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Recently, wireless communications started incorporating FSO systems to a large extent due to their high bandwidth and the low installation and operational cost. However, their performance deteriora...

The last decade optical wireless communication has attracted significant commercial and research interest mostly due to the many advantages for point-to-point connections. Nevertheless, the operation of these systems is strongly affected on weather conditions and especially by atmospheric turbulence. In order to counterbalance the negative effects of turbulence for a given propagation distance several techniques have been proposed in the literature. One of the most well-known and effective among them is the receivers’ diversity. Motivated by this, in this work, the influence of the modulation scheme in the total average block error rate of a single input multiple output (SIMO) free space optical (FSO) system over strong turbulent channels is estimated and new closed form analytical expressions are derived.

In the recent years, Free Space Optics (FSO) technology has attracted significant research and commercial interest mostly because of its many advantages in comparison with other radio systems used for point-to-point connections. However, the reliable operation of these systems significantly depends on the conditions of the atmosphere in the area in which the optical beam propagates. The most important of these conditions are atmospheric turbulence and the misalignment between the optical beam and the receiver, which is also known as the pointing errors effect. In this work, in order to obviate the performance mitigation caused by these phenomena, we examined the most widely accepted and one of the most effective techniques, i.e., the implementation of receivers’ diversity. Various metrics have been investigated to evaluate the performance of such systems, but most of them do not take into account that the ultra-fast modern optical communication systems use blocks of bits for the transmission and codes for the detection and/or correction of erroneous bits. Thus, by taking these aspects into account, in this work, we investigated the combined impact of spatial jitter and atmospheric turbulence on the total average block error rate of an optical wireless system with receivers’ diversity. Novel closed-form analytical formulas were derived.

The performance of an underwater optical wireless communication link is investigated by taking into account&mdash, for the first time and to the best of our knowledge&mdash, the simultaneous influence of the chromatic dispersion, the time jitter and the turbulence effects, by assuming chirped longitudinal Gaussian pulse propagation as information carriers. The estimation procedure is presented and a novel probability density function is extracted in order to describe the irradiance fluctuations at the receiver side. Furthermore, the availability of the link is investigated by means of its probability of fade and various numerical results are presented using typical parameters for the underwater optical wireless communication systems.

During the last few years, the need for high performance and security in communication systems, have set the underwater optical wireless communications (UOWC) as a very effective solution. Such systems can provide high bit rates with low installation and operational cost but on the other hand, oceanic environment affects the performance and an UOWC system as the beam that propagates through the seawater suffers from group velocity dispersion (GVD) that causes pulse broadening. Furthermore, the system is also affected by time jitter due to errors of synchronization between the transceivers. In order to achieve an acceptable performance, the distance between the receiver and the transmitter has to be relatively short. An effective technique to increase the link distance is the use of serial nodes deploying a multihop system. In this work, the availability and the performance of an UOWC multihop system will be investigated under the effect of GVD and time jitter. More specifically, closed form mathematical expression will be extracted for the maximum bit rate and the probability of fade, and the corresponding results will be presented.

The obsolete communication systems used in the underwater environment necessitates the development and use of modern telecommunications technologies. One such technology is the optical wireless communications, which can provide very high data rates, almost infinite bandwidth and very high transmission speed for real time fast and secure underwater links. However, the composition and the optical density of seawater hinder the communication between transmitter and receiver, while many significant effects strongly mitigate the underwater optical wireless communication (UOWC) systems&rsquo, performance. In this work, the influences of chromatic dispersion and time jitter are investigated. Chromatic dispersion causes the temporal broadening or narrowing of the pulse, while time jitter complicates the detection process at the receiver. Thus, the broadening of the optical pulse due to chromatic dispersion is studied and the influence of the initial chirp is examined. Moreover, the effect of the time jitter is also taken into consideration and for the first time, to the best of our knowledge, a mathematical expression for the probability of fade is extracted, taking into account the influence of both of the above-mentioned effects for a UOWC system. Finally, the appropriate numerical results are presented.

Visible Light Communication (VLC) systems use light-emitting diode (LED) technology to provide high-capacity optical links. The advantages they offer, such as the high data rate and the low installation and operational cost, have identified them as a significant solution for modern networks. However, such systems are vulnerable to various exogenous factors, with the background sunlight noise having the greatest impact. In order to reduce the negative influence of the background noise effect, optical filters can be used. In this work, for the first time, a low-cost optical vanadium dioxide (VO2) optical filter has been designed and experimentally implemented based on the requirements of typical and realistic VLC systems in order to significantly increase their performance by reducing the transmittance of background noise. The functionality of the specific filter is investigated by means of its bit error rate (BER) performance estimation, taking into account its experimentally measured characteristics. Numerous results are provided in order to prove the significant performance enhancement of the VLC systems which, as it is shown, reaches almost six orders of magnitude in some cases, using the specific experimental optical filter.

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 single-input multiple-output FSO system with wavelength, spatial, or time diversity over the turbulence and non-zero boresight PE effects is thoroughly investigated. A versatile mixture composite model which accurately describes both impairments is employed for the performance evaluation. Novel mathematical expressions of the outage probability and the average bit-error rate assuming intensity modulation/direct detection and optimal combining at the reception are provided.

Part 2: Poster Papers; International audience; Underwater optical wireless communications (UOWC) have gained attention due to the advantages they offer that can greatly alter the performance of a link. But such systems are affected by absorption and non predictable factors that may decrease the availability and the reliability of the system. In this work, the bit error rate (BER) of an underwater optical link with heterodyne detection modulated with M-QAM technique in presence of turbulence and pointing errors will be investigated. This investigation will lead to a closed form mathematical expression for the BER as a function of link parameters, that is very important in order to deploy an effective link. Various numerical results will also be presented for the reliability of the system.

The continuously expanding demand for faster and more efficient communication, dictates the research and development of more contemporary telecommunication systems, such as the FSO, characterized by their very high data rates and bandwidth. However, the optical beam, propagating through the atmosphere, suffers from phenomena with negative impact on the performance of the overall communication system. A commonly used technique to counterbalance these obstacles is to use a hybrid FSO/RF or FSO/MMW system. In this work, we further develop this idea, by studying a triple hybrid FSO/MMW/RF system, operating over turbulent atmospheric channel with pointing errors, along with Weibull and Rayleigh fading for the MMW and RF links, respectively. The mathematical expression for the outage performance estimation of the triple hybrid system is derived and its efficiency is verified through the numerical results.

The last years, FSO technologies raised interest from both scientific and commercial point of view. However, due to the optical beam propagation through the atmosphere, the signal is impaired by several phenomena like the scintillation effect, mainly because of atmospheric turbulence and imperfect misalignment between optical beam and destination terminal. In order to mitigate their negative influence, various countermeasures have been proposed. A well-known technique to preserve their performance over long distances is the employment of decode-and-forward (DF) relay nodes. Nevertheless, when the signal propagates over composite channels, characterized by atmospheric turbulence along with pointing errors effects, the employment of several DF relays increases significantly the complexity of the mathematical models used for performance evaluation. Motivated by this, we are trying to reduce the complexity of these expressions in the current work by replacing the multi-hop relay configuration via an equivalent dual-hop scheme. For first time, to the best of our knowledge, we are trying to emulate such an FSO system taking into account the simultaneous influence of both, atmospheric turbulence and pointing errors effects, in order to derive closed form mathematical expressions, which can be used in practice for the design of very fast optical wireless communication systems which can be used in the 5G/5G+ networks, mainly as backhaul communication links and support reliable their operation.

The interest for the optical wireless communication systems increases significantly the last years due to the very high advantages of this technology. More specifically, the FSO links can achieve very high data rate and secure communications with low installation and operational cost. However, the main disadvantage of the FSO links is that their performance is dominated by the weather conditions and the turbulence of the atmosphere, where the optical beam propagates. The atmospheric turbulence mitigates significantly the performance of the FSO links and causes the scintillation effect, which results in rapid irradiance fluctuations at the receivers. Furthermore, another factor which increases the influence of the atmospheric turbulence and causes further fast changes at the receivers’ irradianceis the pointing errors. Additionally, the performance of most of the high data rate communication systems, is reduced by the time jitter effect, which causes the detection of each digital pulse before or later than the ideal time spot. Thus, in this work, the performance of a terrestrial FSO link is investigated, for first time under the simultaneous action of the M(alaga) atmospheric turbulence, the pointing errors and the time jitter effects for various, commonly used in FSO links, modulation schemes. Taking into account their joint influence, new accurate closed form mathematical expressions are derived for the average BER estimation. Finally, the corresponding numerical results and conclusions are shown and derived.

Visible Light Communications (VLC) systems have attracted research and comercial interest over the last few years due to the remarkable characteristics such as the high data rate, low installation and operational cost and the fact that they are environmentally friendly. The transmitter in such systems can be a LED that offers advantageous properties such as brightness, extremely high data transmission and long lifetime, whereas photodiodes are employed as receivers. Therefore, VLC is already used for applications of 5G technology communication networks. However indoor VLC's performance is decreased due to the background noise which is mainly caused by the sunlight radiation. In this work, we study the improvement of a VLC system's SNR after applying a Vanadium dioxide (VO2) optical filter in front of its receiver to reduce the background sunlight noise. The obtained results are illustrated through the suitable three dimensional figures.

In this work, we investigate the performance of a radio-on-free-space optical (RoFSO) communication system for transmission of CDMA signals. The optical signal propagation is affected by the combined effects of turbulence-induced fading, modelled by the gamma distribution, and the generalized nonzero boresight pointing errors. The performance assessment is implemented with the average BER metric evaluation for each user. Finally, the corresponding numerical results are presented for various parameter values concerning the CDMA wireless optical transmission.

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 keying and quadrature amplitude modulation (QAM) formats are considered, and the performance is investigated over the weak to strong atmospheric turbulence regime characterized by the recently launched Malaga or $M$ -distribution probability density function (pdf). This pdf acts as a unifying statistical model, which incorporates several common irradiance scintillation distributions extensively used by researchers working in the FSO area. We particularly obtain useful mathematical expressions of some critical metrics, i.e., the average bit error rate (BER) and the probability of outage. Proper numerical results are also provided and depicted using suitable graphs to verify the accuracy of the derived expressions.

The coverage area of an indoor visible light communication (VLC) system with multiple transmitters and one receiver using the enhanced space shift keying (eSSK) modulation format is examined in this study. In eSSK scheme, every LED transmits a unique symbol in a specific time slot and the receiver is able to detect the signals from all transmitters. The area where this is possible is very important for a proper operation of the system. The dependence of the coverage area on the fundamental physical parameters is investigated in details.

Free-space optical communication systems are gaining popularity as a high-capacity, cost-effective and license-free wireless technology, addressing the bandwidth demands of existing and future wireless networks. The deployment scenarios of free pace optical links usually concern secure, fast and reliable connections. Thus, in this work, the performance of optical wireless communication systems is studied in terms of the average block error rate which constitutes a very significant metric for their reliability. The optical signal transmission is assumed to be hampered by the joint effects of strong atmospheric turbulence, modeled by the Negative Exponential and the pointing errors effect which affects the alignment between the transmitter and the receiver. Accurate closed-form expression for the evaluation of the average block error rate is obtained, including the aforementioned effects, while finally the corresponding numerical results, for realistic optical wireless links, are presented.

The optical wireless and in particular the radio-on-free-space-optical (RoFSO) communication systems are gaining popularity due to their high date rates, license free spectrum and adequate reliability at installation and operational costs which are much lower than comparable technologies. One significant disadvantage of these systems concerns the randomly time varying characteristics of the propagation path mainly caused by the atmospheric turbulence. In this work, we study the BER performance of a multi-hop RoFSO system which is using an orthogonal frequency division multiplexing (OFDM) scheme, with either quadrature amplitude modulation (QAM) or phase shift keying format (PSK), over atmospheric turbulence channels modeled with the gamma gamma or the negative exponential distribution. The individual RoFSO parts of the whole optical link are connected to each other by using regenerators relay nodes. The dominant impairments which are the most significant and have been taken into account are the atmospheric turbulence, the path losses, the nonlinear responsivity of the laser diode and the inter-modulation distortion effect. For this setup, we derive closed form mathematical expressions for the estimation of the BER performance for each individual OFDM RoFSO link and for the whole relayed optical communication system, as well. Finally, the corresponding numerical results, for common link׳s parameters, are presented.

Terrestrial free space optical telecommunication systems offer license-free very high bandwidth access characteristics with significantly low installation and operational cost. On the other hand, the performance of such a system depends strongly on the weather conditions in the area between the transmitter and the receiver due to the fact that the transmission media is the atmosphere. A very significant phenomenon which decreases a FSO links' performance is atmospheric turbulence. In order to counterbalance this reduction, in this work, we consider a free space optical system with a multiple receivers' scheme and diversity in space that operates under weak to strong atmospheric turbulence conditions modeled by the gamma–gamma distribution. We derive closed form mathematical expressions for the estimation of the outage probability and the average bit error rate of the multiple receivers' system. Additionally, we compare the performance capabilities of the single point to point link with those of the spatia...

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