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Free-Space Optical Communication Systems for Beyond 5G/6G Mobile Networks
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Free-Space Optical Communication Systems for Beyond 5G/6G Mobile Networks

A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Optical Sensors".

Deadline for manuscript submissions: closed (20 June 2024) | Viewed by 12900

Special Issue Editor

Dr. Antonio Jurado-Navas

E-Mail Website
Guest Editor
Departamento de Ingeniería de Comunicaciones, Universidad de Málaga, Malaga, Spain
Interests: atmospheric (FSO) optical communications; Terahertz communications; hybrid fiber-FSO networks; UAV-UAV and UAV-ground optical communications; satellite-satellite and satellite-ground links; applications of FSO and Terahertz communications to new generations of mobile networks (6G and beyond)

Special Issue Information

Dear Colleagues,

Free-space optical (FSO) technology is one of the key solutions that have been widely used for communication and sensing. Furthermore, it has become a very favorable complementary technology to radio frequency (RF)-based wireless technologies for future communication networks, namely fifth-and-beyond- and sixth-generation (5G+ and 6G, respectively) communication systems. Among other reasons for its popularity, we can cite some of its inherent features: wide spectrum, high-data-rate, low latency, high security, low cost, and low energy consumption, combined with the ability to address the highly demanding requirements of 5G+ and 6G communications.

This Special Issue will explore key enabling technologies of signal processing methods for optical communication, optical computing, and optical sensing in different scenarios as well as future perspectives and trends. Topics of interest include but are not limited to the following areas:

  • FSO system architectures and transceiver design;
  • Fiber/FSO systems;
  • FSO and integration with mmWave/THz links;
  • FSO-based vertical backhaul/fronthaul framework; 
  • Satellite–aerial 6G networks;
  • Machine learning algorithms for FSO systems;
  • Digital signal processing for sensing and communication;
  • Orbital angular momentum (OAM);
  • Quantum key distribution and quantum communications;
  • Energy-efficient FSO/RF systems;
  • Applications and/or experimental demonstrations of environmental surveillance, disaster prevention, etc. that help to mitigate the increasingly evident global climate change.

Dr. Antonio Jurado-Navas
Guest Editor

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Published Papers (5 papers)

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Research

12 pages, 3060 KiB  
Article
Adaptive Beam Divergence Control to Mitigate Scintillation Effect Caused by Pointing Error in Vertical FSO Transmissions
by Hye-Min Park, Young-Jin Hyun and Sang-Kook Han
Sensors 2023, 23(11), 5045; https://doi.org/10.3390/s23115045 - 24 May 2023
Cited by 3 | Viewed by 1655
Abstract
Free-space optical (FSO) communication has been studied for next-generation network systems. Because an FSO system establishes point-to-point communication links, maintaining alignment among the transceivers is a critical challenge. In addition, atmospheric turbulence causes significant signal loss in FSO vertical links. Even in clear [...] Read more.
Free-space optical (FSO) communication has been studied for next-generation network systems. Because an FSO system establishes point-to-point communication links, maintaining alignment among the transceivers is a critical challenge. In addition, atmospheric turbulence causes significant signal loss in FSO vertical links. Even in clear weather conditions, transmitted optical signals suffer significant scintillation losses due to random variations. Thus, the effect of atmospheric turbulence should be considered in vertical links. In this paper, we analyze the relationship between pointing error and scintillation from the aspect of beam divergence angle. Furthermore, we propose an adaptive beam that optimizes its divergence angle according to the pointing error between the communicating optical transceivers to mitigate the effect of scintillation due to pointing error. We performed a beam divergence angle optimization and compared it with adaptive beamwidth. The proposed technique was demonstrated using simulations, which revealed an enhanced signal-to-noise ratio and the mitigation of the scintillation effect. The proposed technique would be useful in minimizing the scintillation effect in vertical FSO links. Full article
(This article belongs to the Special Issue Free-Space Optical Communication Systems for Beyond 5G/6G Mobile Networks)
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23 pages, 3624 KiB  
Article
Beyond 5G Fronthaul Based on FSO Using Spread Spectrum Codes and Graphene Modulators
by Daniel Neves, Anderson Sanches, Rafael Nobrega, Hichem Mrabet, Iyad Dayoub, Kohei Ohno, Shyqyri Haxha, Ivan Glesk, Antonio Jurado-Navas and Thiago Raddo
Sensors 2023, 23(8), 3791; https://doi.org/10.3390/s23083791 - 7 Apr 2023
Cited by 8 | Viewed by 2991
Abstract
High data rate coverage, security, and energy efficiency will play a key role in the continued performance scaling of next-generation mobile systems. Dense, small mobile cells based on a novel network architecture are part of the answer. Motivated by the recent mounting interest [...] Read more.
High data rate coverage, security, and energy efficiency will play a key role in the continued performance scaling of next-generation mobile systems. Dense, small mobile cells based on a novel network architecture are part of the answer. Motivated by the recent mounting interest in free-space optical (FSO) technologies, this paper addresses a novel mobile fronthaul network architecture based on FSO, spread spectrum codes, and graphene modulators for the creation of dense small cells. The network uses an energy-efficient graphene modulator to send data bits to be coded with spread codes for achieving higher security before their transmission to remote units via high-speed FSO transmitters. Analytical results show the new fronthaul mobile network can accommodate up to 32 remote antennas under error-free transmissions with forward error correction. Furthermore, the modulator is optimized to provide maximum efficiency in terms of energy consumption per bit. The optimization procedure is carried out by optimizing both the amount of graphene used on the ring resonator and the modulator’s design. The optimized graphene modulator is used in the new fronthaul network and requires as low as 4.6 fJ/bit while enabling high-speed performance up to 42.6 GHz and remarkably using one-quarter of graphene only. Full article
(This article belongs to the Special Issue Free-Space Optical Communication Systems for Beyond 5G/6G Mobile Networks)
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18 pages, 3937 KiB  
Article
Ultra-High Capacity Optical Satellite Communication System Using PDM-256-QAM and Optical Angular Momentum Beams
by Shippu Sachdeva, Simarpreet Kaur, Romisha Arora, Manoj Sindhwani, Krishan Arora, Woong Cho, Gyanendra Prasad Joshi and Ill Chul Doo
Sensors 2023, 23(2), 786; https://doi.org/10.3390/s23020786 - 10 Jan 2023
Cited by 9 | Viewed by 2693
Abstract
Twisted light beams such as optical angular momentum (OAM) with numerous possible orthogonal states have drawn the prodigious contemplation of researchers. OAM multiplexing is a futuristic multi-access technique that has not been scrutinized for optical satellite communication (OSC) systems thus far, and it [...] Read more.
Twisted light beams such as optical angular momentum (OAM) with numerous possible orthogonal states have drawn the prodigious contemplation of researchers. OAM multiplexing is a futuristic multi-access technique that has not been scrutinized for optical satellite communication (OSC) systems thus far, and it opens up a new window for ultra-high-capacity systems. This paper presents the 4.8 Tbps (5 wavelengths × 3 OAM beams × 320 Gbps) ultra-high capacity OSC system by incorporating polarization division multiplexed (PDM) 256-Quadrature amplitude modulation (256-QAM) and OAM beams. To realize OAM multiplexing, Laguerre Gaussian (LG) transverse mode profiles such as LG00, LG140, and LG400 were used in the proposed study. The effects of the receiver’s digital signal processing (DSP) module were also investigated, and performance improvement was observed using DSP for its potential to compensate for the effects of dispersion, phase errors, and nonlinear effects using the blind phase search (BPS), Viterbi phase estimation (VPE), and the constant modulus algorithm (CMA). The results revealed that the proposed OAM-OSC system successfully covered the 22,000 km OSC link distance and, out of three OAM beams, fundamental mode LG00 offered excellent performance. Further, a detailed comparison of the proposed system and reported state-of-the-art schemes was performed. Full article
(This article belongs to the Special Issue Free-Space Optical Communication Systems for Beyond 5G/6G Mobile Networks)
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10 pages, 2030 KiB  
Article
Demonstration of Spatial Modulation Using a Novel Active Transmitter Detection Scheme with Signal Space Diversity in Optical Wireless Communications
by Tingting Song, Ampalavanapillai Nirmalathas and Christina Lim
Sensors 2022, 22(22), 9014; https://doi.org/10.3390/s22229014 - 21 Nov 2022
Cited by 2 | Viewed by 1506
Abstract
Line-of-sight (LOS) indoor optical wireless communications (OWC) enable a high data rate transmission while potentially suffering from optical channel obstructions. Additional LOS links using diversity techniques can tackle the received signal performance degradation, where channel gains often differ in multiple LOS channels. In [...] Read more.
Line-of-sight (LOS) indoor optical wireless communications (OWC) enable a high data rate transmission while potentially suffering from optical channel obstructions. Additional LOS links using diversity techniques can tackle the received signal performance degradation, where channel gains often differ in multiple LOS channels. In this paper, a novel active transmitter detection scheme in spatial modulation (SM) is proposed to be incorporated with signal space diversity (SSD) technique to enable an increased OWC system throughput with an improved bit-error-rate (BER). This transmitter detection scheme is composed of a signal pre-distortion technique at the transmitter and a power-based statistical detection method at the receiver, which can address the problem of power-based transmitter detection in SM using carrierless amplitude and phase modulation waveforms with numerous signal levels. Experimental results show that, with the proposed transmitter detection scheme, SSD can be effectively provided with ~0.61 dB signal-to-noise-ratio (SNR) improvement. Additionally, an improved data rate ~7.5 Gbit/s is expected due to effective transmitter detection in SM. The SSD performances at different constellation rotation angles and under different channel gain distributions are also investigated, respectively. The proposed scheme provides a practical solution to implement power-based SM and thus aids the SSD realization for improving system performance. Full article
(This article belongs to the Special Issue Free-Space Optical Communication Systems for Beyond 5G/6G Mobile Networks)
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14 pages, 8842 KiB  
Article
Optical Beam Steerable Visible Light Communication (VLC) System Supporting Multiple Users Using RGB and Orthogonal Frequency Division Multiplexed (OFDM) Non-Orthogonal Multiple Access (NOMA)
by Wahyu Hendra Gunawan, Chi-Wai Chow, Yang Liu, Yun-Han Chang and Chien-Hung Yeh
Sensors 2022, 22(22), 8707; https://doi.org/10.3390/s22228707 - 11 Nov 2022
Cited by 8 | Viewed by 2188
Abstract
In order to achieve high-capacity visible light communication (VLC), five dimensions in physics, including frequency, time, quadrature modulation, space, and polarization can be utilized. Orthogonality should be maintained in order to reduce the crosstalk among different dimensions. In this work, we illustrate a [...] Read more.
In order to achieve high-capacity visible light communication (VLC), five dimensions in physics, including frequency, time, quadrature modulation, space, and polarization can be utilized. Orthogonality should be maintained in order to reduce the crosstalk among different dimensions. In this work, we illustrate a high-capacity 21.01 Gbit/s optical beam steerable VLC system with vibration mitigation based on orthogonal frequency division multiplexed (OFDM) non-orthogonal multiple access (NOMA) signals using red, green, and blue (RGB) laser-diodes (LDs). The OFDM-NOMA can increase the spectral efficiency of VLC signal by allowing high overlapping of different data channel spectra in the power domain to maximize the bandwidth utilization. In the NOMA scheme, different data channels are digitally multiplexed using different levels of power with superposition coding at the transmitter (Tx). Successive interference cancellation (SIC) is then utilized at the receiver (Rx) to retrieve different power multiplexed data channels. The total data rates (i.e., Data 1 and Data 2) achieved by the R/G/B OFDM-NOMA channels are 8.07, 6.62, and 6.32 Gbit/s, respectively, achieving an aggregated data rate of 21.01 Gbit/s. The corresponding average signal-to-noise ratios (SNRs) of Data 1 in the R, G, and B channels are 9.05, 9.18 and 8.94 dB, respectively, while that of Data 2 in the R, G, and B channels are 14.92, 14.29, and 13.80 dB, respectively. Full article
(This article belongs to the Special Issue Free-Space Optical Communication Systems for Beyond 5G/6G Mobile Networks)
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