Search

This study demonstrates a significant reduction in the bit error rate (BER) within free space optical (FSO) communication systems, even in highly turbulent optical channels. The strategic application of spatial diversity techniques emphasizes the feasibility of achieving low BER values. In the presence of light fog, our system achieves a transmission range of 700 m, while medium and heavy fog conditions reduce it to 450 and 350 m, respectively. Under light dust conditions, the range extends to 350 m and decreases to 120 and 48 m in medium and heavy dust conditions. In a clear sky, our non-return-to-zero orbital angular momentum (OAM) multiplexing-based FSO system successfully transmits 40 Gb/s of data over a distance of 1500 m with reliable performance. The utilization of spatial diversity and beamforming techniques further enhances system reliability, making it robust even in challenging real-world scenarios. However, it is essential to address the impact of adverse weather conditions, such as fog and dust, by developing weather-resistant technologies for reliable FSO communication. While fog generally exhibits better performance, the significance of spatial diversity remains crucial in adverse conditions, encompassing both fog and dust weather factors. The integration of OAM beams and FSO technology holds promise for high-speed and efficient optical communication. This research addresses the mitigation of weather-induced fading through OAM multiplexing. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the impact of both static and dynamic effects of motion on Underwater visible light communication (UVLC) channels. While previous studies have focused on static channel modeling, we argue that dynamic channel modeling is crucial for accurate UVLC analysis. To model static and dynamic UVLC channels, we use the Monte Carlo ray tracing (MCRT) method in Zemax Optics Studio; a reliable and practical setup simulator that produces results similar to experimental data. We evaluate the effect of channel coding on system performance by comparing nine different combinations and using Goodness-of-Fit (GoF) tests to determine the best-fit distribution. Our results reveal that the static case outperforms the dynamic case in terms of raw performance without any coding. However, we also show that the bit error rate (BER) is severely impacted in various realistic scenarios for a dynamic environment. To improve the BER and achieve adequate received signal quality, we recommend using convolutional codes. This paper emphasizes the importance of dynamic channel modeling in UVLC and provides practical solutions to enhance the UVLC performance in dynamic environments. The findings of our study provide valuable insights into the performance of UVLC systems and emphasize the need for researchers and designers to account for the dynamic realistic behavior in the underwater channel to achieve optimal performance in UVLC systems for underwater communication applications. [ABSTRACT FROM AUTHOR]

This paper investigates and enhances unmanned aerial vehicle (UAV) relay-assisted free-space optics (FSO) optical wireless communication (OWC) systems under the effects of pointing errors (PEs) and atmospheric turbulences (ATs). The incorporation of UAVs as buffer-aided moving relays in the conventional FSO (CFSO) relay-assisted systems is proposed for enhancing the performance of PEs through AT. Using M-PSK (phase shift keying) and M-QAM (quadrature amplitude modulation), the impact of PEs on transmission quality is evaluated in this work. We evaluate and optimize the symbol error rate, outage probability (OP), and signal-to-noise ratio (SNR) for the UAV-to-ground station-based FSO communications systems. The spatial diversity-based relay-assisted CFSO systems can enhance the performance of the UAV-UAV FSO links. In this paper, a new FSO (NFSO) channel model for the hovering UAV-FSO OWC fluctuations under the PEs, AT effects, jitter, deviation, receiving an error, and wind resistance effects are established. To improve the performance of hovering UAV-based FSO relay OWC systems. We reduce the influence of UAV-FSO OWC fluctuations under PEs and AT effects. By receiving incoherent signals at various locations, the spatial diversity-based relay-assisted NFSO systems can significantly increase the system's redundancy and enhance connection stability. Numerical results show that to achieve a bit-error-rate (BER) of ≤ 10 - 5 , the required SNR is ≥ 23 dB when the wind variance of the UAVs σ α 2 increases from 0 to 7 mrad with FSO link distance L = 2000 m. The required SNR is ≥ 25 dB when the wind variance σ α 2 is 1 mrad at an OP of 10 - 6 . To obtain an average BER of 10 - 6 , the SNR should be 16.23 dB, 17.64 dB, and 21.45 dB when σ α 2 is 0 mrad, 1 mrad, and 2 mrad, respectively. Using 8-PSK modulation without PEs requires 23.5 dB at BER of 10 - 8 while 16-QAM without PEs requires 26.5 dB to maintain the same BER of 10 - 8 . Compared with 16-QAM without PEs, the SNR gain of 8-PSK without PEs is 3 dB. The results show the relay-assisted UAV-FSO system with five stationary relays can achieve BER 10 - 8 at 25 dB SNR in the ideal case and 10 - 5 at 27 dB SNR with AT and PE at FSO length 1000 m. The results show the relay UAV-FSO system outperforms the CFSO at the BER and SNR performance. The effects of UAV'FSO s fluctuation increase when the UAV-FSO link length, L fso increases. The results of the weak turbulence achieve better SER compared with MT and ST. The obtained results show that decreasing L fso can compensate for the effects of UAV-FSO link fluctuation on the proposed system. Finally, we investigated the CFSO relay-assisted UAV-FSO system with aided NFSO-UAVs spatial diversity-based relay-based on NFSO OWC and revealed the benefits of the resulting hybrid architecture. [ABSTRACT FROM AUTHOR]

In the past few decades, the academic research and industrial synergy is dramatically accelerating to conceptualize high data rate services. The congestion in the radio frequency (RF) spectrum has imposed many inherent limitations in the growth of future wireless networks. These limitations have spurred global research activities to open new parts of the electromagnetic wave spectrum. More researches and developments in new modulation schemes, channel modelling and signal processing techniques are yet to be explored. Optical wireless communication (OWC) has appeared as an emerging complementary technology to RF systems. It is deemed as a promising alternative to address RF spectrum congestion and enhance system's capacity. OWC has gained widespread attention due to its high confidentiality, large spectrum resources and strong resistance to electromagnetic interference (EMI). In this paper, we envisage OWC systems as a promising solution for the bandwidth shortage of RF spectrum. We have also discussed the current upsurge of diversified OWCs in fifth generation (5G) and Internet-of-Things (IoT) solutions which has spurred heated discussion for future technologies. In this study, we have outlined a holistic vision of several OWC enabling technologies and survey of potential issues in OWC systems. We investigate visible light communication (VLC) and free space optics (FSO) as potential implementation approaches for OWC systems. Generally, the intent of this extant study includes (i) potential features and classifications of OWC systems, (ii) key enabling technologies, (iii) link design requirements and modulation schemes, (iv) main impairments and solutions to reduce the impairments, and (v) security issues and techniques to secure OWC. At last, open research challenges and future research directions in OWC systems are investigated. In this regard, we believe this survey will be helpful to aggregate the research efforts and eliminate the technical uncertainties towards breakthrough novelties of OWC technologies. [ABSTRACT FROM AUTHOR]

Wireless communication refers to data transfer in an unguided propagation medium through wireless carriers such as visible light (VL) and radio frequency (RF). The rapidly growing demand for high data rates overloads conventional RF wireless communication. Therefore, technologies such as cognitive radios and millimeter waves (mmWaves) have been utilized to overcome capacity limitation and spectrum scarcity of RF systems. In parallel, optical wireless communication (OWC) is a promising alternative solution to its radio frequency (RF) compeer. OWC has been revolutionized to support fifth generation (5G) wireless communication and Internet-of-Things (IoT) terminals. In addition, OWC has no health hazard, low power consumption, unlicensed spectrum and shows immunity to interferences from electromagnetic sources. As RF and OWC are compatible, so a joint application scenario is referred as an excellent solution to support 5G and beyond systems. Hybrid optical/optical and RF/optical system is a promising approach to remove the limitations of each system as well as to enable supporting features of each technology. An optical/optical hybrid system is based on two or more OWC technologies while RF/optical hybrid system contains both RF and OWC technologies. The hybrid systems can enhance system performance in terms of energy efficiency, reliability and throughput of each system. Thus, hybrid RF/optical systems are envisioned as a key enabler to enhance user mobility and data rate on the one hand and to optimize power consumption, network load, interference and network capacity on the other hand. This survey seeks to provide the state-of-the-art and future research directions regarding optical wireless hybrid networks. This paper represents a technological overview of existing optical wireless hybrid networks. We have discussed optical-based free-space optics (FSO), optical camera communication (OCC), light fidelity (LiFi) which extends the concept of visible light communication (VLC) to attain bi-directional and fully networked wireless communication, as well as RF-based Bluetooth, wireless fidelity (WiFi), small cell, macrocell, mmWave and microwave. In addition, we have also considered underwater acoustic communication for acoustic/optical and acoustic/RF hybrid networks. An extensive range of applications such as indoor, vehicular communication, eHealth, backhaul connectivity solution and underwater communication is considered. We have addressed potential challenges and open research issues for design and successful deployment of hybrid wireless networks. [ABSTRACT FROM AUTHOR]