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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.

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.

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.

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.

DC-Offset Orthogonal Frequency Division Multiplexing (DCO-OFDM) is a popular modulation method for Optical Wireless Communication (OWC) as it can assign specific power levels and constellations to different subcarrier frequencies across the low-pass response of the LED. However, LEDs exhibit dynamic non-linearities to which OFDM is very sensitive. As LED signals are subject to non-linear memory effects in photon generation, different OFDM subcarriers experience different amounts of distortion. This letter translates the LED behavior into a communication channel model for OFDM modulation. It gives an experimentally verified expression for the Signal-to-Distortion Ratio (SDR) as it varies per subcarrier in OFDM systems.

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 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.

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.

This paper proposes a novel design of an optical wireless communications (OWC) receiver using a solar panel as a photodetector. The proposed system is capable of simultaneous data transmission and energy harvesting. The solar panel can convert a modulated light signal into an electrical signal without any external power requirements. Furthermore, the direct current (DC) component of the modulated light can be harvested in the proposed receiver. The generated energy can potentially be used to power a user terminal or at least to prolong its operation time. The current work discusses the various parameters which need to be considered in the design of a system using a solar panel for simultaneous communication and energy harvesting. The presented theory is supported with an experimental implementation of orthogonal frequency division multiplexing (OFDM), thus, proving the validity of the analysis and demonstrating the feasibility of the proposed receiver. Using the propounded system, a communication link with a data rate of 11.84 Mbps is established for a received optical signal with a peak-to-peak amplitude of 0.7×10-3 W/cm2.

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.

Light Emitting Diode (LED), which is the most promising technology for lighting, offers potential synergy for illumination and wireless data transmission. Optical wireless communication (OWC) based on white LEDs provides several advantages over the radio based wireless systems, i.e. license free spectrum, low power consumption, high privacy. Here, we report two indicative indoor OWC configurations assuming illumination levels at the receiver compliant with the standards demonstrated by our group.

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.