Optical Wireless Communication System Research Articles

Influence of underwater composite channel on performance of GMSK wireless optical communication system

Influence of underwater composite channel on performance of GMSK wireless optical communication system

Performance Analysis of Underwater Wireless Optical Communication System with Strong Turbulence Channels Based on Strong Fluctuation Theory

Performance Analysis of Underwater Wireless Optical Communication System with Strong Turbulence Channels Based on Strong Fluctuation Theory

Performance of Double-headed Pulse Interval Modulated Wireless Optical Communication System in Anisotropic Ocean Turbulence

Performance of Double-headed Pulse Interval Modulated Wireless Optical Communication System in Anisotropic Ocean Turbulence

Optical Wireless Systems Channel Modelling

With the development of society, the users of mobile devices and electronic devices increase exponentially. As a result, the demand of high-performance communication system becomes more and more significant. Optical wireless communication (OWC) is an effective method to address the increasing number of internet users, which is a promising field. It is significantly important to understand the parameters and characteristics of communication channel if researchers want to design, generate, accomplish, and operate the OWC systems. In this paper, the propagation model discussed in optical wireless communication can be divided into two types: directed Line of Sight (LOS) propagation model and non-Line of Sight propagation model. In case of directed LOS, multipath reflection does not need to be addressed, which is easier to calculate the LOS channel gain. In case of non-Line of Sight propagation, there are some reflections produced from room ceilings and walls, which can be divided mainly into two methods: first order reflection and second order reflection. Based on the conventional diffuse systems and optical wireless systems with angle diversity receivers, the impulse response, delay spread and signal to noise ratio (SNR) will be calculated. In order to optimize the optical wireless system access point and wavelength allocation to users so as to maximize the sum rate offered to all users, the mixed-integer linear programming (MILP) model was proposed and developed.

Review of fibreless optical communication technology: history, evolution, and emerging trends

AbstractIn the present era of technology, it is quite fascinating to design a system capable of transmitting information from one end to another by using the optical spectrum. This system differs from optical fibre communication in terms of channel medium. Optical fibre technology uses the end-to-end physical connection via fibre. In contrast, Light-based wireless communication networks, also known as wireless optical communication (WOC) networks or fibreless optical communication networks, use light as a carrier and air as an unguided propagation media for transmission. Fibreless optical communication eliminates the need for Licensing and Buried Fibre Cables; also, its installation is relatively easy. This survey article describes the evolution of WOC technologies right from the old methods of communication to today’s deep-space optical satellite communication. This article briefly describes the WOC system working principle, categorization of wireless optical systems (based on the carrier frequency wavelength, distance covered, and application), different modulation techniques adopted for wireless optical communication, challenges associated with channel medium and channel modelling, performance analysis of WOC system, various application areas of WOC network, commercial developments in the field of WOC, and some other emerging trends associated with WOC.

Perovskite solar cell using HTLs copper iodide and spiro-OMeTAD comparative analysis in terms of efficiency and resource utilization

The researcher's nature to search for better solar cells despite their performance issues has engendered efficient solar cells. The general idea behind solar cell design is similar for all the structures except for substance selection and the imposition of a morphological order, which greatly affects its performance. A solar panel comprised of particular self-designed solar cell structures are utilized to harness energy and convert optical signals to electrical signals. Research on solar cell design is crucial for future communication systems. The morphological order of different layers demonstrates the performance of solar cells. Some of the electron transport layers (ETLs) and the hole transport layers (HTLs) employ toxic substances that have detrimental environmental effects. We present a comparative analysis of perovskite solar cell (PSC) design and simulation using SCAPS software. With the integration of two different HTLs, Spiro-OMeTAD and CuI, the individual outcomes are effective. The results illustrate that the proposed design is efficient. Replacing the HTL with CuI also showed enough competitive results as compared to existing models. Present and future solar cell design research demonstrates its importance in optical wireless communication, free-space optical communication, light communication, and other communication systems.

Demonstration of a 2 × 2 MIMO-UWOC system with large spot against air bubbles

In order to reduce turbulence-induced scintillation and deal with alignment problems, a 2×2 multiple-input multiple-output (MIMO) underwater wireless optical communication (UWOC) system is proposed and experimentally demonstrated. With help of the large divergence angle of light beams and large field of view (FOV) of the detectors, the effect of high-density air bubbles is greatly eliminated. Simulation and experimental results confirm that, in most intensity-modulation/direct-detection (IM/DD) MIMO-UWOC systems, the repetition coding (RC) scheme performs better than the space-time block coding (STBC) scheme. In a 50 m swimming pool, the maximum horizontal offset can reach 97.9 cm, which is 421% and 192% higher than that of STBC multiple-input single-output (MISO) and RC-MISO/STBC-MIMO schemes, respectively. With a data rate of 233 Mbps and a transmission distance of 50 m, the large detection range can meet a variety of underwater wireless communication requirements. The experiment indicates that, when the difference in the transmission distance between the two optical signals is higher than 1 m, the bit error rate (BER) of the RC scheme increases sharply, while the BER of the STBC scheme is stable. The MIMO coding scheme needs to be selected according to the actual application environment.

Experimental demonstration of an OFDM-UWOC system using a direct decoding FC-DNN-based receiver

In this paper, a novel fully-connected deep neural network (FC-DNN)-based receiver is proposed and experimentally demonstrated in an underwater wireless optical communication (UWOC) system, with the objective of direct decoding orthogonal frequency division multiplexing (OFDM) signals via deep learning methods. Unlike existing schemes, which treat deep neural networks as a single equalizer or a symbol classifier that requires pre-processed labels, the receiver we proposed can achieve direct output from received OFDM signals to the desired bit stream without any redundant pre-processing and post-processing. The feasibility of the proposed receiver has been validated by changing the transmission data rate and the received optical power of experimental setups. Furthermore, our experiments indicate that the proposed direct decoding FC-DNN-based receiver can perform as well as the typical conventional bulky multi-structure receiver without using pilots and cyclic prefixes (CPs) in OFDM-UWOC systems.

Filter-Enhanced Spatial Modulation and Multiplexing in Indoor Optical Wireless Systems

Optical wireless communication (OWC) systems have been widely studied to provide high-speed connections in indoor environments. In this paper, we propose a filter-enhanced indoor OWC system with hybrid spatial modulation (SM) and spatial multiplexing (SMUX) to further increase the data rate. The filter-enhanced SM enables extra information be transmitted via the spatial indices of OWC transmitters, and the SMUX further increases the data rate via the parallel transmission of multiple signals even under highly-similar channels. The proposed scheme is experimentally demonstrated. Up to 35 Gb/s data rate can be achieved with 2.5 GBaud/s symbol rate and four transmitters. Compared with the filter-enhanced SM scheme, the achievable data rate can be increased by 100%. Compared with the conventional SM and SMUX, the bit-error-rate (BER) is improved by over two orders-of-magnitude.

Performance analysis of dual-mode adaptive switching blind equalization algorithm in an underwater wireless optical communication system

In a high-power underwater wireless optical communication (UWOC) system, the bandwidth limitations of high-power optical sources and high-sensitivity detectors and the multipath effect of seawater channels can cause intersymbol interference, which seriously affects the performance of the UWOC system. Based on the attenuation characteristics and time-domain broadening characteristics of underwater wireless optical signals, a dual-mode adaptive switching blind equalization algorithm is proposed; it combines the variable step size constant-to-mode fractional spaced equalizer (FSE) algorithm and the decision directed least-mean-square mode-FSE algorithm to improve the performance of long-distance UWOC systems. Simulations show that the proposed algorithm has antinoise performance under different seawater qualities. In particular, with a bit error rate performance of 10 − 4 in coastal seawater, the signal-to-noise ratio of the proposed algorithm is 5.2 dB lower than the traditional constant-to-mode decision directed least-mean-square algorithm and 9.2 dB lower than that when the algorithm is not equalized.

Experimental demonstration of underwater wireless optical OFDM communication system with a single SPAD receiver

Generally, only binary modulation formats, such as on–off keying (OOK) and pulse position modulation (PPM), can be detected by a single photon avalanche diode (SPAD). In this paper, we propose to use a single SPAD receiver to achieve underwater wireless optical communication (UWOC) with high-order modulation formats. The feasibility is theoretically analyzed, and firstly demonstrated in a proof-of-concept orthogonal frequency division multiplexing (OFDM) experiment. The proposed OFDM system using quadrature phase shift keying (QPSK) and 16 quadrature amplitude modulation (16-QAM) can work with less than 68 and 390 photons per symbol, and with receiver sensitivities below the forward error correction (FEC) limit as high as −84.5 dBm and −77.8 dBm, respectively. These extraordinarily sensitive results indicate that the proposed scheme is a promising solution to long-distance UWOC systems or internet of underwater things (IoUT).

Dual-Hop Underwater Optical Wireless Communication System With Simultaneous Lightwave Information and Power Transfer

The most significant challenge of underwater optical wireless communication (UOWC) system is to overcome its limited coverage. To expand the achievable communication range, we investigate the performance of the dual-hop UOWC system with simultaneous lightwave information and power transfer (SLIPT). The time splitting (TS) method is adopted for wireless power transfer in the proposed system, where the information and energy are transmitted in different phases. A suitable transmission strategy is designed for the model without additional power supply, which contains three phases, i.e. information transmission, energy transmission, and forwarding process. The expressions of the average bit error rate (BER) at the target node and the energy harvested by the relay node are derived over underwater attenuation channel. Then, the effects of the TS factor and the distances on the system performance are investigated in two sub-problems, which minimize the average BER while satisfying the energy harvesting and transmitting rate constraints. Numerical results indicate the performance improvement by adopting the relay node with SLIPT.

SUPPRESSED CARRIER FREQUENCY DIVISION MULTIPLEXING FOR INDOOR OPTICAL WIRELESS COMMUNICATION

Asymmetrically clipped orthogonal frequency division multiplexing (ACO-OFDM) is one of the optical modulation techniques for indoor optical wireless communication systems (OWC) to enable intensity (IM) modulation and direct detection (DD). As compared to other techniques, ACO-OFDM is power efficient, bandwidth efficient and has zero impact of clipping noise. However, its high peak to average power ratio (PAPR) may lead to performance deterioration and also introduce nonlinear distortion in optical source. To further enhance its performance by reducing the PAPR, suppressed carrier frequency division multiplexing (SC-FDM) is proposed and the system is titled as interleaved coded ACO (ICACO)-OFDM. To evaluate the performance of the system, simulation has been carried out for 16-QAM, 256 subcarriers, 1000 symbols. By observing the curves generated by Complementary cumulative distribution function (CCDF) at the probability of 10-3, PAPR has been characterized. It is observed that PAPR of ICACO-OFDM is 4.98 dB less as compared to ACO-OFDM system.

Analysis of wavy surface effects on the characteristics of wireless optical communication downlinks

The wave surface effect will be a major constraint when a wireless optical communication system is applied in an air water interface environment. In this paper, a downlink optical model based on Monte Carlo numerical method is developed and simulated to explore the characteristics of the effect. And then, the comprehensive influence of wave surface, link distance, water turbidity and receiver parameters on the communication link power is evaluated. The results show that the wind-induced power loss is more significant at low turbidity but a higher turbidity or a longer transmission depth can help to eliminate the fluctuation effect. Particularly in coastal waters, when the underwater distance exceeds 35 m, the power curves estimated by different wind speeds are consistent. Furthermore, an air–water optical communication link experiment is also installed in a water-tank to verify the simulation conclusions. It is demonstrated that whether in tap water or artificial turbid water, the experiment data show relative consistency with the emulation, and the model established in this paper is feasible and reasonable and which can be used to describe and analyze the wireless optical communication system on a wavy air–water interface.

Multihop underwater optical wireless communication system for internet of underwater things applications

SummaryInternet of underwater things (IoUT) has garnered significant attention for monitoring and exploration applications in underwater scenarios. The interconnected devices used in IoUT have power constraint as batteries are difficult to recharge or replace. Multihop cooperative communication can help reduce the power requirement of a single node by breaking the long distance links into two or more high quality segments. In this paper, we investigate the end‐to‐end average bit error rate (BER) of the multihop underwater relay network. The nodes are connected to each other using optical wireless communication link which provides high data rates with low latency. Closed form expressions for average BER are derived for two scenarios: (1) where every hop channel has the same statistical behavior and (2) each channel is characterized by different statistical behavior. Further, the impact of channel parameters on the system performance is analyzed and discussed.

A 400-Gb/s WDM-PAM4 OWC system through the free-space transmission with a water\u2013air\u2013water link

A 400-Gb/s wavelength-division-multiplexing (WDM) four-level pulse amplitude modulation (PAM4) optical wireless communication (OWC) system through a 200-m free-space transmission with either an 8.8-m piped water–air–piped water link or a 6.5-m turbid water–air–turbid water link is successfully constructed. Incorporating PAM4 modulation with an 8-wavelength WDM scheme greatly increases the total transmission rate of the WDM-PAM4 OWC system to 400 Gb/s (50 Gb/s/λ × 8 λs). By adopting doublet lenses in free-space transmission, a laser beam reducer/expander and a reflective spatial light modulator (SLM) with an angle expander through the water–air–water link, good bit error rate performance and acceptable PAM4 eye diagrams are obtained. Using a reflective SLM with an angle expander not only adaptively adjusts the laser beam, but also effectively solves the oceanic engineering problems. This demonstrates WDM-PAM4 OWC system outperforms existing OWC systems through the free-space transmission with an air–water–air link because it can solve the practical engineering problems in actual oceanic environments.

Effects of adaptive optics on bit error rate of M-ary PPM oceanic optical wireless communication systems with aperture averaging in strong turbulence

Scintillation is the result of oceanic turbulence reducing the bit error rate (BER) performance of oceanic optical wireless communication (OWC) systems. The scintillation, also known as intensity fluctuations, occurs due to the turbulence-induced wavefront deformations. The correction of deformations by adaptive optics (AO) reduces the scintillation effect of turbulence and results in improved BER performance. In this paper, an oceanic OWC (OOWC) system that has a Gaussian laser beam at the transmitter, finite-sized circular aperture at the receiver, employing M-ary pulse position modulation (PPM) and operating in strong oceanic turbulence, is considered. Improvement in the BER performance of the OOWC system is examined with the implementation of AO correction. Comparison of BER performances between the AO and non-adaptive optics OOWC systems is shown by calculating the metric defined. BER of M-ary PPM OOWC links is evaluated over gamma–gamma fading channels. The modified Rytov theory together with the Zernike filter functions is used to find the AO corrected aperture averaged scintillation index where extended Huygens–Fresnel technique is used to obtain the average received signal power.

LiFi Positioning for Industry 4.0

Precise position information is considered as the main enabler for the implementation of smart manufacturing systems in Industry 4.0. In this article, a time-of-flight based indoor positioning system for LiFi is presented based on the ITU - T recommendation G.9991. Our objective is to realize positioning by reusing already existing functions of the LiFi communication protocol which has been adopted by several vendors. Our positioning algorithm is based on a coarse timing measurement using the frame synchronization preamble, similar to the ranging, and a fine timing measurement using the channel estimation preamble. This approach works in various environments and it requires neither knowledge about the beam characteristics of transmitters and receivers nor the use of fingerprinting. The new algorithm is validated through both, simulations and experiments. Results in an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\text{1}\;{\rm{m}} \times \text{1}\;{\rm{m}} \times \text{2}\;{\rm{m}}$</tex-math></inline-formula> area indicate that G.9991-based positioning can reach an average distance error of a few centimeters in three dimension. Considering the common use of lighting in indoor environments and the availability of a mature optical wireless communication system using G.9991, the proposed LiFi positioning is a promising new feature that can be added to the existing protocols and enhance the capabilities of smart lighting systems further for the benefit of Industry 4.0.

Performance analysis of optical wireless communications with aperture averaging over exponentiated Weibull turbulence with pointing errors

Aperture averaging (AA) is a potential technique to reduce the effect of atmospheric turbulence in optical wireless communications (OWC). Although there is significant research on point-like detectors, there is a gap in the study on the analytical performance evaluation of OWC systems with AA over atmospheric turbulence and pointing errors. In this paper, we analyze the performance of a single-link OWC system by considering the three-parameter exponentiated Weibull (EW) model for the atmospheric turbulence and the zero boresight fading model for pointing errors. We derive analytical expressions for moments of signal-to-noise ratio (SNR), ergodic capacity, outage probability, average bit-error-rate (BER), and average energy consumption under the combined effect of atmospheric turbulence and pointing errors in terms of system parameters. To provide insights on the system behavior, we develop asymptotic bounds at high SNR on the performance of the considered system. We also derive analytical expressions for the performance of OWC system under the atmospheric turbulence with negligible pointing errors. We demonstrate the performance of OWC system over EW turbulence with a comparison to the performance obtained using the Gamma–Gamma (GG) model and demonstrate the tightness of the derived performance bounds through numerical and simulation analysis.

Optical Wireless Communications Using Signal Space Diversity with Spatial Modulation

A signal space diversity (SSD) scheme was proposed to be incorporated with spatial modulation (SM) in an intensity-modulation/direct-detection-based multiple-input-single-output (MISO) indoor optical wireless communication (OWC) system to improve bit-error-rate (BER) performance and system throughput. SSD was realized via signal constellation rotation and diversity interleaving using different channel gains to improve the BER. With SM incorporated, the MISO-OWC system throughput increased. Theoretical BER expressions of the SSD scheme were established for the first time by investigating the distance of neighboring constellation symbols upon maximum-likelihood detection. Such BER expressions were further verified by numerical results. The results showed that, except for the slightly-lower-accuracy performance brought by comparable distances of neighboring constellation symbols in cases of low signal-to-noise ratios, these BER expressions were accurate in most scenarios. Moreover, theoretical investigations of channel gain distributions were performed at different signal constellation rotation angles to show the capability of the SSD scheme to improve the BER. The results showed that a significantly improved BER by two orders of magnitude could be achieved using a reasonably high channel-gain ratio and a larger constellation rotation angle. The SSD-SM scheme provides a promising option to achieve transmitter diversity with an enhanced throughput in high-speed indoor OWC systems.