# Harilaos G. Sandalidis's research while affiliated with University of Thessaly and other places

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## Publications (73)

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...

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...

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...

More often than not, transmitters (Txs) in wireless systems operate using directional radiation patterns where the main radiation lobe creates a three-dimensional conic-shaped volume. In this context, any receiver (Rx) placed inside it can establish a strong communication link. Since the Rx location is not always known, it is desirable to investiga...

The ambitious goal of light-fidelity (LiFi) technology to provide seamless user mobility in indoor environments requires strong link connections to confront any stochasticity that possibly comes out. In this context, a robust LiFi network should effectively address the spatial random terminal locations inside its coverage volume. In contrast with t...

The sterilization properties of the C-band of the ultraviolet (UV) light have been well-known for many years; however, their application has become more vital and widespread today due to the Covid-19 pandemic. Nevertheless, minimal work has been devoted to simulating UV-C propagation for surface disinfection in indoor environments. UV light has als...

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...

Abstract With the advent of the new decade, unmanned aerial vehicles (UAVs) will increasingly play an active role mainly as broadband transmission relays for broadcast applications. In the present study, we consider a feasible network where a transmitter, mounted on a hill, is connected through an optical wireless link with a UAV, hovering at a cer...

The continuous positioning of a mobile user equipment (MU) in a prompt way is a fundamental requirement in several indoor applications related to ubiquitous computation, assisted living environments, and security/surveillance systems. Motivated by this fact, the current contribution reports a low-complexity visible light positioning (VLP) method su...

We investigate the impact of the channel statistics on the average harvested energy when directive lightwave power transfer (DLPT) is used for both indoor and outdoor environments. More specifically, for the indoor scenario, the channel randomness is subject to misalignment effects, while for the outdoor one, atmospheric turbulence is further consi...

The performance of free‐space optics links strongly depends on scintillation effects caused by the atmospheric turbulence appearance. A widely adopted way to counterbalance the expected deterioration due to scintillation is to employ cooperative and multi‐hop arrangements. However, the use of multiple relays increases significantly the complexity o...

The current work investigates the outage probability of a vertical diffused line-of-sight underwater optical wireless communication link where a fixed transmitter at the sea surface communicates with a receiver floated below sea level, which may be still but randomly placed at a given location or moving following the random waypoint model. In both...

The optimal trade-off between coverage and depth for a vertical underwater optical wireless communication (UOWC) link is thoroughly investigated in this letter. In the scenario under consideration, the optical transmitter is mounted at a fixed position on the sea surface and illuminates a subsea area through a Lambertian radiation pattern. A generi...

The performance of a network consisting of several underwater sensors communicating with a terrestrial destination is studied for the first time in terms of the outage probability. In the scenario under consideration,
$K$
sensors emit data to a decode-and-forward relay using underwater optical wireless communication links. The relay transfers the...

Free space optics (FSO) technology has demonstrated an increasingly scientific and commercial interest over the past few years. However, due to signal propagation in the atmosphere, the operation depends strongly on the atmospheric conditions and some random impairments, including turbulence and pointing error (PE) effects. In the present study, a...

Terrestrial free-space optical (FSO) communication systems with subcarrier intensity modulation have experienced a particular research attention in the recent past. However, their performance strongly degrades in the presence of atmospheric turbulence, pointing errors, and phase noise impairments. In order to overcome these limitations, the authors...

The authors consider a point-to-point optical wireless communication link with on–off keying (OOK) modulation scheme. The propagation is deteriorated by the joint effects of gamma–gamma atmospheric turbulence and misalignment induced fading described by a non-zero boresight pointing error model. Mathematical expressions are derived for the average...

Radio-on-Free-Space Optical (RoFSO) systems constitute a very attractive option for interconnecting central base stations (CBS) with remote antenna units (RAUs). Nonetheless, the optical signal propagation through the atmosphere is tremendously affected by turbulence- and misalignment-induced fading. In the present study, we investigate the transmi...

Subcarrier free-space optical (FSO) systems using coherent recovery techniques at the receiver have acquired growing research interest in recent times. However, their optimal performance is diminished by the non-perfect synchronization of carrier frequency and phase, which is mainly due to phase noise problems. Moreover, turbulence and pointing err...

Wide bandwidth and dense spatial reuse are of extreme importance for future wireless communication networks, including 5G and beyond. In particular, these properties are important to enable future wireless networks to cope with the explosive increase in the demand for high data-rate communications. Optical wireless communications (OWC) is a promisi...

Visible light communication (VLC) is a promising technology that meets illumination and information transmission requirements in an indoor environment. Because light waves convey energy, a VLC link may exploit that fact for energy harvesting purposes. In this context, a single light emitting diode lamp located at a close distance over a tablet or l...

Composite models for the combined effect of both scintillation- and misalignment-induced fading in terrestrial optical wireless systems are often expressed in terms of higher order special functions, making, thus, the performance evaluation of such links quite complicated. In order to overcome this problem, we propose the mixture Gamma distribution...

Achieving both illumination and data reception with probability almost one inside a specific indoor environment is not an effortless task in visible light communication (VLC) networks. Several factors such as error probability, transmitted power, dimming factor, or node failure affect coverage probability to a large extent. To assure reliable signa...

The aim of this paper is to develop link layer transmission schemes for hybrid optical wireless (OW)/radio frequency (RF) systems, with constraints on both per-link and total average power consumption at the transmitter. In this context, we adopt a timeslot structure with a queue for storing the data packets for transmission and model the hybrid ch...

The need to find reliable and simultaneously simplistic propagation models in the majority of frequency bands, where wireless body area networks (WBANs) operate in, is the driving force leading to the appearance of many studies on that topic during recent years. Transmission in WBANS is significantly affected by human body tissues and is frequency...

In this paper, optical wireless has been addressed as a promising technology to provide high-bandwidth services for underwater communications. However, the significant attenuation degree due to high absorption and scattering of optical transmission in the water confines the achievable range of optical links to only few meters. One way to achieve tr...

This paper investigates link layer transmission schemes for hybrid optical wireless (OW)/radio frequency (RF) systems with constraints on both per-link and total power consumption at the transmitter. Assuming timeslot structure and using a queue for storing the random data packet arrivals, we formulate a stochastic optimization problem where intell...

Free-Space Optical (FSO) technology can effectively transfer multiple radio-frequency signals, and this new technique is commonly referred in the technical literature as radio on FSO (RoFSO). In the present study, we investigate the evaluation of an RoFSO scenario employing the orthogonal frequency-division multiplexing scheme. Both phase shift key...

Transferring wireless broadband services across extremely far distances on Earth is usually implemented nowadays either by ground-based or satellite communications. Terrestrial networks require, however, heavy installation and maintenance costs, whereas satellite networks suffer from excessively high power requirements. An alternative but highly ch...

The use of relays is one of the most promising methods for mitigating impairments of the performance of free-space optical (FSO) systems and extending their limited transmission range. However, several factors contribute to significant link performance degradation. Most severe is the influence of the adverse atmospheric conditions that frequently a...

The transmission of multiple wireless signals over optical links has attained a great research interest nowadays. In case where optical fibers are difficult to be deployed, or installation cost is prohibited, optical wireless systems provide an efficient alternative means. In this paper, we consider the WiMAX (IEEE802.16) standard and construct a s...

Non-line-of-sight optical wireless transmission, operated in the unlicensed ultraviolet UV-C band, has been recently suggested as an alternative means of communication. However, due to limited coverage, relayed UV-C networks need to be deployed in order to supply communication services at large distances. In this paper, we consider a serial multi-h...

The Inverse Gaussian (IG) distribution has been recently proposed as a less complex alternative to the classical log-normal distribution to describe shadowing phenomena. This paper investigates the performance of digital communications systems over IG fading channels. Closed-form expressions for the outage probability and the average bit-error rate...

We propose the inverse Gaussian distribution, as a less complex alternative to the classical log-normal model, to describe turbulence-induced fading in free-space optical (FSO) systems operating in weak turbulence conditions and/or in the presence of aperture averaging effects. By conducting goodness of fit tests, we define the range of values of t...

The performance of optical wireless systems deteriorates to a large extent from the presence of turbulence and pointing error effects. To meet the typical bit error rate (BER) targets for reliable communications within the practical ranges of signal-to-noise ratio, error control coding schemes are often proposed. This paper investigates the error p...

This paper focuses on the connectivity issues of a non-line-of-sight (NLOS) optical wireless network operating in the ultraviolet UV-C spectral region. NLOS UV-C transmitters have a limited effective coverage and, hence, a dense node distribution is required in order to efficiently cover a large geographical area. Under this assumption, the concept...

We present an analytical framework for the performance evaluation of laser satellite uplinks over the major probabilistic impairments, i.e., atmospheric turbulence and beam wander. Specifically, we consider a ground-station-to-space laser uplink with a Gaussian beam wave model, and we focus on the particular regime assuming untracked beams where be...

The performance of a ground-station-to-space laser uplink with a Gaussian-beam wave model subject to turbulence and beam wander effects
b50
is the topic of the present study. The modulated gamma distribution is used to describe the combined effect of the above two deteriorating factors. At first, a versatile expression of the above probability dens...

In this paper, we propose the Inverse Gaussian (IG) distribution, as a less complex alternative to Log-normal (LN), to describe turbulence-induced fading in free-space optical (FSO) systems operating in weak turbulence conditions and/or in the presence of a large amount of aperture averaging. By conducting goodness of fit tests, we define the range...

In this paper, we propose a statistical channel model, named as Double-Weibull, to describe the irradiance fluctuations in moderate and strong turbulence for free-space optical (FSO) systems. The proposed stochastic model is based on the scintillation theory and derived via the product of two Weibull random variables. Closed-form expressions of pro...

We study the error performance of an heterodyne differential phase-shift keying (DPSK) optical wireless (OW) communication system operating under various intensity fluctuations conditions. Specifically, it is assumed that the propagating signal suffers from the combined effects of atmospheric turbulence-induced fading, misalignment fading (i.e., po...

Optical wireless, also known as free-space optics, has received much attention in recent years as a cost-effective, license-free and wide-bandwidth access technique for high data rates applications. The performance of free-space optical (FSO) communication, however, severely suffers from turbulence-induced fading caused by atmospheric conditions. M...

We consider a free-space optical (FSO) channel model affected by misalignment fading (pointing error) effects. Assuming intensity modulation/direct detection (IM/DD) with on-off keying (OOK), new closed form expressions for the bit-error rate (BER) and the outage probability are presented. Furthermore, four optimization models are formulated and so...

In this letter, we investigate the error rate performance of free-space optical (FSO) links over strong turbulence fading channels together with misalignment (pointing error) effects. First, we present a novel closed-form expression for the distribution of a stochastic FSO channel model which takes into account both atmospheric turbulence-induced f...

The performance of a free-space optical (FSO) communication system under strong turbulence regime that follows the K distribution is evaluated. Some useful channel statistics are derived in closed form and the outage probability and ergodic capacity for a single-input single-output FSO link are evaluated. Numerical examples are further presented to...

Free-space optical (FSO) communication has received much attention in recent years as a cost-effective, license-free and wide-bandwidth access technique for high data rates applications. The performance of FSO communication, however, severely suffers from turbulence-induced fading caused by atmospheric conditions. Multiple laser transmitters and/or...

In this paper, we study the performance of multihop free-space optical (FSO) wireless systems over turbulence-induced fading channels. The analysis is carried out for systems employing amplify-and-forward (AF) or decode-and-forward (DF) relays and for turbulence channels which can be modeled by the Gamma-Gamma distribution. An exact analytical expr...

Free space optical (FSO) communication is highly sensitive to atmospheric turbulence. The use of relays where the distance between the transmitter and the receiver is scaling down via multi-hop routing can improve the performance of an FSO link. In this reported work, the outage probability of a multi-hop FSO communication system with amplify-and-f...

This paper presents a neural network model for routing in the space segment of a Satellite Personal Communication System. At first, a proper energy function is constructed from the constraints of the system, which are clearly indicated. The combinatorial nature of the problem is clearly shown and hence a properly modified Hopfield neural network ca...

Using the idea of probabilistic routing, calls in an ant based decentralized scheme are not routed according to the largest probabilities in the pheromone tables but randomly according to these probabilities. This principle can be particularly helpful in order to further minimize possible node congestion problems. An additional incorporation of the...

IntroductionKey Issues in Survivable Cellular SystemsSurvivability in Wireless Mobile NetworksReferences

Chapter 3 describes fixed channel assignment schemes in cellular networks, with emphasis on recent heuristic algorithms that apply genetic algorithms, tabu search, neural networks, fuzzy logic and other heuristics in solving problems. Dynamic channel assignment, channel borrowing and hybrid channel assignment problems are also discussed.

Designing telecommunications for world- class events, in 2000 and beyond, can be regarded as a testbed for robust networks. In such cases, communications will include critical emergency and security traffic. Personal communications will be by wireless services. Wireless will integrate multiple media, voice telephony, internet data access and short...

Swarm intelligence is a new challenging branch of artificial life which takes advantage of the collective behaviour of animals
with limited intellectual faculties (insects, flocking birds, schools of fish) to solve algorithmically complex problems.
Recently a new routing method based on the way that ants are communicating with each other has been a...

Over the last decade two distinct communication technologies have experienced unprecedented growth and commercial success and become the major vehicles for multimedia services provision. These are the Mobile Systems and the Internet supported by the IP. The development attracted the interest of communications engineers and computer scientists as we...

An efficient model for ATM routing in the IRIDIUM system is
presented in this paper. The model tries to be as realistic as possible.
A proper energy function is constructed from the constraints of the ATM
routing concept which are clearly indicated. The combinatorial nature of
the problem is clearly shown and a properly modified Hopfield neural
net...

Channel allocation schemes in a cellular network can be modeled as combinatorial optimization problems. Genetic algorithms (GAs) have been shown to be effective and robust tools in providing adequate solutions of such problems. This paper investigates the application of GAs to two common assignment strategies from the field of cellular communicatio...

The study of image compression has been risen dramatically. Many new ideas have come out with impressive results. Since images can be regarded as two-dimensional signals with the independent variables being the coordinates of two-dimensional space, many digital compression techniques can be extended, for instance from one-dimensional signals. This...

Three established channel allocation schemes for cellular networks
are compared using some commonly acceptable quality-of-service measures.
These schemes assign channels on an efficient and robust heuristic
technique, derived from the well known family of evolutionary
algorithms, called combinatorial evolution strategy. Their performance
is examine...

The demand for more efficient and fast channel allocation techniques in cellular systems increases day by day. Borrowing channel assignment (BCA) was introduced in the literature as a compromise between the classic fixed and dynamic channel allocation schemes. This paper examines the behavior of three heuristic BCA techniques based alternatively on...

Modern cellular mobile communications systems are characterized by
a high degree of capacity. Consequently, they have to serve the maximum
possible number of calls while the number of channels per cell is
limited. The objective of channel allocation is to assign a required
number of channels to each cell such that both efficient frequency
spectrum...

Dynamic channel assignment (DCA) has been discussed in the literature as a way to achieve improved resource management in cellular networks. In the simplest dynamic allocation scheme, all channels are kept in a central pool and are used on a call-by-call basis. DCA is therefore a complex real time operation and various heuristic methods have been d...

Computational intelligence methods such as neural networks (NNs)
and evolutionary algorithms (EAs) have found a wide use in the field of
communications. This paper examines and compares two specific heuristic
techniques: the Hopfield NN and the combinatorial evolution strategy
(CES) concerning their application to a borrowing channel assignment
(BC...

The dynamic channel assignment (DCA) problem has been extensively
studied and various algorithmic methods have been tried as solutions.
However, the majority of these techniques suffers from the high
computational cost that reduces the possibility of hardware
implementation of a DCA controller for online operation in geographic
cellular environment...

## Citations

... In [38], an analytical model that assess the overall impact of turbulence on THz systems was presented. Building upon this model, in [39], the authors extracted closed-form expression for the average error rate and channel capacity of THz wireless systems in the presence of turbulence, while, in [40], the authors statistically characterized the end-to-end channel of multi-RIS assisted THz wireless systems that experience turbulence. Finally, in [41], the joint impact of snow, turbulence, and beam misalignment on the bit error rate and channel capacity of THz wireless systems were quantified. ...

... The joint PDF of a random point location inside the truncated cone of Fig. 1 has recently been derived in [22] as ...

... Amongst these algorithms, RSS is typically used in VLP, where a PD is utilized to measure the strength of the received information from multiple LEDs. After that, the position is estimated based on the trilateration or the triangulation approaches, where the intersection of multiple circles is obtained based on the inferred distance between the Rx and the Txs [16], [17]. ...

... Because of that, the most often is used a dual-hop link in order to simplify the performance analysis. In [31], mathematical derivations for the evaluation of the outage probability and the average bit error rate were made by assuming typical turbulence models. ...

... Naturally, there is a trade-off between the sea depth and the coverage area of the vertical link. The coverage problem in the downlink direction is investigated in [113], [114], in which the transmitter is fixed at the ocean surface, whereas the underwater receiver is randomly placed or moving. In [113], both the outage probability and the average BER are deduced mathematically, and in [114], the relationship between the coverage and the sea depth is investigated for the vertical link. ...

... Outage probability and BER performance of the RF-UWOC system presented in Naik et al. (2020), where the oceanic turbulence channels was modeled using the hyperbolic tangential log-normal (HTLN) density function. In Christopoulou et al. (2019), the authors proposed a multi-sensor mixed UWOC-FSO system and verified the performance of the underwater sensor networks (UWSN) in terms of the outage probability. A converging UWOC-FSO system for internet of underwater things and UWSN applications has recently been proposed. ...

... Starting with outdoor systems, the first four papers focused on the impact of atmospheric effects on the performance of free space optics (FSO) links. Androutsos and co-authors [2] have investigated a single-input multiple-output (SIMO) FSO system with wavelength, spatial, or time diversity at the receiver along with the on-off keying (OOK) and L-PPM (pulse position modulation), together with the optimal combining technique. The turbulence effect, modeled using the mixture Gamma distribution and a non-zero boresight pointing error model, are also investigated. ...

... , with σ mod,m being the joint modified jitter (standard deviation) of σ x,m and σ y,m for the m-th reflected transdermal path, [12,21,30]. ...

... The wide bandgap tunability range of (Al,Ga)N from 3.4 eV for GaN to 6.1 eV for AlN allows for its use in deep ultraviolet (UV) light emitting diodes (LEDs) in fields such as medical disinfection, water purification, biochemical detection and UV curing [1][2][3][4][5][6]. In addition, high power UV laser diodes (LDs) are needed for solar-blind non-line-ofsight communications, UV spectroscopy, laser lithography, and optical data storage [7][8][9][10][11]. Recently, photonics integrated circuits have been of interest for developing self-powered UV photonics systems that can work sustainably and independently with a reduced size and power consumption for future on-chip optical communication [12][13][14][15][16][17][18]. ...