Abstract:

Wireless communications has assumed its unique importance in the past decade, firstly in the form of cellular networks and of recent, due to computer networks (WiFi, WiMAX). The next decade is likely to witness dramatic developments due to increase in system bandwidth and efficiency improvements of autonomous devices and sensors. In order to apprise our readers of new possibilities, we decided to bring out a special issue of International Journal of Performability Engineering (IJPE) on a topical theme of wireless communication systems and related issues of performance of such systems and which may be useful and of interest to the scientific/engineering community and researchers in years to come. This is a special issue on Dependability of Wireless Systems and Networks and the Guest Editors of this special issue are two well-known researchers in the field who happen to be from our editorial board.

Basically, wireless communication facilitates the transfer of information between two or more points that are not physically connected. Distance between the points can range from a few meters as in television remote control to millions of kilometers as in case of deep-space radio communications. It encompasses various types of fixed, mobile, and portable two-way radios, cellular telephones, bluetooth, personal digital assistants (PDAs), satellite TV or radios, and wireless networking. Wireless systems permit operations (e.g., information transfer or control) that are impossible or impractical to implement with the use of wires by using radio frequency (RF), microwave, infrared or acoustic energy, etc. Wireless communication has revolutionized the entire field of communication and system controls and is pervasive in numerous engineering applications.

A wireless ad-hoc network is a decentralized type of wireless networks that does not rely on a preexisting infrastructure, such as routers in wired networks or access points in managed wireless networks. Each node participates in routing by forwarding data for other nodes, and the determination of which nodes to forward data is made dynamically based on the network connectivity. The presence of dynamic and adaptive routing protocols enables ad-hoc networks to be formed quickly. Such feature makes ad hoc networks suitable for emergency situations like natural disasters or military conflicts.

Wireless ad hoc networks can be further classified by their applications:

• mobile ad-hoc networks (MANET)
• wireless mesh networks (WMN)
• wireless sensor networks (WSN)

A mobile ad-hoc network (MANET) is a self-configuring infrastructureless network of mobile devices connected by wireless links. Ad-hoc is Latin which means "for this purpose". The growth of laptops and 802.11/Wi-Fi wireless networking has made MANETs a popular research topic since the mid 1990s. Many academic papers evaluate protocols and their abilities, assuming varying degrees of mobility within a bounded space, usually with all nodes within a few hops of each other. Different protocols are then evaluated based on measure such as the packet drop rate, the overhead introduced by the routing protocol, end-to-end packet delays, network throughput etc. There are several types of MANETs such as:

• Vehicular Ad-hoc Networks (VANETs) are used for communication among vehicles and between vehicles and roadside equipment. A VANET is a technology that uses moving cars as nodes in a network to create a mobile network.
• Intelligent Vehicular Ad-hoc Networks (InVANETs) use WiFi IEEE 802.11p (WAVE standard) and WiMAX IEEE 802.16 for easy and effective communication between vehicles with dynamic mobility. This technology helps vehicles behave in an intelligent manner during vehicle-to-vehicle collisions, accidents, drunken driving etc.
• Internet Based Mobile Ad-hoc Networks (iMANET) are ad-hoc networks that link mobile nodes and fixed Internet-gateway nodes. In such type of networks normal ad hoc routing algorithms do not apply directly.

A wireless mesh network (WMN) is a communications network made up of radio nodes organized in a mesh topology. Wireless mesh networks often consist of mesh clients, mesh routers and gateways. The mesh clients are often laptops, cell phones and other wireless devices while the mesh routers forward traffic to and from the gateways which may but need not connect to the Internet.

A wireless sensor network (WSN) consists of spatially-distributed autonomous sensors to monitor physical or environmental conditions, such as temperature, sound, vibration, pressure, motion or pollutants and to cooperatively pass their data through the network to a main location. The development of WSN was initially motivated by applications such as military surveillance. Later on they have found a variety of application scenarios, including healthcare agriculture, environmental monitoring, air quality/pollution monitoring, construction structural monitoring, railway monitoring, water quality monitoring, home security, manufacturing automation, and so on.

The next-generation mobile networks will consist of heterogeneous access networks ranging from cellular 3G/4G, WiFi (IEEE 802.11), WiMAX (IEEE 802.16), to mesh and ad-hoc networks. The key design objective for future mobile networks will be to enhance efficiency and ease of use, meaning that the future mobile networks must be able to enable users’ communication devices to adopt and adapt automatically, dynamically, seamless and efficiently to various access networks for services available at a given time. The main requirement for such adaptation is to ensure quality of service (QoS) in terms of data throughput, end-to-end delay, and packet error rate that is needed for supporting users’ applications despite the use of the heterogeneous access technologies.

Designing reliable and secure networks is going to be one of the most important challenges for the network designers in the coming decade. The security has always been a major concern for netwok designers. The increase in cyber crimes, spamming, denial of service (DoS)/distributed DoS attacks, deauthentication attacks etc. has generated challenges that need to be met squarely in near future. The operating condition of a network will play a key role in assessing its vulnerability to attack. This requires a thorough understanding of the type of incidences that can adversely affect wireless networks. These incidences may be related to link/node outages and resilience issues. One area related to improving resilience in wireless networks is the need to investigate physical layer potection. For example, through intelligent design of the radio interface and network topology, it may be possible to implement real-time protection against network outages and malicious incursions. There is another aspect to security: instead of securing networks against all types of attacks at all times, it may be prudent to accept that parts of network have different levels of threats at different times. An intrusion tolerant network may be the alternative, which will permit different level service and security in different parts in order to maintain the overall operationof the network during an attack. The design of encryption systems especially for MANETs with emphasis on trade-offs between power, complexity and efficiency will also be important for the next genertion of wireless networks.These are just a few areas to mention, where future challenges in wireless communication lie.

Looking to the current trends and developments in wireless systems and networks, this special issue of IJPE on the dependability aspect of wireless systems and networks would provide the necessary impetus to the on-going research and to generate interest in the issues related to wireless communication in general.