WIRELESS COMMUNICATIONS AND MOBILE COMPUTING Wirel. Commun. Mob. Comput. 2006; 6:889–892 Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/wcm.449 Editorial Wireless ad hoc networks: technologies and challenges by Mohamed Younis and Sebnem Zorlu Ozer Ad hoc networking of wireless devices allows estab- lishing communication links among participating nodes without the existence of a pre-arranged infra- structure. The recent few years have witnessed a growing interest in wireless ad hoc networks (WAHNs), motivated by a number of civil and mili- tary applications and by the continual advancement in wireless technologies. Digital battlefield, disaster management, luggage handling in airports, context aware computing and mobile commerce are examples of a growing list of potential applications of WAHNs. The unique characteristics of such applications have made the design and management of WAHNs signifi- cantly challenging in comparison to contemporary networks and have motivated active investigation and innovation from the research community. In most WAHN setups, nodes are usually con- strained in energy, communication and computation capacities. In addition, many of the WAHN applica- tions may employ a large set of nodes with a diverse set of capabilities and a dynamically changing net- work membership. Moreover, the operation in WAHNs is inherently collaborative and lacks a central management authority. For example, nodes autono- mously form the network, cooperate in managing the network’s topology, collectively perform tasks and share responsibilities for meeting functional and de- pendability goals. Therefore, distributed or hierarch- ical schemes are usually employed. This applies to node discovery protocols, arbitration of the commu- nication medium, setup of data path, management of encryption keys, management of node membership and participation in network operation, recovery from node failure etc. This special issue of Wireless Communications and Mobile Computing reports on recent research results on tackling the design challenges of WAHNs. The selected papers present novel and non-conventional techniques more suited to WAHNs. Among the nu- merous strong submissions we chose papers that address important design issues and report solid research results. In addition, we tried to provide coverage of various layers of the protocol stack and address different quality of service attributes. The papers are ordered according to the layer of the communication stack that they study. In the first paper, Sundaresan and Sivakumar inves- tigate the theoretical benefits of wireless multihop networks where nodes have different antenna technol- ogies, that is omnidirectional, directional, adaptive array and digital adaptive array antennas. Different link combinations are studied for Line of Sight (LOS) and no LOS (NLOS) environments with all randomly located nodes as well as with some nodes deployed in a controlled way that can provide better gains. The performance bounds are then derived through analysis and simulation in order to help the network designer in identifying an optimal percentage of the smart anten- nas in a network to achieve a certain performance level. The authors also propose and simulate MAC and routing algorithms to fully exploit the capabilities of heterogeneous wireless antenna networks. The pro- posed heterogeneous smart antenna-based medium access control (HSMA) protocol exchanges informa- tion regarding the link layer capabilities and adopts a contention resolution based on weighted proportional fairness constraints. In addition, the paper addresses the issue of increasing spatial reuse without causing a severe directional deafness problem which occurs when a node is unable to communicate with another node that is beamforming in a different direction. A reactive heterogeneous smart antenna-based routing (HSR) algorithm is proposed to exploit links with large gains. Although directional antennas increase the net- work capacity in CSMA/CA-based networks, two Copyright # 2006 John Wiley & Sons, Ltd.