Dimitrios J. Vergados

Energy efficiency in wireless sensor networks using sleep mode TDMA scheduling

Power saving is a very critical issue in energy-constrained wireless sensor networks. Many schemes can be found in the literature, which have significant contributions in energy conservation. However, these schemes do not concentrate on reducing the end-to-end packet delay while at the same time retaining the energy-saving capability. Since a long delay can be harmful for either large or small wireless sensor networks, this paper proposes a TDMA-based scheduling scheme that balances energy-saving and end-to-end delay. This balance is achieved by an appropriate scheduling of the wakeup intervals, to allow data packets to be delayed by only one sleep interval for the end-to-end transmission from the sensors to the gateway. The proposed scheme achieves the reduction of the end-to-end delay caused by the sleep mode operation while at the same time it maximizes the energy savings.

CorpWiki: A self-regulating wiki to promote corporate collective intelligence through expert peer matching

One of the main challenges that organizations face nowadays, is the efficient use of individual employee intelligence, through machine-facilitated understanding of the collected corporate knowledge, to develop their collective intelligence. Web 2.0 technologies, like wikis, can be used to address the above issue. Nevertheless, their application in corporate environments is limited, mainly due to their inability to ensure knowledge creation and assessment in a timely and reliable manner. In this study we propose CorpWiki, a self-regulating wiki system for effective acquisition of high-quality knowledge content. Inserted articles undergo a quality assessment control by a large number of corporate peer employees. In case the quality is inadequate, CorpWiki uses a novel expert peer matching algorithm (EPM), based on feed-forward neural networks, that searches the human network of the organization to select the most appropriate peer employee who will improve the quality of the article. Performance evaluation results, obtained through simulation modeling, indicate that CorpWiki improves the final quality levels of the inserted articles as well as the time and effort required to reach them. The proposed system, combining machine-learning intelligence with the individual intelligence of peer employees, aims to create new inferences regarding corporate issues, thus promoting the collective organizational intelligence.

Intelligent services for assisting independent living of elderly people at home

For more than a decade it has been observed that due to the continuously augmenting elderly population, medical expenditures for home health care were exponentially raising every year. Healthcare organizations worldwide are being encouraged to find more efficient methods of providing high-quality care with cost savings. Elderly people who live alone may fear of being unable to obtain help if they are injured or ill. For many families, the specter of such an event can dominate decisions about living arrangements. During the last decades, this fear has generated an industry marketing house automations, alarm-and-notification systems as well as assistive technologies and interventions aiming in the easier and more efficient control of the living environment as well as to the provision of specialized home-care services. In the current paper, the most important aspects of the INHOME project architecture for improving the quality of life of elderly people at home is presented, which is mainly targeted in ameliorating the ways of providing intelligent services for assisting independent living of elderly people at home.

QoS-aware TDMA for end-to-end traffic scheduling in ad hoc networks

The proliferation of low-cost broadband air interfaces has paved the way to the introduction of high-definition multimedia services in mobile and wireless networks. The cost for network resources utilization, when provisioning such services, will play a prominent role in their commercial success, since the more spare resources that can be used, the more cheaply the services can be delivered to the end users. In the context of promoting the role of ad hoc networks as service platforms for high quality multimedia applications, this article first discusses and classifies a set of issues involved in quality of service (QoS) provisioning in ad hoc networks and then presents a congestion-free TDMA algorithm for end-to-end network resources assignment via an optimized mechanism that relies on capacity requests and grants. The article also illustrates a method for invoking this algorithm to achieve efficient end-to-end QoS provisioning and concludes by showing the superiority of the proposed algorithm, as compared to other recently proposed TDMA scheduling algorithms

Energy-efficient route selection strategies for wireless sensor networks

Wireless Sensor Networks (WSNs) facilitate monitoring and controlling of physical environments from remote locations with the best possible accuracy. Sensor networks are wireless networks consisting of groups of small, inexpensive nodes, which collect and disseminate critical data. Also, sensor nodes have various energy and computational constraints due to their inexpensive nature and ad hoc method of deployment. Considerable research has been focused on overcoming these deficiencies through low-energy consumption schemes. Among other factors, the route selection strategy may have an impact on the sensors lifetime, and following on the network lifetime. In this paper, we study various route selection strategies that aim at prolonging the lifetime of WSNs. Also, a new route selection scheme is proposed, that increases further the network lifetime. The performance of these schemes is analyzed through simulation.

Power control schemes in wireless sensor networks for homecare e-health applications

Power control is an important research topic for ad-hoc Wireless Sensor Networks (WSNs). In todays sophisticated and competitive wireless environment, the control of the energy consumption in a WSN for homecare e-health makes it possible to guarantee basic levels of system performance, such as connectivity, throughput, delay, QoS and survivability in the presence of both mobility-immobility and a large number of sensor nodes. Recent advances in sensor fabrication technology, low-power digital and analogue electronics, and low-power wireless communication systems have made it possible to develop low-cost, robust and survivable WSNs to support activities such as assisted living and ambient intelligence (Aml). A large variety of approaches for intelligent energy-efficient schemes have been simulated over different performance metrics. In this paper, various decision support schemes are proposed evaluating the selection of different network infrastructures in terms of routing optimization and signal strength selection.

Increasing Intelligent Wireless Sensor Networks Survivability by Applying Energy-Efficient Schemes

Intelligent Energy efficiency is an important research topic for ad-hoc Wireless Sensor Networks (WSN). Power saving makes it possible to guarantee basic levels of system performance, such as connectivity, throughput and delay, in the presence of both mobility-immobility and a large number of sensor nodes. A large variety of approaches for intelligent energy-efficient schemes have been proposed in the literature focusing on different performance metrics. This article presents a comprehensive survey of recent energy-efficient schemes in ad-hoc wireless sensor networks, the application of which increases nodes’ lifetime and thus, network connectivity and survivability.

FDASH: A Fuzzy-Based MPEG/DASH Adaptation Algorithm

The evolution of broadband connection technologies, along with the explosive growth of mobile handheld devices, has made video content one of the major Internet traffic types. HTTP adaptive streaming (HAS) is one factor assisting the growing popularity of Internet video. One of its standards, the MPEG dynamic adaptive streaming over HTTP (DASH), allows users to access video streams of multiple resolutions available at a central repository. Various adaptation algorithms using the MPEG DASH protocol have been proposed, aiming to adapt the media bit rate delivered at the client to the current network conditions. In this paper, we present the FDASH rate adaptation scheme that employs fuzzy logic to control the buffering time and the video resolution delivered to the client in order to distribute video segments of the best quality, deliver undisrupted video playback, and avoid frequent changes of video resolution. The comparison of FDASH against other rate adaptation schemes shows that the former successfully provides the client with the optimal video rates, avoiding buffer underflows and unnecessary changes of video resolution in case of fluctuations of the available connection throughput.

Fair TDMA scheduling in wireless multihop networks

In wireless multihop networks, communication between two end-nodes is carried out by hopping over multiple wireless links. However, the fact that each node has to transmit not only its own traffic, but also traffic on behalf of other nodes, leads to unfairness among the communication rates of the nodes. Traditional Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) based media access control does not work satisfactory in a multihop scenario, since an intended target of a communication may be subject to mutual interference imposed by concurrent transmissions from nodes, which cannot directly sense each other, thus causing unfair throughput allocation. Although Time Division Multiple Access (TDMA) seems to be a more promising solution, careful transmission scheduling is needed in order to achieve error-free communication and fairness. Several algorithms may be found in the literature for scheduling TDMA transmissions in wireless multihop networks. Their main goal is to determine the optimal scheduling, in order to increase the capacity and reduce the delay for a given network topology, though they do not consider the traffic requirements of the active flows of the multihop network or fairness issues. In this paper, we propose a joint TDMA scheduling/load balancing algorithm, called Load-Balanced-Fair Flow Vector Scheduling Algorithm (LB-FFVSA). This algorithm schedules the transmissions in a fair manner, in terms of throughput per connection, taking into account the communication requirements of the active flows of the network. Simulation results show that the proposed algorithm achieves improved performance compared to other solutions, not only in terms of fairness, but also in terms of throughput. Moreover, it was proved that when a load balancing technique is used, the performance of the scheduling algorithm is further improved.

Collective intelligence system engineering

Collective intelligence (CI) is an emerging research field which aims at combining human and machine intelligence, to improve community processes usually performed by large groups. CI systems may be collaborative, like Wikipedia, or competitive, like a number of recently established problem-solving companies that attempt to find solutions to difficult R&D or marketing problems drawing on the competition among web users. The benefits that CI systems earn user communities, combined with the fact that they share a number of basic common characteristics, open up the prospect for the design of a general methodology that will allow the efficient development and evaluation of CI. In the present work, an attempt is made to establish the analytical foundations and main challenges for the design and construction of a generic collective intelligence system. First, collective intelligence systems are categorized into active and passive and specific examples of each category are provided. Then, the basic modeling framework of CI systems is described. This includes concepts such as the set of possible user actions, the CI system state and the individual and community objectives. Additional functions, which estimate the expected user actions, the future state of the system, as well as the level of objective fulfillment, are also established. In addition, certain key issues that need to be considered prior to system launch are also described. The proposed framework is expected to promote efficient CI design, so that the benefit gained by the community and the individuals through the use of CI systems, will be maximized.