Elli Kartsakli

Persistent RCSMA: A MAC Protocol for a Distributed Cooperative ARQ Scheme in Wireless Networks

The persistent relay carrier sensing multiple access (PRCSMA) protocol is presented in this paper as a novel medium access control (MAC) protocol that allows for the execution of a distributed cooperative automatic retransmission request (ARQ) scheme in IEEE 802.11 wireless networks. The underlying idea of the PRCSMA protocol is to modify the basic rules of the IEEE 802.11 MAC protocol to execute a distributed cooperative ARQ scheme in wireless networks in order to enhance their performance and to extend coverage. A closed formulation of the distributed cooperative ARQ average packet transmission delay in a saturated network is derived in the paper. The analytical equations are then used to evaluate the performance of the protocol under different network configurations. Both the accuracy of the analysis and the performance evaluation of the protocol are supported and validated through computer simulations.

A survey on M2M systems for mHealth: a wireless communications perspective.

In the new era of connectivity, marked by the explosive number of wireless electronic devices and the need for smart and pervasive applications, Machine-to-Machine (M2M) communications are an emerging technology that enables the seamless device interconnection without the need of human interaction. The use of M2M technology can bring to life a wide range of mHealth applications, with considerable benefits for both patients and healthcare providers. Many technological challenges have to be met, however, to ensure the widespread adoption of mHealth solutions in the future. In this context, we aim to provide a comprehensive survey on M2M systems for mHealth applications from a wireless communication perspective. An end-to-end holistic approach is adopted, focusing on different communication aspects of the M2M architecture. Hence, we first provide a systematic review of Wireless Body Area Networks (WBANs), which constitute the enabling technology at the patients side, and then discuss end-to-end solutions that involve the design and implementation of practical mHealth applications. We close the survey by identifying challenges and open research issues, thus paving the way for future research opportunities.

Game theoretic D2D content dissemination in 4G cellular networks

The widespread proliferation of mobile devices has motivated Device-to-Device (D2D) communications as a means of cell offloading toward better Quality of Service (QoS) and higher energy efficiency. Although Wi-Fi networks have the lions share regarding the D2D communications in the unlicensed spectrum, it is uncertain whether they constitute the best option as technology evolves. In particular, the increasing transmission data rates, the novel interference cancelation techniques, as well as the potential of centralized network support, stress the need for new Medium Access Control (MAC) protocols, especially in content dissemination scenarios where all nodes share the same goal. In this article we study the suitability of Wi-Fi technology in content dissemination scenarios with multiple available source nodes, and we propose two energy-aware game theoretic MAC strategies (a distributed and a network-assisted) as possible alternatives. Our simulation results show the effectiveness and the flexibility of our proposed solutions, highlighting the necessity for new MAC designs.

QoS-Aware Energy Management in Body Sensor Nodes Powered by Human Energy Harvesting

Harvesting energy in the human environment has been identified as an effective way to charge the body sensor nodes in wireless body area networks (WBANs). In such networks, the capability of the nodes to detect events is of vital importance and complements the stringent quality of service (QoS) demands in terms of delay, throughput, and packet loss. However, the scarce energy collected by human motions, along with the strict requirements of vital health signals in terms of QoS, raises important challenges for WBANs and stresses the need for new integrated QoS-aware energy management schemes. In this paper, we propose a joint power-QoS (PEH-QoS) control scheme, composed of three modules that interact in order to make optimal use of energy and achieve the best possible QoS. The proposed scheme ensures that a sensor node is able to detect the medical events and transmit the respective data packets efficiently. Extensive simulations, conducted for different human activities (i.e., relaxing, walking, running, and cycling), have shown that the application of PEH-QoS in a medical node increases the detection efficiency, the throughput, and the energy efficiency of the system.

A near-optimum cross-layered distributed queuing protocol for wireless LAN

Distributed queuing collision avoidance (DQCA) is a distributed MAC protocol for WLAN systems that offers near optimum performance. The protocol implements a reservation scheme that ensures collision-free data transmissions for high traffic load and switches smoothly and automatically to a random access mechanism when the traffic load is light, improving the delay performance for this situation. In this article the DQCA protocol operation is thoroughly described, and its algorithm rules are given. Furthermore, an enhanced cross-layer scheduling mechanism is also proposed for inclusion in the protocol procedure. This mechanism employs a virtual priority function to reschedule transmissions according to a cross-layer design. Two possible configurations are described in this article by including a PHY-MAC dialog involving channel stale information and the waiting time of the packets in the system, offering a trade-off between throughput maximization and fairness. The performance in terms of throughput and mean delay of DQCA and the two cross-layer schemes has been evaluated through simulations, and a significant enhancement over legacy IEEE 802.11 operation is achieved. The obtained results emphasize the advantages of the proposed schemes and the importance of cross-layer design in wireless communication systems.

Information Exchange in Randomly Deployed Dense WSNs With Wireless Energy Harvesting Capabilities

As large-scale dense and often randomly deployed wireless sensor networks (WSNs) become widespread, local information exchange between colocated sets of nodes may play a significant role in handling the excessive traffic volume. Moreover, to account for the limited life-span of the wireless devices, harvesting the energy of the network transmissions provides significant benefits to the lifetime of such networks. In this paper, we study the performance of communication in dense networks with wireless energy harvesting (WEH)-enabled sensor nodes. In particular, we examine two different communication scenarios (direct and cooperative) for data exchange and we provide theoretical expressions for the probability of successful communication. Then, considering the importance of lifetime in WSNs, we employ state-of-the-art WEH techniques and realistic energy converters, quantifying the potential energy gains that can be achieved in the network. Our analytical derivations, which are validated by extensive Monte-Carlo simulations, highlight the importance of WEH in dense networks and identify the tradeoffs between the direct and cooperative communication scenarios.

Game theoretic approach for switching off base stations in multi-operator environments

The emerging increase of the number of Base Stations causes redundant energy consumption, especially during low traffic periods, when the Base Stations capacity is underutilized. In this paper, we study energy efficiency issues in multi-operator mobile networks. Our primary goal is to save energy, without compromising the offered Quality of Service, by switching off the excessive Base Stations. To this end, we propose a novel game theoretic strategy using cost-based functions to decide the best suitable Base Stations to remain active. Mathematical analysis and simulations demonstrate that the proposed scheme can significantly reduce the energy consumption.

Energy-efficient infrastructure sharing in multi-operator mobile networks

Network infrastructure sharing and base station switching off mechanisms have been recently introduced as promising solutions toward energy and cost reduction in cellular networks. Although these techniques are usually studied independently, their combination offers new alternatives to MNOs for serving their users and could potentially provide them with additional benefits. In this article we introduce the concept of intra-cell roaming-based infrastructure sharing, where the MNOs may switch off their BSs and roam their traffic to active BSs operated by other MNOs in the same cell. Motivated by the coexistence of multiple operators in the same area, we present possible network deployments and architectures in current and future cellular scenarios, discussing their particular characteristics. In addition, we propose an innovative distributed game theoretic BS switching off scheme, employing an integrated cost function that takes into account all the different cases for a given operator to serve its own traffic (i.e. through active BSs of neighboring cells or exploiting intra-cell roaming-based infrastructure sharing). Finally, we demonstrate some indicative simulation results in realistic scenarios to quantify the potential energy and financial benefits that our proposed scheme offers to the MNOs in multi-operator environments, providing them with the necessary incentives to participate in the infrastructure sharing.

Reliable MAC design for ambient assisted living: moving the coordination to the cloud

AAL technologies constitute a new paradigm that promises quality of life enhancements in chronic care patients and elderly people. From a communication perspective, they involve heterogeneous deployments of body and ambient sensors in complex multihop topologies. Such networks can significantly benefit from the application of cooperative schemes based on network coding, where random linear combinations of the original data packets are transmitted in order to exploit diversity. Nevertheless, network coordination is sometimes required to obtain the full potential of these schemes, especially in the presence of channel errors, requiring the design of efficient, reliable, and versatile MAC protocols. Motivated by the recent advances in cloud computing, we investigate the possibility of transferring the network coordination to the cloud while maintaining the data exchange and storage at a local data plane. Hence, we design a general framework for the development of cloudassisted protocols for AAL applications and propose a high-performance and error-resilient MAC scheme with cloud capabilities.

Dynamic energy efficient distance-aware Base Station switch on/off scheme for LTE-advanced

Reducing the energy consumption in wireless networks has become a significant problem, not only because of its great impact on the global energy crisis, but also because it represents a noteworthy cost for telecommunication operators. The Base Stations (BSs), constituting the main component of wireless infrastructure, are intended to serve their customers during peak time periods. On the other hand, they are more than sufficient when the traffic load is low. Our paper proposes a solution for the problem of inefficient use by using a dynamic BSs switch on/off algorithm. We demonstrate via analysis and simulations that we can achieve significant reduction in energy consumption when we dynamically switch off the unnecessary BSs depending on the traffic variations and the distance between the User Equipments (UEs) and their associated BS. While maintaining the Quality of Service (QoS), we calculate the maximum number of BSs that can be switched off considering the time varying characteristic of the traffic pattern.