Since then, research has expanded intonew areas and covers issues not addressed before, for ex-ample, multimedia services, QoS, network-layer multi-casting, and seamless interfacing of the ad hoc nets to theInternet. Examples of ad hoc networking topics undercurrent investigation are the following:

• Identification of WLAN requirementsand needsstemming from current business scenarios. Devel-opment of business modelsfor the establishmentof ad hoc networks and investigation of the addedvalue for the involved parties.

• Ad hoc network protocolsspanning several layersand including clustering architectures (traffic/mo-bility models) for energy conservation issues,ef-ficient routing techniquesfor the support of QoSoperation of multihop self-organizing networks,global navigation and location information dis-semination—multicasting over the IP gateway,routing functions for terrestrial and satellite net-works.

• End-to-end performance evaluation;physicallayer impact on end-to-end performance.

• Dynamically distributed allocation of IP ad-dresses (IPv6)and selection of appropriate accesstechniquesfor the stand-alone ad hoc configura-tion or for linking to the Internet.

• Management and security issuesfor connectingthe stand-alone ad hoc network to the IP infra-structure.

• Cross-Layer interactionis also a very activetopic. Traditionally, layering has been used tominimize interaction and simplify the design ofdifferent protocols. However, in the context ofcomplex wireless configurations it appears thatmuch is to be gained by increasing this interde-pendency and allowing cross-layer adaptivity, forexample.

The five papers of this special issue, selected amongmany several meritorious contributions, do cover someof the research areas above and in fact also open newones. A brief synopsis of the papers follows.

In the first paper Sun et al. present a method for en-abling the cooperation of Mobile IP and the Ad Hoc On-Demand Distance Vector (AODV) routing protocol,such that mobile nodes that are not within direct trans-mission range of a foreign agent can still obtain Internet

connectivity. In addition, they describe how duplicateaddress detection can be used in these networks to obtaina unique co-located care-of address when a foreign agentis not available.

The work of Johansson et al. compares the PANcapabilities of a Bluetooth-based system with an IEEE802.11b based system. Results are obtained by means ofsimulations in which throughput and delay are measuredfor multihop and overlaid PANs. The results indicate thatas the number of PANs increases, the Bluetooth-basedPANs basically maintain the same bandwidth per PAN,while the corresponding IEEE 802.11-based PANs suffersignificantly from the increased co-channel interference.

In the third paper, Wang et al. present severalenergy-efficient routing algorithms using directionalantennas for wireless ad hoc networks. These algo-rithms are simple to implement, completely distrib-uted, and can be applied to mobile environments. Theyevaluate how directional antennas improve systemthroughput. They study the influence of the battery re-covery effect and mobility on the network throughputduring a network lifetime. They also present an algo-rithm that exploits the broadcast nature of the wirelesscommunication environment to improve end-to-end biterror performance for a Rayleigh fading channel.

In the fourth paper, Habetha and Walke study themobility management in a cluster-based multihop ad hocnetwork. It is shown that the process of clustering thenetwork into groups of stations has similarities with dataanalysis—in particular, pattern recognition. In dataanalysis the term clusteringdesignates the process of un-supervised learning, which also describes the situation ina mobile ad hoc network. In this paper existing data-clus-tering algorithms are first classified into different cate-gories. Some of the most important types of algorithmsare described, and their applicability to the problem ofthe mobility management in an ad hoc network is stud-ied. The authors have developed a new clusteringscheme that incorporates some of the ideas of the dataclassification schemes. The new clustering scheme isbased on a rule-based fuzzy inference engine.

In the last paper, the authors assess, by means of asimulation approach which takes the complete physicaland MAC level aspects into account, the performance ofa Bluetooth-based WLAN adopting a Token Ring MACprotocol under realistic channel conditions, that is, in thepresence of the typical impairments of indoor wirelesscommunications (fading, etc.). Moreover, they proposean analytical formulation to derive the maximumthroughput offered by a Bluetooth link. Based on such aformulation, they suggest a novel call admission controltechnique.

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We believe that the collection of papers in this spe-cial issue provides a cross section of some of the mostinteresting research topics in the field. As is always thecase, because of scarcity of space we were not able to in-clude all the meritorious papers submitted. We wouldlike to express our gratitude to all the authors who sub-mitted their papers to this Special Issue and wish themsuccess in the continuation of their research.

Guest Editors

Fotini-Niovi PavlidouAristotle UniversityDept. of Electrical and Computer EngineeringThessaloniki 54006, Greece

Mario GerlaUniversity of CaliforniaDepartment of Computer ScienceLos Angeles, CA 90024, USA

Werner MohrSiemens AG, ICM N,Hofmannstrasse 51,D-81359 Munich, Germany

REFERENCES

1. manet@itd.nrl.navy.mil2. http://www.ietf.org/html.charters/manet-charter.html)3. http://www.cordis.lu/ist/ka4/mobile/intex.htm4. http://www.wi-fi.org/certified_products.asp

and Wired Communications.” She has served as member of the TPCof many conferences (in some being the TPC chair) supported byIEEE/IEE. She is a permanent reviewer for many international jour-nals and has published about 60 studies in refereed journals and con-ferences. She is a Senior Member of IEEE and is currently chairingthe joint IEEE VT&AES chapter in Greece.

Guest Editorial 73

Fotini-Niovi Pavlidou received the Ph.D. degree in electricalengineering from the Aristotle University of Thessaloniki, Greece, in1988 and the Diploma in Mechanical-Electrical Engineering in 1979from the same Institution. She is currently an Associate Professor inthe Department of Electrical and Computer Engineering at the Aris-totle University. Her research interests are in the areas of mobile andpersonal communications, satellite communications, multiple accesssystems, and routing and traffic flow in networks. She is involvedwith many national and international projects in these areas (IST,Telematics, Tempus, COST,) and is chair of the European COST262Action on “Spread Spectrum Systems and Techniques for Wireless

Mario Gerla received the graduate degree in electrical engi-neering from Politecnico di Milano, Italy, in 1966 and the M.S. andPh.D. degrees in computer science from the University of California,Los Angeles (UCLA) in 1970 and 1973, respectively. From 1973 to1976, he was a manager at the Network Analysis Corporation, GlenCove, NY, where he was involved in several computer network designprojects for both government and industry, including performanceanalysis and topological updating of the ARPANET under a contractfrom the Department of Defense. From 1976 to 1977, he was with TranTelecommunication, Los Angeles, CA, where he participated in the de-velopment of an integrated packet and circuit network. Since 1977, hehas been on the faculty of the Department of Computer Science,UCLA. His research interests include the design, performance evalua-tion, and control of distributed computer communication systems andnetworks. His current research projects cover the following areas:topology design and bandwidth allocation in ATM networks, designand implementation of optical interconnects for supercomputer appli-cations, design and performance evaluation of air/ground wireless com-munications for the Areonautical Telecommunications Network, andnetwork protocol design and implementation for a mobile, integratedservices wireless radio network.

Werner Mohr was graduated from the University of Hannover,Germany, with the Master Degree in electrical engineering in 1981 andwith the Ph.D. degree in 1987. From 1987 to 1990 he has been senior

engineer at the Institute of High-Frequency Technology at the Univer-sity of Hannover.

Dr. Mohr has been with Siemens AG, Mobile Network Di-vision, in Munich, Germany since 1991. He has been responsiblefor propagation measurements and channel modeling and has beeninvolved in the European RACE-II Project ATDMA. From 1995to 1996 he was active in ETSI SMG5 for standardization ofUMTS. Since December 1996 he was project manager of theACTS FRAMES Project up to the time the project finished in Au-

74 Guest Editorial

gust 1999. Dr. Mohr was Director of Strategic Pre-Developmentup to September 1998 and since October 1, 1998 he has been VicePresident Pre-Engineering in the infrastructure division ofSiemens ICM. He is responsible for cross-functional research ac-tivities. Currently, he is involved in the 5th framework program ofthe European Commission. Dr. Mohr is chair of the “WirelessWorld Research Forum—WWRF”. He is a member of VDE and aSenior Member of IEEE. In 1990 he received the ITG award inVDE.