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Nowadays, a variety of underwater activities, such as underwater surveillance, marine monitoring, etc., are becoming crucial worldwide. Underwater sensors and autonomous underwater vehicles (AUVs) are widely adopted for underwater exploration. Underwater communication via radio frequency (RF) or acoustic wave suffers high transmission loss and limited bandwidth. In this work, we present and demonstrate a rolling shutter (RS)-based underwater optical camera communication (UWOCC) system utilizing a long short-term memory neural network (LSTM-NN) with side glow optical fiber (SGOF). SGOF is made of poly-methyl methacrylate (PMMA) SGOF. It is lightweight and flexibly bendable. Most importantly, SGOF is water resistant; hence, it can be installed in an underwater environment to provide 360° "omni-directional" uniform radial light emission around its circumference. This large FOV can fascinate the optical detection in underwater turbulent environments. The proposed LSTM-NN has the time-memorizing characteristics to enhance UWOCC signal decoding. The proposed LSTM-NN is also compared with other decoding methods in the literature, such as the PPB-NN. The experimental results demonstrated that the proposed LSTM-NN outperforms the PPB-NN in the UWOCC system. A data rate of 2.7 kbit/s can be achieved in UWOCC, satisfying the pre-forward error correction (FEC) condition (i.e., bit error rate, BER ≤ 3.8 × 10−3). We also found that thin fiber also allows performing spatial multiplexing to enhance transmission capacity. [ABSTRACT FROM AUTHOR]

Visible Light Communication (VLC) is emerging as a promising technology to meet the demands of fifth-generation (5G) networks and the Internet of Things (IoT). This study introduces a novel RGB-LED-based VLC system design that leverages autoencoders, addressing the often overlooked impact of optical-to-electrical (O/E) conversion efficiency. Unlike traditional methods, our autoencoder-based system not only improves communication performance but also mitigates the negative effects of O/E conversion. Through comprehensive simulations, we show that the proposed autoencoder structure enhances system robustness, achieving superior performance compared to traditional VLC systems. By quantitatively assessing the impact of O/E conversion—a critical aspect previously overlooked in the literature—our work bridges a crucial gap in VLC research. This contribution not only advances the understanding of VLC systems but also provides a strong foundation for future enhancements in 5G and IoT connectivity. [ABSTRACT FROM AUTHOR]

In the realm of future wireless networks, it is anticipated that high altitude platforms (HAP)-satellite links will serve as the primary facilitators. Optical wireless communication has become increasingly important due-to its exceptional features and ability to provide gigabit capacity communication. As such, this work explores an optical code division multiple access scheme centred on high-speed long-haul mode division multiplexing for HAP-to-satellite applications. The proposed design utilizes zero cross-correlation (ZCC) and multi-diagonal (MD) codes at donut modes 0 and 1. The main objective of this research is to create a cost-effective, secure, and cutting-edge last mile linkage that optimizes resource utilization for HAP systems. The results indicate that the system employing ZCC code outperforms the MD code. Moreover, the system accomplishes a minimum bit error rate limit of 10−3 at transmission distances of 5000 km and 4800 km at Donut mode 0 and 1, respectively, for the ZCC code. In addition, the system can tolerate maximum acceptable transmitter pointing errors of 3 µrad and receiver pointing errors of 4 µrad at minimum BER limit. Meanwhile the system using ZCC can offer better performance of maximum 28 dB optical signal to noise ratio till high split ratio of 1:4–1:64. It also indicates optimum performance over other existing ones. [ABSTRACT FROM AUTHOR]

The current paper explores the impact of misalignment between transceivers (referred to as pointing error (PE)) on the performance of transdermal optical wireless (TOW) technology, as indicated by average signal-to-noise ratio (SNR), outage probability (OP), outage rate (OR), and average ergodic capacity (AEC). This study was inspired by the effectiveness of differential phase shift keying (DPSK) in enhancing the reliability of the link in free-space optical communications (FSO). Furthermore, this enhancement was studied and analyzed in consideration of the impact of pointing errors. In particular, this paper presents a mathematical analysis that considers certain characteristics of the channel, limitations within the body, the pointing errors (PEs) between the transceivers, and other specific aspects of the optical unit. The results demonstrate the significant impact of PEs on the reliability of the TOW link and highlight the improvement provided by the DPSK technique. i.e., 3 dB better performance compared to the on-off keying (OOK) modulation technique. Finally, this research demonstrates the practical application of wireless optical technology in the medical field within the wavelength range of 800–1300 nm, with optimal performance observed around 1100 nm. [ABSTRACT FROM AUTHOR]

The underwater optical wireless communication (UOWC) is a relatively new area of research which has generated enthusiasm for the military, industry, and scientific community. The blue–green spectrum provides the most optimum band for optical wireless communication in underwater (sea water) scenario. Considering the limitations of acoustic waves having limited bandwidth, UOWC promises to support higher data rates with low latency compared to RF and acoustic mode of communication. This paper proposes a novel mathematical channel-modeling for UOWC, in a weak turbulent environment. The turbulence-induced irradiance fluctuation is modeled by log normal distribution. The parameters are related to line-of-sight underwater links. The analytical expression for the average bit-error-rate, outage probability, and the average channel capacity is derived for three types of water, i.e., clear ocean, coastal ocean, and turbid harbor. We also analyze the effects of turbulence for the above parameters. For clear and coastal ocean, data rate falls around 10 9 and 10 8 bits per second within 10 m distance, respectively, whereas the data rate in case of turbid harbor hardly reaches 1 Mbps and drops drastically within a few meters. [ABSTRACT FROM AUTHOR]

The necessity for access to a high data rate has been the motivation behind expanding new technologies. The increasing of wireless devices has caused the radio wave spectrum to become congested. Additionally, radio waves cannot be used in EMI-vulnerable places. Hence, the interest in visible light communication (VLC) offers real alternatives to radio-based communications. This paper focuses on the use of visible light as a data communication medium and introduces a designed audio SIMO (Single-Input-Multi-Output) data transmission system from point to multipoint to demonstrate the functionality of the VLC system in audio transmission through modulated LEDs light. The system is made up of the transmitting unit and multi-receiving units. The transmitting unit consists of three stages: audio in, preamplifier, and white LEDs array that transmits the data using the ON-OFF keying (OOK) modulation technique to all receivers. On the other hand, the receiving unit consists of three receivers that have different photodetectors aspects with fixed distances separation between them. The line of sight (LOS) communication between transmitter and receivers for the purpose to transfer audio data has been employed. Based on the LOS link, simulation and experimental analysis have been done in multiple semi-angles for studying the output performance of receivers and the characteristics of the white LEDs such as luminous intensity and received power at 20,45 and 70 semi-angle at half-power through MATLAB® software. [ABSTRACT FROM AUTHOR]

Light-Fidelity (Li-Fi) is the bidirectional communication technique, tenders almost unlimited bandwidth, exploit unlicensed spectrum of light waves. Accordingly, this manuscript illustrates usage of visible light communication (VLC) applied as Li-Fi, an efficient scheme to broadcast data wirelessly as well safer technique in contrary to the customary Wireless-Fidelity (Wi-Fi) networks. In support numerical simulations have been executed over the proposed Li-Fi model for the parametric variation with the data rate, laser power, modulation format and wavelength, communication length. Investigations have showed good output performance, with hike in data rate BER variation as 10−94–10−23 and testing length. Simulations of network with DPSK and NRZ modulation formats at high data transmission of 10 Gbps have showed good output performance with 10−40 with DPSK format. Li-Fi systems are quality solution for the impending communication systems save cost, provide high spectral efficiency. [ABSTRACT FROM AUTHOR]

The automatic modulation recognition (AMR) of optical signals in non-cooperative conditions has recently become one of the most important research projects. The feasibility and effectiveness of using deep learning techniques for automatic modulation format recognition of received wireless optical communication signals is investigated in this framework. Convolutional neural network (CNN) architecture has been developed and refined in recent work to attain performance that outperforms expert-based approaches. An AMR technique based on fan-beam (FB) projection was proposed in this study. The constellation diagram is created by preprocessing the received signal. The constellation diagram is then projected in the FB domain. The FB is used as a tool for extracting features. The (CNN) uses this projected constellation diagram as input to identify different types of modulation formats. For determining the modulation format of an optical signal, three types of classifiers (Alexnet, VGG16, and VGG19) are investigated. For our investigations, we looked at the constellation diagrams of eight common signals, including (2/4/8/16- phase-shift keying (PSK) and 8/16/32/64- quadrature amplitude modulation (QAM). Typical classification accuracy values versus optical signal-to-noise ratio (OSNR) are calculated for evaluation over an OSNR range of (5–30 dB). A study of the effect of increasing the number of samples on the accuracy of the classifiers is also presented for each modulation format. Finally, the phase noise resistance of the (FB) projected diagram is investigated. When compared to traditional modulation format recognition algorithms, simulation results suggest that the proposed algorithm presented in this paper has a greater accuracy rate for signal modulation recognition at low OSNR. [ABSTRACT FROM AUTHOR]

In this work, we put forward and demonstrate a bi-direction free-space visible light communication (VLC) system supporting multiple moveable receivers (Rxs) using a light-diffusing optical fiber (LDOF). The downlink (DL) signal is launched from a head-end or central office (CO) far away to the LDOF at the client side via a free-space transmission. When the DL signal is launched to the LDOF, which acts as an optical antenna to re-transmit the DL signal to different moveable Rxs. The uplink (UL) signal is sent via the LDOF towards the CO. In a proof-of-concept demonstration, the LDOF is 100 cm long, and the free space VLC transmission between the CO and the LDOF is 100 cm. 210 Mbit/s DL and 850 Mbit/s UL transmissions meet the pre-forward-error-correction bit error rate (pre-FEC BER = 3.8 × 10−3) threshold. [ABSTRACT FROM AUTHOR]

The huge bandwidth and immunity to electromagnetic interference make visible light communication (VLC) systems the preferred technique for many applications. Unfortunately, the superposition of multiple subcarriers in VLC orthogonal frequency division multiplexing systems leads to a high peak-to-average power ratio (PAPR). So, in this study, we aim to reduce PAPR in VLC systems and improve the system performance by proposing non-distorting PAPR reduction techniques like precoding techniques as it doesn't affect the system data rate because they do not require any obligatory transmission of side information. Moreover, it has a very good ability to reduce the PAPR without affecting the system BER performance. So, different precoding reduction techniques are proposed like discrete cosine transform (DCT), discrete sine transform (DST), discrete Hatley transform (DHT), and Vandermonde like matrix (VLM), to address the high PAPR and light-emitting diode-restricted linear range problems in VLC systems. The proposed technique using DHT, DCT, DST, and VLM provided a significant advantage in reducing the PAPR by 1.35 dB, 1.46 dB, 2.12 dB, and 2.17 dB, respectively. So the proposed technique is based on using the VLM precoding technique to achieve maximum reachable PAPR reduction value. Also, a comparison of the presented work and related literature reviews for PAPR reduction techniques are held to ensure the validity and effectiveness of the proposed scheme. [ABSTRACT FROM AUTHOR]

In this paper, we propose and investigate a hybrid multi-band carrierless amplitude and phase modulation and non-orthogonal multiple access (mCAP-NOMA) scheme for quality-of-service (QoS)-aware uplink multi-user optical wireless communication (OWC) systems. Considering the users' distinctive channel conditions and QoS requirements, we further design three user pairing approaches for the mCAP-NOMA-based uplink OWC system, including channel gain-based user pairing, modulation order-based user pairing and adaptive user pairing. More specifically, the adaptive user pairing approach can dynamically select from the individual channel gain-based or modulation order-based user pairing approaches aiming to obtain a lower average bit error rate (BER) of the uplink OWC system. Simulation results verify the feasibility and superiority of the mCAP-NOMA scheme with adaptive user pairing in an uplink four-user OWC system. [ABSTRACT FROM AUTHOR]

Summary: The integrated OWC‐PON architecture has a potential to overcome the limitations of existent RF technology and eliminate the last mile bottleneck in geographically constrained access networks thus providing real sense broadband from core to user. However, phenomenon such as atmospheric turbulence causes performance degradation in such systems. In the dissemination of multimedia services, the performance is the ultimate quality as perceived by end user's visual senses. To ascertain this quality in quantitative terms, full reference quality metrics are employed for communication purposes. This paper deals with classification, evaluation and analysis of various image quality assessment metrics for image transmission over OWC channel under varying turbulent conditions. The performance enhancement in terms of these metrics is investigated by deploying MIMO diversity reception. Moreover, a prediction model for SSIM is developed and compared for both SISO and MIMO links. The results show an improvement in IQA metrics with diversity reception. SSIM can be predicted in terms of log of refractive index structure parameter by a fourth order polynomial model for both SISO and MIMO receptions under all regimes of turbulence. The goodness of the fit statistics is presented along with the models to provide for their accuracy and reliability. [ABSTRACT FROM AUTHOR]

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The high precision three-dimensional (3D) visible light-based indoor positioning (VLIP) systems have gained much attention recently for people or robot navigation, access tracking, etc. In this work, we put forward and present the first demonstration, up to the authors' knowledge, of a 3D VLIP system utilizing a two-stage neural network (TSNN) model. The positioning performance would degrade when the distance between the light emitting diode (LED) plane and the receiver (Rx) plane increases; however, because of the finite LED field-of-view (FOV), light non-overlap zones are created. These light non-overlap zones will produce high positioning error particularly for the 3D VLIP systems. Here, we also propose and demonstrate the Received-Intensity-Selective-Enhancement scheme, known as RISE, to alleviate the light non-overlap zones in the VLIP system. In a practical test-room with dimensions of 200 × 150 × 300 cm3, the experimental results show that the mean errors in the training and testing data sets are reduced by 54.1% and 27.9% when using the TSNN model with RISE in the z-direction, and they are reduced by 39.1% and 37.8% in the xy-direction, respectively, when comparing that with using a one stage NN model only. At the cumulative distribution function (CDF) P90, the TSNN model with RISE can reduce the errors by 36.78% when compared with that in the one stage NN model. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This paper studies the capacity of the two-user intensity-modulation/direct-detection (IM/DD) interference channel (IC), which is relevant in the context of multi-user optical wireless communications. Despite some known single-letter capacity characterizations for general discrete-memoryless ICs, a computable capacity expression for the IM/DD IC is missing. In this paper, we provide tight and easily computable inner and outer bounds for a general two-user IM/DD IC under peak and average optical intensity constraints. The bounds enable characterizing the asymptotic sum-rate capacity in the strong and weak interference regimes, as well as the generalized degrees of freedom (GDoF) in the symmetric case. Using the obtained bounds, the GDoF of the IM/DD IC is shown to have a ‘W’ shape similar to the Gaussian IC with power constraints. The obtained bounds are also evaluated numerically in different interference regimes to show their tightness, and used to study the performance of on-chip and indoor OWC systems. [ABSTRACT FROM AUTHOR]

Summary: The preceding decade has seen successful rollout of 5G and convergence of broadcast broadband and telecom sector. The near future bandwidth demands for services such as advanced immersive multimedia are even more challenging. This has led to advent of 6G. The access technologies need to provide virtually unlimited data rates to support majority of applications in 6G. The optical wireless communication (OWC) with its inherent advantages is a potential enabler in this scenario. However, phenomenon such as atmospheric turbulence poses a serious degradation to performance of such systems. For multimedia services, end user perception is the ultimate quality indicator. To ascertain this quality in quantitative terms, full reference quality metrics are employed for communication purposes. In this paper, digital video broadcasting terrestrial (DVB‐T) videos with varying complexities are transmitted over OWC‐passive optical network (PON) architecture. For performance enhancement 2 × 2 repetitive coding MIMO is employed with maximal ratio combining receiver. A total of 6 video quality assessment (VQA) metrics are evaluated for the system w.r.t channel parameter as Rytov variance. For all the VQA metrics, an enhancement in the performance is observed by using MIMO technique. This performance improvement is more prominent for more complex video as compared to less complex video. As for the limiting case BER of 10−3 gives a limiting link distance of 1350 m; however with VQA metrics, the limiting case distance is 1280 m. By the use of 2 × 2 MIMO techniques, this distance enhances by 20–25 m. [ABSTRACT FROM AUTHOR]

Visible light communication (VLC) is a versatile enabling technology for following high-speed wireless communication because of its broad unlicensed spectrum. In this perspective, white light-emitting diodes (LED) provide both illumination and data transmission simultaneously. To accomplish a VLC system, receiver antennas play a crucial role in receiving light signals and guiding them toward a photodetector to be converted into electrical signals. This paper demonstrates an optical receiver antenna based on luminescent solar concentrator (LSC) technology to exceed the conservation of etendue and reach a high signal-to-noise ratio. This optical antenna is compatible with all colors of LEDs and achieves an optical efficiency of 3.75%, which is considerably higher than the similar reported antenna. This antenna is fast due to the small attached photodetector—small enough that it can be adapted for electronic devices—which does not need any tracking system. Moreover, numerical simulation is performed using a Monte Carlo ray-tracing model, and results are extracted in the spectral domain. Finally, the fate of each photon and the chromaticity diagram of the collected photons' spectra are specified. [ABSTRACT FROM AUTHOR]

In this letter, we propose and experimentally demonstrate an optical wireless communication (OWC) system with embedded localization functionalities based on reflectometry, that share both the OWC hardware platform and the orthogonal frequency division multiplexing (OFDM) communication waveform. Using a low-cost off-the-shelf laser diode we experimentally demonstrate a joint OWC and sensing system, with data rates of approximately 3.6 Gbit/s with EVM around 8% and simultaneously able to localize targets with non-ideal reflectance surfaces, with 15 cm resolution. Our approach reduces installation and operational costs, alleviates the calibration process, as well as allows for cooperation between communication and localization functionalities at the physical layer. [ABSTRACT FROM AUTHOR]

Keywords: passive optical networks (PON); visible-light communication (VLC); light-emitting diodes (LED); optical wireless communication (OWC); infrared LED (IR-LED) EN passive optical networks (PON) visible-light communication (VLC) light-emitting diodes (LED) optical wireless communication (OWC) infrared LED (IR-LED) 379 383 5 07/05/22 20220701 NES 220701 1 Introduction Nowadays, requirements for high-speed and high-capacity networks are increasing with a great pace, more often in buildings, due to the greater use of Internet services and online games [[1], [3]]. To provide solution to microwave frequency-dependent communication, optical wireless communication using visible-light communication (VLC) is recognized as the potential way out and premier alternative based on low-cost light-emitting diodes (LEDs) [[5]]. Passive optical networks (PON), visible-light communication (VLC), light-emitting diodes (LED), optical wireless communication (OWC), infrared LED (IR-LED) 5 Wang Y, Wang Y, Chi N, Yu J, Shang H. Demonstration of 575-Mb/s downlink and 225-Mb/s uplink bi-directional SCM-WDM visible light communication using RGB LED and phosphor-based LED. [Extracted from the article]

With the remarkable advances in vertical-cavity surface-emitting lasers (VCSELs) in recent decades, VCSELs have been considered promising light sources in the field of optical wireless communications. However, off-the-shelf VCSELs still have a limited modulation bandwidth to meet the multi-Gb/s data rate requirements imposed on the next-generation wireless communication system. Recently, employing machine learning (ML) techniques as a method to tackle such issues has been intriguing for researchers in wireless communication. In this work, through a systematic analysis, it is shown that the ML technique is also very effective in VCSEL-based visible light communication. Using a commercial VCSEL and bidirectional long short-term memory (Bi-LSTM)-based ML scheme, a high-speed visible light communication (VLC) link with a data rate of 13.5 Gbps is demonstrated, which is the fastest single channel result from a cost-effective, off-the-shelf VCSEL device, to the best of the authors' knowledge. [ABSTRACT FROM AUTHOR]

Intensity modulation and direct detection (IM-DD) based optical wireless communication (OWC), requires the modulated signal to be real and non-negative. To satisfy the requirements, this paper proposes two types of mixed orthogonal frequency division multiplexing (X-OFDM) waveforms. The Hermitian symmetry (HS) characteristic of the sub-carriers in the frequency domain, guarantees the signal in the time domain to be real, which reduces the spectral efficiency to 1/2. For the odd sub-carriers in the frequency domain, the signal in the time domain after the inverse fast fourier transform (IFFT) is antisymmetric. For the even sub-carriers in the frequency domain, the signal in the time domain after the IFFT is symmetric. Based on the antisymmetric and symmetric characteristics, the two types of X-OFDM waveforms are designed to guarantee the signal in the time domain to be non-negative. With $M$ sub-carriers in the frequency domain, the generated signal in the time domain has $3M/2$ points, which further reduces the spectral efficiency to 1/3. The numerical simulations show that, the two types of X-OFDM waveforms greatly enhance the power efficiency considering the OWC channel with the signal-dependent noise and/or the signal-independent noise. [ABSTRACT FROM AUTHOR]

For upcoming futuristic communication systems, the Optical Wireless Communication (OWC) with its inherent advantages is becoming popular among service providers. The research in the past has primarily focused on Quality of service (QoS) aspect for OWC in the presence of atmospheric turbulence however, to assess the real time outcome of a service, the evaluation of both QoS and Quality of Experience (QoE) deliver a holistic approach. A much Less effort in the existing literature has been paid to this. Authors in this work attempt to determine the QoE for image transmission over a turbulent OWC link while considering the Structure Similarity Index (SSIM) as a visual performance indicator under varying turbulence strengths (regimes). A functional model to forecast the performance of SSIM practicable for all the regimes is proposed. The most suitable model is bimodal Gaussian mixture model which aptly describes the system performance. To improve the performance, spatial domain filters such as Median and Wiener filters have been employed. An increase of 125 m in the propagation distance and 5.88 dB in received SNR can be achieved while maintaining the SSIM at a 90% for median filter restoration in moderate turbulence regime for simulated values while predicted values suggest an increase of 115 m and 5.18 dB at same level. The results show that the proposed model is in good agreement with simulated values and median filter in moderate turbulence performs best out of all the situations. [ABSTRACT FROM AUTHOR]

Machine-learning (ML) can be employed to enhance the positioning accuracy of visible-light-positioning (VLP) system. To diminish the training time and complexity, the whole area is usually divided into several positioning unit cells. Most literatures only focus on the positioning performance within an unit cell, and assume the unit cell can be repeatedly duplicated to cover the whole area. In this work, we propose and demonstrate a positioning unit cell model duplication scheme, named as spatial sequence adaptation (SSA) process. We also propose and demonstrate a residual concatenation neural network (RCNN) and transfer learning (TL) to refine the model of the target positioning unit cell. A practical test-bed with vertical distance of 2.8 m consisting of two unit cells with dimensions of about 1.55 m × 2 m per cell is constructed. The client side is an autonomous mobile robot (AMR) for acquiring continuous training and testing data. Our experimental results reveal that high precision positioning in the duplicated unit cell duplication can be achieved. [ABSTRACT FROM AUTHOR]

This paper explores the effects of sunlight on using a low-cost off-the-shelf silicon solar panel as an optical wireless communication (OWC) receiver. A receiver circuit structure has been proposed to maximize simultaneous energy harvesting and data communication performance. An equivalent circuit model of the solar panel for simultaneous energy harvesting and wireless optical communication is discussed. By using the solar panel model, the effects of varying sunlight conditions on the performance of the model as an OWC receiver are estimated. Furthermore, an experimental setup is developed to study the effects and verify the simulated estimations. The experimental setup consists of a 3.5 m wireless optical link with a full Transmission Control Protocol and Internet Protocol (TCP/IP) network stack. The system uses DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM) to use the available communication bandwidth efficiently. A 940 nm low-cost off-the-shelf laser device along with an off-the-shelf off-axis-parabolic mirror is used as the transmitter. The maximum user throughput achieved over the air is 28.3 Mb/s while simultaneously harvesting energy using the maximum power point tracking (MPPT) technique. The peak power harvested with simultaneous communication is 4.5 W. The harvested energy is stored in a 38 Wh lithium-ion (Li-ion) battery. [ABSTRACT FROM AUTHOR]

To optimize the high-speed modulation package of the TO-can mounted violet laser diode (VLD) for optical wireless communication, three different impedance matching methods with adding or removing resistor/inductor/capacitor (R/L/C) elements are employed to discuss their effects on the direct encoding bandwidth of the VLD. With reducing the parasitic inductance by shortening the cathode/anode pin length of the TO-can VLD, the 2.5-mm-long pin acts as a series inductance to 1.74 nH to enormously improve the modulation bandwidth of the VLD for encoding the 16 quadrature amplitude modulation orthogonal frequency division multiplexing data as high as 20.4 GB/s. Neither the surface mounted device (SMD) resistor nor the SMD inductor in series connection can further improve the modulation bandwidth of the VLD. In contrast, a parallel connection of the VLD with Teflon ring capacitor can somewhat broaden its encodable bandwidth at low biased conditions, whereas the allowable bandwidth still degrades when increasing the VLD bias to enlarge its modulation throughput. Numerical simulations also verify that the shortening pin length (with reducing the inductance) of TO-can VLD is the best selection for bandwidth enlargement. With optimized impedance matching design, the comparison on data transmission characteristics for several 2.5-mm-pin VLDs with different rated powers is presented. [ABSTRACT FROM AUTHOR]

Optical wireless communication (OWC) has emerged as a complementary or alternative technology to the radio-frequency (RF) communication. OWC based on image sensor, which is also called optical camera communication (OCC) has attracted much attention from industrial and academic societies. Here, we discuss several recent OCC technologies. We propose and demonstrate a light emitting diode (LED) light panel and rolling shutter image sensor based OCC system using frame-averaging background removal (FABR) technique, Z-score normalization, and neural network (NN). Here, a driver circuit for the LED display panel based on a bipolar-junction-transistor (BJT) and a metal-oxide-semiconductor field-effect-transistor (MOSFET) is also discussed. It can provide low enough driving frequency from a few Hz to kHz and high bias current for the LED light panel. Experimental results show that the proposed scheme can mitigate the inter-symbol interference (ISI) observed in the rolling shutter pattern produced by the high noise-ratio (NR) of the display contents. [ABSTRACT FROM AUTHOR]

Optical wireless communication (OWC) technology has attracted many attentions recently. Lighting luminaries equipped with red-green-blue (RGB) based light-emitting-diodes (LEDs) or laser-diode (LDs) can modify the perceived color of illumination. These highly directional light sources with adjustable perceived colors makes them very suitable for high speed and high security data transmissions. Here, we propose and demonstrate a two-level LD based color-shift-keying orthogonal-frequency- division-multiplexing (CSK OFDM) signal for the OWC systems. This scheme cannot only provide non-flickering effect to minimize human health concern, but also can enhance the transmission data rate of the CSK system. Here, the system model and the implementation of bit and power loading algorithm on the LD-CSK-OFDM are discussed. Experimentally results show that the demonstrated LD-CSK-OFDM signal can achieve data rate of 28.4 Gbit/s with 1.25 m free-space transmission distance satisfying the forward-error-correction (FEC) threshold. [ABSTRACT FROM AUTHOR]

Featured Application: Wireless Communications and Networking. To meet the growing demand for wireless capacity, communications in the Terahertz (THz) and optical bands are being broadly explored. Communications within these bands provide massive bandwidth potential along with highly directional beam steering capabilities. While the available bandwidth offers incredible link capacity, the directionality of these technologies offers an even more significant potential for spatial capacity or area spectral efficiency. However, this directionality also implies a challenge related to the network's ability to quickly establish a connection. In this paper, we introduce a multi-tier heterogeneous (MTH) beamform management strategy that utilizes various wireless technologies in order to quickly acquire a highly directional indoor free space optical communication (FSO) link. The multi-tier design offers the high resolution of indoor FSO while the millimeter-wave (mmWave) system narrows the FSO search space. By narrowing the search space, the system relaxes the requirements of the FSO network in order to assure a practical search time. This paper introduces the necessary components of the proposed beam management strategy and provides a foundational analysis framework to demonstrate the relative impact of coverage, resolution, and steering velocity across tiers. Furthermore, an optimization analysis is used to define the top tier resolution that minimizes worst-case search time as a function of lower tier resolution and top tier range. [ABSTRACT FROM AUTHOR]

With the convergence of Information, telecom and broadband services, the digital TV broadcast has undergone a drastic change. For 5G and beyond, the Optical Wireless Communication (OWC) is gaining popularity as a distribution technology in access networks. However, OWC channel is undeterministic in nature due to its interaction with the atmosphere. A great deal of effort has been devoted in the existing literature to determine Quality of Service (QoS) performance for broadcast over an OWC channel whereas Quality of Experience (QoE) has been frequently overlooked. With this motivation, a holistic performance appraisal comprising of both QoS evaluation in terms of Symbol Error Rate (SER) and QoE assessment in terms of a visual indicator i.e. Structure Similarity Index (SSIM) is presented for a DVB-t image transmission over an OWC link under different turbulence regimes with Single Input Single Output (SISO) and Multiple Input Multiple Output (MIMO) systems. The results show that the improvements suggested by QoS from designer perspective need not necessarily pertain to quality enhancement at the end user side. [ABSTRACT FROM AUTHOR]

Visible light communication (VLC), popularly known as light fidelity (Li-Fi), is a promising alternative to overcome the limitations of radio-wave communication. VLC is a green technology which uses light-emitting diode (LED) illumination to transmit data without needing fibre cables. VLC is applicable for both indoor and outdoor communication. In this study, we investigate the effect of sandstorms on VLC via simulating a vehicular-to-road VLC (V2LC) outdoor application. Sandstorms are a weather phenomenon which frequently occurs in the Arab peninsula and other parts of the world; in this context, researchers have not thus far addressed the effect of sand particles, which absorb and scatter light, on VLC. Our simulation is conducted using MATLAB software (Natick, Massachusetts, U.S.A.), and the results show that the effect of sandstorms on VLC is similar to that of fog and rain as investigated by other researchers. However, sandstorms are also different in terms of the nature of sandstorm particles, with different sizes and refraction indices when compared with rain and fog particles. We also find that high-density-clay sandstorms, among other types of storms, most severely affect VLC communication and limit the transmission range. Other low- and medium-density storms less severely affect VLC while exhibiting a relatively larger communication range. [ABSTRACT FROM AUTHOR]

The atmospheric foggy condition is a major bottleneck for the deployment of optical wireless communication (OWC) systems in outdoor environments. Although the attenuation coefficient in the foggy channel follows the simple Gamma distribution, the distribution of its channel state is quite complicated similar to the well-studied Gamma–Gamma turbulence channel. Furthermore, existing literature suggested schemes that require feedback of the channel state information (CSI) to improve the outage performance of the OWC system under foggy conditions. In this article, we study the average signal-to-noise ratio (SNR), ergodic rate, and energy consumption performance of OWC systems under foggy conditions. First, we show that a single-aperture OWC system suffers significantly from the fog attenuation by deriving analytical expressions on the ergodic rate and energy consumption. Then, we consider a multiaperture OWC system equipped with an opportunistic receiver beam selection (RBS) scheme. The RBS scheme is based on the simple selection combining diversity algorithm, which does not require the knowledge of CSI. We analyze the proposed scheme by deriving computable bounds on the average SNR, ergodic rate, and energy consumption using system parameters and show the performance improvement of the RBS scheme comparing the single-aperture system. We demonstrate the performance of the considered scheme and validate derived expressions using computer simulations. [ABSTRACT FROM AUTHOR]

In the work, we propose and investigate a real-time optical wireless communication (OWC) system with 1 Gbps on–off keying (OOK) traffic rate for indoor and outdoor transmissions. Here, 1 Gbps OWC traffic with error-free operation can be achieved indoors under the free space transmission length of 500 m based on the simulation and experimental results. In addition, 952, 904, 476 Mbps throughput rates of proposed real-time OWC system are measured outdoors after passing through the wireless transmission lengths of 120, 300 and 500 m, respectively. [ABSTRACT FROM AUTHOR]

In this paper, we construct the autoencoder (AE) for optical wireless communication (OWC) systems with non-negativity and peak power constraints, which provides effective transceiver design in log-normal channel. We consider the cases where perfect channel state information (CSI) or noisy CSI can be obtained under three kinds of communication rate, which is defined as the ratio of channel use number to bit number. Meanwhile, we present the block error rate (BLER) performance to further demonstrate our transceivers’ superior performance than common model-based methods. The learned constellation points distribution is provided to understand the transmitter's performance. Numerical simulations are conducted to ensure the best convergence. The results indicate that AE-based transceivers can achieve model-based optimal BLER performance or provide significantly better BLER performance. [ABSTRACT FROM AUTHOR]

Among the challenges of realizing the full potential of light-fidelity (LiFi) cellular networks are user mobility, random device orientation, and blockage. In this paper, we study the impact of those challenges on the performance of LiFi networks in an indoor environment using measurement-based channel models, unlike existing studies that rely on theoretical channel models. In our paper, we adopt spatial modulation (SM) and consider two configurations for the user equipment (UE). A multi-directional receiver (MDR) structure is proposed, in which the PDs are located on different sides of the UE, e.g., a smartphone. This configuration is motivated by the fact that conventional structures exhibit poor performance in the presence of random device orientation and blockage. In fact, we show that the MDR outperforms the benchmark structure by over 10 dB at bit-error ratio (BER) of $3.8\times 10^{-3}$. Moreover, an adaptive access point (AP) selection scheme for the SM is considered, where the number of APs is chosen adaptively in an effort to achieve the lowest energy requirement for a target BER and spectral efficiency. The user performance with random orientation and blockage in the entire room is evaluated for sitting and walking activities, for which the orientation-based random waypoint (ORWP) mobility model is invoked. Furthermore, we demonstrate that the proposed adaptive technique with SM outperforms the conventional spatial multiplexing system. We also study the performance of the underlying system on the uplink channel where we apply the same techniques used for the downlink channel. It is shown analytically that the multi-directional transmitter (MDT) with adaptive SM is highly energy efficient. [ABSTRACT FROM AUTHOR]

This paper proposes a novel method of training and applying a neural network to act as an adaptive decoder for a modulation scheme used in optical camera communication (OCC). We present a brief discussion on trending artificial intelligence applications, the contemporary ways of applying them in a wireless communication field, such as visible light communication (VLC), optical wireless communication (OWC) and OCC, and its potential contribution in the development of this research area. Furthermore, we proposed an OCC vehicular system architecture with artificial intelligence (AI) functionalities, where dimmable spatial 8-phase shift keying (DS8-PSK) is employed as one out of two modulation schemes to form a hybrid waveform. Further demonstration of simulating the blurring process on a transmitter image, as well as our proposed method of using a neural network as a decoder for DS8-PSK, is provided in detail. Finally, experimental results are given to prove the effectiveness and efficiency of the proposed method over an investigating channel condition. [ABSTRACT FROM AUTHOR]

In optical wireless communication (OWC), conventional superimposed optical orthogonal frequency division multiplexing (OOFDM) techniques, such as hybrid asymmetrically clipped OOFDM (HACO-OFDM), require an additional operation of interference cancellation to decode transmitted symbols, which leads to relatively high receiver complexity with processing delay. In this letter, we propose a novel superimposed OOFDM scheme with low-complexity receiver, named as interference-free hybrid OOFDM (IFHO-OFDM), for OWC. In the proposed IFHO-OFDM, two hybrid OOFDM components are combined for simultaneous transmission to achieve the appealing advantages of high spectral efficiency, and a time-selective bias is designed to guarantee the non-negativity while maintaining high power efficiency. Moreover, we propose to superimpose the two hybrid OOFDM components in an interference-free way, and thus, it can be readily demodulated by a standard low-complexity OFDM receiver. Simulation results verified the superiority of the proposed IFHO-OFDM in terms of both peak-to-average-power ratio (PAPR) and bit error rate (BER) compared to HACO-OFDM. [ABSTRACT FROM AUTHOR]

In this paper, we consider a latency tolerant $2 \times n_{r}$ free space optical multiple-input multiple-output (FSO-MIMO) communication with a time diversity order of two. For this configuration, we propose an extended golden light code (E-GLC) construction that encodes data over two independent optical MIMO channel realizations. The main objective of this code construction is to jointly extract the spatial and the temporal diversity while keeping a multiplexing gain of two symbols per channel use. The proposed coding scheme is compliant with the optical intensity modulation and direct detection constraints that restrict the laser outputs to positive magnitude values with peak and average constraints. The error rate performance evaluations show that the E-GLC outperforms the other known replication-based schemes. [ABSTRACT FROM AUTHOR]

Layered/enhanced asymmetrically clipped optical orthogonal frequency division multiplexing (L/e-ACO-OFDM, shortened as L/e-ACO) has recently attracted increasing interests for the intensity-modulated directed-detected (IM/DD) optical wireless communication (OWC). This form of optical OFDM can achieve a high spectrum efficiency without a DC bias; however, similar to the conventional OFDM, L/e-ACO can results in a high peak-to-average power ratio (PAPR). In this paper, interleaved discrete-Fourier-transform-spread L/e-ACO (IDFTS-L/e-ACO) is proposed for the IM/DD OWC. Specifically, two kinds of IDFTS-L/e-ACO techniques are proposed. For readability, one is denoted as HS-IDFTS that implements Hermitian symmetry (HS) to generate real-valued signals, and the other is denoted as RI-IDFTS that employs the real and imaginary separation (RIS) to transform complex signals to real-valued ones. The theoretical analysis and Monte Carlo simulation show that both the IDFTS-L/e-ACO techniques have a smaller PAPR than the conventional L/e-ACO, and RI-IDFTS has even further smaller PAPR. In addition, bit-error-rate (BER) comparison indicates both HS-IDFTS and RI-IDFTS have better BER performance compared to the conventional L/e-ACO, and RI-IDFTS is least sensitive to LED nonlinearity and has the best BER performance. [ABSTRACT FROM AUTHOR]

Due to the extremely large path loss of non-line of sight optical wireless communication, the received signal exhibits the characteristics of discrete photoelectrons. In this paper, we investigate the achievable rates and signal detection of on-off keying modulation for discrete-time Poisson multiple access channel. Both non-orthogonal multiple access and code division multiple access are considered, for both single-rate and multi-rate multiple access channels. Maximum likelihood (ML) detections are adopted as the optimal criterion for signal detection, whose complexity grows exponentially with the number of users. Low computational complexity detections are proposed with $\mathcal {M}$ -order correction that can perform closely to the ML detection. Numerical and simulation results are presented to show the achievable rate regions, optimal power allocations, the performance of ML, and proposed low-complexity detections. Finally, the experimental results of the proposed detection approaches agree with the simulation results. [ABSTRACT FROM AUTHOR]

Optical wireless communication (OWC) is an age-long technology, which is based on optical data transmission through free space, and it can be implemented in both indoor and outdoor applications. Asymmetrically clipped DC-biased optical orthogonal frequency division multiplexing (ADO-OFDM) is a modulation scheme that can be utilized in indoor OWC systems. It is based on transmitting DC-biased optical OFDM (DCO-OFDM) for even-frequency subcarriers and asymmetrically clipped optical OFDM (ACO-OFDM) for odd-frequency subcarriers. The ADO-OFDM exhibits better optical power performance than those of the conventional ACO-OFDM and DCO-OFDM. The main disadvantage of ADO-OFDM is the clipping noise, which mainly affects the even subcarriers. So, in this paper, convolutional and turbo coding techniques are investigated to improve the bit error rate performance of the ADO-OFDM over Additive white Gaussian noise and diffuse channels. Simulation results show that the proposed coded ADO-OFDM using convolutional and turbo coding techniques achieves significantly lower BERs compared to that of the uncoded ADO-OFDM. In addition, turbo-coded ADO-OFDM gives the best BER performance. [ABSTRACT FROM AUTHOR]

In this paper, we consider a kind of optical wireless communications cooperative relaying systems where the relay node not only forwards the source's signal, but also transmits its own signal simultaneously. We propose an addition-decomposable relaying (ADR) protocol for the relay node. In the protocol, the demodulated signal from the source and the signal from the relay are superposed with a signal design method called additively uniquely decomposable constellation pair (AUDCP). An extended Farey sequence is established to formulate the feasible power ratio region of the AUDCP signal. The error performance of the signal pair is dominated by two consecutive terms in the sequence. Making full use of the properties of the extended Farey sequence, we analyze the transmission performance of the protocol, and derive the closed-form dominant terms of symbol error rates (SERs) of the signal pair. In addition, under the average optical power constraint, we optimize power allocation for the cooperative system to minimize the average SER at the destination node. Simulation results demonstrate that the approximate SERs derived are close to the actual ones in high signal to noise ratio regimes, and the error performance of ADR outperforms that of conventional schemes. [ABSTRACT FROM AUTHOR]

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In this paper, we propose an indoor image sensor communication (ISC) system comprising an attentive indoor environment in which rolling-shutter cameras (including smart phone cameras) are used to receive data from light sources. The challenges of intended system mainly come from the receiver side, including its rolling shutter mechanism, its low and time-variant frame rate (e.g., no greater than 30 fps), and the narrow bandwidth response (i.e. several kHz baseband). Also, the requirements of flicker-free modulation enabling the dimming capacity, and indoor distance (i.e., up to 10 m) are unmitigated challenges. To resolve all mentioned challenges, we propose new hybrid modulation schemes, including M-ary frequency-shift keying (M-FSK) modulation and a hybrid modulation of M-FSK and phase-shift keying (2-PSK) for ISC. Simulation, numerical analysis and experiment results are given to illustrate the feasibility of the intended system. [ABSTRACT FROM AUTHOR]

We experimentally evaluate the performance of underwater wireless optical communication (UWOC) links in the presence of different air bubbles. Air bubbles of different sizes and densities are generated by using an air pipe in conjunction with a submersible water pump of variable flow rate that helps break up large bubbles into smaller bubbles. Received signal intensity measurements show that bubbles significantly degrade the performance of UWOC links. Large bubbles completely obstruct the optical beam and cause a deep fade. However, as the bubble size decreases, the level of deep fade also decreases because the optical beam is less susceptible to complete obstruction, and more light reaches the detector. We also show that beam expansion could help mitigate the performance degradation due to the deep fade caused by air bubbles scatters in the channel. [ABSTRACT FROM PUBLISHER]

This technical paper introduces an optical camera communication system for vehicles. The purpose of the communication system incorporated into car (using existing light-emitting diode (LED) lights and ordinary cameras) is to add region-of-interest signaling functionality for cars via either their headlights or taillights. A low-data-rate but reliable link via the optical channel is the objective. In particular, the communication system, contributes a spatial modulation approach called spatial-2-phase-shift keying (S2-PSK) that uses a pair of optical light sources on a car (either a pair of rear-LEDs or a pair of front-LEDs) as a transmitter. A typical camera (i.e., less than 30 frames/s), either a global shutter or a rolling shutter, can be used to receive light-modulated data. As a remarkable physical layer (PHY) operating mode among image sensor communication PHY modes recently contributed to IEEE 802.15.7r1 (TG7r1), the communication system, along with technical details on the S2-PSK communication protocol, is described in this paper. In addition, in order to deal with the noisy optical channel and the low-performance challenge of a camera receiver, we have suggested a rate-1/2 line coding and an intelligent decoding approach in our intended vehicular communication scenario. Finally, numerical analyses on the performance of our system and experiment results are addressed. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a space time code construction with a symbol rate of two for free space optical multiple input multiple output (FSO-MIMO) communication systems. Unlike the radio-frequency space time coding design that deals with complex symbols holding phase and magnitude information, the phase detection in wireless optical communications remains very challenging. This restricts optical MIMO codes to carry positive magnitude information belonging to a finite range. To meet these requirements, we propose to design the FSO-MIMO codes considering first the whole real space \mathbb R , followed by a bipolar to unipolar conversion to fit in the intensity margin. We consider the MIMO configurations with two or four transmitters (lasers). We base our shape-preserving construction on quadratic extension fields that linearly combine the real symbols to form a full diversity space time code with a symbol rate equal to two. For each configuration, we show how to optimize the choice of the algebraic field numbers to jointly optimize the non-vanishing code determinant and the bipolar to unipolar attenuation factor. [ABSTRACT FROM PUBLISHER]

LED-based visible light communications can provide high data rates to users. This can be further increased by the use of wavelength division multiplexing using the different colours required to generate white light to transmit different data streams. In this paper, a trichromatic approach is described and the influence of colour combination on achievable data rate is analysed. A demonstration of LED-based communications which achieves a data rate of >10 Gb/s by using a rate adaptive orthogonal-frequency-division-multiplexing scheme is also reported. [ABSTRACT FROM PUBLISHER]

This paper presents a modulation scheme in the time domain based on On-Off-Keying and proposes various compatible supports for different types of image sensors. The content of this article is a sub-proposal to the IEEE 802.15.7r1 Task Group (TG7r1) aimed at Optical Wireless Communication (OWC) using an image sensor as the receiver. The compatibility support is indispensable for Image Sensor Communications (ISC) because the rolling shutter image sensors currently available have different frame rates, shutter speeds, sampling rates, and resolutions. However, focusing on unidirectional communications (i.e., data broadcasting, beacons), an asynchronous communication prototype is also discussed in the paper. Due to the physical limitations associated with typical image sensors (including low and varying frame rates, long exposures, and low shutter speeds), the link speed performance is critically considered. Based on the practical measurement of camera response to modulated light, an operating frequency range is suggested along with the similar system architecture, decoding procedure, and algorithms. A significant feature of our novel data frame structure is that it can support both typical frame rate cameras (in the oversampling mode) as well as very low frame rate cameras (in the error detection mode for a camera whose frame rate is lower than the transmission packet rate). A high frame rate camera, i.e., no less than 20 fps, is supported in an oversampling mode in which a majority voting scheme for decoding data is applied. A low frame rate camera, i.e., when the frame rate drops to less than 20 fps at some certain time, is supported by an error detection mode in which any missing data sub-packet is detected in decoding and later corrected by external code. Numerical results and valuable analysis are also included to indicate the capability of the proposed schemes. [ABSTRACT FROM AUTHOR]

As a spatial diversity transmission scheme, repetition code (RC) is conjectured to be optimal in the sense of error performance for an intensity modulated direct detection multi-input-multi-output optical wireless communication (IM/DD MIMO-OWC) over log-normal fading channels. Despite the fact that all the experimental evidences thus far have strongly demonstrated that this hypothesis is indeed true, its mathematical proof remains a long-standing open problem mainly due to the lack of an explicit signal design criterion like MIMO radio frequency communications. In this letter, subject to two commonly used power constraints, we prove the optimality of RC under a much weaker condition in the sense of maximizing both large-scale and small-scale diversity gains for any space signalling using the recently established pair-wise error probability design criterion for a maximum likelihood (ML) detector. [ABSTRACT FROM PUBLISHER]