Effect of Energy Harvesting on Stable Throughput in Cooperative Relay Systems

Pappas, Nikolaos,Kountouris, Marios,Jeon, Jeongho,Ephremides, Anthony,Traganitis, Apostolos The Korea Institute of Information and Commucation 2016 Journal of communications and networks Vol.18 No.2

In this paper, the impact of energy constraints on a two-hop network with a source, a relay and a destination under random medium access is studied. A collision channel with erasures is considered, and the source and the relay nodes have energy harvesting capabilities and an unlimited battery to store the harvested energy. Additionally, the source and the relay node have external traffic arrivals and the relay forwards a fraction of the source node's traffic to the destination; the cooperation is performed at the network level. An inner and an outer bound of the stability region for a given transmission probability vector are obtained. Then, the closure of the inner and the outer bound is obtained separately and they turn out to be identical. This work is not only a step in connecting information theory and networking, by studying the maximum stable throughput region metric but also it taps the relatively unexplored and important domain of energy harvesting and assesses the effect of that on this important measure.

State-aware Real-time Tracking and Remote Reconstruction of a Markov Source

Salimnejad, Mehrdad,Kountouris, Marios,Pappas, Nikolaos 한국통신학회 2023 Journal of communications and networks Vol.25 No.5

The problem of real-time remote tracking and reconstruction of a two-state Markov process is considered here. A transmitter sends samples from an observed information source to a remote monitor over an unreliable wireless channel. The receiver, in turn, performs an action according to the state of the reconstructed source. We propose a state-aware randomized stationary sampling and transmission policy which accounts for the importance of different states of the information source, and their impact on the goal of the communication process. We then analyze the performance of the proposed policy, and compare it with existing goal-oriented joint sampling and transmission policies, with respect to a set of performance metrics. Specifically, we study the real-time reconstruction error, the cost of actuation error, the consecutive error, and a new metric, coined importance-aware consecutive error. In addition, we formulate and solve a constrained optimization problem that aims to obtain the optimal sampling probabilities that minimize the average cost of actuation error. Our results show that in the scenario of constrained sampling generation, the optimal state-aware randomized stationary policy outperforms all other sampling policies for fast evolving sources, and, under certain conditions, for slowly varying sources. Otherwise, a semantics-aware policy performs better only when the source is slowly varying.

Effect of Energy Harvesting on Stable Throughput in Cooperative Relay Systems

Nikolaos Pappas,Marios Kountouris,전정호,Anthony Ephremides,Apostolos Traganitis 한국통신학회 2016 Journal of communications and networks Vol.18 No.2

In this paper, the impact of energy constraints on a twohopnetwork with a source, a relay and a destination under randommedium access is studied. A collision channel with erasures is considered,and the source and the relay nodes have energy harvestingcapabilities and an unlimited battery to store the harvested energy. Additionally, the source and the relay node have external trafficarrivals and the relay forwards a fraction of the source node’s traf-fic to the destination; the cooperation is performed at the networklevel. An inner and an outer bound of the stability region for agiven transmission probability vector are obtained. Then, the closureof the inner and the outer bound is obtained separately andthey turn out to be identical. Thiswork is not only a step in connectinginformation theory and networking, by studying the maximumstable throughput region metric but also it taps the relatively unexploredand important domain of energy harvesting and assessesthe effect of that on this important measure.

Energy Efficient Heterogeneous Cellular Networks

Yong Sheng Soh,Quek, T. Q. S.,Kountouris, M.,Hyundong Shin IEEE 2013 IEEE journal on selected areas in communications Vol.31 No.5

<P>With the exponential increase in mobile internet traffic driven by a new generation of wireless devices, future cellular networks face a great challenge to meet this overwhelming demand of network capacity. At the same time, the demand for higher data rates and the ever-increasing number of wireless users led to rapid increases in power consumption and operating cost of cellular networks. One potential solution to address these issues is to overlay small cell networks with macrocell networks as a means to provide higher network capacity and better coverage. However, the dense and random deployment of small cells and their uncoordinated operation raise important questions about the energy efficiency implications of such multi-tier networks. Another technique to improve energy efficiency in cellular networks is to introduce active/sleep (on/off) modes in macrocell base stations. In this paper, we investigate the design and the associated tradeoffs of energy efficient cellular networks through the deployment of sleeping strategies and small cells. Using a stochastic geometry based model, we derive the success probability and energy efficiency in homogeneous macrocell (single-tier) and heterogeneous K-tier wireless networks under different sleeping policies. In addition, we formulate the power consumption minimization and energy efficiency maximization problems, and determine the optimal operating regimes for macrocell base stations. Numerical results confirm the effectiveness of switching off base stations in homogeneous macrocell networks. Nevertheless, the gains in terms of energy efficiency depend on the type of sleeping strategy used. In addition, the deployment of small cells generally leads to higher energy efficiency but this gain saturates as the density of small cells increases. In a nutshell, our proposed framework provides an essential understanding on the deployment of future green heterogeneous networks.</P>

Cooperative Caching and Transmission Design in Cluster-Centric Small Cell Networks

Chen, Zheng,Lee, Jemin,Quek, Tony Q. S.,Kountouris, Marios INSTITUTE OF ELECTRICAL AND ELECTRONICS ENGINEERS 2017 IEEE Transactions on Wireless Communications Vol. No.

<P>Wireless content caching in small cell networks (SCNs) has recently been considered as an efficient way to reduce the data traffic and the energy consumption of the backhaul in emerging heterogeneous cellular networks. In this paper, we consider a cluster-centric SCN with combined design of cooperative caching and transmission policy. Small base stations (SBSs) are grouped into disjoint clusters, in which in-cluster cache space is utilized as an entity. We propose a combined caching scheme, where part of the cache space in each cluster is reserved for caching the most popular content in every SBS, while the remaining is used for cooperatively caching different partitions of the less popular content in different SBSs, as a means to increase local content diversity. Depending on the availability and placement of the requested content, coordinated multi-point technique with either joint transmission or parallel transmission is used to deliver content to the served user. Using Poisson point process for the SBS location distribution and a hexagonal grid model for the clusters, we provide analytical results on the successful content delivery probability of both transmission schemes for a user located at the cluster center. Our analysis shows an inherent tradeoff between transmission diversity and content diversity in our cooperation design. We also study the optimal cache space assignment for two objective functions: maximization of the cache service performance and the energy efficiency. Simulation results show that the proposed scheme achieves performance gain by leveraging cache-level and signal-level cooperation and adapting to the network environment and user quality-of-service requirements.</P>

Antioxidant Properties of Raisins (Vitis vinifera L.)

Andriana C. Kaliora,Aggeliki M. Kountouri,Vaios T. Karathanos 한국식품영양과학회 2009 Journal of medicinal food Vol.12 No.6

Currants and sultanas (Vitis vinifera L., Family Vitaceae) are dried vine products produced in Greece and used widely in the Mediterranean diet. We investigated the polar methanol extracts from the raisins for the antiradical activity, polyphenol content, cytotoxicity in peripheral blood mononuclear cells, total glutathione (GSH) levels, oxidized glutathione (GSSG) levels, and inhibition of low-density lipoprotein (LDL) oxidation. Extracts exhibited 1,1-diphenyl-2-picrylhydrazyl scavenging activity and inhibited tert-butylhydroperoxide (tBHP)-induced cytotoxicity, GSH decrease, and LDL oxidation. Fluorescence microscopy revealed the characteristic apoptotic patterns with tBHP and inhibition with the extracts. Elevated levels of total GSH and unaltered levels of GSSG with extract treatment demonstrated the induction of γ-glutamylcysteine synthetase. The antioxidant activity was correlated to the polyphenolic content. Greek currants and sultanas are suggested as antioxidant components of the Mediterranean basin.