PAPERS LISTED AS MOST POPULAR FOR March 2021!

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Some good news! Four of our paper have been included to the list of most popular ones for the month March 2021. In particular, the paper’s titles are:


1. “Machine learning in nano-scale biomedical engineering,” published in IEEE Transactions on Molecular, Biological and Multi-scale Communications

2. “All-optical cochlear implants,” published in IEEE Transactions on Molecular, Biological and Multi-scale Communications

3. “How Much do Hardware Imperfections Affect the Performance of Reconfigurable Intelligent Surface-Assisted Systems?” published in IEEE Open Journal of the Communications Society

4. “Coverage Analysis of Reconfigurable Intelligent Surface Assisted THz Wireless Systems,” published in IEEE Open Journal of the Vehicular Technology

Next, let me briefly present the paper’s concepts.

Machine learning in nano-scale biomedical engineering

Abstract: Machine learning (ML) empowers biomedical systems with the capability to optimize their performance through modeling of the available data extremely well, without using strong assumptions about the modeled system. Especially in nano-scale biosystems, where the generated data sets are too vast and complex to mentally parse without computational assist, ML is instrumental in analyzing and extracting new insights, accelerating material and structure discoveries and designing experience as well as supporting nano-scale communications and networks. However, despite these efforts, the use of ML in nano-scale biomedical engineering remains still under-explored in certain areas and research challenges are still open in fields such as structure and material design and simulations, communications and signal processing, and bio-medicine applications. In this article, we review the existing research regarding the use of ML in nano-scale biomedical engineering. In more detail, we first identify and discuss the main challenges that can be formulated as ML problems. These challenges are classified in three main categories: structure and material design and simulation, communications and signal processing and biomedicine applications. Next, we discuss the state of the art ML methodologies that are used to countermeasure the aforementioned challenges. For each of the presented methodologies, special emphasis is given to its principles, applications and limitations. Finally, we conclude the article with insightful discussions, that reveal research gaps and highlight possible future research directions.

Authors: Alexandros-Apostolos A. Boulogeorgos, Stylianos E. Trevlakis, Sotiris A. Tegos, Vasilis K. Papanikolaou, and George K. Karagiannidis

All-optical cochlear implants

Abstract: In the present work, we introduce a novel cochlear implant (CI) architecture, namely all-optical CI (AOCI), which directly converts acoustic to optical signals capable of stimulating the cochlear neurons. First, we describe the building-blocks (BBs) of the AOCI, and explain their functionalities as well as their interconnections. Next, we present a comprehensive system model that incorporates the technical characteristics and constraints of each BB, the transdermal-optical-channel particularities, i.e., optical path-loss and external-implanted device stochastic pointing-errors, and the cochlear neurons biological properties. Additionally, in order to prove the feasibility of the AOCI architecture, we conduct a link-budget analysis that outputs novel closed-form expressions for the instantaneous and average photon flux that is emitted on the cochlear neurons. Likewise, we define three new key-performance-indicators (KPIs), namely probability of hearing, probability of false-hearing, and probability of neural damage. The proposed theoretical framework is verified through respective simulations, which not only quantify the efficiency of the proposed architecture, but also reveal an equilibrium between the optical transmission power and the patient’s safety, as well as the AOCI BBs specifications. Finally, it is highlighted that the AOCI approach is greener and safer than the conventional CIs.

Authors: Stylianos E. Trevlakis, Alexandros-Apostolos A. Boulogeorgos, Nestor D. Chatzidiamantis, and George K. Karagiannidis

How Much do Hardware Imperfections Affect the Performance of Reconfigurable Intelligent Surface-Assisted Systems?

Abstract: 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 expressions for the instantaneous end-to-end signal-to-noise-plus-distortion-ratio (SNDR). Building upon these expressions, we extract an exact closed-form expression for the system’s outage probability, which allows us not only to quantify RIS-assisted systems’ outage performance but also reveals that the maximum allowed spectral efficiency of the transmission scheme is limited by the levels of the transceiver hardware imperfection. Likewise, a diversity analysis is provided. Moreover, in order to characterize the capacity of RIS-assisted systems, we report a new upper-bound for the ergodic capacity, which takes into account the number of the RIS’s reflective units (RUs), the level of TX and RX hardware imperfection, as well as the transmission signal-to-noise-ratio (SNR). Finally, two insightful ergodic capacity ceilings are extracted for the high-SNR and high-RUs regimes. Our results highlight the importance of accurately modeling the transceiver hardware imperfection and reveals that they significantly limit the RIS-assisted wireless system performance.

Authors: Alexandros-Apostolos A. Boulogeorgos, and Angeliki Alexiou

Coverage Analysis of Reconfigurable Intelligent Surface Assisted THz Wireless Systems

Abstract: 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.

Authors: Alexandros-Apostolos A. Boulogeorgos, and Angeliki Alexiou

Suggestions

Topic: Communications in biomedical applications

For readers that are interested in communications in biomedical applications, some other good suggestions are:

[S1] A. -A. A. Boulogeorgos, S. E. Trevlakis and N. D. Chatzidiamantis, “Optical Wireless Communications for In-Body and Transdermal Biomedical Applications,” in IEEE Communications Magazine, vol. 59, no. 1, pp. 119-125, January 2021, doi: 10.1109/MCOM.001.2000280.

and

[S2] S. E. Trevlakis, A.-A. A. Boulogeorgos, N. D. Chatzidiamantis, G. K. Karagiannidis and X. Lei, “Electrical vs Optical Cell Stimulation: A Communication Perspective,” in IEEE Access, vol. 8, pp. 192259-192269, 2020, doi: 10.1109/ACCESS.2020.3032481.

Optical Wireless Communications for In-Body and Transdermal Biomedical Applications

Abstract: This article discusses the fundamental architectures for optical-wireless-systems for biomedical-ap-plications. After summarizing the main applications and reporting their requirements, we describe the characteristics of the transdermal and in-body optical channels (OCs) as well as the challenges that they impose in the design of communication systems. Specifically, we provide three possible architectures for transdermal communications, namely electro-optical monitoring, opto-electrical, and all-optical (AO), for neural stimulation, which are currently under investigation, whereas for in-body communications, we provide a nano-scale AO concept. For each architecture, we discuss the main operation principles, the technology enablers, and research directions for their development. Finally, we highlight the necessity of designing an infor-mation-theoretic framework for the analysis and design of the physical and medium access control layers, which takes into account the channels’ characteristics.

Authors: Alexandros-Apostolos A. Boulogeorgos, Stylianos E. Trevlakis, and Nestor D. Chatzidiamantis

Electrical vs Optical Cell Stimulation: A Communication Perspective

Abstract: This article discusses the fundamental architectures for optical-wireless-systems for biomedical-ap-plications. After summarizing the main applications and reporting their requirements, we describe the characteristics of the transdermal and in-body optical channels (OCs) as well as the challenges that they impose in the design of communication systems. Specifically, we provide three possible architectures for transdermal communications, namely electro-optical monitoring, opto-electrical, and all-optical (AO), for neural stimulation, which are currently under investigation, whereas for in-body communications, we provide a nano-scale AO concept. For each architecture, we discuss the main operation principles, the technology enablers, and research directions for their development. Finally, we highlight the necessity of designing an infor-mation-theoretic framework for the analysis and design of the physical and medium access control layers, which takes into account the channels’ characteristics.

Authors: Stylianos E. Trevlakis, Alexandros-Apostolos A. Boulogeorgos, Stylianos E. Trevlakis, Nestor D. Chatzidiamantis, George K. Karagiannidis, and Xianfu Lei

Topic: Reconfigurable intelligent surface assisted wireless systems

For readers that are interested in reconfigurable intelligent surface (RIS)-assisted wireless systems, some other good suggestions are:

[S3] A.-A. A. Boulogeorgos, and A. Alexiou, “Performance Analysis of Reconfigurable Intelligent Surface-Assisted Wireless Systems and Comparison With Relaying,” in IEEE Access, vol. 8, pp. 94463-94483, 2020, doi: 10.1109/ACCESS.2020.2995435

[S4] K. Ntontin, A. -A. A. Boulogeorgos, D. G. Selimis, F. I. Lazarakis, A. Alexiou and S. Chatzinotas, “Reconfigurable Intelligent Surface Optimal Placement in Millimeter-Wave Networks,” in IEEE Open Journal of the Communications Society, vol. 2, pp. 704-718, 2021, doi: 10.1109/OJCOMS.2021.3068790.

Performance Analysis of Reconfigurable Intelligent Surface-Assisted Wireless Systems and Comparison With Relaying

Abstract: 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 density function (PDF) and cumulative density function (CDF), we extract novel closed-form expressions for the instantaneous and average e2e signal-to-noise ratio (SNR) for both the RIS-assisted and AF-relaying wireless systems. Building upon these expressions, we derive the diversity gain of the RIS-assisted wireless system as well as the outage probability (OP) and symbol error rate (SER) for a large variety of Gray-mapped modulation schemes of both systems under investigation. Additionally, the diversity order of the RIS-assisted wireless system is presented as well as the ergodic capacity (EC) of both the RIS-assisted and AF-relaying wireless systems. Likewise, high-SNR and high-number of metasurfaces (MS) approximations for the SER and EC for the RIS-assisted wireless system are reported. Finally, for the sake of completeness, the special case in which the RIS is equipped with only one MS is also investigated. For this case, the instantaneous and average e2e SNR are derived, as well as the OP, SER and EC. Our analysis is verified through respective Monte Carlo simulations, which reveal the accuracy of the presented theoretical framework. Moreover, our results highlight that, in general, RIS-assisted wireless systems outperform the corresponding AF-relaying ones in terms of average SNR, OP, SER and EC.

Authors: Alexandros-Apostolos A. Boulogeorgos, and Angeliki Alexiou

Reconfigurable Intelligent Surface Optimal Placement in Millimeter-Wave Networks

Abstract: 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.

Authors: Konstantions Ntontin, Alexandros-Apostolos A. Boulogeorgos, Dimitrios G. Selimis, Fotis I. Lazarakis, Angeliki Alexiou, Symeon Chatzinotas

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