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The work offered the analysis comparison study of optical wireless intersatellite link (ISL) for both different bit sequence generators and filters. The study clarifies the impact of varying sorts of both bit sequence generator (data source) in the transmitter and electrical filters in receiver on system performance. The two bit sequence generators used are pseudo random bit sequence generator (PRBSG) and user-defined bit sequence generator (UDBSG). The used filters in this study are low pass (LP) Bessel filter, LP Gaussian filter, LPCROF (cosine roll-off filter), and LPSCROF (squared CROF). Performance of the filter depends on the order of filter and filter bandwidth. The performance parameters in our study are quality factor, Bit Error Rate (BER), and optical received power. In this study, variation of optical received power depends on the type of sequence generator because it is measured after the channel directly.

In the realm of optical wireless communication (OWC), augmented spectral efficiency discrete multitone (ASE-DMT) has been widely recognized as a promising modulation due to its outstanding spectral efficiency and high power efficiency. However, ASE-DMT exhibits an inherently high peak-to-average power ratio (PAPR), which exacerbates error propagation and leads to a substantial transmission performance degradation in the successive interference cancellation (SIC) receiver of ASE-DMT. Therefore, a novel low-PAPR ASE-DMT scheme (LP-ASE-DMT) is proposed in the paper. Given the intricate multi-depth signal superposition of ASE-DMT, a progressive multi-level constellation extension algorithm is developed to effectively suppress the PAPR of the transmitted signal, while simultaneously achieving much lower computational complexity compared to conventional constellation extension schemes. Furthermore, a dedicated receiver architecture is designed for LP-ASE-DMT, in which a low-complexity modulo operation is employed to eliminate the impact of constellation extension without incurring significant additional receiver complexity. The effectiveness of the proposed LP-ASE-DMT scheme is validated through simulation, revealing a substantial mitigation of PAPR compared to its counterparts. This improvement notably strengthens the system’s robustness to nonlinear impairments. Consequently, LP-ASE-DMT enjoys superior performance across multiple metrics, including bit error rate (BER), power efficiency, and spectral efficiency.

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.

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.

The Internet of Underwater Things (IoUT) is revolutionizing underwater communication by enabling real-time data exchange, environmental monitoring, and exploration in aquatic environments. Among emerging technologies, optical wireless communication (OWC) has gained prominence due to its high-speed data rates and superior efficiency compared to traditional acoustic and radio frequency (RF) methods. This paper presents a comprehensive study of OWC channel modeling and simulation tailored for IoUT applications. The research investigates the physical characteristics of underwater optical channels, focusing on the effects of absorption, scattering, turbulence, and various noise sources on light propagation across diverse water types, including pure seawater, clear coastal waters, and turbid harbor waters. A central aspect of the study is the comparative evaluation of two transmitter types—light-emitting diode photo sources (LED-PS) and laser diode photo sources (LD-PS)—both operating at a 520 nm wavelength (green light). Their performance is assessed under varying environmental conditions, incorporating three turbulence models: log-normal, generalized gamma, and Weibull distributions. Simulation models are developed and implemented using MATLAB and Python to analyze key parameters such as transmission distance, water type, transmitter characteristics, wavelength, and turbulence intensity. Performance metrics, including received optical power, signal-to-noise ratio (SNR), and bit error rate (BER), are evaluated to provide in-depth insights into system behavior. Results show that LD-PS consistently outperforms LED-PS across all scenarios. For instance, at a received power threshold of − 53.4 dBm, LD-PS achieves a communication distance of up to 68.39 m in pure seawater (compared to 27.36 m for LED-PS), while in turbid harbor, the range is reduced to 3.08 m. At a BER of 10 −5 , LD-PS reaches 67.69 m in pure seawater and 3.18 m in turbid harbor conditions. Under a fixed SNR of 50 dB, LD-PS achieves a maximum range of 73.34 m in pure sea. The minimum SNR required to maintain a BER of 10 −5 is 12.19 dB in pure seawater and rises to 91.94 dB in turbid harbor conditions. These findings advance the development of OWC systems by providing practical guidelines for optimizing underwater communication performance. The insights presented serve as a foundation for designing robust and efficient IoUT networks capable of reliable data transmission across a range of aquatic environments.

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.

We demonstrated a full duplex hybrid passive optical network and indoor optical wireless system employing coherent optical frequency division multiplexing. To accomplish reliable transmission in passive optical networks integrated visible-light communication (VLC), yellow light-emitting diode and infrared LED is used in downstream and upstream, respectively, for intra building network. In order to support high data rate, pulse-width reduction scheme based on dispersion compensation fiber is incorporated and system successfully covered the distance of 50 km. A data stream at the rate of 30 Gb/s is transmitted for each user out of eight users. VLC-supported users are catered with the bit rate of 1.87 Gb/s over 150 cm and in order to realize a low-cost system, visible and infrared LEDs are used in downlink and uplink, 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.

The extensive use of wireless communication in recent years is due to the requirement of huge data transfer. Nowadays the optical wireless communication (OWC) in which the light is used for wireless connectivity is extensively used. Huge spectral resource, low bandwidth requirements and high speed of operation are the main asset of OWC. The major challenge of OWC system is the effect of different weather conditions as the air is used as a transmission medium in OWC. The variations in different weather conditions have a significant impact on the effectiveness of OWC system as they degrade the performance of OWC system. This paper compares the performance of NRZ-DQPSK OWC system with different filters (Bessel filer, Gaussian Filter and Trapezoidal filter) and the effect of different weather conditions (rain, haze and clear weather) on NRZ-DQPSK system is analyzed over different transmission distances. The comparison is done in terms of quality factor or Q-factor.

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.