Terminal-embedded beamforming for wireless local area networks [accepted from open call]

In dense traffic areas, wireless local area networks (WLANs) suffer from interference problems due to the congestion of the open and unlicensed ISM band. To mitigate these problems, a terminal-embedded beamforming framework is proposed. This beamforming is capable of focusing the transmission and the reception in the direction of the relevant access point. At the same time, the framework is backward compatible with existing WLAN networks. The beam- forming enabled terminal benefits in terms of capacity, security, and energy efficiency without requiring any changes on the network side or requiring new investment on the part of network providers. The beamforming solution is seen as an attractive value-added feature, as well as a low-cost solution for the future WLAN terminal design. This opens the door for mobile device manufacturers to include the proposed solution in their product line. In this work, the backward- compatibility challenges are addressed, and possible solutions and limitations are discussed. A prototype design built on a laptop computer also is described. The experimental results show a significant capacity increase in both an interference-free scenario and an interference-limited scenario.     

Vertical QoS mapping over wireless interfaces [accepted from open call]

This article focuses on the problem of quality of service mapping between layers in a cascade. Protocol stacks in telecommunications networks are composed of functional layers. QoS provision depends on the performance achieved at each layer and is based on functions performed at layer interfaces. In practice, QoS derives from reliable physical and link layers that can offer specific transport services to upper network layers. The data flows (or bundles of flows) generated by the upper layers (e.g., the network layers) are forwarded down to a physical interface that transports the information along a channel that provides, if possible, the expected QoS to the upper layers. The action is called vertical QoS mapping and poses many challenges for a communication scientist, in particular if it is applied to wireless interfaces. This article states the definition of vertical QoS mapping, proposes a formal separation between technology-dependent and technology-independent layers, models each functional layer as a battery of buffers, generalizes the relation between layers through a chain of buffers in a cascade, formalizes the theoretical problems of vertical QoS mapping, and suggests possible solutions that use dynamic bandwidth allocation schemes.     

Securing resource-constrained wireless ad hoc networks [accepted from open call]

Huge interest in and demand for services over the information superhighway have pressed various telecommunications research fronts and led to a new form of future Internet consisting of wired and wireless segments where resourceconstrained devices such as mobile devices, smart phones, palm pilots, and wireless sensors may become integral parts of the Internet rather than access-only platforms. One of the key design problems is the security in such heterogeneous networks, particularly over wireless networks with resource constraints. In this tutorial article we discuss a novel approach to addressing security issues, and articulate why and how IDbased cryptography can be effectively applied to address various security problems in resourceconstrained wireless networks.     

Address autoconfiguration in wireless ad hoc networks: protocols and techniques [accepted from open call]

With the advent of smaller devices having higher computational capacity and wireless communication capabilities, the world is becoming completely networked. Although, the mobile nature of these devices provides ubiquitous services, it also poses many challenges. In this article, we look in depth at the problem of addressing in wireless ad hoc networks and the currently available techniques and protocols for both IPv4 and IPv6. We present an exhaustive study of the literature and summarize the features of each technique. We believe that this analysis will be helpful for network and application designers, as well as for researchers.     

Prediction in wireless networks by Markov chains [accepted from open call]

Discrete sequence modeling and prediction is an important goal and a challenge for pervasive computing. Mobile clients? data request forecasting and location tracking in wireless cellular networks are characteristic application areas of sequence prediction in pervasive computing. This article presents information-theoretic techniques for discrete sequence prediction. It surveys, classifies, and compares the state-of-the-art solutions, suggesting routes for further research by discussing the critical issues and challenges of prediction in wireless networks.     

Networking for critical conditions [accepted from open call]

To enhance the preparedness of federal and state agencies to effectively manage federal or state recovery efforts in response to a broad spectrum of emergencies, we propose a hybrid adaptive network that will adopt currently available off-the-shelf wireless network devices and integrate them quickly into a scalable, reliable, and secure network with a minimum of human intervention for configuration and management. This model will serve as the framework for various rescue missions for securing and distributing critical resources. We investigate different technologies and network strategies and integrate them into the proposed network model to provide seamless support to heterogeneous environments including wireline nodes, ad hoc and sensor network nodes, and network devices based on different standards. In this article we present the network architecture and identify the key technical aspects of its management, security, QoS, and implementation.     

SIP-based mobility management in next generation networks [accepted from open call]

The ITU-T definition of next generation networks includes the ability to make use of multiple broadband transport technologies and to support generalized mobility. Next generation networks must integrate several IP-based access technologies in a seamless way. In this article, we first describe the requirements of a mobility management scheme for multimedia real-time communication services; then, we report a survey of the mobility management schemes proposed in the recent literature to perform vertical handovers between heterogeneous networks. Based on this analysis, we propose an application-layer solution for mobility management that is based on the SIP protocol and satisfies the most important requirements for a proper implementation of vertical handovers. We also implemented our proposed solution, testing it in the field, and proving its overall feasibility and its interoperability with different terminals and SIP servers.     

DV-Loc: a scalable localization protocol using Voronoi diagrams for wireless sensor networks [accepted from open call]

Localization systems have been identified as a key issue in the development and operation of wireless ssensor networks. DV-Hop, a wellknown localization algorithm, has recently been proposed for WSNs. Its basic idea relies on transforming the distance to all beacon nodes from hops to meters by using the computed average size of a hop. Despite its advantages, the DV-Hop algorithm has some limitations, mainly due to its high communication cost and energy consumption, which unfortunately limit its applicability to small or medium-sized sensor networks. The scalability issue of DV-Hop is a challenging problem that needs to be addressed. In this article we propose a novel localizationbased protocol and show how Voronoi diagrams can be used efficiently to scale a DV-Hop algorithm while maintaining and/or reducing further DV-Hop?s localization error. In our localization scheme, nodes can also be localized by their Voronoi cells. In order to evaluate the performance of our scheme, we present an extensive set of simulation experiments using ns-2. Our results clearly indicate that our proposed algorithm performs and scales better than DV-Hop.     

Challenging issues in visual sensor networks [accepted from open call]

Wireless sensor networks are an important research area that has attracted considerable attention. Most of this attention, however, has been concentrated on WSNs that collect scalar data such as temperature and vibration. Scalar data can be insufficient for many applications such as automated surveillance and traffic monitoring. In contrast, camera sensors collect visual data, which are rich in information and hence offer tremendous potential when used in WSNs. However, they raise new challenges such as the transmission of visual data with high computational and bandwidth requirements in mainly low-power visual sensor networks. In this article we highlight the challenges and opportunities of VSNs. We discuss major research issues of VSNs, specifically camera coverage optimization, network architecture, and low-power visual data processing and communication, and identify enabling approaches in this area.     

An open baseband processing architecture for future mobile terminal design [accepted from open call]

This article introduces an open wireless architecture (OWA) mobile terminal design, focusing on the open baseband processing platform, to support different existing and future wireless communication standards through multi-dimensional open baseband processing modules with open interface parameters and baseband management systems. The article describes a multilayer, open architecture platform to maximize system flexibility and minimize terminal power consumption, so as to provide an integrated and converged next-generation wireless and mobile communication terminal system. The OWA platform is fully compatible with the computer architecture, with interface-based rather than transmission-specific system architecture, for complete openness and simplicity.     

OFDM for cognitive radio: merits and challenges [accepted from open call]

Cognitive radio is a novel concept that enables wireless systems to sense the environment, adapt, and learn from previous experience to improve the quality of the communication. However, CR requires a flexible and adaptive physical layer in order to perform the required tasks efficiently. In this article, CR systems and their requirement of a physical layer are discussed, and the orthogonal frequency division multiplexing technique is investigated as a candidate transmission technology for CR. The challenges that arise from employing OFDM in CR systems are identified. The cognitive properties of some OFDM-based wireless standards also are discussed to indicate the trend toward a more cognitive radio.     

Evaluation of signaling loads in 3GPP networks [accepted from open call]

3GPP Release 5 is the first step toward an all-IP cellular network. While Release 99 is still heavily based on a core network inherited from 2G networks, Release 5 introduces a new core network architecture based on IETF protocols. In particular, SIP is used for initiating, managing, and terminating media sessions. However, the use of SIP can result in a significant increase of the signaling and computational loads inside the core network, due to its larger message size and increased requirements on network nodes. This article compares the core network signaling loads of 3GPP Release 99 and Release 5, and elaborates on possible enhancements to improve the bandwidth efficiency of the signaling in Release 5.     

IP2P: a peer-to-peer system for mobile devices [accepted from open call]

Peer-to-peer communications is a major trend in wireless Internet. In a P2P system, the calling peer must identify the network address of the called peer before establishing a P2P connection. This article proposes iP2P, a hybrid P2P system for mobile devices. iP2P utilizes the short message service as the control protocol to identify the address of the called peer. Our approach provides an efficient identification mechanism without the requirement for the maintenance of a centralized registrar server in a hybrid P2P system. We also show how iP2P can integrate effectively with the existing Network Address Translation traversal mechanisms to solve the private IP address issue.     

Cognitive radio for next-generation wireless networks: an approach to opportunistic channel selection in ieee 802.11-based wireless mesh - [accepted from open call]

?Cognitive radio? has emerged as a new design paradigm for next-generation wireless networks that aims to increase utilization of the scarce radio spectrum (both licensed and unlicensed). Learning and adaptation are two significant features of a cognitive radio transceiver. Intelligent algorithms are used to learn the surrounding environment, and the knowledge thus obtained is utilized by the transceiver to choose the frequency band (i.e., channel) of transmission as well as transmission parameters to achieve the best performance. In this article we first provide an overview of the different components to achieve adaptability in a cognitive radio transceiver and discuss the related approaches. A survey of the cognitive radio techniques used in the different wireless systems is then presented. To this end, a dynamic opportunistic channel selection scheme based on the cognitive radio concept is presented for an IEEE 802.11-based wireless mesh network.     

Certificate status validation in mobile ad hoc networks - [accepted from open call]

Certificate validation is much more complex in mobile ad hoc networks than in conventional networks because online access to trusted authorities is not always guaranteed. For this reason, we require new solutions to overcome both the lack of infrastructure and the limited capabilities of several user devices. In this article we study the application of different mechanisms for certificate validation in MANETs and present a cooperative mechanism for certificate validation suitable for MANETs.     

Efficient and flexible location management techniques for wireless communication systems

We consider the problem of managing the information required to locate users in a wireless communication system, with a focus on designing and evaluating location management techniques that are efficient, scalable, and flexible. The three key contributions of this paper are: (1) a family of location management techniques, HiPER (for Hierarchical ProfilE Replication), that efficiently provide life‐long (non‐geographic) numbering with fast location lookup; (2) Pleiades, a scalable event‐driven wireless system simulator with realistic calling and mobility patterns derived from several months of real traffic traces; and (3) multi‐day simulations comparing our proposed location management techniques with current and previously proposed techniques on a realistic geographical and network topology. This revised version was published online in June 2006 with corrections to the Cover Date.     

A comparative investigation of acknowledgment mechanisms for data transport in space internet [accepted from open call]

As the Internet is changing the world dramatically, an initiative is being proposed within NASA and in the military to expand the Internet into space and for network-centric warfare using network protocols. An end-to-end effective data transport protocol is critical to the reliable transfer of information in space and for a battlefield environment. Consequently, a reliable and efficient acknowledgment mechanism is required to accommodate these unreliable communication conditions. In this article we conduct a comparative investigation of existing data transport acknowledgment mechanisms for possible adoption in the unreliable environment of space or a similarly stressed communication environment. We also introduce the selective negative acknowledgment (SNACK), which is designed as a reliable retransmission mechanism for space and stressed tactical communications, followed by a brief performance evaluation of the effectiveness of SNACK compared to the standard SACK mechanism.     

Networking with cooperative communications: holistic design and realistic evaluation - [Accepted from open call]

Cooperative communications fundamentally changes the abstraction of a wireless link and offers significant potential advantages for wireless networks. However, such technologies are evaluated with idealized scenarios where many control costs are assumed to be negligible. Moreover, even if these costs appear small in simple network scenarios, they increase significantly with the size and traffic level of the network, requiring careful evaluation, or even innovative design, of cooperative protocols to ensure their usefulness in realistic networks. This article describes a realistic evaluation of cooperative communications in a networking context. Insights obtained from this evaluation help guide work on cooperative communications toward practical and potentially beneficial protocols.     

Wake-up receivers for wireless sensor networks: benefits and challenges - [Accepted from open call]

For successful data delivery, the destination nodes should be listening to the medium to receive data when the sender node starts data communication. To achieve this synchronization, there are different rendezvous schemes, among which the most energy-efficient is utilizing wakeup receivers. Current hardware technologies of wake-up receivers enable us to evaluate them as a promising solution for wireless sensor networks. In this article the benefits achieved with wake-up receivers are investigated along with the challenges observed. In addition, an overview of state-of-the-art hardware and networking protocol proposals is presented. As wake-up receivers offer new opportunities, new potential application areas are also presented and discussed.     

Radio resource management of heterogeneous services in mobile WiMAX systems [Radio Resource Management and Protocol Engineering for IEEE 802.16]

IEEE 802.16e, known as mobile WiMAX, has gained much attention recently for its capability to support high transmission rates in cellular environments and QoS for different applications. Beyond what the standard can define, in order to effectively support video streaming, VoIP, and data services, proprietary radio resource management, including multiconnection assignment, scheduling controls, and call admission controls, are essential. In this study we evaluate the downlink performance of a mobile WiMAX cellular system with different radio resource management, especially the scheduler for QoS control and the implementation of multiconnection for streaming applications