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.

Wireless communication technologies are dramatically changing the way in which the world conducts its day to day business. People's daily life is also becoming more and more dependent on wireless and mobile services. On the other hand, critical dependability risks and challenges arise for wireless systems and networks because data that is sent over wireless environments could easily get corrupted and/or compromised due to factors such as channel and user interferences, noises, and malicious attacks. This special issue presents current research and application focusing on reliability, performability, fault-tolerance, and security aspects of wireless systems and networks.

This issue starts with an invited paper, On the Reliability of Safety Applications in VANETs, by Ma, Yin, and Trivedi, which presents an overview of reliability issues in vehicular ad-hoc networks (VANETs) for safety-related applications and recent development of analytic models for the evaluation of reliability metrics for safety applications in VANETs.

The second paper, Computing Performability for Wireless Sensor Networks, by Herrmann, Soh, Rai, and ?korjanc, proposes a method based on Augmented Ordered Multivariate Decision Diagram (OMDD-A) to evaluate the performability metrics including reliability, expected hop count, and expected message delay for wireless sensor networks with both device and link failures.

The third paper, Infrastructure Communication Reliability of Wireless Sensor Networks Considering Common-Cause Failures, by Shrestha, Xing, Sun, and Vokkarane, illustrates a combinatorial approach for evaluating the infrastructure communication reliability of wireless sensor networks (WSN) subject to non-fatal common-cause failures under three different data delivery models: sink unicast, sink multicast, and sink broadcast. The evaluation approach is demonstrated though the analyses of two WSN examples with mesh and hierarchical clustered topologies, respectively.

The fourth paper, Mobile Sensor Deployment and Coverage Using Multi-Agent-based Collective Formation Schemes, by Cheng, Bai, Choudhury, Biswas, and Wu, proposes a mobile wireless sensor deployment and network coverage technique using multi-agent-based collective formation control approaches to achieve system robustness, fault-tolerance, and flexibility.

The fifth paper, Scalable Video Transmission over Cognitive Radio Networks Using LDPC Code, by Huang, H. Wang, Bai, W. Wang, and Liu, studies a joint design of low-density parity-check (LDPC) coding and scalable source coding for optimized error-resistant video transmission over cognitive radio networks. Such joint design scheme allows more efficient use of limited spectrum resources by primary and secondary users.

The sixth paper, Long PN Code Based Traceback in Wireless Networks, by Pan, Huang, Ling, Lu, and Fu, proposes a long Pseudo-Noise (PN) code based Direct Sequence Spread Spectrum (DSSS) watermarking technique to trace suspect communication over encrypted and open wireless networks and anonymous communication networks on the Internet. This proposed traceback technique has good invisibility and broad usage in the cyber crime scene investigations.

The seventh paper, Assessing the Effect of WiMAX System Parameter Settings on MAC-level Local DoS Vulnerability, by Deng, Brooks, and Martin, analyzes how WiMAX system parameter settings increase or decrease the Denial of Service (DoS) vulnerabilities of WiMAX networks. Analysis of Variance (ANOVA) techniques are used to identify combinations of bandwidth contention resolution parameter specified in IEEE 802.16 standards that are crucial for configuring WiMAX to be less vulnerable to DoS security attacks.

The eighth paper, A Key Distribution Scheme for Distributed Group with Authentication Capability, by Adusumilli, Sui, Zou, Ramamurthy, and Li, proposes a new distributed group key distribution (DGKD) protocol for group key management in secure group communication. Based on DGKD, a new distributed dynamic conferencing scheme is also proposed to enforce group/conference membership management. The proposed schemes are well suited for wireless networks such as Mobile Ad-Hoc Networks (MANETs).

We would like to thank all the authors for contributing to this special issue. We are grateful to the authors for their patience and cooperation in helping to achieve the high quality of the papers. We are immensely grateful to referees who spent their valuable time reviewing the papers in a prompt manner. Lastly, we would like to thank Editor-in-Chief, Prof. Krishna B. Misra, for providing us the opportunity to organize this special issue and his continuous support and help in this endeavor.

Liudong Xing is an Associate Professor in the Department of Electrical and Computer Engineering at the University of Massachusetts (UMass), Dartmouth, USA. She received her M.S. and Ph.D. degrees in Electrical Engineering from the University of Virginia, Charlottesville, USA. She is Assistant Editor-in-Chief for the International Journal of Performability Engineering and Associate Editor for the International Journal of Systems Science. Dr. Xing is the recipient of the 2010 Scholar of the Year Award and 2011 Outstanding Women Award of UMass Dartmouth, and the 2007 IEEE Region 1 Technological Innovation (Academic) Award. She is also co-recipient of the Best Paper Award at the IEEE International Conference on Networking, Architecture, and Storage in 2009. Her current research focuses on combinatorial reliability analysis of complex systems and networks. Her research has been supported by the US National Science Foundation (NSF). She is a senior member of IEEE, and a member of Eta Kappa Nu. (Email: lxing@umassd.edu)

Suresh Rai obtained his B.S. from Institute of Technology, BHU; M.S. from IIT, Roorkee, and Ph.D. from Kurukshetra University in 1972, 1974, and 1980, respectively. After a brief sojourn at NIT, Kurukshetra, IIT Roorkee, and North Carolina State University, Raleigh he joined Louisiana State University, Baton Rouge where he is a Professor in the Department of Electrical and Computer Engineering. Dr. Rai has taught and researched in the area of network traffic engineering, ATM, reliability engineering, fault diagnosis, neural net-based logic testing, network security, and steganography. He is a co-author of the book Wave Shaping and Digital Circuits, and tutorial texts Distributed Computing Network Reliability and Advances in Distributed System Reliability; last two published from IEEE Computer Society Press. Dr. Rai has delivered invited lectures on Internet routing at different universities in Australia and India. He has guest-edited a special issue of IEEE Transactions on Reliability on the topic Reliability of Parallel and Distributed Computing Networks. He was an Associate Editor for IEEE Transactions on Reliability from 1990 to 2004. Currently, he is on the editorial board of International Journal of Performability Engineering. Dr. Rai has worked as program committee member for several international conferences and as referee for papers from various international journals. Dr. Rai has published about 120 technical papers in the refereed journals and conference proceedings. He received the best paper award at the 1998 IEEE International Performance, Computing, & Communication Conference (Feb. 16-18, Tempe, Arizona; paper title: S. Rai and Y. C. Oh, Analyzing packetized voice and video traffic in an ATM multiplexer). Dr. Rai’s research has been funded by AFOSR, NSF, and ARO. Dr. Rai is a Senior Member of the IEEE. (Email: suresh@ece.lsu.edu)

This paper provides an overview of reliability issues in vehicular ad-hoc networks (VANETs) for safety-related applications. First, IEEE 802.11p based DSRC system, communication environment, and applications on safety related services are introduced. The factors affecting the reliability of safety services provided by VANETs are identified. Second, the features and requirements of VANETs for safety applications are discussed. Third, the relevant reliability issues are raised, and the reliability metrics are defined for the evaluation of such systems. Fourth, the analytical models from recent literature for both one-hop message broadcast and multi-hop broadcast are listed, described, and compared. Finally, having summarized drawbacks of the current analytical models for safety applications in VANETs, some potential topics for future research are suggested.

The performability of a wireless sensor network (WSN) can be measured using a range of metrics, including reliability (REL) and expected hop count (EHC). EHC assumes each link has a delay value of 1 and devices have no delay or vice versa, which is not necessarily appropriate for WSNs. This paper generalizes the EHC metric into an expected message delay (EMD) that permits arbitrary delay values for both links and devices. Further, it proposes a method based on Augmented Ordered Multivariate Decision Diagram (OMDD-A) that can be used to compute REL, EHC and EMD for WSN with both device and link failures. Simulation results on various networks show the benefits of the OMDD-A approach.

This paper considers the problem of modeling and analyzing the infrastructure communication reliability (ICR) of wireless sensor networks (WSN) subject to common-cause failures (CCF). Three different data delivery models, i.e., sink unicast, sink multicast, and sink broadcast are considered, and three ICR metrics are developed correspondingly. The reliability problems and evaluation approaches are formulated for WSN with a hierarchical clustered architecture. Nevertheless, the proposed generic approach can be easily adapted for the reliability analysis of WSN with other communication topologies such as mesh, star, and tree. The evaluation approach integrates a progressive reduction scheme based on binary decision diagrams for the reliability analysis, and a divide-and-conquer approach for considering the effect of CCF. Two WSN examples with mesh and hierarchical clustered topologies respectively are analyzed to illustrate the advantages and application of the proposed approach.

In this paper, we present a novel mobile wireless sensor deployment and network coverage technique using multi-agent-based collective formation control. Most of the existing approaches of sensor deployment are focused on centralized methods, which restrain the sensor nodes to maintain fixed distance among all neighboring nodes. Therefore, these approaches have some drawbacks, vulnerabilities and inflexibility, especially when some of the sensor nodes are not functioning due to unexpected node failure, e.g., power loss. As a result, sensor coverage could be compromised or diminished. To address these problems, we propose to incorporate an attractive/repulsive (AR) collective formation model to control the dynamics of wireless sensor nodes which are considered as autonomous agents. We show that sensor deployment with AR model provides robustness and flexibility. When some sensor nodes are lost unexpectedly, movement of neighboring nodes are relatively localized so that the least amount of energy will be used to regain control of the network coverage. Consequently, the proposed method can significantly improve the time-efficiency, network stability and sensing coverage when sensor nodes are deployed to explore harsh terrains and unpredictable environments.
Received on October 30, 2010, revised on April 18, 2011
References:19

Either licensed or un-licensed spectrum resource is becoming increasingly demanding by many multimedia applications which are traffic intensive and quality sensitive. Cognitive Radio (CR) network offers a promising solution to meet this demand by fully utilizing available spectrum resource. In this paper, we studied a scalable video transmission scheme using LDPC code over Cognitive Radio networks, which allows Primary User (PU) and Secondary Users (SU) to fully utilize current unused resources and is to meet Quality-driven video transmission requirements. Specifically, the object-based scalable video coding and low-density parity-check (LDPC) coding are designed jointly for resisting channel errors and reducing the delay. We evaluate the performance of the proposed multimedia system and demonstrate the efficiency of the proposed scheme.

Cyber criminals may abuse open wireless networks or those with weak encryption for cyber crimes. To locate such criminals, law enforcement has to first identify which mobile (MAC) is generating suspect traffic behind a wireless router. The challenge is how to correlate the private wireless traffic and the identified suspect public traffic on the Internet. In this paper, we propose a new technique called long Pseudo-Noise (PN) code based Direct Sequence Spread Spectrum (DSSS) flow marking technique for invisibly tracing suspect anonymous wireless flows. In this technique, a long PN code is shared by two investigators, interferer and sniffer. Different bits of the signal will be encoded with different segments of the long PN code. By interfering with a sender's traffic and marginally varying its rate, interferer can embed a secret spread spectrum signal into the sender's traffic. By tracing where the embedded signal goes, sniffer can trace the sender and receiver of the suspect flow despite the use of anonymous encrypted wireless networks. Traffic embedded with long PN code modulated watermarks is much harder to detect. We have conducted extensive analysis and experiments to show the effectiveness of this new technique. We are able to prove that existing detection approaches cannot detect the long PN code modulated traffic. The technique is generic and has broad usage.

The research community has established that WiMAX networks suffer from Denial of Service (DoS) vulnerabilities. In this paper, we analyze how WiMAX system parameter settings increase or decrease DoS vulnerabilities of WiMAX networks. The behavior of the WiMAX MAC level protocol is sensitive to the settings of core system parameters. Unlike traditional network-based DoS attacks, attacks resulting from parameter misconfiguration are difficult for network operators to detect. We focus on bandwidth contention resolution aspects of the WiMAX MAC protocol. Simulations are performed using the ns-2 simulator. Analysis of Variance (ANOVA) techniques on the resulting simulation data identify which bandwidth contention resolution parameter combinations are crucial for configuring WiMAX to be less vulnerable to DoS attacks.

Group key management (GKM) is one of the most important issues in secure group communication (SGC). The existing GKM protocols fall into three typical classes: centralized group key distribution (CGKD), decentralized group key management (DGKM), and distributed/contributory group key agreement (CGKA). Serious problems remains in these protocols, as they require existence of central trusted entities (such as group controller or subgroup controllers), relaying of messages (by subgroup controllers), or strict member synchronization (for multiple round stepwise key agreement), thus suffering from the single point of failure and attack, performance bottleneck, or misoperations in the situation of transmission delay or network failure. We proposed a new class of GKM protocols: distributed group key distribution (DGKD) [1]. The new DGKD protocol solves the above problems and surpasses the existing GKM protocols in terms of simplicity, efficiency, scalability, and robustness. In this paper, we extend the conference paper [1] with detailed experiments and discussions. Also based on DGKD, we propose a new distributed dynamic conferencing scheme which enforces group/conference membership management. Due to its distributed feature without the requirement of a central control, the proposed scheme is well suited in wireless networks such as Mobile Ad-hoc Networks (MANETs).

This paper models and analyzes the infrastructure communication reliability of wireless sensor networks (WSN) with tree topology. Reliability metrics are developed for WSN under five different data delivery models, including sink unicast, anycast, multicast, manycast, and broadcast. An example of WSN with tree topology is analyzed to illustrate the application of the proposed reliability metrics. Reliability results for the five data delivery models are compared and discussed.

The Multi-state Weighted k-out-of-n System model is the generalization of the Multi-state k-out-of-n System model, which finds wide applications in industry. However only Multi-state Weighted k-out-of-n: G System models have been defined and studied in most recent research works. The mirror image of the Multi-state Weighted k-out-of-n: G System – the Multi-state Weighted k-out-of-n: F System has not been clearly defined and discussed. In this short communication, the basic definition of the Multi-state Weighted k-out-of-n: F System model is proposed. The relationship between the Multi-state Weighted k-out-of-n: G System and the Multi-state Weighted k-out-of-n: F System is also analyzed.