Ahmed M. Mahdy

Wireless optical communications: a survey

The demand for wireless broadband communications has been growing steadily for last several years. The congestion and the limitations on bandwidths of the radio spectrum have inhibited unrestricted growth of radio wireless systems. Wireless optical, however, holds the promise of delivering data rates that can meet the broadband requirements. As a result, wireless optical is believed to be a viable long term option for many applications of wireless communications. Nevertheless, the advantages of optical wireless have not yet been fully exploited. Basic and applied research is needed at the laboratory and commercial levels to bring the performance of real-life wireless optical systems into higher levels. The Gb/s level data rate has been validated in laboratory, however, available indoor systems only realize a data rate of 155Mb/s. Current research in wireless optical concentrates on increasing the communication capacity and improving the performance. In this paper, we survey the wireless optical discipline emphasizing major design, performance, and safety issues. Research directions that have the potential to close the gap between theory and practice, in wireless optical communications, are also presented.

Marine Wireless Sensor Networks: Challenges and Applications

Current research on wireless sensor networks is based on the assumption that these networks are deployed in a terrestrial environment. Relevant protocols and design specifications are developed under this condition. This makes the deployment of currently existing wireless sensor networks in marine environments extremely challenging. We present major challenges and applications of underwater wireless sensor networks focusing on their military aspect. The paper addresses the armys immediate needs for secure agile broadband communications for future digital battlefields emphasizing the role of marine sensors. A novel architecture for broadband ad hoc and sensor networks that can provide warfighters with a secure on-the-move means for high- capacity communications is proposed. The architecture is designed with the role of ad hoc and sensor networks in future warfare scenarios and anticipated demand for broadband applications.

A Dynamic Approach for the Selection of Super Peers in Ad Hoc Networks

Peer-to-peer and mobile ad hoc networks have established a strong connection due to the fact that peer-to-peer models present effective solutions for decentralized systems. Pure and hybrid peer-to-peer networks have propagated as design models for such decentralized systems. Super-peer networks, in which some nodes (super peers) are selected and assigned special roles, have been proposed as a compromise tradeoff between the two models. In this paper, we study the selection of super peers in mobile ad hoc networks. We investigate two approaches to selection and study their impacts on network performance. Based on the analysis of empirical results, we propose and evaluate a new dynamic approach. Simulation results show a significant improvement over existing selection techniques.

Multicast optimization in broadband adaptive optical wireless networks

Optical wireless networks (OWNs) are expected to have a major role in the evolution of broadband wireless networks and the wireless Internet. This is due in large to the high data rates that OWNs can deliver. The deployment of OWNs in these domains necessitates the need for new techniques and approaches that can secure a place for OWNs in the future of wireless communications. The adaptive model of OWNs is considered a major step towards this goal. It has a great impact on the future of OWNs because of the new design concepts it brought to the optical wireless arena. In this paper, we study the multicast process in adaptive OWNs. We prove the NP-hardness of the multicast optimization problem and accordingly propose two optimization heuristics. Simulation results show that networks adapting our multicast heuristics achieve improvements of up to 42% and 62% on average packet delay and overhead-related metrics, respectively, as compared to networks with conventional multicast.

Identifying domain patterns using software stability

The fact that domain applications share core aspects has turned software reuse into a viable option. System development has experienced time saving, cost saving, and the luxury of deploying proven-to-work solutions as main advantages of software reuse. Software patterns represent a major approach for reuse. Domain patterns capture system components shared by different applications that belong to the same context. In this paper, we propose a new approach to identifying and reusing domain patterns based on software stability. We show that enduring business themes and business objects, together, can form a pattern among domain applications. We, also, present three case studies to show how the new approach can be applied.

Extracting Domain-Specific and Domain-Neutral Patterns Using Software Stability Concepts

Extracting domain-specific patterns and domain-neutral patterns is a challenge for both expert and novice software engineers. Currently, no mature guidelines or methodologies exist for extracting patterns. Software stability model proposed in [3] provides a base for extracting the core knowledge of the domain and identifying atomic notions that can be thought of as patterns by extracting another level of abstraction using software stability concepts. This paper proposes and demonstrates, through examples, how to extract both domain-specific and domain-neutral patterns from systems that are built using software stability concepts.

Broadband optical wireless Internet: delay optimization

In this paper, we investigate the link flexibility constraints imposed on the deployment of the optical wireless Internet. We formulate the topology control problem under link delay conditions, and accordingly propose a new optimization algorithm for networks with two-transceiver nodes. Simulation results show that networks applying the proposed algorithm achieve a reduction in average packet delay up to 55% over networks with rigid topologies.

End-to-end delay heuristics for adaptive optical wireless networks

Wireless communications offer an attractive option for many military, commercial as well as personal communication needs because of flexibility, cost effectiveness, and mobility. The quality features of wireless communications have led to tremendous growth in the development of novel technologies that raise the need for broadband wireless communications. Optical wireless systems offer high transmission rates that can accommodate these broadband needs. Optical wireless links can be prone to the atmosphere, which can result in a performance degradation. Therefore, optical wireless networks should be adaptive with flexible links. In this paper we emphasize the adaptability of optical wireless networks and propose new heuristics for the optimization of communication delay in a flexible link regime for networks with unbounded degree transceivers. Extensive simulations are conducted to evaluate the performance of the proposed heuristics and validate the improvement in network functionality as compared to the unadaptable environment. Empirical results show that a 50% reduction in average packet delay, as compared to unadaptable networks, can be achieved by a network based on the proposed heuristics.

GPS-Free Localization Schemes for Underwater Wireless Sensor Networks

Compared to other localization algorithms, the SemiDefinite Programming (SDP) approach has proved to deliver accurate results even in noisy backgrounds. In this paper, we propose a novel design for underwater localization systems using SemiDefinite Programming. The objective is to provide marine scientists with a cost-effective efficient way in conducting relevant research. Two designs, fixed-position and magnified-range, are proposed. Both schemes have shown a high accuracy and an outstanding performance according to simulation results. Future research directions are discussed at the end of this paper.

Extracting domain- specific and domain-independent patterns

There are no mature guidelines or methodologies exist for extracting patterns. Software Stability Model [2] can provide a base for extracting patterns. This poster presents the concept of extracting both domain-specific and domain- independent patterns from systems that are built using software stability concepts.