Special Issue "Light Communication: Latest Advances and Prospects"

A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Optics and Lasers".

Deadline for manuscript submissions: 30 June 2019

Special Issue Editors

Guest Editor
Prof. Dr. Anthony C. Boucouvalas

Communication Networks and Applications Laboratory, University of Peloponnese, in Tripoli, Arcadia, Greece
Website | E-Mail
Interests: optical wireless communications; communication protocols; sensor networks; power efficient communications; wireless communications; optical communications; optical fibers; Web applications; human–computer interaction
Guest Editor
Dr. Kostas Yiannopoulos

Communication Networks and Applications Laboratory, University of Peloponnese, in Tripoli, Arcadia, Greece
Website | E-Mail
Interests: optical wireless systems; short-range infrared systems; protocol analysis and optimization; outdoor systems; optical wireless channel equalization; compensation techniques
Guest Editor
Dr. Asghar Gholami

Optoelectronics and Optical Communications Research Laboratory (OOCRL), Dept. of Electrical and Computer Engineering, Isfahan University of Technology, Isfahan 84156, Iran
Website | E-Mail
Interests: fiber optics communication; free space optical communication (FSO); VCSEL; fiber optics; photonics
Guest Editor
Dr. Volker Jungnickel

Head of Metro-, Access and Inhouse Systems Group, Photonic Networks and Systems Department, Fraunhofer Heinrich Hertz Institute, Einsteinufer 37, 10587 Berlin, Germany
Website | E-Mail
Interests: optical wireless communications; optical communication systems; photonics and networks
Guest Editor
Prof. Dr. Zabih Ghassemlooy

Professor of Optical Communications, Head of Northumbria Communications Research Lab. and Optical Communications Research Group, University of Northumbria at Newcastle, UK
Website | E-Mail
Phone: +44 (0)191 227 4902/+44 (0)191 227 3684
Interests: optical wireless communications; optical communication systems

Special Issue Information

Dear Colleagues,

The wireless information carrier shift from radio frequencies to optical frequencies has been studied in increasing detail since the invention of the laser. With the advent of optical fiber, optical wireless as a communication information carrier has also been studied. It has found niche applications in a wide range of systems, from short range indoor links to outdoor links to deep space and inter-satellite links, and also underwater sensor and links. New component, such as visible light emitting sources and techniques, such as MIMO (Multi-input Multi-output )and optical angular momentum technology promise to push optical wireless frequencies into new applications in 5G networks, vehicular communications, as well as medical applications, to mention just a few.

This Special Issue aims to provide a forum to allow researchers to publish their new techniques and innovations in this exciting area of research. We welcome both theoretical and practical papers and applications making use of optical wireless technology. You are invited to submit original manuscripts on topics including, but not limited to: 

  •    Indoor Short Range Optical Communication Systems
  •    Outdoor Optical Communications Systems
  •    Multihop Optical Wireless Systems
  •    Visible Light Communications
  •    Vehicular Optical Wireless Communications and Techniques
  •    Positioning Techniques using Optical Wireless
  •    Underwater Optical Wireless Communications
  •    Optical Wireless Sensor Networks
  •    Camera Optical Communications
  •    Modulation Encoding and Capacity of Optical Wireless Systems
  •    MIMO techniques for Optical Wireless Communications
  •    The use of Optical Wireless in 5G Networks
  •    Orbital Angular Momentum Multiplexing
  •    Quantum communication over optical wireless links
  •    Resource allocation and energy efficiency in OWC
  •    Topology control and routing for free space optical networks
  •    Satellite and Space Optical Communications
  •    High Altitude Platforms and FSO systems
  •    Atmospheric effects on the performance of FSO links
  •    Hybrid Optical/RF communication systems

Prof. Dr. Anthony C. Boucouvalas
Dr. Kostas Yiannopoulos
Dr. Asghar Gholami
Dr. Volker Jungnickel
Prof. Fary Ghassemlooy
Guest Editors

Manuscript Submission Information

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 papers will be 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. Applied Sciences is an international peer-reviewed open access semimonthly 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 1500 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.

Keywords

  • Optical wireless communications
  • Visible light communications
  • Infrared communications
  • Ultraviolet communications
  • Free space optics

Published Papers (15 papers)

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Research

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Open AccessArticle Adaptive Polling Medium Access Control Protocol for Optic Wireless Networks
Appl. Sci. 2019, 9(6), 1071; https://doi.org/10.3390/app9061071
Received: 17 February 2019 / Revised: 5 March 2019 / Accepted: 12 March 2019 / Published: 14 March 2019
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Abstract
The emergence of optical wireless networks (OWNs) is a potential solution to the quest for the increasing bandwidth demand. Existing bandwidth assignment strategies are not suitable for OWNs, considering factors such as differences between the physical properties of radio networks and OWNs. In [...] Read more.
The emergence of optical wireless networks (OWNs) is a potential solution to the quest for the increasing bandwidth demand. Existing bandwidth assignment strategies are not suitable for OWNs, considering factors such as differences between the physical properties of radio networks and OWNs. In order to eliminate collision, minimize delay and enhance system utilization and fairness, we propose the non-contention bandwidth assignment protocol called adaptive polling medium access control (APMAC) protocol for OWNs. The APMAC protocol involves association, data transmission and dissociation phases. Moreover, the APMAC protocol exploits features of the IEEE 802.15.7 visible light communication (VLC) standard. While assigning bandwidth to the visible light nodes (VLNs), the visible light access point (VLAP) establishes a polling table that contains the identity, buffer size and round-trip time of each VLN that issued bandwidth request. The contents of the polling table enable the computation of the maximum transmission unit and time-slot for each VLN that requests bandwidth assignment. In order to achieve convincing results, we simulate the protocol under varying network sizes ranging from 1 to 10 VLNs per access point, then we compare the results against the medium transparent medium access control (MT–MAC) protocol that is a non-contention MAC protocol. We demonstrate numerical results of our study considering average waiting time, packet collision, system utilization and fairness. Numerical results reveal that the APMAC protocol outperforms the MT–MAC protocol. Full article
(This article belongs to the Special Issue Light Communication: Latest Advances and Prospects)
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Open AccessArticle Improved Visible Light-Based Indoor Positioning System Using Machine Learning Classification and Regression
Appl. Sci. 2019, 9(6), 1048; https://doi.org/10.3390/app9061048
Received: 11 February 2019 / Revised: 6 March 2019 / Accepted: 7 March 2019 / Published: 13 March 2019
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Abstract
Recently, indoor positioning systems have attracted a great deal of research attention, as they have a variety of applications in the fields of science and industry. In this study, we propose an innovative and easily implemented solution for indoor positioning. The solution is [...] Read more.
Recently, indoor positioning systems have attracted a great deal of research attention, as they have a variety of applications in the fields of science and industry. In this study, we propose an innovative and easily implemented solution for indoor positioning. The solution is based on an indoor visible light positioning system and dual-function machine learning (ML) algorithms. Our solution increases positioning accuracy under the negative effect of multipath reflections and decreases the computational time for ML algorithms. Initially, we perform a noise reduction process to eliminate low-intensity reflective signals and minimize noise. Then, we divide the floor of the room into two separate areas using the ML classification function. This significantly reduces the computational time and partially improves the positioning accuracy of our system. Finally, the regression function of those ML algorithms is applied to predict the location of the optical receiver. By using extensive computer simulations, we have demonstrated that the execution time required by certain dual-function algorithms to determine indoor positioning is decreased after area division and noise reduction have been applied. In the best case, the proposed solution took 78.26% less time and provided a 52.55% improvement in positioning accuracy. Full article
(This article belongs to the Special Issue Light Communication: Latest Advances and Prospects)
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Open AccessArticle A Pulse Shaping Based Optical Transmission System of 128QAM for DWDM with N × 904 Gbps
Appl. Sci. 2019, 9(5), 988; https://doi.org/10.3390/app9050988
Received: 20 December 2018 / Revised: 17 February 2019 / Accepted: 4 March 2019 / Published: 8 March 2019
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Abstract
In this paper, we propose an optical transmission system of 128 quadrature amplitude modulation for dense wavelength division multiplexing. In such a system, Gaussian optical filtering is used to get an appropriate photonic carrier. Theoretical analysis and simulation computation show that the modulated [...] Read more.
In this paper, we propose an optical transmission system of 128 quadrature amplitude modulation for dense wavelength division multiplexing. In such a system, Gaussian optical filtering is used to get an appropriate photonic carrier. Theoretical analysis and simulation computation show that the modulated multi-carrier photonic signals with the wavelength spacing of 0.7 nm can transmit for over 80 km with the standard single mode fiber. Using digital signal processing algorithms to compensate the transmission impairments, the transmission rate of the single-carrier photonic signal can reach up to 904 Gbps and the spectral efficiency of the transmission can reach up to 10.33 bps/Hz. When this technology is applied to a dense wavelength division multiplexing system with N channels, the huge message capacity of N × 904 Gbps can be realized. Furthermore, we find that the bit error rate and the error vector magnitude are similarly influenced by the optical signal-to-noise ratio and the bandwidth of the Gaussian optical filter. The influence presents mostly a synchronization trend with the change of the optical signal-to-noise ratio and the bandwidth of Gaussian optical filter. Full article
(This article belongs to the Special Issue Light Communication: Latest Advances and Prospects)
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Open AccessArticle Bandwidth and BER Improvement Employing a Pre-Equalization Circuit with White LED Arrays in a MISO VLC System
Appl. Sci. 2019, 9(5), 986; https://doi.org/10.3390/app9050986
Received: 1 February 2019 / Revised: 27 February 2019 / Accepted: 3 March 2019 / Published: 8 March 2019
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Abstract
This paper aims to extend the limited bandwidth of phosphorescent white LEDs for a multiple-input single-output (MISO) visible light communication (VLC) system. A proposed LED arrangement model is presented, resulting in improved results as compared to those previously discussed in the literature. In [...] Read more.
This paper aims to extend the limited bandwidth of phosphorescent white LEDs for a multiple-input single-output (MISO) visible light communication (VLC) system. A proposed LED arrangement model is presented, resulting in improved results as compared to those previously discussed in the literature. In this paper, the impact of the receiver field of view (FOV) angle, the LED transmission angle, and the number of LED arrays used on the transmission are studied at different speeds. The system performance is measured by the signal to noise ratio (SNR) and the corresponding bit error rate (BER) at different data rates. The obtained results show that the proposed model is able to improve the illumination uniformity across the room with a higher SNR using the same number of LEDs in the investigated indoor environment. The paper also introduces a pre-equalization circuit in the transmitter end in order to extend the limited bandwidth of the used white LEDs. This bandwidth extension using the proposed circuit results in an increased data rate with the aid of a blue filter. A number of experiments are executed to optimize the key parameters for maximum bandwidth enhancement. The proposed circuit offers 28% bandwidth enhancement over the most recent study in this area while eradicating the BER at 200 Mb/s when compared to un-equalized LED circuits. Full article
(This article belongs to the Special Issue Light Communication: Latest Advances and Prospects)
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Open AccessArticle Phase Offset Tracking for Free Space Digital Coherent Optical Communication System
Appl. Sci. 2019, 9(5), 836; https://doi.org/10.3390/app9050836
Received: 10 January 2019 / Revised: 16 February 2019 / Accepted: 22 February 2019 / Published: 26 February 2019
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Abstract
The coherent receiving method can improve the sensitivity of an optical signal receiver for free space optical communication system effectively. To implement coherent receiving, the phase offset between the local laser in the receiver and the received optical signal through the atmosphere needs [...] Read more.
The coherent receiving method can improve the sensitivity of an optical signal receiver for free space optical communication system effectively. To implement coherent receiving, the phase offset between the local laser in the receiver and the received optical signal through the atmosphere needs to be measured and estimated. The commonly used algorithm is the Viterbi-Viterbi phase offset estimation method (VVPE) and this method always produces great errors especially with low SNR (signal to noise ratio). To improve the estimation performance, we present a new method combing the VVPE with the Kalman filter (VVPE-KF) to estimate the phase offset. This method can lower the estimation error by no less than 60%, when the SNR is low. To verify the performance of this new method, the constant parameter channel and atmosphere turbulence channel are employed to evaluate the algorithm. The impact of the atmosphere turbulence intensity on the tracking error is discussed. Full article
(This article belongs to the Special Issue Light Communication: Latest Advances and Prospects)
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Open AccessFeature PaperArticle Accurate Evaluation of the Average Probability of Error of Pulse Position Modulation in Amplified Optical Wireless Communications under Turbulence
Appl. Sci. 2019, 9(4), 749; https://doi.org/10.3390/app9040749
Received: 15 January 2019 / Revised: 15 February 2019 / Accepted: 18 February 2019 / Published: 21 February 2019
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Abstract
We present exact and approximate results on the average probability of error (PER) for pulse position modulation (PPM) in pre-amplified optical wireless communication systems with diversity. The approximate results are obtained by combining a new mathematical formula that we derive for binary PPM [...] Read more.
We present exact and approximate results on the average probability of error (PER) for pulse position modulation (PPM) in pre-amplified optical wireless communication systems with diversity. The approximate results are obtained by combining a new mathematical formula that we derive for binary PPM and an existing formula that associates higher-order PPM PERs with their binary PPM counterpart. The approximate results are compared with the exact in weak, moderate, and strong turbulence, and it is demonstrated that they are in good agreement under all fading conditions. Moreover, the accuracy of the approximation improves with the optical signal-to-noise ratio and the number of diversity branches that are used, which correspond to implementation scenarios that are typically anticipated in practice. Full article
(This article belongs to the Special Issue Light Communication: Latest Advances and Prospects)
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Open AccessArticle Free Space Optic Receiver with Strongly Overlapped Photodetectors’ Field of View
Appl. Sci. 2019, 9(2), 343; https://doi.org/10.3390/app9020343
Received: 9 December 2018 / Revised: 10 January 2019 / Accepted: 17 January 2019 / Published: 19 January 2019
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Abstract
In this study, we designed a mobile free space optic receiver that uses several photodetectors to provide omnidirectional receiving capability. Assuming only one transmitter, it is a receiver which builds a single input multiple output optical channel. The photodetectors are fixed to truncated [...] Read more.
In this study, we designed a mobile free space optic receiver that uses several photodetectors to provide omnidirectional receiving capability. Assuming only one transmitter, it is a receiver which builds a single input multiple output optical channel. The photodetectors are fixed to truncated pyramid walls. Electrical signals from the photodetectors are processed using an equal gain combining technique. This architecture allows simple circuits and enables additive noise suppression. The minimum angle between the pyramid base and the direction of falling rays was calculated to determine the threshold for additive noise suppression. Two areas of interest presented themselves: the processing of very weak electrical signals often drowned in noise, and optimization of the number of photodetectors whose fields of view overlapped strongly. We outline the design of the optical receiver circuitry and provide some practical hints concerning its assembly. The receiver was evaluated using bit error rate measurements and comparing signal-to-noise ratio parameters for various photodetector numbers. The measured data confirm the theoretical assumptions. Full article
(This article belongs to the Special Issue Light Communication: Latest Advances and Prospects)
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Open AccessArticle Channel and Bit Adaptive Power Control Strategy for Uplink NOMA VLC Systems
Appl. Sci. 2019, 9(2), 220; https://doi.org/10.3390/app9020220
Received: 30 November 2018 / Revised: 1 January 2019 / Accepted: 3 January 2019 / Published: 9 January 2019
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Abstract
Non-orthogonal multiple access (NOMA) can be an effective solution to the limited bandwidth of light emitting diodes for visible light communication (VLC) systems to support multiuser communication. The current available works for NOMA VLC systems mainly concentrate on downlinks and the existing power [...] Read more.
Non-orthogonal multiple access (NOMA) can be an effective solution to the limited bandwidth of light emitting diodes for visible light communication (VLC) systems to support multiuser communication. The current available works for NOMA VLC systems mainly concentrate on downlinks and the existing power allocation algorithms mainly focus on the channel state information and ignore the influence of transmitted signals. In this paper, we propose a channel and bit adaptive power control strategy for uplink NOMA VLC systems by jointly considering the channel state information and the transmission bit rate. Under this adaptive power control strategy, it is proved that the received signal at the photodiode (PD) receiver constitutes a sizeable pulse amplitude modulation constellation and low-complexity maximum likelihood detection is admitted. The simulation results indicate that our proposed adaptive power control strategy outperforms the gain ratio power allocation scheme, fixed power allocation scheme, and time division multiple access scheme. Full article
(This article belongs to the Special Issue Light Communication: Latest Advances and Prospects)
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Open AccessArticle Analysis of SNR for High-Orbit Target Detected by Ground-Based Photoelectric System
Appl. Sci. 2018, 8(12), 2604; https://doi.org/10.3390/app8122604
Received: 5 November 2018 / Revised: 7 December 2018 / Accepted: 9 December 2018 / Published: 13 December 2018
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Abstract
To determine the feasibility of observing high-orbit targets with a large aperture telescope, we created a simulation based on electronics to evaluate the signal-to-noise ratio (SNR) model for an infrared ground-based photoelectric system. Atmosphere transmission and sky background radiation data were obtained using [...] Read more.
To determine the feasibility of observing high-orbit targets with a large aperture telescope, we created a simulation based on electronics to evaluate the signal-to-noise ratio (SNR) model for an infrared ground-based photoelectric system. Atmosphere transmission and sky background radiation data were obtained using MODTRAN software, then the SNRs of the high-orbit target (HOT) in different temperatures and orbit heights were calculated separately. The results showed that the observation of the HOT in a short band was possible, and the effect of short-wave was excellent at low temperatures. On the basis of this model, some space targets were observed by a K-band photoelectric telescope for verification and had constructive results. Thus, the model can be used as a basis for whether a HOT can be detected. Full article
(This article belongs to the Special Issue Light Communication: Latest Advances and Prospects)
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Open AccessArticle Experimental Setup to Validate the Effects of Major Environmental Parameters on the Performance of FSO Communication Link in Qatar
Appl. Sci. 2018, 8(12), 2599; https://doi.org/10.3390/app8122599
Received: 22 October 2018 / Revised: 24 November 2018 / Accepted: 28 November 2018 / Published: 13 December 2018
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Abstract
Weather conditions and chemical composition of the atmosphere are the most uncontrollable challenges for free-space optical (FSO) communications. Environmental parameters contribute directly in the characterization of atmospheric turbulence. Thus, it is very interesting to prepare a test setup to study the effect of [...] Read more.
Weather conditions and chemical composition of the atmosphere are the most uncontrollable challenges for free-space optical (FSO) communications. Environmental parameters contribute directly in the characterization of atmospheric turbulence. Thus, it is very interesting to prepare a test setup to study the effect of such parameters on FSO transmissions especially in a region like Qatar, which is arid and has harsh climate. Unlike that of Europe and USA, Qatar’s climate is characterized by high temperatures throughout the year, exceeding 14 °C even in winter. The experiment was carried at Qatar University (QU) using a system that comprises of two Field Programmable Gate Array (FPGA) boards and two FSO terminals installed at 600 m apart from each other. Each terminal operates at 1550 nm and had a capacity of 1 Gb/s. On the other hand, the environment parameters were recorded using a weather station installed near the transmitter. To have a wider set of data for analysis, parameters from four different seasons were recorded and analyzed. We present a comparison between the FSO performances for the different seasons in terms of Packet Delivery Ratio (PDR). We notice a significant difference in the behavior of FSO during summer and winter seasons. Furthermore, using statistics on the data collected from the weather station and based on Blaunstein model (BKB), we correlate the FSO behavior to the variation of refractive index (Cn2) in winter. Also a closed form expression, estimated from the statistical data, has been derived to relate the PDR with environmental parameters for the summer season. Full article
(This article belongs to the Special Issue Light Communication: Latest Advances and Prospects)
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Open AccessArticle Performance Analysis of Satellite-to-Ground Coherent Optical Communication System with Aperture Averaging
Appl. Sci. 2018, 8(12), 2496; https://doi.org/10.3390/app8122496
Received: 10 October 2018 / Revised: 12 November 2018 / Accepted: 27 November 2018 / Published: 5 December 2018
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Abstract
The satellite-to-ground optical communication system suffers from atmosphere turbulence severely. It is well-known that the coherent detection can increase the receiver sensitivity and performing aperture averaging can reduce the scintillation caused by the atmosphere turbulence. In this paper, the bit error rate, the [...] Read more.
The satellite-to-ground optical communication system suffers from atmosphere turbulence severely. It is well-known that the coherent detection can increase the receiver sensitivity and performing aperture averaging can reduce the scintillation caused by the atmosphere turbulence. In this paper, the bit error rate, the outage probability and the average capacity of a coherent satellite-to-ground optical communication downlink with aperture averaging are analyzed. The Log-normal atmosphere turbulence model and BPSK (Binary Phase Shift Keying) modulation is employed. The analyzing focuses on the improvement of aperture averaging with different atmospheric conditions and zenith angles of the satellite. The bit error rate performance based on measuring data is given too. The results demonstrate the bit error rate and the outage probability can be reduced and the average capacity can be improved by aperture averaging efficiently. When the turbulence is stronger and the zenith angle is larger, the effect of aperture averaging is more obvious. The aperture averaging effect on BER (Bit Error Rate) is better than the effect on average capacity. Full article
(This article belongs to the Special Issue Light Communication: Latest Advances and Prospects)
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Open AccessArticle Blind Detection for Serial Relays in Free Space Optical Communication Systems
Appl. Sci. 2018, 8(11), 2074; https://doi.org/10.3390/app8112074
Received: 7 September 2018 / Revised: 24 October 2018 / Accepted: 25 October 2018 / Published: 27 October 2018
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Abstract
Free-space optical (FSO) communication systems have attracted considerable research interest owing to its high transmission rates and its efficient solution for the last mile problem. Atmospheric turbulence degrades the performance of FSO systems. To estimate the received signal, Channel State Information (CSI) or [...] Read more.
Free-space optical (FSO) communication systems have attracted considerable research interest owing to its high transmission rates and its efficient solution for the last mile problem. Atmospheric turbulence degrades the performance of FSO systems. To estimate the received signal, Channel State Information (CSI) or blind detection is used. The blind detection estimates the received signal without the need for pilot signals which reduce the throughput and increase the complexity of the signal. In this paper, we have proposed a relay technique which utilizes the blind detection method for FSO communications. This proposed technique would improve the performance of the FSO system compared to the direct link method. It is observed that the proposed method achieves a signal-to-noise ratio (SNR) close to the SNR reported by CSI method maintaining the same average bit error rate, provided that only a small observation window is employed. Moreover, Monte Carlo simulation results are further provided to demonstrate the validity of the derived approximated average bit error rate. Full article
(This article belongs to the Special Issue Light Communication: Latest Advances and Prospects)
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Open AccessArticle Enhanced Spectral Amplitude Coding OCDMA System Utilizing a Single Photodiode Detection
Appl. Sci. 2018, 8(10), 1861; https://doi.org/10.3390/app8101861
Received: 19 September 2018 / Revised: 1 October 2018 / Accepted: 2 October 2018 / Published: 10 October 2018
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Abstract
In this paper, the performance of a spectral amplitude coding-optical code division multiple access (SAC-OCDMA) system is investigated utilizing a single photodiode (SPD) detection technique. The proposed system uses enhanced double weight (EDW) codes as signature codes with three simultaneous users to overcome [...] Read more.
In this paper, the performance of a spectral amplitude coding-optical code division multiple access (SAC-OCDMA) system is investigated utilizing a single photodiode (SPD) detection technique. The proposed system uses enhanced double weight (EDW) codes as signature codes with three simultaneous users to overcome both phase-induced intensity noise (PIIN) and multiple access interference (MAI). In addition, a dispersion compensating fiber (DCF) is used in order to decrease the group velocity dispersion (GVD) caused in the single mode fiber. An erbium-doped fiber amplifier (EDFA) is used to overcome the attenuation. The use of both DCF and EDFA leads to an appreciable enhancement in the system performance. The system performance is evaluated through its bit error rate (BER), Q-factor, and received power. A comparison between the EDW codes and modified double weight (MDW) codes on the SAC-OCDMA system is demonstrated. Simulation is carried out through Optisystem ver. 7. The simulation results show that: (a) using an avalanche photodiode (APD) over PIN photodiode allows data transmission over longer distances; (b) the use of DCF improves the system BER;(c) using MDW codes gives better BER than using EDW codes. Full article
(This article belongs to the Special Issue Light Communication: Latest Advances and Prospects)
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Open AccessArticle A Modified Disturbance Observer Structure Based on Acceleration Measurement for Disturbance Suppression in Tracking Control System
Appl. Sci. 2018, 8(9), 1571; https://doi.org/10.3390/app8091571
Received: 1 August 2018 / Revised: 27 August 2018 / Accepted: 3 September 2018 / Published: 6 September 2018
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Abstract
The micro-electro-mechanical system (MEMS) accelerometer is widely adopted in many engineering control systems due to its extraordinary performance with high bandwidth, small size and low weight. However, massive drift caused by its insensitively at low frequency is the main factor which limits its [...] Read more.
The micro-electro-mechanical system (MEMS) accelerometer is widely adopted in many engineering control systems due to its extraordinary performance with high bandwidth, small size and low weight. However, massive drift caused by its insensitively at low frequency is the main factor which limits its performance. It leads to integral saturation when the feedforward method is used and hinders the improvement of disturbance suppression ability at low frequency, which is a significant factor for evaluating the closed-loop performance of a high-precision tracking system. To solve this problem, a modified disturbance observer structure and its corresponding new controller, which can improve disturbance suppression performance at low frequency by effectively rejecting more drift and weakening the occurrence possibility of integral saturation when drift exists, are proposed. Detailed analyses and a series of comparative experimental results verify that the proposed method can effectively enhance disturbance suppression performance at low frequency. Full article
(This article belongs to the Special Issue Light Communication: Latest Advances and Prospects)
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Review

Jump to: Research

Open AccessReview Resonant Transmission Line Method for Unconventional Fibers
Appl. Sci. 2019, 9(2), 270; https://doi.org/10.3390/app9020270
Received: 2 December 2018 / Revised: 4 January 2019 / Accepted: 7 January 2019 / Published: 14 January 2019
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Abstract
We provide a very general review of the resonant transmission line method for optical fiber problems. The method has been found to work seamlessly for a variety of difficult problems including elliptical and eccentric core fibers as well as “holey” photonic crystal fibers. [...] Read more.
We provide a very general review of the resonant transmission line method for optical fiber problems. The method has been found to work seamlessly for a variety of difficult problems including elliptical and eccentric core fibers as well as “holey” photonic crystal fibers. This new version has been shown to offer great versatility with respect to cases of unconventional, inhomogeneous index profiles. Full article
(This article belongs to the Special Issue Light Communication: Latest Advances and Prospects)
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