Christophoros Christophorou

dblp:84/6722 · DBLP profile ↗
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22ranked-venue papers
8as first author
9since 2021 · last 2026
0000-0002-1852-8642ORCID · reported

Domains — the database's venue-derived domains; a paper can count in several

Computer networks · 16 · 6 first-author · 8 since 2021Security and privacy · 1 · 1 since 2021Databases, data management, data science and information retrieval · 1Applied, interdisciplinary, general and emerging computing · 1
YearPublicationVenuePosition
2026 A novel two-stage distributed radio resource allocation framework using deep machine learning in 6G cell-free dynamic communication networks
Iacovos Ioannou, Gusan Mufti, Christophoros Christophorou, Charalambos Klitis, Vasos Vassiliou, Christos V. Verikoukis
Comput. Networks3
2026 Adaptive active-defense hardening of ML-based NIDS against RL-driven adversaries: A comparative analysis with static defenses
Iacovos Ioannou, Christophoros Christophorou, Andreas Andreou, Marios Raspopoulos, Constandinos X. Mavromoustakis, Vasos Vassiliou, Fabrizio Granelli
J. Inf. Secur. Appl.2
2025 Deep Learning-Driven Two-Stage Distributed Radio Resource Allocation in 6G Cell-Free Communication Systems
Iacovos Ioannou, Christophoros Christophorou, Gussan Mufti, Charalambos Klitis, Vasos Vassiliou, Christos V. Verikoukis
Networking2
2025 Enhancing 5G and 6G networks through a dynamic dual-stage machine learning heuristic framework for selecting UEs as UE-VBSs
Iacovos Ioannou, Jansi Rani Sella Veluswami, Prabagarane Nagaradjane, Christophoros Christophorou, Vasos Vassiliou, Andreas Pitsillides
Ad Hoc Networks4
2025 Access Point Selection and Localization for Cluster-Based Realization of a Device-to-Device Cell-Free 6G Communications Network
abstract
ABSTRACT The increasing demand for ultra‐reliable, low‐latency, and high‐throughput connectivity in dense urban environments presents significant challenges for next‐generation 6G networks. Traditional cellular networks, with their fixed cell boundaries and centralized base station control, are inadequate to meet the dynamic needs of such environments. A promising solution is the cell‐free network architecture, where a distributed set of access points (APs) jointly serve users without fixed cell boundaries. However, efficient access point selection and accurate user localization are crucial to achieving high performance in such networks. This paper presents a decentralized approach using Belief‐Desire‐Intention eXtended (BDIx) agents for dynamic AP selection and localization within a cluster‐based cell‐free 6G communications network. Various clustering algorithms (K‐means, DBSCAN, self‐organizing maps, MeanShift, ClusterGAN, and Autoencoders) are evaluated for their ability to optimize network throughput, energy efficiency, and spectral utilization. A hybrid localization framework, such as centroid‐based, differential circles, and multilateration methods, is employed to achieve accurate user positioning. The results demonstrate that machine learning‐based clustering methods, notably Gaussian mixture model (GMM), self‐organizing map (SOM), and ClusterGAN, offer significant improvements in throughput (up to 46.3%) and power reduction (up to 32.8%) over traditional methods. Regarding localization, deep learning models such as MLP, CNN, and TCN outperform deterministic methods, achieving sub‐meter accuracy with minimal errors (MeanDist < 1 m, > 0.999). Overall, the proposed solution enhances system scalability, energy efficiency, and positioning accuracy, establishing a promising foundation for future 6G networks. In our reference implementation, we instantiate the pipeline with a GMM for AP/UE clustering and a multilayer perceptron (MLP) regressor for localization.
Iacovos Ioannou, Marios Raspopoulos, Prabagarane Nagaradjane, Christophoros Christophorou, Andreas Gregoriades, Vasos Vassiliou
IET Commun.4
2023 Detection of DDoS attacks in D2D communications using machine learning approach
Jansi Rani Sella Veluswami, Iacovos Ioannou, Prabagarane Nagaradjane, Christophoros Christophorou, Vasos Vassiliou, Sai Charan, Sai Prakash, Niel Parekh, Andreas Pitsillides
Comput. Commun.4
2022 A distributed AI/ML framework for D2D Transmission Mode Selection in 5G and beyond
Iacovos Ioannou, Christophoros Christophorou, Vasos Vassiliou, Andreas Pitsillides
Comput. Networks2
2022 A novel Distributed AI framework with ML for D2D communication in 5G/6G networks
Iacovos Ioannou, Christophoros Christophorou, Vasos Vassiliou, Andreas Pitsillides
Comput. Networks2
2021 Using UE-VBS for dynamic virtual small cells deployment and backhauling in 5G Ultra-Dense networks
Kuna Venkateswararao, Pravati Swain, Christophoros Christophorou, Andreas Pitsillides
Comput. Networks3
2019 A Safe, Efficient and Integrated Indoor Robotic Fleet for Logistic Applications in Healthcare and Commercial Spaces: The ENDORSE Concept
abstract
Hospitals are rightfully considered a field of indoor logistic robotics of high commercial potential. However, today, only a handful of mobile robotic solutions for hospital logistics exist that have failed to trigger widespread acceptance by the market. This is because existing systems require costly infrastructure installation, they do not easily integrate to corporate IT solutions, are not adequately shielded from cybersecurity threats, and as a result, they do not fully automate procedures and traceability of the items they carry. Moreover, existing systems are limited on scope, focusing only on delivery services, and hence do not provide any other type of support to the medical and nursing staff. ENDORSE system will address the aforementioned technical challenges and functional limitations by pursuing four innovation pillars: (i) infrastructure-less multi-robot indoor navigation; (ii) advanced Human-Robot Interaction (HRI) for resolving deadlocks and achieving efficient sharing of space resources in crowded environments; (iii) deployment of the ENDORSE software as a cloud-based service facilitating its integration with corporate software solutions, complying with GDPR data security requirements; (iv) reconfigurable and modular hardware architectures so that diverse modules can be easily swapped. ENDORSE functionality will be demonstrated via the integration of an e-diagnostic support module for vital signs monitoring on a fleet of mobile robots, facilitating connectivity to cloud-based Electronic Health Records (EHR), and validated in an operational hospital environment for realistic assessment.
Nacim Ramdani, Andreas Panayides, Michalis Karamousadakis, Martín Mellado, Rafael Lopez, Christophoros Christophorou, Mohamed Rebiai, Myriam Blouin, Eleftheria Vellidou, Dimitris Koutsouris
MDM6
2018 Selection of UE-based Virtual Small Cell Base Stations using Affinity Propagation Clustering
abstract
5G will require a number of Key Technological Components to meet its very ambitious goals, including Heterogeneous Networks a nd Small Cells. The Dense Deployme nt of Small Cell Base Stations (SBSs) will play a major role as they can be installed in a more targeted manner to relieve traffic in hot spot areas, increase coverage, and spectral efficiency. However, the current deployment of the SBS is static (examples include Femto, Pico, and Nano cells), normally deployed on demand around hotspots. In the scenario of unpredictable crowd movement, these static deployment of small cell can be inefficient with high CAPEX and OPEX. This paper focuses on the scenario where UE-based Virtual Small Cell Base Stations (UE-VBSs) can be dynamically selected among UEs to deal effectively with the non-stationary, non-uniform distribution of mobile traffic with respect to time and space domain. To implement this concept, we propose an efficient clustering technique (Affinity Propagation Clustering) to select the best set of UE-VBSs to supplement an overlay loaded SBS. Simulative evaluation highlights salient features of the technique, as well as its limitations with regard to scalability. Further, we discuss the modification of the algorithm according to our objec tive sc enario focusing on red ucing the message passing procedure to and from only a number of eligible UE-VBSs using the power received by a UE from the eligible UE-VBSs as a parameter. The algorithm is implemented and evaluated in MATLAB and, also validated using NS3 simulator.
Pravati Swain, Christophoros Christophorou, Upasana Bhattacharjee, Cristiano M. Silva, Andreas Pitsillides
IWCMC2
2017 CelEc framework for reconfigurable small cells as part of 5G ultra-dense networks
abstract
This paper proposes the Cella Ecosystem (CelEc) concept for emerging 5G ultra dense Networks, to evolve and supplement the Mobile Radio Network by using the crowd's User Equipments (UEs), densely distributed in our physical world and environment, as an integral part of the Infrastructure. Towards this end, CelEc establishes a decentralized ecosystem (the CelEc Tier) of numerous, unbound and ubiquitous networking and computing elements offering their networking functionalities and computing and storage resources to bridge coverage gaps, supplement capacity, increase data rates, and boost computing, whenever the Network is stressed. This is in the same spirit as the introduction of smaller sized cells throughout the evolution of mobile telephony, to maximize spectrum resource efficiency. Specifically CelEc, by enhancing the UEs with eNodeB's functionalities and additional networking operation functions, realises the smallest, portable, and reconfigurable cells (i.e., the Cella cells) allowing for dynamic massive deployment, and enables the efficient flows of data, whenever and wherever needed. As such CelEc provides for a dynamic reconfiguration of the Mobile Network infrastructure, in an effortless, costless (in terms of CAPEX) and flexible manner, hence removing the restrains of existing Small Cells beyond their static positioning. A preliminary evaluation of some of the ideas discussed in this paper for CelEc, showed among others, scalable massive mobile support, and significant improvements on the overall capacity, data rates, energy and spectral efficiency, as envisioned for 5G.
Christophoros Christophorou, Andreas Pitsillides, Ian F. Akyildiz
ICC1
2017 Verification Methodology of Ethical Compliance for Users, Researchers and Developers of Personal Care Robots
Carina Dantas, Pedro Balhau, Ana Luísa Jegundo, Luís Santos 0001, Christophoros Christophorou, Cindy Wings, João Quintas, Eleni Christodoulou
WorldCIST (2)5
2011 Enhanced radio resource management algorithms for efficient MBMS service provision in UTRAN
Christophoros Christophorou, Andreas Pitsillides, Tomas Lundborg
Comput. Networks1
2008 A new approach for efficient MBMS service provision in UTRAN
abstract
As currently specified by 3GPP, MBMS services can be provided in a cell either by point-to-point (PtP) or point-to-multipoint (PtM) transmission mode, but not both at the same time. With PtP transmission mode, one dedicated channel (DCH) is established for each MBMS user within the cell. With PtM transmission mode one forward access channel (FACH) is established, covering the whole cellpsilas area and commonly shared by all the MBMS users within. In this paper we describe the existing 3GPP MBMS service provision approach, highlight its deficiencies, and propose a new approach to address them. To achieve this we introduce the ldquodual transmission mode cellsrdquo in which PtP and PtM transmissions can coexist and where FACHpsilas coverage range can be dynamically adapted (shrink or expand) through time based on the MBMS userspsila location within the cell. The performance evaluation performed, showed that our approach outperforms the existing 3GPP approach in terms of capacity, signaling and processing effort efficiency.
Christophoros Christophorou, Andreas Pitsillides
ISCC1
2008 An enhanced approach for efficient MBMS handovers in 3G networks
abstract
With MBMS, a mobile terminal (MT) that is on the move and receive an MBMS service may have to handover from a common to a dedicated channel when crossing the cellpsilas edge. In previous work, we highlighted the possible inefficiencies which might arise if the existing 3GPP handover control approach is adopted to execute these types of handovers and proposed a specific MBMS handover control approach that compensated for them. This approach, although effective in terms of capacity and QoS, was not very viable. Thus in this paper, using a different approach, we enhance previous work in order to address its deficiencies and make the whole solution practical. The performance evaluation showed that our enhanced proposed approach even with the enhancements made simplifying the whole handover procedure, still outperforms the existing 3GPP handover control approach in terms of capacity and QoS efficiency.
Christophoros Christophorou, Andreas Pitsillides
ISCC1
2008 Power counting for optimized capacity in MBMS enabled UTRAN
abstract
MBMS bearer services can be provided in each cell by either point-to-point or point-to-multipoint transmission mode but for efficiency a decision has to be made between the two approaches. Initially, the fundamental criterion used to make this decision was the number of MBMS users in a cell (UE counting). In this paper we extend our previous work, which proposed the power transmitted by the base station (BS) as the channel switching criterion (power counting). We evaluate our approach and illustrate its capability to dynamically adapt to continuously varying cell conditions by selecting the transmission mode in a more efficient way, preserving in this way the networkpsilas resources. At the same time we demonstrate the limitations of the conventional approach, in terms of radio resource efficiency. We show that by having the power used by the BS as the limiting factor we achieve optimized capacity during the transmission of MBMS bearer services in UTRAN.
Andreas Panayides, Christophoros Christophorou, Josephine Antoniou, Andreas Pitsillides, Vasos Vassiliou
ISCC2
2008 A NEHO based MBMS Handover Control approach
abstract
Handover Control is one of the essential means to guarantee the continuity of mobile services to a user traveling in a cellular infrastructure, without interruption. In previous work we illustrated that using the current 3GPP specified handover control algorithm to provide continuity of MBMS (Multimedia Broadcast Multicast Service) services to a user crossing cell boundaries results either in capacity or QoS inefficiencies and proposed a new MEHO (Mobile Evaluated Handover) based MBMS handover control algorithm that compensated for them. This algorithm, although effective in terms of capacity and QoS, has some limitations concerning the way certain parameters vital for the efficient MBMS handover execution are estimated. In this paper, using a different approach (Network Evaluated Handover (NEHO)), we enhance previous work and propose a different method, that eliminates all of its predecessorpsilas deficiencies while achieving the same capacity and QoS efficiencies.
Christophoros Christophorou, Andreas Pitsillides
PIMRC1
2008 An enhanced radio resource allocation approach for efficient MBMS service provision in UTRAN
abstract
As currently specified by 3GPP, MBMS (multimedia broadcast multicast service) content can be provided in a cell by either point-to-point (P-t-P) or point-to-multipoint (P-t-M) transmission mode, but not both at the same time. In earlier work we highlighted the deficiencies of the current approach and proposed the concept of the ldquodual transmission mode cellrdquo, in which P-t-P (DCH) and P-t-M (FACH) transmissions can coexist and allowed to dynamically adapt through time, to address them. In this paper we further analyze the deficiencies of the current 3GPP approach and enhance our previous work to efficiently address the problem in high mobility scenarios as well. The proposed algorithm takes into consideration both the distribution and the movement of the MBMS userspsila within the cell (using the CPICH Ec/No signal strength as a reference) and dynamically decides which MBMS users should be served using FACH and which should be served using DCH. Simulation results show significant transmission power savings, considerable reduction on the aggregated signaling and processing effort introduced, while QoS requirements are still fulfilled.
Christophoros Christophorou, Andreas Pitsillides, Vasos Vassiliou
PIMRC1
2007 MBMS Handover control: A new approach for efficient handover in MBMS enabled 3G cellular networks
Andreas Pitsillides, Christophoros Christophorou
Comput. Networks2
2006 MBMS Handover Control for Efficient Multicasting in IP-Based 3G Mobile Networks
abstract
Handover Control in a cellular infrastructure aims to provide continuity of mobile services to a user traveling over cell boundaries. So far, Handover Control is considered only between cells supporting the service using Dedicated Resources and the handover decision making is based on a comparison between an observed signal strength value and a predetermined threshold chosen in a manner so as to maximize the overall system capacity. With the introduction of Multimedia Broadcast Multicast Service (MBMS), for radio efficiency reasons, one cell can use either Common or Dedicated resources for the distribution of the same content in a Cell. Thus, the mobile users that are on the move may have to deal with dynamic changes of network resources when crossing the cell edge, introducing new types of handovers (MBMS Handovers). Using the current Handover Algorithm when an MBMS Handover is executing will not be so efficient. For the efficient execution of these new types of handover a different approach has to be followed. This paper proposes a new Handover Algorithm which efficiently maximizes the overall system capacity when mobile MBMS users have to deal with these new types of handovers.
Christophoros Christophorou, Andreas Pitsillides
ICC1
2006 An Efficient Handover Algorithm for MBMS Enabled 3G Mobile Cellular Networks
abstract
With the introduction of Multimedia Broadcast Multicast Service (MBMS) in 3rd Generation (3G) Networks, the Radio Network Controller (RNC) for radio efficiency reasons can use either Dedicated or Common resources to distribute the same content in a Cell. Thus the mobile users that are on the move may have to deal with dynamic changes of network resources when crossing the cell edge, introducing new types of handovers (MBMS Handovers). Executing an MBMS Handover using the current Handover Algorithm will result in inefficiencies. Therefore, for efficient execution of these new types of handover a different approach has to be followed. This paper proposes a new Handover Algorithm which efficiently maximizes the overall system capacity when mobile MBMS users have to deal with these new types of handovers.
Christophoros Christophorou, Andreas Pitsillides
ISCC1