Project

ARIADNE-ARTIFICIAL INTELLIGENCE AIDED D-BAND NETWORK FOR 5G LONG TERM EVOLUTION

Goal: The ARIADNE project plans to bring together a novel high-frequency advanced radio architecture and an Artificial Intelligence (AI) network processing and management approach into a new type of intelligent communications system Beyond 5G. The new intelligent system approach is necessary because the scale and complexity of the new radio attributes in the new frequency ranges cannot be optimally operated using traditional network management approaches.

Updates
0 new
0
Recommendations
0 new
0
Followers
0 new
6
Reads
0 new
85

Project log

Alexandros-Apostolos A. Boulogeorgos
added a research item
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 harvesting and power consumption model. Furthermore, we formulate and solve the problem of the optimal RIS placement together with the amplitude and phase response adjustment of its elements in order to maximize the signal-to-noise ratio (SNR) while harvesting sufficient energy for its operation. Finally, numerical results validate the autonomous operation potential and reveal the range of power consumption values that enables it. Index Terms-Reconfigurable intelligent surface, wireless energy harvesting, optimal placement.
Alexandros-Apostolos A. Boulogeorgos
added a research item
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 for both cases, i.e., in the absence as well as in the presence of disorientation and mis-alignment, by extracting closed-form formulas for the probability density function (PDF) and the cumulative distribution function (CDF). Building on the aforementioned expressions, we extract novel closed-form expressions for the outage probability (OP) in the absence and the presence of disorientation and misalignment as well as hardware imperfections. In addition, high signal-to-noise ratio OP approximations are derived, leading to the extraction of the diversity order. Finally, an OP floor due to disorientation and misalignment is presented.
Alexandros-Apostolos A. Boulogeorgos
added a research item
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 the impact of different design parameters, including antenna gain and transceivers hardware imperfections, atmospheric conditions, such as rain, and parameters, like temperature, humidity and pressure, as well as stochastic beam misalignment that can be caused by thermal expansion, dynamic wind loads and/or weak earthquakes. For this model, we extract novel closed-form expressions for the probability density and cumulative distribution functions of the THz wireless channel that captures the impact of geometric loss, beam misalignment and rain attenuation. We capitalized the aforementioned expressions by presenting closed-form formulas for the outage probability and achievable throughput of the system. Finally, we document an analytical policy that returns the optimal transmission spectral efficiency that maximizes the achievable throughput. INDEX TERMS Hardware imperfections, misalignment fading, outage probability, performance analysis, radio frequency chain imperfections, rain attenuation, statistical characterization, throughput, terahertz wireless systems, wireless fiber extender.
Alexandros-Apostolos A. Boulogeorgos
added a research item
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 for both cases, i.e., in the absence as well as in the presence of disorientation and misalignment, by extracting closed-form formulas for the probability density function (PDF) and the cumulative distribution function (CDF). Building on the aforementioned expressions, we extract novel closed-form expressions for the outage probability (OP) in the absence and the presence of disorientation and misalignment as well as hardware imperfections. In addition, high signal-to-noise ratio OP approximations are derived, leading to the extraction of the diversity order. Finally, an OP floor due to disorientation and misalignment is presented.
Alexandros-Apostolos A. Boulogeorgos
added a research item
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 turbulence and misalignment as well as the effect of transceivers' hardware imperfections. Our results highlight the importance of accurately modeling both turbulence and misalignment when assessing the performance of multi-RIS-empowered THz wireless systems.
Alexandros-Apostolos A. Boulogeorgos
added a research item
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 assessment of RIS-empowered wireless systems ignore the impact of the aforementioned phenomena. Motivated by this, the current contribution presents a theoretical framework for statistically characterizing cascaded composite turbulence and misalignment channels. More specifically, we present the probability density and cumulative distribution functions for the cascaded composite turbulence and misalignment channels. Building upon the derived analytical expressions and in order to demonstrate the applicability and importance of the extracted framework in different use case cases of interest, we present novel closed-form formulas that quantify the joint impact of turbulence and misalignment on the outage performance for two scenarios, namely cascaded multi-RIS-empowered free space optics (FSO) and terahertz (THz) wireless systems. For the aforementioned scenarios, the diversity order is extracted. In addition, we provide an insightful outage probability upper bound for a third scenario that considers parallel multi-RIS-empowered FSO systems. Our results highlight the importance of accurately modeling both turbulence and misalignment when assessing the performance of such systems.
Alexandros-Apostolos A. Boulogeorgos
added a research item
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 consumption, as well as their need to operate in an unfavorable electromagnetic wave propagation environment. As a remedy, the exploitation of the implicit randomness of the propagation environment through reconfigurable intelligent surfaces (RIS) to improve the quality of experience, attracts the eyes of both academia and industry. RISs transform wireless systems into smart platforms capable of sensing the environment and applying customized transformations to the radio waves. The RIS-assisted smart environments have the potential to provide B5G wireless networks with uninterrupted wireless connectivity and enable data transmission without generating new signals but recycling existing radio waves. Motivated by the advances in this area, this chapter focuses on presenting the technology enablers and the state-of-the-art of RIS-assisted wireless systems, the need for the new channel and system models as well as theoretical frameworks for their analysis and design, as well as the long-term and open research issues to be solved towards their massive deployment.
Alexandros-Apostolos A. Boulogeorgos
added a research item
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 high propagation losses of THz signals, which require the utilization of high-gain directional antennas with strict beam alignment requirements, as well as the low signal penetration of (sub) millimetric waves, which leads to intermittent blockage and shadow areas. In this paper, a quantitative discussion of these phenomena and their implications in both backhaul and fronthaul applications of the THz spectrum is provided. Starting from state-of-the-art demonstrated THz technology parameters, the directivity requirements, the impact of beam misalignment and the opportunities for multi-hop relaying in two different application scenarios are described. For the same conditions, the impact of blockage is quantified, and the benefits of reconfigurable intelligent surfaces are studied. Finally, the implications of blockage on the physical layer security of THz systems are presented.
Alexandros-Apostolos A. Boulogeorgos
added a research item
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 Kolmogorov-Smirnov (KS) and Kullback-Leibler (KL) divergence tests. The results show that the α-µ and Rice distributions achieve a good fit to the empirical data, wheras the Nakagami-m distribution fails to provide an adequate fit in the majority of the examined THz links.
Alexandros-Apostolos A. Boulogeorgos
added a research item
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 contiguous bandwidth can be exploited. As a result, novel wireless systems and network architectures have been reported promising excellence in terms of reliability, massive connectivity, and data rates. To assess their feasibility and efficiency, it is necessary to develop stochastic channel models that account for the small-scale fading. However, to the best of our knowledge, only initial steps have been so far performed. Motivated by this, this contribution is devoted to take a new look to fading in THz wireless systems, based on three sets of experimental measurements. In more detail, measurements, which have been conducted in a shopping mall, an airport check-in area, and an entrance hall of a university towards different time periods, are used to accurately model the fading distribution. Interestingly, our analysis shows that conventional distributions, such as Rayleigh, Rice, and Nakagami-m, lack fitting accuracy, whereas, the more general, yet tractable, α-µ distribution has an almost-excellent fit. In order to quantify their fitting efficiency, we used two well-defined and widely accepted tests, namely the Kolmogorov-Smirnov and the Kullback-Leibler tests. By accurately modeling the THz wireless channel, this work creates the fundamental tools for developing the theoretical and optimization frameworks for such systems and networks.
Alexandros-Apostolos A. Boulogeorgos
added a research item
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 applications of THz wireless systems in the beyond fifth-generation era and discuss their enabling technologies and fundamental challenges that can be formulated as AI problems. These problems are related to physical, medium/multiple access control, radio resource management, network, and transport layer. For each of them, we report the AI approaches, which have been recognized as possible solutions in the technical literature, emphasizing their principles and limitations. Finally, we provide an insightful discussion concerning research gaps and possible future directions.
Alexandros-Apostolos A. Boulogeorgos
added a research item
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 obstacles laid in the propagation environment. The only way to establish a connection between the transceivers is by employing a RIS, consisting of a large number of electrically conductive elements placed in a rectangular array format. This scenario is examined under different levels of RX beam misalignment, transmission distances, number of RIS reflection units, and transmit power levels. The examined performance metrics are extracted by novel and low complexity closed-form expressions.
Alexandros-Apostolos A. Boulogeorgos
added a research item
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 assessment of RIS-empowered wireless systems ignore the impact of the aforementioned phenomena. Motivated by this, the current contribution presents a theoretical framework for analyzing the performance of multi-RIS empowered HF wireless systems. More specifically, we statistically characterize the cascaded composite turbulence and misalignment channels in terms of probability density and cumulative distribution functions. Building upon the derived analytical expressions, we present novel closed-form formulas that quantify the joint impact of turbulence and misalignment on the outage performance for two scenarios of high interest namely cascaded multi-RIS-empowered free space optics (FSO) and terahertz (THz) wireless systems. In addition, we provide an insightful outage probability upper-bound for a third scenario that considers parallel multi-RIS-empowered FSO systems. Our results highlight the importance of accurately modeling both turbulence and misalignment when assessing the performance of such systems.
Alexandros-Apostolos A. Boulogeorgos
added 3 research items
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 networks. A family of neural networks is presented which are, generally speaking, non-linear statistical data modeling and decision-making tools. They are typically used to model complex relationships between input and output parameters of a system or to find patterns in data. Feed-forward neural networks, deep neural networks, recurrent neural networks, and convolutional neural networks belong to this family. Reinforcement learning is concerned with how intelligent agents must take actions in order to maximize a collective reward, e.g., to improve a property of the system. Deep reinforcement learning combines deep neural networks and has the benefit that is can operate on non-structured data. Hybrid solutions are presented such as combined analytical and machine learning modeling as well as expert knowledge aided machine learning. Finally, other specific methods are presented, such as generative adversarial networks and unsupervised learning and clustering.
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 misalignment mitigation approach. In more detail, two relay selection policies are employed, namely best and random relay selection. The system performance under both policies is evaluated and compared in terms of average throughput and the probability that the throughput of a link to be below a predetermined quality of service (QoS) threshold, using Monte Carlo simulations.
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 pathloss model is validated through extensive electromagnetic simulations and is expected to play a key role in the design of RIS-assisted THz wireless systems.
Alexandros-Apostolos A. Boulogeorgos
added a research item
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-µ distribution to capture the fading characteristics of THz wireless channels. To highlight the importance of this study and the applicability to the theoretical analysis of THz wireless systems, for indicative values of α and µ, the ergodic capacity of THz wireless systems is assessed.
Alexandros-Apostolos A. Boulogeorgos
added a research item
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 station and user equipment, and its performance is quantified under different wireless environments. Moreover, a hierarchical beam tracking approach is discussed that ensures alignment between the base station (BS) and mobile user equipment (UE) with low-overhead. Furthermore, random access and scheduled access issues are addressed. Finally, low-complexity relaying approaches are presented as countermeasures to antenna misalignment and blockage.
Konstantinos Ntontin
added a research item
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 harvesting and power consumption model. Furthermore, we formulate and solve the problem of the optimal RIS placement together with the amplitude and phase response adjustment of its elements in order to maximize the signal-to-noise ratio (SNR) while harvesting sufficient energy for its operation. Finally, numerical results validate the autonomous operation potential and reveal the range of power consumption values that enables it.
Alexandros-Apostolos A. Boulogeorgos
added a research item
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 expression of the received signal power and, furthermore, provide approximate closed-form expressions in the case that the RIS size is either much smaller or at least equal to the transmission beam footprint. Moreover, building upon the expressions, we derive the optimal RIS placement that maximizes the end-to-end signal-to-noise ratio. Finally, we substantiate the analytical findings by means of simulations, which reveal important trends regarding the optimal RIS placement according to the system parameters.
Alexandros-Apostolos A. Boulogeorgos
added 5 research items
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 terms of the average number of pilots and mean square error (MSE) and is compared with the corresponding performance of the fast channel tracking (FCT) algorithm. Our results highlight the superiority of the proposed approach in comparison with FCT, in terms of tracking efficiency with low overhead.
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 framework that quantifies the RIS gain loss in the case that the transmission beam footprint in the RIS plane is smaller than the RIS size, and the beam waste for the case in which the transmission beam footprint in the RIS plane is larger than the RIS size, by extracting closed-form expressions for the received power and the end-to-end signal-to-noise-ratio (SNR) for both cases. Subsequently, building upon the expressions, we provide SNR maximization policies for both cases. Finally, we perform a comparison, in terms end-to-end SNR, between the RIS-aided link and its relay-aided counterpart.
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 employing stochastic geometry, we model the propagation environment of indoor THz wireless systems and provide the analytical characterization of the CCI in the presence of PN, in terms of its expected value. The analysis is verified through computer simulations that reveal the accuracy of the presented theory with moderate numbers of users. The paper provides readily available tools for analyzing and designing indoor THz networks.
Alexandros-Apostolos A. Boulogeorgos
added a research item
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. Based on this formula, we derive a closed-form expression that returns the optimal phase shifting of each reflection unit (RU) of the RIS. Moreover, we provide a tractable e2e channel coefficient approximation that is suitable for analyzing the RIS-assisted THz wireless system performance. Building upon the aforementioned approximation as well as the assumption that the user equipments are located in random positions within a circular cluster, we present the theoretical framework that quantifies the coverage performance of the system under investigation. In more detail, we deliver a novel closed-form expression for the coverage probability that reveals that there exists a minimum transmission power that guarantees 100% coverage probability. Both the derived channel model as well as the coverage probability are validated through extensive simulations and reveal the importance of taking into account both the THz channel particularities and the RIS characteristics, when assessing the system's performance and designing RIS-assisted THz wireless systems.
Alexandros-Apostolos A. Boulogeorgos
added a research item
In this work, we examine the use of reconfigurable intelligent surfaces (RISs) to create alternative paths from a transmitter to a receiver in millimeter-wave (mmWave) networks, when the direct link is blocked. In this direction, we evaluate the end-to-end signal-to-noise ratio (SNR) expression of the transmitter-RIS-receiver links that take into account the transmitter-RIS and RIS receiver distances and enable us to acquire important insights regarding the RIS position that maximizes it. Finally, the insights are corroborated by numerical results.
Alexandros-Apostolos A. Boulogeorgos
added 14 research items
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 reconfigurable-intelligent-surface (RIS) to restore the link between a transmitter (TX) and a receiver (RX), operating in the D-band (110-170 GHz) is investigated. The system performance is evaluated in terms of pathgain and capacity considering the RIS design parameters, the TX/RX-RIS distance and the elevation angles from the center of the RIS to the transceivers.
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 the importance of taking into account the impact of beam misalignment when characterizing the outage performance of the system as well as when selecting the transmission frequencies.
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 investigated. Our analysis is verified through respective Monte Carlo simulations, which highlight the accuracy of the proposed framework.
Alexandros-Apostolos A. Boulogeorgos
added a project goal
The ARIADNE project plans to bring together a novel high-frequency advanced radio architecture and an Artificial Intelligence (AI) network processing and management approach into a new type of intelligent communications system Beyond 5G. The new intelligent system approach is necessary because the scale and complexity of the new radio attributes in the new frequency ranges cannot be optimally operated using traditional network management approaches.