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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]

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]

This study presents insights into high-speed optical wireless communication (OWC) within plastic pipes, introducing a Gbps-capable alternative for challenging environments. Utilizing a 1W LED with five wavelengths, the experiment explores signal power, attenuation, and bandwidth characteristics. Notably, the blue LED achieves an unprecedented 58.64 MHz bandwidth, red and purple LEDs demonstrate novel bandwidths of approximately 25.23 MHz, and green and yellow LEDs exhibit unique bandwidths of 23.75 MHz and 9.62 MHz, respectively. The attenuation parameters for different wavelengths provide numerous insights, showcasing the novelty of this research and its potential applications in robot communication within plastic pipes. Concurrently, the paper introduces an approach to address the temperature impact on five distinct wavelength LEDs in OWC. By focusing on variations in LED bandwidth and optical power, an optimal heat sink design is proposed. This design achieves a remarkable minimum temperature of 27.06°C and reduces the chip LED device’s response time from 15 to 9 seconds. The significance lies in the novelty of the proposed heat sink, which incorporates variables such as fin thickness, height, air gap width, number of fins, and airflow rate, marking a substantial advancement in thermal management for OWC systems.

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.

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.

Optical wireless communication (OWC) has emerged as a promising solution to the radio spectrum crunch. OWC technology requires more access points (APs) compared to other wireless technologies, making it crucial to have reliable OWC APs to ensure low repair rates and optimal network availability. To address this, our paper provides methods to enhance the reliability of duplex OWC AP transceivers and calculates their reliability parameters. The transceiver design consists of several independent modules, and we calculate the failure in time (FIT) for each module using MTBF calculator software and component datasheets. Our reliability analysis includes two methods: mean time between failure (MTBF) calculations using reliability block diagrams and Markov chain modeling. The former identifies modules with a high failure rate and determines the system’s cumulative downtime or repair time, while the latter accounts for the repair rates of individual modules for availability calculations. Both methods complement each other and provide insight into fault-tolerant system designs. Furthermore, we perform a life cycle cost analysis of the proposed fault-tolerant transceiver designs to facilitate appropriate design choices for different applications.

We put forward and demonstrate a steerable optical beam visible light communication (VLC) system combining orthogonal frequency division multiplexing (OFDM) and non-orthogonal multiple access (NOMA) schemes, and utilizing a spatial light modulator (SLM)-based reconfigurable intelligent surface (RIS) for beam steering. When utilizing the SLM as RIS for optical beam steering, its operation principle, maximum achievable steering angle (i.e., field-of-view, FOV), as well as the corresponding loss should be analyzed. We theoretically and experimentally analyzed in detail the characters of SLM when acting as the RIS. Experimental results demonstrate the flexibility of both active beam control and data rate allocation for multiple users. The SLM-based RIS can independently and simultaneously control multiple beams, and significantly reduce the deploying cost of the increase in the devices for the multi-beam handling scenario. All of the specified channels under evaluation satisfy the pre-forward error correction bit-error rate limit (pre-FEC BER = 3.8 × 10−3).

Single-photon avalanche diodes (SPADs) capable of single photon detection are promising optical sensors for use as receivers in optical wireless communication (OWC) systems. In SPAD-based receivers, the intersymbol interference (ISI) effect caused by dead time is an important drawback that limits performance. In this paper, we propose two novel SPAD operation modes to reduce the ISI effect in SPAD-based OWC. To validate the feasibility of these two modes, we designed a free-running SPAD front-end circuit with post-layout transient simulation results and some measurements to show its function and performance. This SPAD circuit is improved by a novel mixed passive-active quench and reset front-end circuit that achieves a very short dead time. Based on the traditional free-running mode, we design the clock-driven mode and time-gated mode to reduce the ISI effect through time-controlled operating signals. To accurately evaluate these three modes, we develop a new simulation system to assess the ISI effect in On-Off Keying (OOK) modulated communication. The simulation results demonstrate that the clock-driven mode and time-gated mode receivers can improve the bit error rate (BER) performance in low data rate communication and high data rate high optical power communication, respectively. Moreover, compared to the free-running mode, the two proposed time-controlled modes achieve higher data rate communication and better noise tolerance ability in SPAD-based OWC.

The combined use of distributed multiple-input multiple-output (D-MIMO) and orthogonal frequency division multiplexing (OFDM) with adaptive bit and power loading is seen as a powerful tool to overcome limitations of the optical wireless communication (OWC) channel and of light-emitting diodes (LED)s. Although extensive research into efficient MIMO algorithms has been performed for communications via radio, these may not be indiscriminately re-used in LED-based OWC systems. The main reasons are that the OWC channel has different properties, the LEDs have power-constraints, and eye-safety regulations apply. For adoption in a practical system, the computational complexity of the algorithms must also be taken into account. Fortunately, physical properties of the LED D-MIMO channel allow us to reduce signalling overhead, estimation effort and complexity. This paper presents, compares, and discusses both the performance and the computational cost of several new power-loading strategies to enhance the throughput of LED-based OFDM D-MIMO OWC systems respecting the individual power constraints of the light sources. To cope with the low-pass nature of LEDs, we optimize how much power to load on each MIMO spatial stream, on each sub-carrier and what bandwidths to use. The CVX toolbox for convex optimization gives us an optimum but it is orders of magnitude more complex than highly effective heuristic approaches. A simple approach stays 1 dB short of the optimum: it equally splits power among MIMO streams within the LED power constraints, and it uniformly spreads the power over a bandwidth that is optimized per stream. A similar strategy, but selecting optimized powers per stream brings us as near as 0.1 dB to the optimum. To evaluate the complexity of bit and power allocations, we investigate, optimize, and accelerate the speed of iterative schemes. The proposed approaches give new choices for chipset manufacturers and LED-based OFDM D-MIMO OWC system designers to improve performance and to reduce overhead.

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]

This paper introduces a new hybrid system for high-bandwidth and high-transmission-capacity communication. The system integrates a multi-mode fiber (MMF) cable with free space optics (FSO) using orbital angular momentum (OAM) multiplexing. The proposed system uses a single wavelength to simultaneously transmit 40 Gb/s data on four distinct OAM beams ((LG0,0, LG0,17, LG0,40, and LG0,75)) with a symmetric circular shape. The performance of the system was evaluated with a fixed MMF length of 100 m and varying FSO ranges, according to extreme climate changes such as rain and fog, and atmospheric turbulences. The results indicate that the suggested system is capable of transmit up to 1250 m (100 m MMF length + 1150 m FSO range) under clear weather (CW) and weak turbulence (WT), with a minimum transmission distance of 440 m (100 m MMF length + 340 m FSO range) under heavy fog (HF). The performance of the system was also demonstrated based on actual meteorological data for two different cities, Alexandria, Egypt and Chandigarh, India, with different visibility ranges and geographical locations. Since Alexandria has a longer visibility range than Chandigarh, our proposed model could spread over a larger area than it could be in Chandigarh. The obtained ranges were within an acceptable bit error rate (BER) of less than 10−9. The system’s maximum range was 1200 m for Alexandria and 1100 m for Chandigarh. The proposed model can be suggested for use in next generation (NG) passive optical networks (PON) for supporting symmetric 40 Gb/s data.

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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]

We put forward and provide the first illustration of a high capacity and high spectral efficient free space optical communication (FSOC) system using digital domain power division multiplexing orthogonal-frequency-division-multiplexed (DDPD-O-OFDM) signal utilizing 10-GHz class optical components. In the proof-of-concept demonstration, a data rate of 2 × 30.8 Gbit/s can be achieved for each polarization multiplexed wavelength channel, fulfilling the pre-forward-error-correction bit-error-ratio (pre-FEC BER = 3.8 × 10−3). By employing the DDPD-O-OFDM here, the FSOC per channel capacity can be enhanced not only allowing the spectral overlapping of different orthogonal subcarriers, as in the case of OFDM; but also allowing channel multiplexing in the power domain to increase the spectral efficiency. The principle of DDPD-O-OFDM is discussed; and BER and signal-to-noise ratio (SNR) of different DDPD channels are experimentally measured.

We propose to utilize a commercially available DIALux lighting design software for simulation and planning of machine learning (ML) based angle-of-arrival (AOA) visible light positioning (VLP) systems. Here, different ML models, for example, second order linear regression (LR), artificial neural-network (ANN), and convolutional neural-network (CNN) are employed. The proposed VLP simulator works well with different ML algorithms. The results show that the proposed scheme can acts as an effective indoor VLP planning and design tool. Besides, it may also alleviate the training data collection in ML based VLP systems.

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]

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 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.

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]

Optical wireless communication (OWC), the IEEE 802.15.7 standard (revised 2018) is developed in normative reference to low-rate wireless personal area networks IEEE 802.15.4 standard. One significant difference between the two standards is the highly directional transmitters in the OWC networks. This difference opens up the possibility of adding full-duplex communication to wireless networks. Our work proposes adding full-duplex functionality in the contention-free period (CFP) of the OWC media access control (MAC) layer. We justify the significance of our proposal by implementing IEEE 802.15.7 resource allocation scheme for both our proposed full-duplex optical MAC (FD-OMAC) and the IEEE 802.15.7 MAC. Our simulation results demonstrate that the proposed work improves the spectral efficiency in the CFP without compromising delays. We also discuss the minor changes required in the IEEE 802.15.7 MAC for implementing FD-OMAC. We further extend the FD-OMAC to a multiple access point network and evaluate its performance in comparison with IEEE 802.15.7 MAC.

Recently, traffic demand for wireless data has increased the need for extending the spectrum to transmit numerous signals. However, the bandwidth of radio waves has been scrunching in the last few years with tremendous development of technology such as 4G, 5G, Internet of Thing (IoT) and so on. Therefore, in a few recent years, LiFi technology which is considered a complement solution for radio frequency technology has attracted a lot of attention in scientific community. LiFi, which is a part of optical wireless communication (OWC), employs visible light from the green and eco-friendly light emitting diode (LED) to forward signals. In addition, LiFi is best-known for high-speed, bi-directional connection, save energy, security network, and safe for human. Because of the potential advantages that LiFi benefits in, we investigated to analyze the possibility to deploy indoor wireless networks based on LiFi technology with the existing infrastructure of LEDs and PoE cables. Moreover, in this study, we proposed the wireless network model in a typical office with nine LED luminaires positioned in the center of the room ceiling that support to intensify the illumination and communication in an entire room. Additionally, the received power of optical signals and signal-to-noise ratio (SNR) level in the proposed model were calculated and simulated with the MATLAB program. The study of these parameters advocates deploying the network system more effectively.

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.

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.

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]

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.

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.

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]

This paper introduces a new hybrid waveform for optical wireless communication (OWC)/optical camera communication (OCC) systems and discusses the technical considerations of these systems. In a challenged vehicular communication environment, which requires high-speed, high-mobility, and long-distance communication support, implementing a hybrid waveform guarantees high-speed data transmission while reducing the cost of the OWC/OCC systems. The application of a hybrid waveform in the OWC/OCC systems is known as the region-of-interest (RoI)-signaling technique. This technique allows the OWC/OCC systems to simultaneously transmit low-rate and high-rate data streams. The low-rate data stream is used to detect and track the RoI of light sources for setting up the communication link, whereas the high-rate data stream is used for high-speed data transmission. Selection of proper modulation schemes for two simultaneous data streams is also discussed in this paper. A new modulation scheme, such as spatial-2-phase-shift-keying (S2-PSK), is proposed for the low-rate data stream. This scheme has been used to modify the IEEE 802.15.7-2018 standard, which is the revised version of the IEEE 802.15.7-2011 standard. For the high-rate data stream, single-carrier modulation or multiple-carrier modulation, such as the proposed hybrid-spatial-phase-shift-keying (HS-PSK) or variable pulse-position modulation (VPPM), can serve as viable solutions. Technical considerations for the modulation schemes of each type of data stream are analyzed to determine the feasibility of the proposed schemes. Finally, the experimental results and numerical parameters of the intended system are presented.

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.

In this work, we demonstrate an integrated optical baseband, free space optical (FSO) communication and millimeter-wave (MMW) traffics through the present passive optical network (PON) architecture by utilizing single wavelength for broadcasting triple-play services. In the execution, we exploit 10 Gbit/s on-off keying (OOK) modulation on 10 GHz Mach-Zehnder modulator (MZM) to produce the downstream baseband signal. And the 10 Gbit/s baseband signal also can cause FSO traffic within the forward error correction (FEC) target after 25 km fiber and 160 m free space transmissions. Moreover, we can utilize the fiber to the extension (FTTE) scheme to provide the 36.42 GHz MMW with 10 Gbit/s OOK data after 25 km fiber link and 8 km extended fiber transmission.

The use of solar cells as photodetectors in Optical Wireless Communications (OWC) systems, is acquiring an increasing attention. This is due to the fact that a solar cell can detect an incident optical signal without the need to be biased by an external dc source, unlike traditional photodetectors. Basically, solar cells are designed to be used in solar energy harvesting systems. However, the solar cells are used during the day time and they remain idle at night. Then, they can be used in other applications, such as optical signal detection during night hours. Moreover, the efficiency of solar systems and solar receivers can be maximized by using dual axis light source tracking, to keep the cell orientation at the direction that results in the maximum electrical output. Therefore, in this paper, a solar cell positioning algorithm is proposed to track the maximum power point of both of the sun at day time and the optical communication signal at night. The proposed system can automatically distinguish between its two operation modes and then provides the necessary control. The proposed system is implemented and tested under realistic outdoor environment. It showed an accurate detection of the operation situation and also an accurate and smooth positioning during the specific operation mode. The measurement of the generated and consumed power by the designed system has emphasized it feasibility.

In order to increase transmission capacity, multiplexing schemes in different physical dimensions, including time, frequency, modulation quadrature, polarization, and space, can be employed. In this work, we propose and demonstrate a red color laser-diode (LD) based visible-light-communication (VLC) system using two kinds of digital domain multiplexing schemes, orthogonal-frequency-division-multiplexing (OFDM) and power-domain division-multiplexing (PowDM). The two digital domain multiplexed data can achieve data rates of 1.66 Gbit/s and 6.41 Gbit/s, respectively, providing a total data rate of 8.07 Gbit/s, fulfilling the pre-forward error correction (pre-FEC) bit-error-rate (BER) limit. The measured signal-to-noise ratios (SNRs) are 10.96 dB and 14.45 dB, respectively. Here, similar to OFDM, the PowDM can enhance the total system capacity by allowing acceptable signal spectra overlapping among different power division signals to maximize the bandwidth utilization. An experiment to verify and evaluate the proposed work is performed. The modulation and demodulation of OFDM and PowDM are discussed. The optimum power levels of the individual signals in the PowDM signal are also analyzed.

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]

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]

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.

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.

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.

The IEEE 802.15.7r1 Optical Wireless Communications Task Group (TG7r1), also known as the revision of the IEEE 802.15.7 Visible Light Communication standard targeting the commercial usage of visible light communication systems, is of interest in this paper. The paper is mainly concerned with Image Sensor Communications (ISC) of TG7r1; however, the major challenge facing ISC, as addressed in the Technical Consideration Document (TCD) of TG7r1, is Image Sensor Compatibility among the variety of different commercial cameras on the market. One of the most challenging but interesting compatibility requirements is the need to support the verified presence of frame rate variation. This paper proposes a novel design for 2D-sequential color code. Compared to a QR-code-based sequential transmission, the proposed design of 2D-sequential code can overcome the above challenge that it is compatible with different frame rate variations and different shutter operations, and has the ability to mitigate the rolling effect as well as the rotating effect while effectively minimizing transmission overhead. Practical implementations are demonstrated and a performance comparison is presented.

In this paper, the design of linear full-diversity space code (FDSC) is considered for an intensity-modulated direct-detection multiple-input-multiple-output optical wireless communication (IM/DD MIMO-OWC) system, in which the channel suffers from log-normal fading and different links have different variances. Utilizing our recently established error performance criterion for the design of FDSC with a maximum-likelihood detector, we formulate the design problem of optimizing both large-scale diversity gain and small-scale diversity into a max-min optimization problem with continuous-discrete mixed design variables. We propose the use of the Farey sequence in number theory as a powerful tool to solve this kind of optimization problem. By taking advantage of some available properties and by developing some new interesting properties on the Farey sequence, a closed-form solution is attained for IM/DD MIMO-OWC equipped with two transmitters and multiple receivers. This optimal design shows that a repetition code with an optimal power allocation is optimal.

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]

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]

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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