Angeliki Alexiou

Angeliki Alexiou
University of Piraeus

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170
Publications
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2,581
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Publications

Publications (170)
Conference Paper
Reconfigurable intelligent surface (RIS)-assisted un-manned areal vehicles (UAV) communications have been identified as a key enabler of a number of next-generation applications. However, to the best of our knowledge, there is no generalized framework for the quantification of the throughput performance of RIS-assisted UAV systems. Motivated by thi...
Article
Terahertz (THz) band offers a vast amount of bandwidth and is envisioned to become a key enabler for a number of next generation wireless applications. In this direction, appropriate channel models, encapsulating the large and small-scale fading phenomena, need to be developed for both indoor and outdoor communications environments. The THz large-s...
Preprint
Full-text available
Terahertz (THz) band offers a vast amount of bandwidth and is envisioned to become a key enabler for a number of nextgeneration wireless applications. In this direction, appropriate channel models, encapsulating the large and small-scale fadingphenomena, need to be developed for both indoor and outdoor communications environments. The THz large-sca...
Conference Paper
Full-text available
In this paper, we examine the potential for a reconfigurable intelligent surface (RIS) to be powered by energy harvested from information signals. This feature might be key to reap the benefits of RIS technology's lower power consumption compared to active relays. We first identify the main RIS power-consuming components and then propose an energy...
Article
Full-text available
In this paper, we analyze the performance of a reconfigurable intelligent surface (RIS)-assisted unmanned aerial vehicle (UAV) wireless system that is affected by mixture-gamma small-scale fading, stochastic disorientation and misalignment, as well as transceivers hardware imperfections. First, we statistically characterize the end-to-end channel f...
Article
Full-text available
This contribution focuses on extracting the theoretical framework for the assessment and evaluation of the joint effect of rain, beam misalignment and hardware imperfections at long-range outdoor terahertz (THz) wireless systems. In this direction, we first report an appropriate system model for outdoor THz wireless systems that take into account t...
Preprint
Full-text available
A Reconfigurable Intelligent Surface (RIS) redirects and possibly modifies the properties of incident waves, with the aim to restore non-line-of-sight communication links. Composed of elementary scatterers, the RIS has been so far treated as a collection of point scatterers with properties similar to antennas in an equivalent massive MIMO communica...
Preprint
Full-text available
In this paper, we introduce a theoretical framework for analyzing the performance of multi-reconfigurable intelligence surface (RIS) empowered terahertz (THz) wireless systems subject to turbulence and stochastic beam misalignment. In more detail, we extract a closed-form expression for the outage probability that quantifies the joint impact of tur...
Preprint
Full-text available
In this paper, we analyze the performance of a reconfigurable intelligent surface (RIS)-assisted unmanned aerial vehicle (UAV) wireless system that is affected by mixture-gamma small-scale fading, stochastic disorientation, and misalignment, as well as transceivers hardware imperfections. First, we statistically characterize the end-to-end channel...
Conference Paper
Full-text available
In this paper, we introduce a theoretical framework for analyzing the performance of multi-reconfigurable intelligence surface (RIS) empowered terahertz (THz) wireless systems subject to turbulence and stochastic beam misalignment. In more detail, we extract a closed-form expression for the outage probability that quantifies the joint impact of tur...
Article
Full-text available
Reconfigurable intelligent surfaces (RISs) empowered high-frequency (HF) wireless systems are expected to become the supporting pillar for several reliability and data-rate hungry applications. Such systems are, however, sensitive to misalignment and atmospheric phenomena including turbulence. Most of the existing studies on the performance assessm...
Chapter
As the wireless world moves towards the beyond fifth-generation (B5G) era, innovative applications require higher reliability, data rates, and traffic demands. Technological advances, such as massive multiple-input multiple-output, full-duplexing, and high-frequency communications, have been advocated, due to their unfordable cost, power consumptio...
Article
Full-text available
As the wireless world moves towards the sixth generation (6G) era, the demand for supporting bandwidth-hungry applications in ultra-dense deployments becomes more and more imperative. Driven by this requirement, both the research and development communities have turned their attention to the terahertz (THz) band, where more than 20 GHz of contiguou...
Article
Full-text available
Sustaining a flexible and ubiquitously available high-data-rate network, capable of supporting a massive number of end-users, demands the exploitation of higher frequency bands, such as the terahertz (THz) band (0.1-10~THz). However, the utilization of THz wireless systems comes with a number of challenges, many of them associated with the very hig...
Conference Paper
Full-text available
In this work, the performance of a reconfigurable intelligent surface (RIS) assisted terahertz (THz) (0.1 − 10 THz) wireless system is evaluated in terms of average signal-to-noise ratio (SNR), ergodic capacity, and outage probability. It is assumed that the line-of-sight (LoS) link between the transmitter (TX) and the receiver (RX) is blocked by o...
Conference Paper
Full-text available
This contribution aims at experimentally validating the suitability of well known fading distributions in modeling the channel of indoor THz wireless systems. In particular the suitability of α-µ, Rice and Nakagami-m distributions is evaluated by fitting them to empirical channel measurements. The fitting performance is expressed in terms of the Ko...
Article
Full-text available
Future wireless networks designed to operate in the millimeter-wave and terahertz bands are expected to be highly assisted by Reconfigurable Intelligent Surfaces (RIS). The role of the RIS will be to mediate possible non-line-of-sight link by redirecting the incident beam from the transmitter to the receiver and possibly modifying its characteristi...
Preprint
Full-text available
In this work, we examine the potential of autonomous operation of a reconfigurable intelligent surface (RIS) using wireless energy harvesting from information signals. To this end, we first identify the main RIS power-consuming components and introduce a suitable power-consumption model. Subsequently, we introduce a novel RIS power-splitting archit...
Article
Full-text available
With the vision to transform the current wireless network into a cyber-physical intelligent platform capable of supporting bandwidth-hungry and latency-constrained applications, both academia and industry turned their attention to the development of artificial intelligence (AI) enabled terahertz (THz) wireless networks. In this article, we list the...
Preprint
Full-text available
Reconfigurable intelligent surfaces (RISs) empowered high-frequency (HF) wireless systems are expected to become the supporting pillar for several reliability and data rate hungry applications. Such systems are, however, sensitive to misalignment and atmospheric phenomena including turbulence. Most of the existing studies on the performance assessm...
Conference Paper
Full-text available
This work investigates the suitability of α-µ distribution to model line-of-sight (LoS) and non-line-of-sight (NLoS) multi-path fading in terahertz (THz) wireless systems. The goodness of fit of α-µ to the small-scale fading of the measured channels is evaluated in terms of the Kolmogorov-Smirnov (KS) test. The KS test revealed the capability of α-...
Chapter
This chapter presents medium access control (MAC) approaches that are tailored to the terahertz (THz) communications systems. In more detail, after presenting the THz wireless communication systems particularities that are expected to influence the MAC, initial access (IA) scheme is presented that can be used to guarantee alignment between the base...
Technical Report
Full-text available
This white paper on AI and ML as enablers of beyond 5G (B5G) networks is based on contributions from 5G PPP projects that research, implement and validate 5G and B5G network systems. The white paper introduces the main relevant mechanisms in Artificial Intelligence (AI) and Machine Learning (ML), currently investigated and exploited for 5G and B5G...
Preprint
Full-text available
In this paper, we examine the potential for a reconfigurable intelligent surface (RIS) to be powered by energy harvested from information signals. This feature might be key to reap the benefits of RIS technology's lower power consumption compared to active relays. We first identify the main RIS power-consuming components and then propose an energy...
Article
Full-text available
This work discusses the optimal reconfigurable intelligent surface placement in highly-directional millimeter-wave links. In particular, we present a novel system model that takes into account the relationship between the transmission beam footprint at the RIS plane and the RIS size. Subsequently, based on the model we derive the end-to-end express...
Preprint
This paper presents an analytical pathloss model for reconfigurable intelligent surface (RIS) assisted terahertz (THz) wireless systems. Specifically, the model accommodates both the THz link and the RIS particularities. Finally, we derive a closed-form expression that returns the optimal phase shifting of each RIS reflection unit. The derived path...
Conference Paper
This paper presents an analytical pathloss model for reconfigurable intelligent surface (RIS) assisted terahertz (THz) wireless systems. Specifically, the model accommodates both the THz link and the RIS particularities. Finally, we derive a closed-form expression that returns the optimal phase shifting of each RIS reflection unit. The derived path...
Article
Full-text available
This paper presents a connectivity analysis of reconfigurable intelligent surface (RIS) assisted terahertz (THz) wireless systems. Specifically, a system model that accommodates the particularities of THz band links as well as the characteristics of the RIS is reported, accompanied by a novel general end-to-end (e2e) channel attenuation formula. Ba...
Preprint
Full-text available
This work discusses the optimal placement of a reconfigurable intelligent surface (RIS) in a millimeter wave (mmWave) point-to-point link. In particular, we present a novel system model that takes into account the relationship between the transmission beam footprint size at the RIS plane and the RIS size. Moreover, we present the theoretical framew...
Preprint
In the recent years, the proliferation of wireless data traffic has led the scientific community to explore the use of higher unallocated frequency bands, such as the millimeter wave and terahertz (0.1-10 THz) bands. However, they are prone to blockages from obstacles laid in the transceiver path. To address this, in this work, the use of a reconfi...
Preprint
This paper presents the analytic framework for evaluating the ergodic capacity (EC) of the reconfigurable intelligent surface (RIS) assisted systems. Moreover, high-signal-to-noise-ratio and high-number of reflection units (RUs) approximations for the EC are provided. Finally, the special case in which the RIS is equipped with a single RU is invest...
Article
Full-text available
In the present work, we investigate the impact of transceiver hardware imperfection on reconfigurable intelligent surface (RIS)-assisted wireless systems. In this direction, first, we present a general model that accommodates the impact of the transmitter (TX) and receiver (RX) radio frequency impairments. Next, we derive novel closed-form expressi...
Conference Paper
This paper presents the analytic framework for evaluating the ergodic capacity (EC) of the reconfigurable intelligent surface (RIS) assisted systems. Moreover, high-signal-to-noise-ratio and high-number of reflection units (RUs) approximations for the EC are provided. Finally, the special case in which the RIS is equipped with a single RU is invest...
Conference Paper
In the recent years, the proliferation of wireless data traffic has led the scientific community to explore the use of higher unallocated frequency bands, such as the millimeter-wave (mmWave) and terahertz (0.1 - 10) (THz) bands. However, they are prone to blockages from obstacles laid in the transceiver path. To address this, in this work the use...
Preprint
This paper focuses on quantifying the outage performance of terahertz (THz) relaying systems. In this direction, novel closed-form expressions for the outage probability of a dual-hop relaying system, in which both the source-relay and relay-destination links suffer from fading and stochastic beam misalignment, are extracted. Our results reveal the...
Conference Paper
This paper focuses on quantifying the outage performance of terahertz (THz) relaying systems. In this direction, novel closed-form expressions for the outage probability of a dual-hop relaying systems, in which both the source-relay and relay-destination links suffer from fading and stochastic beam misalignment, are extracted. Our results reveal th...
Conference Paper
Full-text available
The paper studies the joint impact of phase noise (PN) and co-channel interference (CCI) in indoor terahertz (THz) uplink. We formulate the theoretical framework that quantifies the impact of PN on the transceiver antenna directivity by extracting exact closed-form and low-complexity tight approximations for the expected gains. Additionally, by emp...
Article
Full-text available
In this paper, we provide the theoretical framework for the performance comparison of reconfigurable intelligent surfaces (RISs) and amplify-and-forward (AF) relaying wireless systems. In particular, after statistically characterizing the end-to-end (e2e) wireless channel coefficient of the RIS- assisted wireless system, in terms of probability den...
Preprint
In this paper, a novel hierarchical beamtracking approach, which is suitable for terahertz (THz) wireless systems, is presented. The main idea is to employ a prediction based algorithm with a multi-resolution codebook, in order to decrease the required overhead of tracking and increase its robustness. The efficiency of the algorithm is evaluated in...
Conference Paper
In this paper, a novel hierarchical beam-tracking approach, which is suitable for terahertz (THz) wireless systems, is presented. The main idea is to employ a prediction based algorithm with a multi-resolution codebook, in order to decrease the required overhead of tracking and increase its robustness. The efficiency of the algorithm is evaluated i...
Chapter
In order to countermeasure the high channel attenuation of the terahertz (THz) band, wireless systems operating in these frequencies employ high-gain antennas in both the transmitter (TX) and receiver (RX). The use of such antennas requires perfect antenna alignment, which, in practical implementations, is not possible. Moreover, due to the high pe...
Article
Full-text available
This paper focuses on deriving expected values for the transmit (TX) and receive (RX) antenna gains in terahertz (THz) wireless fronthaul and backhaul links under stochastic beam misalignment, which is created by antenna movement coming from the building or antenna mast swaying. In particular, four different antenna movement models are considered:...
Article
Full-text available
This work aims to present the theoretical framework for the outage performance assessment of the joint impact of antenna misalignment and local oscillator (LO) phase noise (PHN) on terahertz (THz) wireless systems. In more detail, a closed form expression for the outage probability and a tight high signal to noise ratio (SNR) approximation were ext...
Preprint
The proliferation of wireless devices in recent years has caused a spectrum shortage, which led the scientific community to explore the potential of using terahertz (THz) communications. However, THz systems suffer from severe path attenuation, blockage, and antenna misalignment. In this paper, we present a relay-based blockage and antenna misalign...
Conference Paper
The proliferation of wireless devices in recent years has caused spectrum shortage, which led the scientific community to explore the potential of using terahertz (THz) communications. However, THz systems suffer from severe path attenuation, blockage, and antenna misalignment. In this paper, we present a relay-based blockage and antenna misalignme...
Article
Full-text available
In this letter, we introduce a novel mixed terahertz (THz)-radio frequency (RF) wireless system architecture, which can be used for backhaul/fronthaul applications, and we deliver the theoretical framework for its performance assessment. In more detail, after identifying the main design parameters and characteristics, we derive novel closed-form ex...
Preprint
In this letter, we introduce a novel mixed terahertz (THz)-radio frequency (RF) wireless system architecture, which can be used for backhaul/fronthaul applications, and we deliver the theoretical framework for its performance assessment. In more detail, after identifying the main design parameters and characteristics, we derive novel closed-form ex...
Preprint
In this paper, a novel cooperation-aided localization and tracking approach, suitable for terahertz (THz) wireless systems is presented. It combines an angle of arrival (AoA) tracking algorithm with the two-way time of arrival method, in order to accurately track the user equipment (UE) position and reduce the deafness caused by the estimation erro...
Preprint
In this paper, we provide the mathematical framework to evaluate and quantify the performance of wireless systems, which employ beamforming, in the presence of hardware imperfections at both the basestation and the user equipment. In more detail, by taking a macroscopic view of the joint impact of hardware imperfections, we introduce a general mode...
Preprint
This paper focuses on delivering quantified results for the evaluation of the aggregated impact of stochastic antenna misalignment, multipath fading and hardware imperfections on the terahertz (THz) wireless fiber extenders. In this line, we present the appropriate signal model that accommodates the different technical and environmental parameters....
Preprint
This paper presents the theoretical framework for the performance evaluation of terahertz (THz) wireless fiber extender in the presence of misalignment and multipath fading. In more detail, after providing the appropriate system model that incorporates the different operation, design, and environmental parameters, such as the operation frequency, t...
Conference Paper
Full-text available
This paper presents the theoretical framework for the performance evaluation of terahertz (THz) wireless fiber extender in the presence of misalignment and multipath fading. In more detail, after providing the appropriate system model that incorporates the different operation, design, and environmental parameters, such as the operation frequency, t...
Conference Paper
This paper is focused on presenting the analytical framework for the performance evaluation of the initial access (IA) procedure in THz directional wireless systems. In more detail, after revisiting the IA procedure, explaining that it consists of two phases namely cell search (CS) and random access (RA) and identifying as key performance indicator...
Preprint
In this paper, we investigate the joint impact of misalignment fading and local oscillator (LO) phase noise (PHN) in multi-carrier terahertz (THz) wireless systems. In more detail, after establishing a suitable system model that takes into account the particularities of the THz channel, as well as the transceivers characteristics, we present simula...
Conference Paper
In this paper, we investigate the joint impact of misalignment fading and local oscillator (LO) phase noise (PHN) in multi-carrier terahertz (THz) wireless systems. In more detail, after establishing a suitable system model that takes into account the particularities of the THz channel, as well as the transceivers characteristics, we present simula...
Conference Paper
In this paper, we provide the mathematical framework to evaluate and quantify the performance of wireless systems, which employ beamforming, in the presence of hardware imperfections at both the basestation and the user equipment. In more detail, by taking a macroscopic view of the joint impact of hardware imperfections, we introduce a general mode...
Conference Paper
n this paper, a novel cooperation-aided localization approach, suitable for terahertz (THz) wireless systems is presented. It combines an angle of arrival (AoA) tracking algorithm with the two-way time of arrival method, in order to accurately track the user equipments (UE) position and reduce the deafness caused by the estimation errors of the tra...
Article
Full-text available
This paper is focused on providing the analytical framework for the quantification and evaluation of the joint effect of misalignment fading and hardware imperfections in the presence of multipath fading at terahertz (THz) wireless fiber extenders. In this context, we present the appropriate system model that incorporates the different operation, d...
Preprint
Full-text available
The present white paper focuses on the system requirements of TERRANOVA. Initially details the key use cases for the TERRANOVA technology and presents the description of the network architecture. In more detail, the use cases are classified into two categories, namely backhaul & fronthaul and access and small cell backhaul. The first category refer...
Conference Paper
In this paper, we present a novel two-array channel model for wireless terahertz (THz) systems operat- ing in the range of 275 to 400 GHz, which accommodates both the channel particularities and the transceivers pa- rameters. The channel particularities include the frequency selectivity, path-loss, as well as the atmospheric conditions, namely temp...
Research
The present white paper focuses on the system requirements of TERRANOVA. Initially details the key use cases for the TERRANOVA technology and presents the description of the network architecture. In more detail, the use cases are classified into two categories, namely backhaul & fronthaul and access and small cell backhaul. The first category refer...
Conference Paper
In this paper, we provide a novel distance and frequency dependent adaptive modulation scheme, which is suitable for communication systems operationg in the THz band. After determining the transmission bandwidth, the proposed scheme evaluates the subcarrier bandwidth of the orthogonal frequency division modulated (OFDM) transmission signal, in orde...
Conference Paper
In this paper, we formulate a novel throughput aware user association scheme for ultra dense terahertz (THz) networks. In more detail, we introduce a user association problem , which takes into account the THz channel particularities, the directivity of the BSs' and UEs' antennas, as well as their position and the UEs' minimum rate requirements. Mo...
Conference Paper
In this paper, we establish the appropriate system model for the terahertz (THz) wireless link in the range of 275 to 400 GHz, which accommodates the channel particularities and transceivers parameters. The channel particularities include the frequency selectivity, pathloss, as well as the atmospheric conditions, namely temperature and pressure, wh...
Article
One of the most significant 5G technology enablers will be Device-to-Device (D2D) communications. D2D communications constitute a promising way to improve spectral, energy and latency performance, exploiting the physical proximity of communicating devices and increasing resource utilization. Furthermore, network infrastructure densification has bee...
Article
Advances in cellular networks such as device-to-device communications and full-duplex radios, as well as the inherent elimination of intra-cell interference achieved by network-controlled multiple access schemes, motivates the investigation of the cross-mode interference under a guard region corresponding to the Voronoi cell of an access point. By...
Article
Full-text available
Recent trends in wireless networking such as small cells and network function virtualization, strongly suggest that the future cellular network will consist of many sub-networks controlled by self-interest operators competing for a share of the revenues associated with the high demand for service. This paper attempts to analyze the future network p...
Chapter
This chapter discusses the radio&;#x02010;resource management (RRM) aspects of homogeneous single&;#x02010;technology ultradense networks (UDNs), with emphasis on centralized optimization problem modeling and solving. It provides a short list of the optimization tools and methods for modeling and solving RRM problems in the envisioned 5G&;#x02010;U...
Conference Paper
Recent trends in wireless networking, such as small cells and network function virtualization, strongly suggest that the future cellular network will consist of many sub-networks controlled by self-interest operators competing for a share of the revenues associated with the high demand for service. This paper attempts to analyze the future network...
Article
The extreme traffic load that future wireless networks are expected to accommodate requires a re-thinking of the system design. Initial estimations indicate that, different from the evolutionary path of previous cellular generations that was based on spectral efficiency improvements, the most substantial amount of future system performance gains wi...