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Papers by Michail Karavolos

Research paper thumbnail of Energy-aware clustering of CoMP-DPS transmission points

Research paper thumbnail of An Unsupervised Machine Learning Approach for UAV-Aided Offloading of 5G Cellular Networks

Telecom, 2022

Today’s terrestrial cellular communications networks face difficulties in serving coexisting user... more Today’s terrestrial cellular communications networks face difficulties in serving coexisting users and devices due to the enormous demands of mass connectivity. Further, natural disasters and unexpected events lead to an unpredictable amount of data traffic, thus causing congestion to the network. In such cases, the addition of on-demand network entities, such as fixed or aerial base stations, has been proposed as a viable solution for managing high data traffic and offloading the existing terrestrial infrastructure. This paper presents an unmanned aerial vehicles (UAVs) aided offloading strategy of the terrestrial network, utilizing an unsupervised machine learning method for the best placement of UAVs in sites with high data traffic. The proposed scheme forms clusters of users located in the affected area using the k-medoid algorithm. Followingly, based on the number of available UAVs, a cluster selection scheme is employed to select the available UAVs that will be deployed to ach...

Research paper thumbnail of A Dynamic Hybrid Clustering Scheme for LTE-A networks employing CoMP-DPS

2017 IEEE 22nd International Workshop on Computer Aided Modeling and Design of Communication Links and Networks (CAMAD), 2017

In this paper, we propose a low complexity Dynamic Hybrid Clustering (DHC) scheme for LTE-A netwo... more In this paper, we propose a low complexity Dynamic Hybrid Clustering (DHC) scheme for LTE-A networks employing Coordinated MultiPoint with Dynamic Point Selection (CoMP-DPS). Although CoMP-DPS is considered to be a simpler CoMP scheme, its simplicity allows us to define more efficient cell clustering procedures. Thus, DHC is able to provide backhaul load balancing for the eNBs while offering high quality wireless connections and high data rates to the users. DHC exploits the feedback from the mobile devices and takes into account the backhaul load conditions in order to adjust the backhaul latency to tolerable levels and maintain optimal channel quality. Numerical results and comparisons with other schemes are provided showing improved performance by the proposed solution.

Research paper thumbnail of HST-NNC: A Novel Hybrid Satellite-Terrestrial Communication With NOMA and Network Coding Systems

IEEE Open Journal of the Communications Society, 2021

Hybrid satellite-terrestrial networks (HSTNs) are considered to be a promising solution in dealin... more Hybrid satellite-terrestrial networks (HSTNs) are considered to be a promising solution in dealing with coverage and mobility challenges encountered in 5 th generation (5G) networks that employ novel multiple access and connectivity schemes. In this respect, non-orthogonal multiple access (NOMA) as well as network coding (NC) schemes have attracted significant attention due to their performance gains which not only improve the quality of wireless transmission but also effectively exploit the available spectrum. In this paper, a combined NOMA-NC (NNC) scheme is presented and integrated into an HSTN consisting of a low earth orbit (LEO) satellite belonging to an LEO constellation, a terrestrial base station (BS), and multiple terrestrial mobile terminals (MTs). The proposed scheme, termed HST-NNC (Hybrid satellite terrestrial-NNC), allows pairs of users to be simultaneously served through NOMA via the terrestrial BS link and the satellite link. Furthermore, the satellite employs random linear network coding (RLNC), within the general framework of systematic network coding (SNC), to improve the reception of the MTs when errors occur. The proposed HST-NNC, as compared to standalone NOMA, does not require additional channel state information (CSI) overheads because the satellite needs only the indices of user pairs to perform RLNC. Performance comparisons of HST-NNC with conventional orthogonal multiple access (OMA) and NOMA optimal user pairing schemes have shown that significant sum rate and BER gains can be obtained under various operating system parameters, such as varying number of MTs and different channel conditions.

Research paper thumbnail of Enhanced Integrated Satellite-Terrestrial NOMA with Cooperative Device-to-Device Communication

Telecom, 2020

The currently deployed terrestrial wireless networks experience difficulties while coping with th... more The currently deployed terrestrial wireless networks experience difficulties while coping with the massive connectivity demands of coexisting users and devices. The addition of satellite segments has been proposed as a viable way of providing improved coverage and capacity, leading to the formation of integrated satellite-terrestrial networks. In such topologies, non-orthogonal multiple access (NOMA) can further enhance the efficient use of wireless resources by simultaneously serving multiple users. In this paper, an integrated satellite-terrestrial NOMA network is studied where cooperation between ground users is allowed, following the device-to-device (D2D) paradigm. More specifically, the proposed satellite NOMA cooperative (SANOCO) D2D scheme optimally selects pairs of users, by considering the channel conditions of the satellite and the terrestrial D2D links. In SANOCO-D2D users are served through NOMA in the satellite link, and then, if the weak user fails to decode its signa...

Research paper thumbnail of Energy-aware clustering of CoMP-DPS transmission points

Computer Communications, 2018

Research paper thumbnail of A load and channel aware dynamic point selection algorithm for LTE-A CoMP networks

2016 International Conference on Telecommunications and Multimedia (TEMU), 2016

In this work, in order to exploit the benefits of the Coordinated MultiPoint Dynamic Point Select... more In this work, in order to exploit the benefits of the Coordinated MultiPoint Dynamic Point Selection technique (CoMP/DPS), we propose a LOad and CHannel aware (LOCH) DPS algorithm that avoids unnecessary Base Station (BS) switching and, therefore, it significantly reduces the ping-pong effect. The performance of the proposed scheme is evaluated via simulations and comparisons with another state-of-the-art DPS selection scheme, in terms of UE transitions between Transmission Points (TPs) and throughput. The results show that LOCH achieves significantly less transitions, while having the same or better throughput performance. Thus, the current work can be the base for other future works that will aim to the reduction of the CoMP signaling load, as well as to the reduction of the CoMP traffic load at the backhaul network.

Research paper thumbnail of Botnet Command and Control Architectures Revisited: Tor Hidden Services and Fluxing

Lecture Notes in Computer Science, 2017

Botnet armies constitute a major and continuous threat to the Internet. Their number, diversity, ... more Botnet armies constitute a major and continuous threat to the Internet. Their number, diversity, and power grows with each passing day, and the last years we are witnessing their rapid expansion to mobile and even IoT devices. The work at hand focuses on botnets which comprise mobile devices (e.g. smartphones), and aims to raise the alarm on a couple of advanced Command and Control (CC first to further obfuscate their identity and minimize the botnet’s forensic signal, and second to augment the resilience of their army. The novelty of the introduced architectures is that it does not rely on static C&C servers, but on rotating ones, which can be reached by other botnet members through their (varied) onion address. Also, we propose a scheme called “Tor fluxing”, which opposite to legacy IP or DNS fluxing, does not rely on A type of DNS resource records but on TXT ones. We demonstrate the soundness and effectiveness of the introduced C&C constructions via a proof-of-concept implementation.

Research paper thumbnail of Energy-aware clustering of CoMP-DPS transmission points

Research paper thumbnail of An Unsupervised Machine Learning Approach for UAV-Aided Offloading of 5G Cellular Networks

Telecom, 2022

Today’s terrestrial cellular communications networks face difficulties in serving coexisting user... more Today’s terrestrial cellular communications networks face difficulties in serving coexisting users and devices due to the enormous demands of mass connectivity. Further, natural disasters and unexpected events lead to an unpredictable amount of data traffic, thus causing congestion to the network. In such cases, the addition of on-demand network entities, such as fixed or aerial base stations, has been proposed as a viable solution for managing high data traffic and offloading the existing terrestrial infrastructure. This paper presents an unmanned aerial vehicles (UAVs) aided offloading strategy of the terrestrial network, utilizing an unsupervised machine learning method for the best placement of UAVs in sites with high data traffic. The proposed scheme forms clusters of users located in the affected area using the k-medoid algorithm. Followingly, based on the number of available UAVs, a cluster selection scheme is employed to select the available UAVs that will be deployed to ach...

Research paper thumbnail of A Dynamic Hybrid Clustering Scheme for LTE-A networks employing CoMP-DPS

2017 IEEE 22nd International Workshop on Computer Aided Modeling and Design of Communication Links and Networks (CAMAD), 2017

In this paper, we propose a low complexity Dynamic Hybrid Clustering (DHC) scheme for LTE-A netwo... more In this paper, we propose a low complexity Dynamic Hybrid Clustering (DHC) scheme for LTE-A networks employing Coordinated MultiPoint with Dynamic Point Selection (CoMP-DPS). Although CoMP-DPS is considered to be a simpler CoMP scheme, its simplicity allows us to define more efficient cell clustering procedures. Thus, DHC is able to provide backhaul load balancing for the eNBs while offering high quality wireless connections and high data rates to the users. DHC exploits the feedback from the mobile devices and takes into account the backhaul load conditions in order to adjust the backhaul latency to tolerable levels and maintain optimal channel quality. Numerical results and comparisons with other schemes are provided showing improved performance by the proposed solution.

Research paper thumbnail of HST-NNC: A Novel Hybrid Satellite-Terrestrial Communication With NOMA and Network Coding Systems

IEEE Open Journal of the Communications Society, 2021

Hybrid satellite-terrestrial networks (HSTNs) are considered to be a promising solution in dealin... more Hybrid satellite-terrestrial networks (HSTNs) are considered to be a promising solution in dealing with coverage and mobility challenges encountered in 5 th generation (5G) networks that employ novel multiple access and connectivity schemes. In this respect, non-orthogonal multiple access (NOMA) as well as network coding (NC) schemes have attracted significant attention due to their performance gains which not only improve the quality of wireless transmission but also effectively exploit the available spectrum. In this paper, a combined NOMA-NC (NNC) scheme is presented and integrated into an HSTN consisting of a low earth orbit (LEO) satellite belonging to an LEO constellation, a terrestrial base station (BS), and multiple terrestrial mobile terminals (MTs). The proposed scheme, termed HST-NNC (Hybrid satellite terrestrial-NNC), allows pairs of users to be simultaneously served through NOMA via the terrestrial BS link and the satellite link. Furthermore, the satellite employs random linear network coding (RLNC), within the general framework of systematic network coding (SNC), to improve the reception of the MTs when errors occur. The proposed HST-NNC, as compared to standalone NOMA, does not require additional channel state information (CSI) overheads because the satellite needs only the indices of user pairs to perform RLNC. Performance comparisons of HST-NNC with conventional orthogonal multiple access (OMA) and NOMA optimal user pairing schemes have shown that significant sum rate and BER gains can be obtained under various operating system parameters, such as varying number of MTs and different channel conditions.

Research paper thumbnail of Enhanced Integrated Satellite-Terrestrial NOMA with Cooperative Device-to-Device Communication

Telecom, 2020

The currently deployed terrestrial wireless networks experience difficulties while coping with th... more The currently deployed terrestrial wireless networks experience difficulties while coping with the massive connectivity demands of coexisting users and devices. The addition of satellite segments has been proposed as a viable way of providing improved coverage and capacity, leading to the formation of integrated satellite-terrestrial networks. In such topologies, non-orthogonal multiple access (NOMA) can further enhance the efficient use of wireless resources by simultaneously serving multiple users. In this paper, an integrated satellite-terrestrial NOMA network is studied where cooperation between ground users is allowed, following the device-to-device (D2D) paradigm. More specifically, the proposed satellite NOMA cooperative (SANOCO) D2D scheme optimally selects pairs of users, by considering the channel conditions of the satellite and the terrestrial D2D links. In SANOCO-D2D users are served through NOMA in the satellite link, and then, if the weak user fails to decode its signa...

Research paper thumbnail of Energy-aware clustering of CoMP-DPS transmission points

Computer Communications, 2018

Research paper thumbnail of A load and channel aware dynamic point selection algorithm for LTE-A CoMP networks

2016 International Conference on Telecommunications and Multimedia (TEMU), 2016

In this work, in order to exploit the benefits of the Coordinated MultiPoint Dynamic Point Select... more In this work, in order to exploit the benefits of the Coordinated MultiPoint Dynamic Point Selection technique (CoMP/DPS), we propose a LOad and CHannel aware (LOCH) DPS algorithm that avoids unnecessary Base Station (BS) switching and, therefore, it significantly reduces the ping-pong effect. The performance of the proposed scheme is evaluated via simulations and comparisons with another state-of-the-art DPS selection scheme, in terms of UE transitions between Transmission Points (TPs) and throughput. The results show that LOCH achieves significantly less transitions, while having the same or better throughput performance. Thus, the current work can be the base for other future works that will aim to the reduction of the CoMP signaling load, as well as to the reduction of the CoMP traffic load at the backhaul network.

Research paper thumbnail of Botnet Command and Control Architectures Revisited: Tor Hidden Services and Fluxing

Lecture Notes in Computer Science, 2017

Botnet armies constitute a major and continuous threat to the Internet. Their number, diversity, ... more Botnet armies constitute a major and continuous threat to the Internet. Their number, diversity, and power grows with each passing day, and the last years we are witnessing their rapid expansion to mobile and even IoT devices. The work at hand focuses on botnets which comprise mobile devices (e.g. smartphones), and aims to raise the alarm on a couple of advanced Command and Control (CC first to further obfuscate their identity and minimize the botnet’s forensic signal, and second to augment the resilience of their army. The novelty of the introduced architectures is that it does not rely on static C&C servers, but on rotating ones, which can be reached by other botnet members through their (varied) onion address. Also, we propose a scheme called “Tor fluxing”, which opposite to legacy IP or DNS fluxing, does not rely on A type of DNS resource records but on TXT ones. We demonstrate the soundness and effectiveness of the introduced C&C constructions via a proof-of-concept implementation.