Christos Bouras
Short CV: Christos Bouras is Professor in the University of Patras, Department of Computer Engineering and Informatics. Also he is a scientific advisor of Research Unit 6 in Computer Technology Institute and Press – Diophantus, Patras, Greece. His research interests include Analysis of Performance of Networking and Computer Systems, Computer Networks and Protocols, Mobile and Wireless Communications, Telematics and New Services, QoS and Pricing for Networks and Services, e-learning, Networked Virtual Environments and WWW Issues. He has extended professional experience in Design and Analysis of Networks, Protocols, Telematics and New Services. He has published more than 450 papers in various well-known refereed books, conferences and journals. He is a co-author of 9 books in Greek and editor of 2 in English. He has been member of editorial board for international journals and PC member and referee in various international journals and conferences. He has participated in R&D projects.
Journal Articles
Bouras, Christos; Kalogeropoulos, Rafail
A QoS driven adaptive mechanism for Downlink and Uplink Decoupling in 5G Journal Article
In: Internet of Things: Engineering Cyber Physical Human Systems, Elsevier Science, vol. 11, pp. 1-11, 2020.
Abstract | Links | BibTeX | Tags:
@article{4466,
title = {A QoS driven adaptive mechanism for Downlink and Uplink Decoupling in 5G},
author = {Christos Bouras and Rafail Kalogeropoulos},
url = {https://telematics.upatras.gr/1-s2-0-s2542660520300524-main/},
year = {2020},
date = {2020-01-01},
urldate = {2020-01-01},
journal = {Internet of Things: Engineering Cyber Physical Human Systems, Elsevier Science},
volume = {11},
pages = {1-11},
abstract = {In current cellular networks, cell association is heavily based on the Downlink signal power and all devices are associated with the same Base Station (BS) in Downlink (DL) and Uplink (UL). While as of now this technique has been proved adequate in homogeneous networks where all BSs have similar transmission levels, in increasingly dense heterogeneous networks (HetNets) rate is heavily dependent on the load, which can significantly vary from BS to BS. Due to increased demands for usage over several devices in HetNets, large disparities in the DL pose a threat to the quality of services (QoS) rendered by the network and this technique seems obsolete. Decoupling Uplink and Downlink is the proposed solution, where the UL cell association is not necessarily based on the same criteria as the DL association. We propose using Signal to Noise Ratio (SINR) and Path Loss with Range Extension (PLRE) as factors for choosing the appropriate BS for connection in DL and UL respectively for every user, taking into consideration the BS’s Resource Block availability, to avoid overloading BSs. We will use simulations to test our approach, with different Path Loss offsets for PLRE, to note the importance of adaptive mechanisms.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
In current cellular networks, cell association is heavily based on the Downlink signal power and all devices are associated with the same Base Station (BS) in Downlink (DL) and Uplink (UL). While as of now this technique has been proved adequate in homogeneous networks where all BSs have similar transmission levels, in increasingly dense heterogeneous networks (HetNets) rate is heavily dependent on the load, which can significantly vary from BS to BS. Due to increased demands for usage over several devices in HetNets, large disparities in the DL pose a threat to the quality of services (QoS) rendered by the network and this technique seems obsolete. Decoupling Uplink and Downlink is the proposed solution, where the UL cell association is not necessarily based on the same criteria as the DL association. We propose using Signal to Noise Ratio (SINR) and Path Loss with Range Extension (PLRE) as factors for choosing the appropriate BS for connection in DL and UL respectively for every user, taking into consideration the BS’s Resource Block availability, to avoid overloading BSs. We will use simulations to test our approach, with different Path Loss offsets for PLRE, to note the importance of adaptive mechanisms.
Bouras, Christos; Kollia, Anastasia; Maligianni, Eleftheria
Techno - economic comparison of Cognitive Radio and Software Defined Network (SDN) cost models in 5G networks Journal Article
In: Wireless Personal Communications, Springer Verlang, vol. 114, pp. 1403–1430, 2020.
Abstract | Links | BibTeX | Tags:
@article{4468,
title = {Techno - economic comparison of Cognitive Radio and Software Defined Network (SDN) cost models in 5G networks},
author = {Christos Bouras and Anastasia Kollia and Eleftheria Maligianni},
url = {https://telematics.upatras.gr/bouras2020_article_techno-economiccomparisonofcog/},
year = {2020},
date = {2020-01-01},
urldate = {2020-01-01},
journal = {Wireless Personal Communications, Springer Verlang},
volume = {114},
pages = {1403–1430},
abstract = {5G is anticipated in 2020. In this generation of mobile networks, a great deal of requirements have been set. Although, there are many strong technologies in the telecommunications’ sector they do not respond to the 5G goals. On the other hand, telecommunication operators and providers do not want to invest in new equipment/architectures. Cognitive Radio (CR) and Software Defined Networking (SDN) are two technologies with special and vigorous advantages. In this paper, several technical and economic models are developed. The CR is combined with the Stackelberg game. A Sensitivity Analysis (SA) is implemented and the parameters that impact mostly on the model are pinpointed. It is shown that the CR technology could offer all its fundamental cognitive advantages and even financial profits to the telecommunication companies.},
keywords = {},
pubstate = {published},
tppubtype = {article}
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5G is anticipated in 2020. In this generation of mobile networks, a great deal of requirements have been set. Although, there are many strong technologies in the telecommunications’ sector they do not respond to the 5G goals. On the other hand, telecommunication operators and providers do not want to invest in new equipment/architectures. Cognitive Radio (CR) and Software Defined Networking (SDN) are two technologies with special and vigorous advantages. In this paper, several technical and economic models are developed. The CR is combined with the Stackelberg game. A Sensitivity Analysis (SA) is implemented and the parameters that impact mostly on the model are pinpointed. It is shown that the CR technology could offer all its fundamental cognitive advantages and even financial profits to the telecommunication companies.
Bouras, Christos; Kokkalis, Stylianos; Kollia, Anastasia; Papazois, Andreas
Techno-economic comparison of MIMO and DAS cost models in 5G networks Journal Article
In: Wireless Networks, Springer Verlang, vol. 26, pp. 1-15, 2020.
Abstract | Links | BibTeX | Tags:
@article{4311,
title = {Techno-economic comparison of MIMO and DAS cost models in 5G networks},
author = {Christos Bouras and Stylianos Kokkalis and Anastasia Kollia and Andreas Papazois},
url = {https://telematics.upatras.gr/bouras2020_article_techno-economiccomparisonofmim/},
year = {2020},
date = {2020-01-01},
urldate = {2020-01-01},
journal = {Wireless Networks, Springer Verlang},
volume = {26},
pages = {1-15},
abstract = {High communicational standards have been set for the 5G mobile networks. Therefore, it is of great importance that technological solutions that include all the significant features, such as the high coverage and capacity and low round-trip delays, are adopted for the next generation of mobile networks. Except for their technical efficiency, these technologies should be profitable for providers as well. As a result, the need for limiting the costs spent for the development of these technologies emerges. In this papers, four models two for each one of the two solutions for 5G networks are developed, namely the Multiple Input Multiple Output (MIMO) and the Distributed Antenna System. The architectural models assumed for the techno-economic analyses are presented. The mathematical models for both technologies are developed. Experiments are conducted using prices of the Greek market and also Sensitivity Analysis (SA) is used to pinpoint, which cost parameters are the most expensive ones and therefore it is likely that they discourage providers to invest in them. To our knowledge there are not many studies comparing and contrasting these technologies and there is no SA for MIMO. Therefore, it is considered that research for these models is of vital importance for the next generation of mobile communication networks, as they are foundation stonesfor the formation of 5G.},
keywords = {},
pubstate = {published},
tppubtype = {article}
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High communicational standards have been set for the 5G mobile networks. Therefore, it is of great importance that technological solutions that include all the significant features, such as the high coverage and capacity and low round-trip delays, are adopted for the next generation of mobile networks. Except for their technical efficiency, these technologies should be profitable for providers as well. As a result, the need for limiting the costs spent for the development of these technologies emerges. In this papers, four models two for each one of the two solutions for 5G networks are developed, namely the Multiple Input Multiple Output (MIMO) and the Distributed Antenna System. The architectural models assumed for the techno-economic analyses are presented. The mathematical models for both technologies are developed. Experiments are conducted using prices of the Greek market and also Sensitivity Analysis (SA) is used to pinpoint, which cost parameters are the most expensive ones and therefore it is likely that they discourage providers to invest in them. To our knowledge there are not many studies comparing and contrasting these technologies and there is no SA for MIMO. Therefore, it is considered that research for these models is of vital importance for the next generation of mobile communication networks, as they are foundation stonesfor the formation of 5G.
Baumann, Kurt; Bouras, Christos; Kokkinos, Vasileios; Papachristos, Nikolaos; Stamos, Kostas
WiFiMon - A Tool for Wi-Fi Performance Monitoring and Verification Journal Article
In: International Journal of Wireless Networks and Broadband Technologies (IJWNBT), IGI Global, vol. 8, pp. 1-18, 2019.
Abstract | Links | BibTeX | Tags:
@article{4405,
title = {WiFiMon - A Tool for Wi-Fi Performance Monitoring and Verification},
author = {Kurt Baumann and Christos Bouras and Vasileios Kokkinos and Nikolaos Papachristos and Kostas Stamos},
url = {https://telematics.upatras.gr/wifimon_-a-tool-for-wi-fi-performance-monitoring-and-verification/},
year = {2019},
date = {2019-01-01},
urldate = {2019-01-01},
journal = {International Journal of Wireless Networks and Broadband Technologies (IJWNBT), IGI Global},
volume = {8},
pages = {1-18},
abstract = {Measuring network quality of a wireless network as experienced by end-users is quite difficult, as there isn’t a single tool available that can record measurements on all sides of the system. The approach presented in this research work is based on the end-user feedback, giving the opportunity of visualization of network performance in real time. We initially present an overview of the developed tool, called WiFiMon, which has the ability to capture, record measurements and export statistics on the quality of Wi-Fi network as perceived by the end-users. The measurements are initiated by the end-users - without their intervention – after they visit a web page or use a mobile application. WiFiMon aims to give a clear understanding of the Wi-Fi network conditions by measuring specific parameters of the network, such as download/upload throughput, and correlate these measurements with raw data from various log files to obtain additional information regarding the performance of specific access points. The results reveal the functionality of the proposed tool and its scalability.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Measuring network quality of a wireless network as experienced by end-users is quite difficult, as there isn’t a single tool available that can record measurements on all sides of the system. The approach presented in this research work is based on the end-user feedback, giving the opportunity of visualization of network performance in real time. We initially present an overview of the developed tool, called WiFiMon, which has the ability to capture, record measurements and export statistics on the quality of Wi-Fi network as perceived by the end-users. The measurements are initiated by the end-users - without their intervention – after they visit a web page or use a mobile application. WiFiMon aims to give a clear understanding of the Wi-Fi network conditions by measuring specific parameters of the network, such as download/upload throughput, and correlate these measurements with raw data from various log files to obtain additional information regarding the performance of specific access points. The results reveal the functionality of the proposed tool and its scalability.
Bouras, Christos; Kollia, Anastasia
Techno - economic analysis for programmable networks Journal Article
In: Wiley 5G Ref: The Essential 5G Reference Online, Wiley InterScience, pp. 1 - 22, 2019.
Abstract | Links | BibTeX | Tags:
@article{4404,
title = {Techno - economic analysis for programmable networks},
author = {Christos Bouras and Anastasia Kollia},
url = {https://telematics.upatras.gr/9781119471509-w5gref114/},
year = {2019},
date = {2019-01-01},
urldate = {2019-01-01},
journal = {Wiley 5G Ref: The Essential 5G Reference Online, Wiley InterScience},
pages = {1 - 22},
abstract = {The forthcoming advent of the fifth generation of mobile networks (5G) will boost technology, as new solutions are needed to meet the growing demands of 5G. These novelties are pinpointed both by scientists and elecommunication providers. Programmable logic solutions are going to be used, as they accumulate financial, performance and environmental benefits. The programmable logic nowadays is represented by the combination of the Software Defined Networking (SDN) technology with the Network Function Virtualization (NFV). This combination not only reduces hardware as most network components are replaced by Network Functions or Virtual Machines (VMs), but also offers better resource allocation and provides more bandwidth, CPU etc. to the parts of the network that become more congested. Solutions, such as SDN, may concentrate fundamental advantages and profits, but they appear to face basic problems and therefore, key questions are raised concerning their cost and safety. One of these issues contains all the expenses that need to be made for the acquisition of the technology and the adjustments that need to be incorporated into current infrastructure so that it is able to cover SDN networks as well. This paper analyses a programmable model of SDN combined with NFVs. A Sensitivity Analysis (SA) is held to enable determining the factors, that largely influence the pricing so as to propose ways to significantly reduce several types of costs and propose solutions or research directions to cut down on the expenses of these network factors.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The forthcoming advent of the fifth generation of mobile networks (5G) will boost technology, as new solutions are needed to meet the growing demands of 5G. These novelties are pinpointed both by scientists and elecommunication providers. Programmable logic solutions are going to be used, as they accumulate financial, performance and environmental benefits. The programmable logic nowadays is represented by the combination of the Software Defined Networking (SDN) technology with the Network Function Virtualization (NFV). This combination not only reduces hardware as most network components are replaced by Network Functions or Virtual Machines (VMs), but also offers better resource allocation and provides more bandwidth, CPU etc. to the parts of the network that become more congested. Solutions, such as SDN, may concentrate fundamental advantages and profits, but they appear to face basic problems and therefore, key questions are raised concerning their cost and safety. One of these issues contains all the expenses that need to be made for the acquisition of the technology and the adjustments that need to be incorporated into current infrastructure so that it is able to cover SDN networks as well. This paper analyses a programmable model of SDN combined with NFVs. A Sensitivity Analysis (SA) is held to enable determining the factors, that largely influence the pricing so as to propose ways to significantly reduce several types of costs and propose solutions or research directions to cut down on the expenses of these network factors.
Ahmad, Shakeel; Bouras, Christos; Buyukkaya, Eliya; Dawood, Muneeb; Hamzaoui, Raouf; Kapoulas, Vaggelis; Papazois, Andreas; Simon, Gwendal
Peer-to-peer live video streaming with rateless codes for massively multiplayer online games Journal Article
In: Peer-to-Peer Networking and Applications, Springer Verlang, vol. 11, pp. 44-62, 2018.
Abstract | Links | BibTeX | Tags:
@article{4132,
title = {Peer-to-peer live video streaming with rateless codes for massively multiplayer online games},
author = {Shakeel Ahmad and Christos Bouras and Eliya Buyukkaya and Muneeb Dawood and Raouf Hamzaoui and Vaggelis Kapoulas and Andreas Papazois and Gwendal Simon},
url = {https://telematics.upatras.gr/10-1007_s12083-016-0495-7/},
year = {2018},
date = {2018-01-01},
urldate = {2018-01-01},
journal = {Peer-to-Peer Networking and Applications, Springer Verlang},
volume = {11},
pages = {44-62},
abstract = {We present a multi-level multi-overlay hybrid peer-to-peer live video system that enables players of Massively Multiplayer Online Games to simultaneously stream the video of their game and watch the game videos of other players. Each live video bitstream is encoded with rateless codes and multiple trees are used to transmit the encoded symbols. Trees are constructed dynamically with the aim to minimize the transmission rate at the source while maximizingthe number of served peers and guaranteeing on-time delivery and reliability. ns-2 simulations and real measurements on the Internet show competitive performance in terms of start-up delay, playback lag, rejection rate, used bandwidth, continuity index, and video quality.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We present a multi-level multi-overlay hybrid peer-to-peer live video system that enables players of Massively Multiplayer Online Games to simultaneously stream the video of their game and watch the game videos of other players. Each live video bitstream is encoded with rateless codes and multiple trees are used to transmit the encoded symbols. Trees are constructed dynamically with the aim to minimize the transmission rate at the source while maximizingthe number of served peers and guaranteeing on-time delivery and reliability. ns-2 simulations and real measurements on the Internet show competitive performance in terms of start-up delay, playback lag, rejection rate, used bandwidth, continuity index, and video quality.
Bouras, Christos; Kollia, Anastasia; Papazois, Andreas
Exploring SDN & NFV in 5G Using ONOS & POX Controllers Journal Article
In: International Journal of Interdisciplinary Telecommunications and Networking, (IJITN), IGI Global 2018, vol. 10, pp. 46-60, 2018.
Abstract | Links | BibTeX | Tags:
@article{4223,
title = {Exploring SDN & NFV in 5G Using ONOS & POX Controllers},
author = {Christos Bouras and Anastasia Kollia and Andreas Papazois},
url = {https://telematics.upatras.gr/ijitn/},
year = {2018},
date = {2018-01-01},
urldate = {2018-01-01},
journal = {International Journal of Interdisciplinary Telecommunications and Networking, (IJITN), IGI Global 2018},
volume = {10},
pages = {46-60},
abstract = {Novel functionalities will take advantage of the cloud networking and will gradually replace the existing infrastructure of mobile networks with a virtualized one. Two technologies, namely Software Defined Networking (SDN) and Network Function Virtualization (NFV), offer their important benefits and a combination of them is an answer to the demands raised, such as Central Office Re-architected as a Data Center (CORD). Open Network Operating System (ONOS) and POX are SDN controllers and offer an option to combine SDN and NFV addressing many ongoing problems in the field of mobile networks. In this paper, technologies and both controllers are compared and contrasted. Indicative cases of topologies are simulated and help evaluating both controllers. According to the experimental findings, ONOS is one of the most important controllers for practical, theoretical, research and educational purposes, while POX is a useful and simpler controller for other educative applications},
keywords = {},
pubstate = {published},
tppubtype = {article}
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Novel functionalities will take advantage of the cloud networking and will gradually replace the existing infrastructure of mobile networks with a virtualized one. Two technologies, namely Software Defined Networking (SDN) and Network Function Virtualization (NFV), offer their important benefits and a combination of them is an answer to the demands raised, such as Central Office Re-architected as a Data Center (CORD). Open Network Operating System (ONOS) and POX are SDN controllers and offer an option to combine SDN and NFV addressing many ongoing problems in the field of mobile networks. In this paper, technologies and both controllers are compared and contrasted. Indicative cases of topologies are simulated and help evaluating both controllers. According to the experimental findings, ONOS is one of the most important controllers for practical, theoretical, research and educational purposes, while POX is a useful and simpler controller for other educative applications
Bouras, Christos; Kanakis, Nikolaos
Evolving AL-FEC application on 5G NGMN-Edge computing systems Journal Article
In: Technology and Engineering Systems Journal, Special Issue on Multidisciplinary Sciences and Engineering (ASTEJS), Advances in Science, vol. 3, pp. 152-160, 2018.
Abstract | Links | BibTeX | Tags:
@article{4326,
title = {Evolving AL-FEC application on 5G NGMN-Edge computing systems},
author = {Christos Bouras and Nikolaos Kanakis},
url = {https://telematics.upatras.gr/galleyproof-118m-07-143-galleyproof-original_astesj_030519/},
year = {2018},
date = {2018-01-01},
urldate = {2018-01-01},
journal = {Technology and Engineering Systems Journal, Special Issue on Multidisciplinary Sciences and Engineering (ASTEJS), Advances in Science},
volume = {3},
pages = {152-160},
abstract = {Fifth generation of mobile networks (5G) comes to cope with the context of the new mobile telecommunications era. Edge computing is a new collaborative technology under standardization utilizing end-user devices or near-end-user edge devices to operate processing, communication, or control operations. The achievement of efficient error control is a very critical aspect in the successful development of 5G Next Generation Mobile Networks (NGMN). Especially utilizing Forward Error Correction (FEC) codes on the application level is an efficient approach on improving error control on NGMN since it is adopted in several mobile multicast standards. FEC is a feedback free error control technique where redundant data are introduced with the source data to enable the recipient recovering from packet losses with an interesting approach on applying AL-FEC error protection introduces deterministic or randomized online algorithms. Based on this we present a novel online scheme on applying AL-FEC application on the context of the AL-FEC policy online problem. In this work we present an online algorithm based on feedback received from mobile end-users which adapts the introduced protection based on this. Another aspect of this work is the utilization of AL-FEC protection on the edge level based on RaptorQ FEC codes.},
keywords = {},
pubstate = {published},
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Fifth generation of mobile networks (5G) comes to cope with the context of the new mobile telecommunications era. Edge computing is a new collaborative technology under standardization utilizing end-user devices or near-end-user edge devices to operate processing, communication, or control operations. The achievement of efficient error control is a very critical aspect in the successful development of 5G Next Generation Mobile Networks (NGMN). Especially utilizing Forward Error Correction (FEC) codes on the application level is an efficient approach on improving error control on NGMN since it is adopted in several mobile multicast standards. FEC is a feedback free error control technique where redundant data are introduced with the source data to enable the recipient recovering from packet losses with an interesting approach on applying AL-FEC error protection introduces deterministic or randomized online algorithms. Based on this we present a novel online scheme on applying AL-FEC application on the context of the AL-FEC policy online problem. In this work we present an online algorithm based on feedback received from mobile end-users which adapts the introduced protection based on this. Another aspect of this work is the utilization of AL-FEC protection on the edge level based on RaptorQ FEC codes.
Bouras, Christos; Kanakis, Nikolaos; Kokkinos, Vasileios; Papachristos, Nikolaos; Vouyioukas, Demosthenes
MCS Selection Exploiting Femtocells Utilization in Multicast Transmissions Journal Article
In: International Journal of Communication Systems, Wiley InterScience, vol. 31, pp. 1 - 13 , 2018.
Abstract | Links | BibTeX | Tags:
@article{4259,
title = {MCS Selection Exploiting Femtocells Utilization in Multicast Transmissions},
author = {Christos Bouras and Nikolaos Kanakis and Vasileios Kokkinos and Nikolaos Papachristos and Demosthenes Vouyioukas},
url = {https://telematics.upatras.gr/bouras_et_al-2018-international_journal_of_communication_systems-1/},
year = {2018},
date = {2018-01-01},
urldate = {2018-01-01},
journal = {International Journal of Communication Systems, Wiley InterScience},
volume = {31},
pages = {1 - 13 },
abstract = {Multicast-Broadcast over Single Frequency Network (MBSFN) technology, as introduced by the Long Term Evolution Advanced (LTE-A) group, is expected to be part of the upcoming cellular systems offering resource efficiency to broadcast services. MBSFN transmission is suitable to serve multicast groups searching the same content. In addition, the fast emerging technology of femtocells networks and their hybrid nature can lead to efficient resource sharing between non-subscribed users when located inside their coverage. The focus of this manuscript is twofold; firstly, we have contacted simulation experiments to compare the MBSFN transmission with the traditional PTP transmission for various femtocell distributions and network topology changes; secondly, a novel multicast transmissions mechanism is proposed from non-subscribed users who exploit femtocells resources for broadcast services, without limiting user’s data requirements. The simulation results lead to a significant system’s performance in terms of average throughput, total capacity and energy consumption.},
keywords = {},
pubstate = {published},
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Multicast-Broadcast over Single Frequency Network (MBSFN) technology, as introduced by the Long Term Evolution Advanced (LTE-A) group, is expected to be part of the upcoming cellular systems offering resource efficiency to broadcast services. MBSFN transmission is suitable to serve multicast groups searching the same content. In addition, the fast emerging technology of femtocells networks and their hybrid nature can lead to efficient resource sharing between non-subscribed users when located inside their coverage. The focus of this manuscript is twofold; firstly, we have contacted simulation experiments to compare the MBSFN transmission with the traditional PTP transmission for various femtocell distributions and network topology changes; secondly, a novel multicast transmissions mechanism is proposed from non-subscribed users who exploit femtocells resources for broadcast services, without limiting user’s data requirements. The simulation results lead to a significant system’s performance in terms of average throughput, total capacity and energy consumption.
Bouras, Christos; Gkamas, Apostolos; Kapoulas, Vaggelis; Politaki, Dimitra; Tsanai, Enea
Video transmission in mobile ad hoc networks using multiple interfaces and multiple channels Journal Article
In: International Journal of Communication Systems, Wiley InterScience, vol. 8, pp. 1-28, 2017.
Abstract | Links | BibTeX | Tags:
@article{4131,
title = {Video transmission in mobile ad hoc networks using multiple interfaces and multiple channels},
author = {Christos Bouras and Apostolos Gkamas and Vaggelis Kapoulas and Dimitra Politaki and Enea Tsanai},
url = {https://telematics.upatras.gr/ijcs/},
year = {2017},
date = {2017-05-01},
urldate = {2017-05-01},
journal = {International Journal of Communication Systems, Wiley InterScience},
volume = {8},
pages = {1-28},
abstract = {Mobile Ad hoc NETworks (MANETs) are an important part of wireless communications and the increasing use of mobile devices is confirming that. MANETs can be of great value in Emergency Response situations where communication between mobile deployed units is critical and wired or wireless infrastructures may not be present or functional. In emergency scenarios, multimedia communication is very important for decision making and situation assessment. This requires up-to-date (on-line) information feed on the situation, including voice and video from the affected zone. However, MANETs do not seem to efficiently support multimedia applications, and this is quite evident in video transmission. One way to remedy this is to use more (wireless) interfaces per mobile node and consequently more communication channels. In this work, we perform an analytical study on the use of multiple interfaces and multiple channels (MIMC) in video transmission with respect to the requirements of Emergency Response Ad hoc Networks. More specifically, we examine and present the impact of using MIMC on MANETs during video transmission applications, we evaluate the performance of three basic routing protocols in MANETs, and we propose a channel selection mechanism in MANET nodes with MIMC for enhanced video transmission. In addition, we evaluate video transmission streams with rate adaptation and present comparative results. The proposed mechanism is evaluated using the ns-2 network simulator and the simulations are performed for a variety of topologies. Simulation results show that the different routing protocols respond differently when MIMC is introduced. The Ad hoc On-Demand Multipath Distance Vector and (especially) the Ad hoc On-Demand Distance Vector routing protocols benefit significantly, while the Destination Sequenced Distance Vector shows fewer improvements. The proposed mechanism is shown to be beneficial for transmitting video streams and enhances the network’s ability to accommodate more streams and reduce packet delay.},
keywords = {},
pubstate = {published},
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Mobile Ad hoc NETworks (MANETs) are an important part of wireless communications and the increasing use of mobile devices is confirming that. MANETs can be of great value in Emergency Response situations where communication between mobile deployed units is critical and wired or wireless infrastructures may not be present or functional. In emergency scenarios, multimedia communication is very important for decision making and situation assessment. This requires up-to-date (on-line) information feed on the situation, including voice and video from the affected zone. However, MANETs do not seem to efficiently support multimedia applications, and this is quite evident in video transmission. One way to remedy this is to use more (wireless) interfaces per mobile node and consequently more communication channels. In this work, we perform an analytical study on the use of multiple interfaces and multiple channels (MIMC) in video transmission with respect to the requirements of Emergency Response Ad hoc Networks. More specifically, we examine and present the impact of using MIMC on MANETs during video transmission applications, we evaluate the performance of three basic routing protocols in MANETs, and we propose a channel selection mechanism in MANET nodes with MIMC for enhanced video transmission. In addition, we evaluate video transmission streams with rate adaptation and present comparative results. The proposed mechanism is evaluated using the ns-2 network simulator and the simulations are performed for a variety of topologies. Simulation results show that the different routing protocols respond differently when MIMC is introduced. The Ad hoc On-Demand Multipath Distance Vector and (especially) the Ad hoc On-Demand Distance Vector routing protocols benefit significantly, while the Destination Sequenced Distance Vector shows fewer improvements. The proposed mechanism is shown to be beneficial for transmitting video streams and enhances the network’s ability to accommodate more streams and reduce packet delay.
Bouras, Christos; Diles, Georgios
Interference Management Strategy for 5G Femtocell Clusters Journal Article
In: Wireless Personal Communications, Springer Verlang, vol. 96, pp. 323-339, 2017.
Abstract | Links | BibTeX | Tags:
@article{4195,
title = {Interference Management Strategy for 5G Femtocell Clusters},
author = {Christos Bouras and Georgios Diles},
url = {https://telematics.upatras.gr/10-1007_s11277-017-4169-4/},
year = {2017},
date = {2017-01-01},
urldate = {2017-01-01},
journal = {Wireless Personal Communications, Springer Verlang},
volume = {96},
pages = {323-339},
abstract = {With the next generation of mobile networks closing in, its main characteristics have already been proposed and adapted. Ultra-dense heterogeneous networks seem to be one of the main drivers to answer the need for larger device connectivity and increased data rate. Multiple Base Stations with different specifications will be deployed to achieve these targets. Femtocells are a type of Base Station that is expected to dominate, due to their low cost and easy deployment and maintenance. However, trying to increase spectral efficiency with the use of femtocells, by multiple base stations utilizing the same spectrum will lead to severe interference phenomena. This can be tackled by sharing spectrum strategies and power control techniques. In this manuscript, we propose a full scheme of resource management that can be applied in instances of femtocell deployments of increased density. The mechanism is based on coordination among the femtocells to achieve better spectrum usage, on power control and on hybrid access configuration aiming to fairness in resource allocation and to the improvement of overall capacity. Conducted simulations showed that our algorithm increases the overall capacity, protects non-subscribed users and balances the hybrid access effect on subscribers.},
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tppubtype = {article}
}
With the next generation of mobile networks closing in, its main characteristics have already been proposed and adapted. Ultra-dense heterogeneous networks seem to be one of the main drivers to answer the need for larger device connectivity and increased data rate. Multiple Base Stations with different specifications will be deployed to achieve these targets. Femtocells are a type of Base Station that is expected to dominate, due to their low cost and easy deployment and maintenance. However, trying to increase spectral efficiency with the use of femtocells, by multiple base stations utilizing the same spectrum will lead to severe interference phenomena. This can be tackled by sharing spectrum strategies and power control techniques. In this manuscript, we propose a full scheme of resource management that can be applied in instances of femtocell deployments of increased density. The mechanism is based on coordination among the femtocells to achieve better spectrum usage, on power control and on hybrid access configuration aiming to fairness in resource allocation and to the improvement of overall capacity. Conducted simulations showed that our algorithm increases the overall capacity, protects non-subscribed users and balances the hybrid access effect on subscribers.
Bouras, Christos; Tsogkas, Vassilis
Improving news articles recommendations via user clustering Journal Article
In: International Journal of Machine Learning and Cybernetics, Springer Verlang, vol. 8, pp. 223-237, 2017.
Abstract | Links | BibTeX | Tags:
@article{4059,
title = {Improving news articles recommendations via user clustering},
author = {Christos Bouras and Vassilis Tsogkas},
url = {https://telematics.upatras.gr/ijmlc2/},
year = {2017},
date = {2017-01-01},
urldate = {2017-01-01},
journal = {International Journal of Machine Learning and Cybernetics, Springer Verlang},
volume = {8},
pages = {223-237},
abstract = {Although commonly only item clustering is suggested by Web mining techniques for news articles recommendation systems, one of the various tasks of personalized recommendation is categorization of Web users. With the rapid explosion of online news articles, predicting user-browsing behavior using collaborative filtering (CF) techniques has gained much attention in the web personalization area. However common CF techniques suffer from problems like low accuracy and performance. This research proposes a new personalized recommendation approach that integrates both user and text clustering based on our developed algorithm, W-kmeans, with other information retrieval (IR) techniques, like text categorization and summarization in order to provide users with the articles that match their profiles. Our system can easily adapt over time to divertive user preferences. Furthermore, experimental results show that by aggregating item and user clustering with multiple IR techniques like categorization and summarization, our recommender generates results that outperform the cases where each or both of them are used, but clustering is not applied.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Although commonly only item clustering is suggested by Web mining techniques for news articles recommendation systems, one of the various tasks of personalized recommendation is categorization of Web users. With the rapid explosion of online news articles, predicting user-browsing behavior using collaborative filtering (CF) techniques has gained much attention in the web personalization area. However common CF techniques suffer from problems like low accuracy and performance. This research proposes a new personalized recommendation approach that integrates both user and text clustering based on our developed algorithm, W-kmeans, with other information retrieval (IR) techniques, like text categorization and summarization in order to provide users with the articles that match their profiles. Our system can easily adapt over time to divertive user preferences. Furthermore, experimental results show that by aggregating item and user clustering with multiple IR techniques like categorization and summarization, our recommender generates results that outperform the cases where each or both of them are used, but clustering is not applied.
Bouras, Christos; Kollia, Anastasia; Papazois, Andreas
Dense deployments and DAS in 5G: a techno-economic comparison Journal Article
In: Wireless Personal Communications, Springer Verlang, vol. 19, 2017.
Abstract | Links | BibTeX | Tags:
@article{4139,
title = {Dense deployments and DAS in 5G: a techno-economic comparison},
author = {Christos Bouras and Anastasia Kollia and Andreas Papazois},
url = {https://telematics.upatras.gr/art2fs11277-016-3711-0/},
year = {2017},
date = {2017-01-01},
urldate = {2017-01-01},
journal = {Wireless Personal Communications, Springer Verlang},
volume = {19},
abstract = {5G wireless telecommunications require rapid data traffic and high network speed. Thus, it is important to focus on technologies that are capable of meeting these high demands. On the other hand, the cost calculation of installing, maintaining and operating a network deployment, plays an important role for its adoption by an enterprise or a network provider. In this paper, there is a presentation of cost models for Distributed Antenna Systems (DAS) and small cells, because these two technologies offer significant benefits and meet the needs of the next generation of mobile networking. A Sensitivity Analysis (SA) of several network components, such as the allocated bandwidth, the running costs, the periodical interest rate, the base station, the equipment, the power consumption, the backhauling, the implementation costs and throughput density is analyzed. Throughput density and several important information are listed and calculated, according to public data. All these components are tested, using parameters and variables to represent them in mathematical equations model resulting in a cost provision for the next five years. Then, the overall and the individual costs are computed, namely the Total Cost of Ownership (TCO), the Capital (CAPEX) and the Operational (OPEX) expenditures for several throughput density prices according to the suggested pricing models. The paper concludes by drawing fundamental conclusions for the expenses and as a result, for the viability of each technological suggestion and it ends up offering ideas for future research activity in the field.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
5G wireless telecommunications require rapid data traffic and high network speed. Thus, it is important to focus on technologies that are capable of meeting these high demands. On the other hand, the cost calculation of installing, maintaining and operating a network deployment, plays an important role for its adoption by an enterprise or a network provider. In this paper, there is a presentation of cost models for Distributed Antenna Systems (DAS) and small cells, because these two technologies offer significant benefits and meet the needs of the next generation of mobile networking. A Sensitivity Analysis (SA) of several network components, such as the allocated bandwidth, the running costs, the periodical interest rate, the base station, the equipment, the power consumption, the backhauling, the implementation costs and throughput density is analyzed. Throughput density and several important information are listed and calculated, according to public data. All these components are tested, using parameters and variables to represent them in mathematical equations model resulting in a cost provision for the next five years. Then, the overall and the individual costs are computed, namely the Total Cost of Ownership (TCO), the Capital (CAPEX) and the Operational (OPEX) expenditures for several throughput density prices according to the suggested pricing models. The paper concludes by drawing fundamental conclusions for the expenses and as a result, for the viability of each technological suggestion and it ends up offering ideas for future research activity in the field.
Bouras, Christos; Kokkinos, Vasileios; Kollia, Anastasia; Papazois, Andreas
Analyzing Small - cells and Distributed Antenna Systems from Techno - economic Perspective Journal Article
In: International Journal of Wireless Networks and Broadband Technologies (IJWNBT), IGI Global, vol. 6, pp. 45-64, 2017.
Abstract | Links | BibTeX | Tags:
@article{4191,
title = {Analyzing Small - cells and Distributed Antenna Systems from Techno - economic Perspective},
author = {Christos Bouras and Vasileios Kokkinos and Anastasia Kollia and Andreas Papazois},
url = {https://telematics.upatras.gr/analyzing-small-cells-and-distributed-antenna-systems-from-techno-economic-perspective/},
year = {2017},
date = {2017-01-01},
urldate = {2017-01-01},
journal = {International Journal of Wireless Networks and Broadband Technologies (IJWNBT), IGI Global},
volume = {6},
pages = {45-64},
abstract = {Next-generation of mobile technologies is expected to largely augment the system’s peak data rates and cut down on the round-trip delays. The main idea of using ultra-density or DAS (Distributed Antenna Systems) based on their properties, is that they are able to increase efficiency and expand network capacity without the need for more spectrum resources by redistributing the existing ones, depict them as the key solutions for the future mobile networks. Small cells and DAS were launched mainly for addressing the issue of limited connectivity indoors. There are several other important benefits of these technologies, which constitute them as bases for future generations of mobile networks, such as 5G (5G-PPP, 2014). Femtocells’ benefit is that they provide ultra-density, which is expected to be one of the essential features of 5G. Ultra-dense networks coexist with the existing macrocellular ones forming altogether heterogeneous networks and fulfill the requirements and the network’s future demands. Scientists and researchers have decided to move towards this direction by conducing several research activity in the area (Networld2020 ETP, 2014; IWPC, 2014). The future mobile networks are going to demand a large network coverage. DAS would be an ideal solution to deal with the limited spectrum, because it provides repeaters, that are connected to the antenna system. It also serves the augmenting numbers of the smart devices, that in the future will be connected to the Internet or the smart home devices of the owner’s home network as we move dynamically to the Internet of Things. This paper studies the techno-economic aspects of ultra-dense and DAS deployments. It presents the characteristics and advantages for all their parts, as well as a techno-economic modeling of these deployment types. The defined models are used for the investigation of the upper technologies from an economic point of view. They provide an insight in the future financial and pricing aspects of these solutions and consist a useful tool for the definition of financing and pricing policies towards economically viable deployments. The authors define models for selecting the most appropriate network architectural solution for public buildings’ indoor coverage. Cost, investment, materials, coverage and capacity are the parameters that are taken into account for the definition of their models. The main scientific contribution of this paper is that it includes multiple case-study examples of the techno-economic models as well as results of conducted experiments. It also analyzes and presents a techno-economic model and summarizes the main research activity in the particular field. The remaining part of this paper is structured as follows: the second section refers to the related research that has been conducted so far. The third section presents the architectures of ultra-dense and DAS deployments used in the models. In the following section we describe cost models for ultra-dense and DAS deployments. In the next section we define the parameterization of the cost models. In the sixth section we conduce some experimental scenarios and analyze the corresponding results. Finally, in the seventh section we conclude our paper with the most fundamental conclusions realized in the experimental procedure and in the final section we list some ideas for future research work in the field of mobile network technologies.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Next-generation of mobile technologies is expected to largely augment the system’s peak data rates and cut down on the round-trip delays. The main idea of using ultra-density or DAS (Distributed Antenna Systems) based on their properties, is that they are able to increase efficiency and expand network capacity without the need for more spectrum resources by redistributing the existing ones, depict them as the key solutions for the future mobile networks. Small cells and DAS were launched mainly for addressing the issue of limited connectivity indoors. There are several other important benefits of these technologies, which constitute them as bases for future generations of mobile networks, such as 5G (5G-PPP, 2014). Femtocells’ benefit is that they provide ultra-density, which is expected to be one of the essential features of 5G. Ultra-dense networks coexist with the existing macrocellular ones forming altogether heterogeneous networks and fulfill the requirements and the network’s future demands. Scientists and researchers have decided to move towards this direction by conducing several research activity in the area (Networld2020 ETP, 2014; IWPC, 2014). The future mobile networks are going to demand a large network coverage. DAS would be an ideal solution to deal with the limited spectrum, because it provides repeaters, that are connected to the antenna system. It also serves the augmenting numbers of the smart devices, that in the future will be connected to the Internet or the smart home devices of the owner’s home network as we move dynamically to the Internet of Things. This paper studies the techno-economic aspects of ultra-dense and DAS deployments. It presents the characteristics and advantages for all their parts, as well as a techno-economic modeling of these deployment types. The defined models are used for the investigation of the upper technologies from an economic point of view. They provide an insight in the future financial and pricing aspects of these solutions and consist a useful tool for the definition of financing and pricing policies towards economically viable deployments. The authors define models for selecting the most appropriate network architectural solution for public buildings’ indoor coverage. Cost, investment, materials, coverage and capacity are the parameters that are taken into account for the definition of their models. The main scientific contribution of this paper is that it includes multiple case-study examples of the techno-economic models as well as results of conducted experiments. It also analyzes and presents a techno-economic model and summarizes the main research activity in the particular field. The remaining part of this paper is structured as follows: the second section refers to the related research that has been conducted so far. The third section presents the architectures of ultra-dense and DAS deployments used in the models. In the following section we describe cost models for ultra-dense and DAS deployments. In the next section we define the parameterization of the cost models. In the sixth section we conduce some experimental scenarios and analyze the corresponding results. Finally, in the seventh section we conclude our paper with the most fundamental conclusions realized in the experimental procedure and in the final section we list some ideas for future research work in the field of mobile network technologies.
Bouras, Christos; Kanakis, Nikolaos
Online AL - FEC Policy Problem on Mobile Unicast Services Journal Article
In: Physical Communication, Elsevier Science, vol. 23, pp. 95-102, 2017.
Abstract | Links | BibTeX | Tags:
@article{4193,
title = {Online AL - FEC Policy Problem on Mobile Unicast Services},
author = {Christos Bouras and Nikolaos Kanakis},
url = {https://telematics.upatras.gr/1-s2-0-s1874490717300745-main_1/},
year = {2017},
date = {2017-01-01},
urldate = {2017-01-01},
journal = {Physical Communication, Elsevier Science},
volume = {23},
pages = {95-102},
abstract = {Forward error correction (FEC) is a method for error control of data transmission adopted in several mobile multicast standards. FEC is a feedback free error recovery method where the sender introduces redundant data in advance with the source data enabling the recipient to recover from different arbitrary packet losses. Recently, the adoption of FEC error control method has been boosted by the introduction of powerful Application Layer FEC (AL-FEC) codes, e.g. RaptorQ codes. Furthermore, several works have emerged aiming to address the shortcomings of AL-FEC protection application utilizing deterministic or randomized online algorithms to enhance the efficiency of AL-FEC error control method. In this work, since the investigation of AL-FEC application as primary or auxiliary error protection method over mobile multicast environments is a well investigated field but the opportunity of utilizing the AL-FEC over mobile unicast services as the only method for error control replacing common feedback based methods that are now considered to be obsolete, we provide an analysis on the feasibility of AL-FEC protection over unicast delivery utilizing online algorithms in conjunction with AL-FEC codes with exceptional recovery performance.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Forward error correction (FEC) is a method for error control of data transmission adopted in several mobile multicast standards. FEC is a feedback free error recovery method where the sender introduces redundant data in advance with the source data enabling the recipient to recover from different arbitrary packet losses. Recently, the adoption of FEC error control method has been boosted by the introduction of powerful Application Layer FEC (AL-FEC) codes, e.g. RaptorQ codes. Furthermore, several works have emerged aiming to address the shortcomings of AL-FEC protection application utilizing deterministic or randomized online algorithms to enhance the efficiency of AL-FEC error control method. In this work, since the investigation of AL-FEC application as primary or auxiliary error protection method over mobile multicast environments is a well investigated field but the opportunity of utilizing the AL-FEC over mobile unicast services as the only method for error control replacing common feedback based methods that are now considered to be obsolete, we provide an analysis on the feasibility of AL-FEC protection over unicast delivery utilizing online algorithms in conjunction with AL-FEC codes with exceptional recovery performance.
Gkypali, Areti; Kokkinos, Vasileios; Bouras, Christos; Tsekouras, Kostas
Science parks and regional innovation performance in fiscal austerity era: Less in more Journal Article
In: Special Issue on GCW 2014, Small Business Economics, Springer Verlang, vol. 47, pp. 313-330, 2016.
Abstract | Links | BibTeX | Tags:
@article{4109,
title = {Science parks and regional innovation performance in fiscal austerity era: Less in more},
author = {Areti Gkypali and Vasileios Kokkinos and Christos Bouras and Kostas Tsekouras},
url = {https://telematics.upatras.gr/sbe2016_si_bouras/},
year = {2016},
date = {2016-08-01},
urldate = {2016-08-01},
journal = {Special Issue on GCW 2014, Small Business Economics, Springer Verlang},
volume = {47},
pages = {313-330},
abstract = {European financial crisis has raised questions about the sustainability and the contribution of innovation anchors especially in Southern European countries such as Greece. This paper utilizes the concept of regional innovation systems (RISs) and introduces a methodological approach that allows for evaluating an Science and Technology Park’s (STP) contribution into the corresponding RIS performance, taking into consideration (1) the RIS idiosyncrasies, (2) the dominant role of government expenditures on R&D and (3) the underlying complexity of knowledge production and management, under alternative sets of restrictions imposed by fiscal consolidation on the preferences of authorities which design and implement Science, Technology and Innovation (STI) policies. Our framework relies on the estimation of a multi-input–multi-output latent knowledge production function approach and the corresponding efficiency indices. Data requirements are sourced from the Regional Innovation Scoreboard, for the four Greek regions and from a small-scale case study, with respect to the examined regional STP covering the period from 2000 to 2012. The main empirical findings highlight that the contribution of the examined STP in the corresponding RIS performance diminishes alongside with the decrease in GERD investment levels, with respect to all the efficiency indices. These findings are attributed to the structural characteristics of both the RIS and the STP under investigation, and capture their dependence on managing public financial resources for STI activities.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
European financial crisis has raised questions about the sustainability and the contribution of innovation anchors especially in Southern European countries such as Greece. This paper utilizes the concept of regional innovation systems (RISs) and introduces a methodological approach that allows for evaluating an Science and Technology Park’s (STP) contribution into the corresponding RIS performance, taking into consideration (1) the RIS idiosyncrasies, (2) the dominant role of government expenditures on R&D and (3) the underlying complexity of knowledge production and management, under alternative sets of restrictions imposed by fiscal consolidation on the preferences of authorities which design and implement Science, Technology and Innovation (STI) policies. Our framework relies on the estimation of a multi-input–multi-output latent knowledge production function approach and the corresponding efficiency indices. Data requirements are sourced from the Regional Innovation Scoreboard, for the four Greek regions and from a small-scale case study, with respect to the examined regional STP covering the period from 2000 to 2012. The main empirical findings highlight that the contribution of the examined STP in the corresponding RIS performance diminishes alongside with the decrease in GERD investment levels, with respect to all the efficiency indices. These findings are attributed to the structural characteristics of both the RIS and the STP under investigation, and capture their dependence on managing public financial resources for STI activities.
Bouras, Christos; Diles, Georgios; Kokkinos, Vasileios; Papazois, Andreas
Transmission optimizing on dense femtocell deployments in 5G Journal Article
In: International Journal of Communication Systems, Wiley InterScience, vol. 29, pp. 2325 - 2438, 2016.
Abstract | Links | BibTeX | Tags:
@article{4108,
title = {Transmission optimizing on dense femtocell deployments in 5G},
author = {Christos Bouras and Georgios Diles and Vasileios Kokkinos and Andreas Papazois},
url = {https://telematics.upatras.gr/bouras_et_al-2015-international_journal_of_communication_systems/},
year = {2016},
date = {2016-01-01},
urldate = {2016-01-01},
journal = {International Journal of Communication Systems, Wiley InterScience},
volume = {29},
pages = {2325 - 2438},
abstract = {In the upcoming generation of mobile networks, femtocells will play a major role because they provide cost-efficient improvement in data rates and coverage. High penetration is expected in the upcoming ultradense 5G networks, increasing the probability of femtocells’ clusters. This, in turn, will require interference mitigation techniques to protect nearby non-subscribed users, especially in weak macrocell signal areas. In this paper, we present a mechanism where multiple femtocells coordinate their transmission to serve multiple non-subscribed users through hybrid access. First, we introduce an algorithm that determines the spectrum allocation of femtocells’ hybrid access. The algorithm aims to compensate for the performance reduction of subscribed users, due to reduced spectrum. For the second step of the mechanism, we introduce a power control algorithm that balances the impact of hybrid access among all the members of the femtocell cluster. First, we investigate the case where only one femtocell operates in hybrid access, and then we refine the power control algorithm by allowing multiple femtocells in the same cluster to operate in hybrid mode and by taking into account the effect that any change in power transmission will have on neighbouring femtocells. Simulations for the evaluation of the hybrid access algorithm compared with closed and other hybrid access schemes show improvement in the throughput of the non-subscribed users connected to femtocell and the most impacted subscribed users at weak macrocell signal areas and in the fairness of the hybrid access application scheme.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
In the upcoming generation of mobile networks, femtocells will play a major role because they provide cost-efficient improvement in data rates and coverage. High penetration is expected in the upcoming ultradense 5G networks, increasing the probability of femtocells’ clusters. This, in turn, will require interference mitigation techniques to protect nearby non-subscribed users, especially in weak macrocell signal areas. In this paper, we present a mechanism where multiple femtocells coordinate their transmission to serve multiple non-subscribed users through hybrid access. First, we introduce an algorithm that determines the spectrum allocation of femtocells’ hybrid access. The algorithm aims to compensate for the performance reduction of subscribed users, due to reduced spectrum. For the second step of the mechanism, we introduce a power control algorithm that balances the impact of hybrid access among all the members of the femtocell cluster. First, we investigate the case where only one femtocell operates in hybrid access, and then we refine the power control algorithm by allowing multiple femtocells in the same cluster to operate in hybrid mode and by taking into account the effect that any change in power transmission will have on neighbouring femtocells. Simulations for the evaluation of the hybrid access algorithm compared with closed and other hybrid access schemes show improvement in the throughput of the non-subscribed users connected to femtocell and the most impacted subscribed users at weak macrocell signal areas and in the fairness of the hybrid access application scheme.
Bouras, Christos; Kapoulas, Vaggelis; Tsanai, Enea
Efficient Mechanism and Performance Analysis of Routing Protocols in VANETs for Realistic Scenarios Journal Article
In: International Journal of Interdisciplinary Telecommunications and Networking, IGI Global, vol. 8, pp. 20-49, 2016.
Abstract | Links | BibTeX | Tags:
@article{4119,
title = {Efficient Mechanism and Performance Analysis of Routing Protocols in VANETs for Realistic Scenarios},
author = {Christos Bouras and Vaggelis Kapoulas and Enea Tsanai},
url = {https://telematics.upatras.gr/efficient-mechanisms-and-performance-analysis-of-routing-protocols-in-vanets-for-realistic-scenarios/},
year = {2016},
date = {2016-01-01},
urldate = {2016-01-01},
journal = {International Journal of Interdisciplinary Telecommunications and Networking, IGI Global},
volume = {8},
pages = {20-49},
abstract = {Vehicular Ad Hoc Networks (VANETs) are considered as a special case of mobile Ad Hoc Networks (MANETs) and are recently gaining a great attention from the research community. The need for improved road safety, traffic efficiency and direct communi-cation along with the great complexity in routing, makes VANETs a highly challeng-ing field. Routing in VANETs has to adapt to special characteristics such as high speed and road pattern movement as well as high linkage break probability. In this work, we show that traditional MANET routing protocols cannot efficiently handle the challeng-es in a VANET environment and thus need further modifications. For this reason, we propose and implement an enhancement mechanism, applied to the GPSR routing pro-tocol that adapts to the needs of a VANET. The proposed mechanism’s performance is evaluated through simulation sets for urban and highway scenarios and compared to the performance of the most common MANET routing protocols adopted in VANETs. The proposed enhancement is shown to be considerably beneficial and it significantly outperforms the rest of the tested routing protocols for almost every topology setting.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Vehicular Ad Hoc Networks (VANETs) are considered as a special case of mobile Ad Hoc Networks (MANETs) and are recently gaining a great attention from the research community. The need for improved road safety, traffic efficiency and direct communi-cation along with the great complexity in routing, makes VANETs a highly challeng-ing field. Routing in VANETs has to adapt to special characteristics such as high speed and road pattern movement as well as high linkage break probability. In this work, we show that traditional MANET routing protocols cannot efficiently handle the challeng-es in a VANET environment and thus need further modifications. For this reason, we propose and implement an enhancement mechanism, applied to the GPSR routing pro-tocol that adapts to the needs of a VANET. The proposed mechanism’s performance is evaluated through simulation sets for urban and highway scenarios and compared to the performance of the most common MANET routing protocols adopted in VANETs. The proposed enhancement is shown to be considerably beneficial and it significantly outperforms the rest of the tested routing protocols for almost every topology setting.
Bouras, Christos; Tsogkas, Vassilis
Assisting cluster coherency via N-grams and clustering as a tool to deal with the new user problem Journal Article
In: International Journal of Machine Learning and Cybernetics, Springer Verlang, vol. 7, pp. 171-184, 2016.
Abstract | Links | BibTeX | Tags:
@article{3437,
title = {Assisting cluster coherency via N-grams and clustering as a tool to deal with the new user problem},
author = {Christos Bouras and Vassilis Tsogkas},
url = {https://telematics.upatras.gr/ijmlc2016_bouras/},
year = {2016},
date = {2016-01-01},
urldate = {2016-01-01},
journal = {International Journal of Machine Learning and Cybernetics, Springer Verlang},
volume = {7},
pages = {171-184},
abstract = {Collaborative filtering systems typically need to acquire some data about the new user in order to start making personalized suggestions, a situation commonly referred to as the “new user problem”. In this work we attempt to address the new user problem via a unique personalized strategy for prompting the user with articles to rate. Our approach makes use of hypernyms extracted from the WordNet database and proves to be converging fast to the actual user interests based on minimal user ratings, which are provided during the registration process. In addition, we explore the possible enhancement of the document clustering results, and in particular clustering of news articles from the web, when using word-based n-grams during the keyword extraction phase. We present and evaluate a weighting approach that combines clustering of news articles derived from the web, using n-grams that are extracted from the articles at an offline stage. This technique is then compared with the single minded “bag-of-words” representation that our clustering algorithm, W-kmeans, previously used. Our experimentation reveals that via fine tuning the weighting parameters between keyword and n-grams, as well as the n value itself, a significant improvement regarding the clustering results metrics can be achieved.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Collaborative filtering systems typically need to acquire some data about the new user in order to start making personalized suggestions, a situation commonly referred to as the “new user problem”. In this work we attempt to address the new user problem via a unique personalized strategy for prompting the user with articles to rate. Our approach makes use of hypernyms extracted from the WordNet database and proves to be converging fast to the actual user interests based on minimal user ratings, which are provided during the registration process. In addition, we explore the possible enhancement of the document clustering results, and in particular clustering of news articles from the web, when using word-based n-grams during the keyword extraction phase. We present and evaluate a weighting approach that combines clustering of news articles derived from the web, using n-grams that are extracted from the articles at an offline stage. This technique is then compared with the single minded “bag-of-words” representation that our clustering algorithm, W-kmeans, previously used. Our experimentation reveals that via fine tuning the weighting parameters between keyword and n-grams, as well as the n value itself, a significant improvement regarding the clustering results metrics can be achieved.
Alexiou, Antonios; Bikos, Anastasios; Bilios, Dimitrios; Bouras, Christos
Power-Aware and QoS Provisioned Real Time Multimedia Transmission in Small Cell Networks Journal Article
In: International Journal of Wireless Networks and Broadband Technologies, IGI Global, vol. 5, pp. 24-45, 2016.
Abstract | Links | BibTeX | Tags:
@article{4130,
title = {Power-Aware and QoS Provisioned Real Time Multimedia Transmission in Small Cell Networks},
author = {Antonios Alexiou and Anastasios Bikos and Dimitrios Bilios and Christos Bouras},
url = {https://telematics.upatras.gr/viewcomplimentarytitle/},
year = {2016},
date = {2016-01-01},
urldate = {2016-01-01},
journal = {International Journal of Wireless Networks and Broadband Technologies, IGI Global},
volume = {5},
pages = {24-45},
abstract = {The recent emergence of ultra-high-speed and high-definition data and video services has pushed wireless network capacity to its limits. Cellular network capacity is therefore a valuable resource, whereas indoor coverage poses itself as a challenging issue. At the same time, real-world paradigms of multimedia transmission require effective Quality-of-Service (QoS) provisioning as well as power admission. To confront issues like delay-sensitive QoS requirements and traffic provisioning, as well as meet the mobile customer needs, this paper presents a traffic-aware Orthogonal Frequency-Division Multiple-Access (OFDMA) hybrid small-cell deployment for QoS provisioning and an optimal admission control strategy for 4G cellular systems. The traffic awareness in the proposed framework is provided by a utility function, which differentiates the traffic QoS levels with the user’s grouping priority indexes, channel conditions, and traffic characteristics. To further enhance the proposed framework, an admission power control algorithm based on an efficient algorithm handover is also proposed.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The recent emergence of ultra-high-speed and high-definition data and video services has pushed wireless network capacity to its limits. Cellular network capacity is therefore a valuable resource, whereas indoor coverage poses itself as a challenging issue. At the same time, real-world paradigms of multimedia transmission require effective Quality-of-Service (QoS) provisioning as well as power admission. To confront issues like delay-sensitive QoS requirements and traffic provisioning, as well as meet the mobile customer needs, this paper presents a traffic-aware Orthogonal Frequency-Division Multiple-Access (OFDMA) hybrid small-cell deployment for QoS provisioning and an optimal admission control strategy for 4G cellular systems. The traffic awareness in the proposed framework is provided by a utility function, which differentiates the traffic QoS levels with the user’s grouping priority indexes, channel conditions, and traffic characteristics. To further enhance the proposed framework, an admission power control algorithm based on an efficient algorithm handover is also proposed.