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Photonics
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Optical Wireless Communications Systems
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Optical Wireless Communications Systems

A special issue of Photonics (ISSN 2304-6732).

Deadline for manuscript submissions: closed (31 May 2022) | Viewed by 25365

Special Issue Editors

Prof. Dr. George S. Tombras

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Guest Editor
Section of Electronic Physics and Systems, Department of Physics, National and Kapodistrian University of Athens, 15784 Athens, Greece
Interests: electronic physics and systems; analog and digital systems; wireless communication systems; free space optical communications
Prof. Dr. Erich Leitgeb

E-Mail Website1 Website2
Guest Editor
Institute of Microwave and Photonic Engineering, Faculty of Electrical and Information Engineering, Graz University of Technology, Inffeldgasse 12/I, A-8010 Graz, Austria
Interests: optical wireless technologies for broadband communications
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Hector E. Nistazakis

E-Mail Website
Guest Editor
Section of Electronic Physics and Systems, Department of Physics, National and Kapodistrian University of Athens, 15784 Athens, Greece
Interests: wireless communication systems; free space optical communications (FSO); fiber optics communications; electronic physics; nonlinear optoelectronic circuits
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Optical wireless communication (OWC) systems have attracted significant commercial and research interest in recent years. Under this concept, numerous important broadband solutions and applications have been thoroughly studied and developed, including terrestrial free space optical (FSO) systems and links, underwater applications with optical wireless signal transmission, satellite and space communications, visible light solutions for both indoor and outdoor applications, mobile and multimedia systems and networks, biomedical applications, etc.

This technology, due to the very high available bandwidth that it offers and the huge data rates it can support, combined with its comparatively low installation and operational costs, the high security level and the unlicensed bandwidth usage, has been proven to represent a highly reliable solution as an alternative to radio frequency (RF) systems. Following that, it has been chosen as a backhaul standard for the next generation communication systems, i.e., 5G, etc., to mainly solve the “last mile problem”. However, its performance strongly depends on the characteristics of its optical path, e.g., temperature, humidity, and pressure fluctuations. It is therefore, both the challenging behavior of the optical channel used as a propagation path, and the abovementioned profound advantages over RF systems that clearly justify and attract significant research interest.

Topics of interest for this Special Issue include but are not limited to:

  • Indoor optical wireless solutions;
  • Optical wireless channel and network modeling;
  • Visible light communications (VLC);
  • Line-of-sight and non-line-of-sight FSO links;
  • Atmospheric turbulence modeling;
  • Radio-on-FSO (RoFSO) links;
  • OFDM communications;
  • Satellite and space scenarios;
  • Novel modulation and coding schemes;
  • High-speed devices for photonics;
  • OWC with energy harvesting;
  • OWC for the Internet of Things (IoT);
  • OWC for underwater scenarios;
  • MIMO for optical wireless concepts;
  • Optical-based indoor positioning;
  • Optical sensor networks and wearables;
  • Biomedical optical wireless links;
  • Signal processing for OWC.

Prof. Dr. George S. Tombras
Prof. Dr. Erich Leitgeb
Dr. Hector E. Nistazakis
Guest Editors

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Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Photonics is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

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Published Papers (8 papers)

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Research

16 pages, 13926 KiB  
Article
A Novel System of Mixed RF/FSO UAV Communication Based on MRR and RIS by Adopting Hybrid Modulation
by Jia Yuan, Xiaoyi Wang, Meng Jin, Wenyi Liu, Ruihuan Wu, Zhongchao Wei, Dongmei Deng and Hongzhan Liu
Photonics 2022, 9(6), 379; https://doi.org/10.3390/photonics9060379 - 26 May 2022
Cited by 4 | Viewed by 2691
Abstract
In this paper, we propose a mixed radio frequency (RF)/free space optical (FSO) unmanned aerial vehicle (UAV) communication system, based on modulating retro-reflector (MRR) and reconfigurable intelligent surface (RIS), which adopts the hybrid L-ary pulse position modulation-binary phase shift keying-subcarrier intensity modulation [...] Read more.
In this paper, we propose a mixed radio frequency (RF)/free space optical (FSO) unmanned aerial vehicle (UAV) communication system, based on modulating retro-reflector (MRR) and reconfigurable intelligent surface (RIS), which adopts the hybrid L-ary pulse position modulation-binary phase shift keying-subcarrier intensity modulation (L-PPM-BPSK-SIM). More specifically, the RF channel follows Rayleigh distribution, while the FSO channel obeys Gamma–Gamma distribution that considers atmospheric turbulence and pointing error. For decode-and-forward (DF) relay, the MRR is installed on the UAV to reduce its weight, size, and power consumption. In particular, the RIS is used as user terminal along with the RF signal generator to achieve signal enhancement. Based on this, closed expressions for the outage probability, average bit error rate (BER) and average channel capacity of the end-to-end uplink and downlink are derived. Numerical results confirm that while the relay limitation is solved by MRR, RIS significantly reduces the outage probability and average BER as well as obviously increases the average channel capacity. Furthermore, the hybrid L-PPM-BPSK-SIM with average symbol length greater than eight can effectively improve the average BER performance of the system. Full article
(This article belongs to the Special Issue Optical Wireless Communications Systems)
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13 pages, 2512 KiB  
Article
The BER Performance of the LDPC-Coded MPPM over Turbulence UWOC Channels
by Hongyan Jiang, Ning He, Xin Liao, Wasiu Popoola and Sujan Rajbhandari
Photonics 2022, 9(5), 349; https://doi.org/10.3390/photonics9050349 - 16 May 2022
Cited by 12 | Viewed by 2873
Abstract
Turbulence-induced fading is a critical performance degrading factor for underwater wireless optical communication (UWOC) systems. In this paper, we propose a quasi-cyclic (QC) low-density parity-check (LDPC) code with multiple-pulse-position modulation (MPPM) to overcome turbulence-induced fading. MPPM is adopted as a compromise between the [...] Read more.
Turbulence-induced fading is a critical performance degrading factor for underwater wireless optical communication (UWOC) systems. In this paper, we propose a quasi-cyclic (QC) low-density parity-check (LDPC) code with multiple-pulse-position modulation (MPPM) to overcome turbulence-induced fading. MPPM is adopted as a compromise between the low-power efficiency of on–off keying (OOK) and the low bandwidth efficiency of pulse position modulation (PPM). The bit error rate (BER) performance of LDPC-coded MPPM over turbulence UWOC channels is investigated. The log-likelihood ratio (LLR) of MPPM is derived, and a simplified approximation is used for iterative decoding. Subsequently, the closed-form expression of the BER, without forward error correction (FEC) code, is obtained for the generalized-gamma (GG) fading model. Finally, Monte-Carlo (MC) simulation results are provided to demonstrate the correctness of the derived closed-form expressions and the effectiveness of the LDPC code with simplified LLR to improve the BER performance for different MPPM formats over fading channels. Full article
(This article belongs to the Special Issue Optical Wireless Communications Systems)
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13 pages, 1988 KiB  
Article
Power Allocation for Reliable and Energy-Efficient Optical LEO-to-Ground Downlinks with Hybrid ARQ Schemes
by Theodore T. Kapsis and Athanasios D. Panagopoulos
Photonics 2022, 9(2), 92; https://doi.org/10.3390/photonics9020092 - 4 Feb 2022
Cited by 5 | Viewed by 2059
Abstract
Satellites in low earth orbit (LEO) are currently being deployed for numerous communication, positioning, space and Earth-imaging missions. To provide higher data rates in direct-to-user links and earth observation downlinks, the free-space optics technology can be employed for LEO-to-ground downlinks. Moreover, the hybrid [...] Read more.
Satellites in low earth orbit (LEO) are currently being deployed for numerous communication, positioning, space and Earth-imaging missions. To provide higher data rates in direct-to-user links and earth observation downlinks, the free-space optics technology can be employed for LEO-to-ground downlinks. Moreover, the hybrid automatic repeat request (HARQ) can be adopted since the propagation latency is low for LEO satellites. In this work, a power allocation methodology is proposed for optical LEO-to-ground downlinks under weak turbulence employing HARQ retransmission schemes. Specifically, the average power consumption is minimized given a maximum transmitted power constraint and a target outage probability threshold to ensure energy efficiency and reliability, respectively. The optimization problem is formulated as a constrained nonlinear programming problem and solved for Type I HARQ, chase combining (CC) and incremental redundancy (IR) schemes. The solutions are derived numerically via iterative algorithms, namely interior-point (IP) and sequential quadratic programming (SQP), and validated through an exhaustive (brute-force) search. The numerical simulations provide insight into the performance of the retransmission schemes regarding average power. More specifically, Type I HARQ has the worst output, CC has a moderate one, and IR exhibits the best performance. Finally, the IP algorithm is a slower but more accurate solver, and SQP is faster but slightly less accurate. Full article
(This article belongs to the Special Issue Optical Wireless Communications Systems)
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11 pages, 1549 KiB  
Article
On the Outage Capacity of Transdermal Optical Wireless Links with Stochastic Spatial Jitter and Skin-Induced Attenuation
by George K. Varotsos, Konstantinos Aidinis and Hector E. Nistazakis
Photonics 2021, 8(12), 553; https://doi.org/10.3390/photonics8120553 - 3 Dec 2021
Cited by 1 | Viewed by 2005
Abstract
The tremendous development of both optical wireless communications (OWC) and implantable medical devices (IMDs) has recently enabled the establishment of transdermal optical wireless (TOW) links that utilize light waves to transfer information inside the living body to the outside world and conversely. Indeed, [...] Read more.
The tremendous development of both optical wireless communications (OWC) and implantable medical devices (IMDs) has recently enabled the establishment of transdermal optical wireless (TOW) links that utilize light waves to transfer information inside the living body to the outside world and conversely. Indeed, numerous emerging medical applications such as cortical recording and telemetry with cochlear implants require extremely high data rates along with low power consumption that only this new technology could accommodate. Thus, in this paper, a typical TOW link is investigated in terms of outage capacity which is a critical performance metric that has so far not been evaluated for such wireless systems in the open technical literature. More precisely, an outage capacity analysis is performed considering both skin-induced attenuation and stochastic spatial jitter, i.e., pointing error effects. Analytical expressions and results for the outage capacity are derived for a variety of skin channel conditions along with varying stochastic pointing errors which demonstrate the feasibility of this cross-field cooperation. Lastly, the corresponding simulation outcomes further validate our suggestions. Full article
(This article belongs to the Special Issue Optical Wireless Communications Systems)
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14 pages, 27459 KiB  
Article
Time and Spatial Jitter Influence on the Performance of FSO Links with DF Relays and OC Diversity Over Turbulence Channels
by Panagiotis J. Gripeos, Hector E. Nistazakis, Andreas D. Tsigopoulos, Vasilis Christofilakis and Evgenia Roditi
Photonics 2021, 8(8), 318; https://doi.org/10.3390/photonics8080318 - 7 Aug 2021
Cited by 1 | Viewed by 2794
Abstract
FSO communication is a viral technology among optical wireless communications, gathering the interest of both researchers and manufacturers. This is because of the many advantages associated with FSO communication, including high data rates, reliability, safety, and economy. However, there are several unavoidable drawbacks [...] Read more.
FSO communication is a viral technology among optical wireless communications, gathering the interest of both researchers and manufacturers. This is because of the many advantages associated with FSO communication, including high data rates, reliability, safety, and economy. However, there are several unavoidable drawbacks that shadow the performance of FSO systems. For example, atmospheric turbulence is a well-known problem related to the weather conditions of the channel, which causes the scintillation effect. Also, spatial jitter due to pointing errors is a critical factor of the link’s performance, caused by occasional misalignments between the transmitter and the receiver. Moreover, time jitter is another limiting agent that deteriorates the total throughput, inducing bit stream misdetections, caused by the arrival of out-of-sync pulses. All three effects have been exhaustively studied and many statistical models and interesting solutions have been proposed in the literature to estimate their magnitude and compensate for their impact. In this work, the turbulence effect was treated by Málaga distribution, the spatial jitter effect was regulated by the non-zero boresight model, and the time jitter effect was modeled by the generalized Gaussian distribution. Various modulation schemes were studied, along with DF multi-hop and optimal combining diversity techniques at the receiver’s end. New, accurate mathematical expressions of average BER performance have been obtained, and valuable conclusions were drawn thanks to the presented numerical results. Full article
(This article belongs to the Special Issue Optical Wireless Communications Systems)
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11 pages, 519 KiB  
Article
Performance Analysis of Dual-Hop Mixed Power Line Communication/Free-Space Optical Cooperative Systems
by Manh Le-Tran and Sunghwan Kim
Photonics 2021, 8(6), 230; https://doi.org/10.3390/photonics8060230 - 21 Jun 2021
Cited by 7 | Viewed by 2336
Abstract
In this paper, we study a mixed cooperative communication system consisting of power line communication (PLC) and free-space optical communication (FSO) links, where the PLC link suffers from log-normal fading and is affected by both impulsive and background noises. Meanwhile, the FSO link [...] Read more.
In this paper, we study a mixed cooperative communication system consisting of power line communication (PLC) and free-space optical communication (FSO) links, where the PLC link suffers from log-normal fading and is affected by both impulsive and background noises. Meanwhile, the FSO link undergoes Gamma-Gamma fading with both atmospheric turbulence and pointing errors. More specifically, we present closed-form expressions for the probability density function and the cumulative distribution function of the end-to-end signal-to-noise ratio of the proposed model. Consequently, the outage probability and the bit error rate (BER) performance are derived in terms of univariate Fox-H and bivariate Fox-H functions. Finally, the analytical results are verified using Monte Carlo simulations, providing useful insights into the capabilities of the proposed system. Full article
(This article belongs to the Special Issue Optical Wireless Communications Systems)
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17 pages, 5011 KiB  
Article
Using Machine Learning Algorithms for Accurate Received Optical Power Prediction of an FSO Link over a Maritime Environment
by Antonios Lionis, Konstantinos Peppas, Hector E. Nistazakis, Andreas Tsigopoulos, Keith Cohn and Athanassios Zagouras
Photonics 2021, 8(6), 212; https://doi.org/10.3390/photonics8060212 - 10 Jun 2021
Cited by 25 | Viewed by 4298
Abstract
The performance prediction of an optical communications link over maritime environments has been extensively researched over the last two decades. The various atmospheric phenomena and turbulence effects have been thoroughly explored, and long-term measurements have allowed for the construction of simple empirical models. [...] Read more.
The performance prediction of an optical communications link over maritime environments has been extensively researched over the last two decades. The various atmospheric phenomena and turbulence effects have been thoroughly explored, and long-term measurements have allowed for the construction of simple empirical models. The aim of this work is to demonstrate the prediction accuracy of various machine learning (ML) algorithms for a free-space optical communication (FSO) link performance, with respect to real time, non-linear atmospheric conditions. A large data set of received signal strength indicators (RSSI) for a laser communications link has been collected and analyzed against seven local atmospheric parameters (i.e., wind speed, pressure, temperature, humidity, dew point, solar flux and air-sea temperature difference). The k-nearest-neighbors (KNN), tree-based methods-decision trees, random forest and gradient boosting- and artificial neural networks (ANN) have been employed and compared among each other using the root mean square error (RMSE) and the coefficient of determination (R2) of each model as the primary performance indices. The regression analysis revealed an excellent fit for all ML models, indicative of their ability to offer a significant improvement in FSO performance modeling as compared to traditional regression models. The best-performing R2 model found to be the ANN approach (0.94867), while random forests achieved the most optimal RMSE result (7.37). Full article
(This article belongs to the Special Issue Optical Wireless Communications Systems)
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15 pages, 423 KiB  
Article
Performance Analysis of Hybrid Radio Frequency and Free Space Optical Communication Networks with Cooperative Spectrum Sharing
by Dong Qin, Yuhao Wang and Tianqing Zhou
Photonics 2021, 8(4), 108; https://doi.org/10.3390/photonics8040108 - 6 Apr 2021
Cited by 5 | Viewed by 3285
Abstract
This paper investigates the impact of cooperative spectrum sharing policy on the performance of hybrid radio frequency and free space optical wireless communication networks, where primary users and secondary users develop a band of the same spectrum resource. The radio frequency links obey [...] Read more.
This paper investigates the impact of cooperative spectrum sharing policy on the performance of hybrid radio frequency and free space optical wireless communication networks, where primary users and secondary users develop a band of the same spectrum resource. The radio frequency links obey Nakagami-m distribution with arbitrary fading parameter m, while the free space optical link follows gamma-gamma distributed atmospheric turbulence with nonzero pointing error. Because the secondary users access the spectrum band without payment, their behavior needs to be restricted. Specifically, the power of the secondary users is dominated by the tolerable threshold of the primary users. Considering both heterodyne and intensity modulation/direct detection strategies in optical receiver, the performance of optical relaying networks is completely different from that of traditional networks. With the help of bivariable Fox’s H function, new expressions for cumulative distribution function of equivalent signal to noise ratio at destination, probability density function, outage probability, ergodic capacity and symbol error probability are built in closed forms. Full article
(This article belongs to the Special Issue Optical Wireless Communications Systems)
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