Indoor Visible Light Communication Channel Research Articles

Development and evaluation of a free-form-based optical antenna with enhanced channel performance

Optical receiving antennas play a pivotal role in enhancing the communication quality of visible light communication (VLC) systems. In this study, we propose an innovative optical receiving antenna based on free-form surfaces. Initially, the layout scheme for the LED array is meticulously optimized to ensure uniform indoor illumination. Subsequently, a three-piece integrated optical receiving antenna is designed using XY polynomial free-form surfaces with the primary objectives of amplifying the optical gain, augmenting the received power, and elevating the signal-to-noise ratio (SNR). To further validate the efficacy of the proposed optical receiving antenna, an indoor VLC channel model is established, and its performance is rigorously analyzed. Experimental outcomes reveal that the mean square error of indoor illumination stands at 113.3 lx, the optical gain of the free-form optical receiving antenna reaches an impressive 11.29, the semiregular field of view spans 35.2°, the average received power amounts to 6.1251 dBm, the average SNR attains 84.7054 dB, and the radius of the optical spot is a mere 1.5 mm. Consequently, the optimized free-form optical receiving antenna can guarantee high-speed and stable communication within indoor VLC systems, thereby furnishing crucial technical support for the advancement of VLC communication technology.

Semantic-empowered visible light communication for image transmission based on deep convolutional generative adversarial network

In this paper, a semantic communication-based scheme was proposed to tackle the optimization challenge of transmission efficiency and link stability in indoor visible light communication (VLC) systems utilizing light-emitting diodes for image transmission. The semantic model, established by deep convolutional generative adversarial network (DCGAN) and vector quantization method, can effectively extract the essential characteristics of images. In addition, indoor VLC channel models including line-of-sight (LOS) and non-line-of-sight (NLOS) links are established in a 5*5*3 room, while incorporating noise interference encountered during signal transmission into the training process of the semantic model to enhance its anti-interference capability. Besides, the performance disparity between the semantic VLC system and the conventional VLC system using Better Portable Graphics (BPG) is assessed across various modulation formats, transmission distances, and receiving locations. The simulation results demonstrate that the semantic VLC system effectively enhances link stability and achieves a signal-to-noise ratio (SNR) gain exceeding 6 dB. Additionally, the semantic VLC system achieves superior performance compared to the conventional VLC system employing convolutional code at a rate of 1/2, without incurring additional bits consumption for error correction. Moreover, the practicality of the semantic VLC system is experimentally validated on an indoor physical testbed online enabled by the field programmable gate array (FPGA) with up to 1 Gbps data rate. In comparison with existing schemes, the semantic VLC system effectively reduces communication overhead by 40% while maintaining similar received image quality. Furthermore, it significantly enlarges the communication coverage of the VLC system by a factor of two without necessitating any hardware modifications and ensures stable transmission of images in high-speed scenarios.

A visible light positioning system for coal mine personnel based on convolutional recurrent neural network

Visible Light Positioning (VLP) technology exhibits promising potential for underground coal mine positioning. While numerous studies have explored VLP in indoor environments, attention to VLP systems for underground mines still needs to be improved. In this paper, based on the traditional indoor visible light communication channel model, the effects of unique features on VLP, such as irregular walls, inclined and rotating receiving ends, and coal dust particles in underground mines, are considered and modeled in detail. In order to improve the accuracy and reliability of personnel VLP in complex mine environments, this paper proposes a deep-learning-based VLP system for underground personnel in coal mines, which consists of two LEDs and four photodetectors (PDs), where the four PDs are mounted on miners' helmets, in conjunction with the actual mine environment. Due to environmental factors and noise, there are apparent spatio-temporal characteristics in the received signal strength of the PDs. Therefore, the system adopts a convolutional recurrent neural network (CRNN) for feature extraction. In the experimental phase, the method's average localization error was 11.24 cm, with 90% of the localization errors within 20.4 cm. The experimental results show that the system has high positioning accuracy and meets the requirements of personnel positioning in underground mines.

Research on channel modeling technology of visible light communication system based on the ray tracing method

Abstract Visible Light Communication (VLC) is a new mode that combines lighting and communication. Because it can meet the needs of large capacity and ultra-high transmission rate, effective analysis of indoor visible light channel characteristics can better provide VLC systems. We provide a reference basis for the design, and VLC technology using Light Emitting Diode (LED) as the light source has become one of the research hotspots in the field of wireless communications. To solve the problems of existing indoor visible light channel modeling methods such as being ideal, high complexity, or poor in versatility, this paper researches indoor visible light communication channel modeling and related theories and methods, using rays with strong scene adaptability. Based on the tracking method, starting from the need to reduce computational complexity and improve tracking accuracy, a channel modeling method for indoor visible light communication is designed. We propose a high-precision indoor visible light communication channel modeling method that combines central ray tubes and bidirectional ray tracing. We use the forward ray tracing method to model indoor visible light communication channels. The simulation experimental results show that the channel modeling method proposed in this article can effectively improve modeling efficiency.

Integrated physical-layer secure visible light communication and positioning system based on polar codes

Visible light communication (VLC) with physical-layer security can provide information-theoretic security for the optical wireless channel based on the characteristics of the channel instead of encryption algorithms and secret keys at application layer. Since precise location information of communication parties is crucial for estimating channel states and designing secure communication schemes, this paper proposes an integrated visible light communication and positioning system which provides triple functionalities of high-accuracy indoor positioning, physical-layer secure visible light communication, and flicker mitigation illumination. A heterogeneous signal hybrid line coding scheme is proposed for the transmitter to converge the high-speed communication data signals and the low-speed positioning data signals, and a hybrid heterogeneous signal extraction scheme is proposed for the receiver to separate the hybrid heterogeneous signals with a high-bandwidth photodetector and a low-pass complementary metal-oxide-semiconductor (CMOS) image sensor. Based on the positioning information and the communication scheme, a polar codes-based forward error correction coding scheme is designed to achieve physical-layer security and transmission reliability simultaneously. Numerical results show that the proposed system can reach a secrecy code rate of 0.76 for a single-input single-output indoor VLC channel and a transmission efficiency of 0.38 without perceivable flicker. Experimental results show that the proposed system can achieve an average positioning accuracy of 3.35 cm and decrease the bit error rate of a legitimate receiver to a near error-free level (lower than 10−7) while keeping the bit error rate of an eavesdropper at 0.4887 (nearly 0.5) with a transmission data rate of 1 Mbps, resulting in near-zero suppression of the eavesdropped information and a high secrecy capacity of 0.9994.

Performance study of visible light communication through non-orthogonal multiple access (noma) – LI-FI

Li-Fi (Light Fidelity) is a new wireless communication technology that is comparable to Wireless Fidelity (Wi-Fi). However, Li-Fi is supposed to be better than Wi-Fi, and this has been theoretically verified. Li-Fi is also thought to make a significant contribution to wireless networks. The practical application of Li-Fi will be discussed in this study. In this paper we chose NOMA because of its ability and efficiency in simultaneously transporting data, as well as its application in 5G cellular networks. VLC stands for visible light communication, as the name implies. In this section, we will investigate how the data transporting capabilities of Li-Fi make use of the visible light emitted by light emitting diodes (LEDs). In this paper, the effectiveness of a non-orthogonal multiple access (NOMA) protocol used in a downlink visible light communication (VLC) system is evaluated for two distinct situations. On a two-user paired NOMA, we create an analytical expression of the system coverage probability for QoS provisioning and show that optimum power allocation coefficients do exist. Additionally, we establish the existence of optimal power allocation coefficients. Last but not least, the numerical and analytical results illustrated in our work show that the VLC single-cell system throughput obtained with our technique is better than that obtained with the earlier strategy. Additionally, it is shown that the suggested alternative lower bound fits the original NOMA-VLC GRPA objective asymptotically using indoor VLC channels.

A Novel 3D Non-Stationary Channel Model for 6G Indoor Visible Light Communication Systems

The visible light communication (VLC) technology has attracted much attention in the research of the sixth generation (6G) communication systems. In this paper, a novel three dimensional (3D) space-time-frequency non-stationary geometry-based stochastic model (GBSM) is proposed for indoor VLC channels. The proposed VLC GBSM can capture unique indoor VLC channel characteristics such as the space-time-frequency non-stationarity caused by large light-emitting diode (LED) arrays in indoor scenarios, long travelling paths, and large bandwidths of visible light waves, respectively. In addition, the proposed model can support special radiation patterns of LEDs, 3D translational and rotational motions of the optical receiver (Rx), and can be applied to angle diversity receivers (ADRs). Key channel properties are simulated and analyzed, including the space-time-frequency correlation function (STFCF), received power, root mean square (RMS) delay spread, and path loss (PL). Simulation results verify the space-time-frequency non-stationarity in indoor VLC channels. In addition, the influence of light source radiation patterns, receiver rotations, and ADRs on channel characteristics have been investigated. Finally, the accuracy and practicality of the proposed model are validated by comparing the simulation result of channel 3dB bandwidth with the existing measurement data. The proposed channel model will play a supporting role in the design of future 6G VLC systems.

Testbed for Experimental Characterization of Indoor Visible Light Communication Channels

In this paper, we describe an experimental testbed designed to evaluate indoor visible light communications (VLC) in realistic scenarios. The system is based on a mockup where the location and orientation of the optical receiver can be modified with precision for a static configuration of walls and ceiling lamp arrangements. The system utilizes a timing synchronization method, which is based on evaluating the training sequence periods used for channel response estimation, which enables robust frame synchronization. In addition, an adaptive rate orthogonal frequency-division multiplexing (OFDM) scheme is used to assess the VLC performance throughout the receiver plane emulating a real communication. The preliminary results obtained with this prototype, considering a multiple-input single-output (MISO) scenario, demonstrate that reflection on walls yields a significant increase in data rates, which can be additionally improved if appropriate orientation of the receiver is implemented. However, vertical orientation upward of the optical receiver still constitutes a simple solution but efficient enough. Moreover, a good agreement between simulation and experimental results is observed, which confirms the suitability of the mockup as an experimental testbed for practical evaluation of indoor VLC systems, where system performance for different lamp arrangements and receiver designs, including multi-user communications, can be studied.

5G Visible Light Communication - OCDMA Setup using Catenated-OFDM Modulation Method

This paper demonstrates a new high-speed architecture of visible light communication (VLC) system combining with zero cross correlation (ZCC) code of optical code division multiplexing (OCDMA) and novel catenated-OFDM modulation scheme. In order to achieved high spectral efficiency and higher bit rate system for 5G application, we embedded multiband catenated-OFDM modulation technique and OCDMA in VLC design system. Moreover, by employing visible laser diode (VLD) in designing VLC system, we achieved 10 Gbps bit rate at 2.5 dBm input power. We investigate this new combination system design to analyze the bit rate and bit error rate (BER) in 3 m indoor VLC channel propagation.

Channel in Multiple Transmitter Visible Light Communication

Visible Light Communication (VLC), which is based on the idea of using the light sources used for lighting in data transmission, is expected to be among the communication technologies of the future. However, for reliable communication, it is important to know and predict indoor VLC channels that are known to have a multipath structure. Therefore, in order to examine the possible channel characteristics, multiple transmitter rooms with different sizes are arranged in the study. Channel Impulse Responses and Channel Frequency Responses were calculated for different receiver locations taking into account mobile users. As a result of the study, it has been shown that multiple transmitters are a powerful factor that changes the characteristics of the channel and frequency selective channels are formed related to the distribution of the sources and the receiver location. In the same room, depending on the receiver location, there may be a completely different fluctuation in the frequency band and some serious fading is observed in some frequencies. This result has attracted attention especially as a problem with pending solution for mobile users. At the end of the study, it was shown by using simulations that using directed illumination or detector with narrow field of view may reduce the frequency selectivity of the channel.

On the average secrecy capacity for indoor visible light communication systems

For visible light communication (VLC), the light signals are transmitted without optical fibers or any sort of wave-guiding. Due to the inherent broadcast nature, physical-layer security emerges as a promising method to protect information delivery from eavesdropping. As for the secrecy capacity of VLC channel, there exist two features. In one way, the limited optical power makes the common capacity expressions in radio-frequency (RF) communication unapplicable for VLC. In another way, several correlated geometrical parameters directly alters the Lambertian model of indoor VLC channel, which gives the secrecy capacity more meanings. However, the issue considering both aspects has not been studied recently. In this paper, from the practical scenarios, we extract a typical geometrical model to reveal the mobility principles of the legitimate receiver and the eavesdroppers. Then, we character two typical distributions of the geometrical parameter. Correspondingly, we derive the upper and lower bounds on the average secrecy capacity, which have the closed forms. Finally, simulation results show that our upper and lower bounds are tight at high optical signal-to-noise rates (OSNRs). Moreover, the geometrical features of VLC systems and distribution parameters of the receiver mobility are effectively reveal by the bounds.

Channel modelling for indoor visible light communications.

Visible light communication (VLC) allows the dual use of light-emitting diodes (LEDs) for wireless communication purposes in addition to their primary purpose of illumination. As in any other communication system, realistic channel modelling is a key for VLC system design, analysis and testing. In this paper, we present a comprehensive survey of indoor VLC channel models. In order to set the background, we start with an overview of infrared (IR) channel modelling, which has received much attention in the past, and highlight the differences between visible and IR optical bands. In the light of these, we present a comparative discussion of existing VLC channel modelling studies and point out the relevant advantages and disadvantages. Then, we provide a detailed description of a site-specific channel modelling approach based on non-sequential ray tracing that precisely captures the optical propagation characteristics of a given indoor environment. We further present channel models for representative deployment scenarios developed through this approach that were adopted by the Institute of Electrical and Electronics Engineering (IEEE) as reference channel models. Finally, we consider mobile VLC scenarios and investigate the effect of receiver location and rotation for a mobile indoor user. This article is part of the theme issue 'Optical wireless communication'.

Indoor Intruder Tracking Using Visible Light Communications.

This paper proposes a comprehensive study of indoor intruder tracking using visible light communication (VLC). A realistic indoor VLC channel was developed, taking into consideration reflections, shadowing, and ambient noise. The intruder was considered smart and aiming to escape tracking. This was modelled by adding noise and disturbance to the intruder’s trajectory. We propose to extend the application of minimax filtering from state estimation in the radio frequency (RF) domain to intruder tracking using VLC. The performance of the proposed method was examined and compared with Kalman filter for both VLC and RF. The simulation results showed that the minimax filter provided marginally better tracking and was more robust to the adversary behavior of the intruder than Kalman filter, with less than 0.5 cm estimation error. In addition, minimax was significantly better than Kalman filter for RF tracking applications.

Modelling noise and pulse width modulation interference in indoor visible light communication channels

Visible light communication (VLC) has the potential to supplement the growing demand for wireless connectivity. In order to achieve the full potential of VLC, channel models are required. Discrete channel models based on semi-hidden Markov models (Fritchman model) for indoor VLC using low data rate LEDs are presented. Each channel considered includes background noise and differing types of interference from fluorescent lights and pulse-width modulated (PWM) LEDs, which could be part of an indoor smart lighting system. Models were developed based on experimental error sequences from a VLC system using an on-off keying (OOK) modulation scheme. The error sequences were input into the Baum-Welch algorithm to determine the model parameters by expectation maximisation. Simulated error sequences generated by the models are compared to and, in most cases, perform better than simpler models with a single bit error rate. The models closely approximate the experimental errors sequences in terms of error distribution. The models performed better in channels where there is less interference. It was also found that periodic errors were introduced as a results of the PWM modulated smart lighting LEDs. These models have use for designing error control codes and simulating indoor VLC environments with different types of interference.

Robust Beamforming-Aided Signal Recovery for MIMO VLC System With Incomplete Channel

Visible light communication (VLC) based on light emitting diodes (LEDs) has attracted much attention because of its high data rate and energy efficiency. However, the shadowing caused by any mobile obstacles could block the light-of-sight (LoS) link which may have a dramatical effect on the indoor VLC channel state information (CSI). Instead of investigating the shadowing channel characteristics, we model the link blockages as the incomplete channel matrix with sparse missing elements and reconstruct the transmitted signal by the l 0 -minimization with additional constraint on shadowing loss. However, the indoor VLC channel is highly correlated especially in cases with small emitter separation. To further improve the accuracy performance, we design the transmit beamforming to reduce the total coherence. Simulation results illustrate the effectiveness of the proposed signal recovery algorithm with incomplete channel and further significant enhancement via the proposed beamforming design.

Improved Joint Generalized Spatial Modulations for MIMO-VLC Systems

In this letter, we propose the computationally efficient constellation design algorithms for single-mode and dual-mode joint generalized spatial modulations (JGSMs) to improve the symbol error rate (SER) performance over highly correlated indoor visible light communication channels. Our simulation results show that the proposed joint and improved dual-mode JGSMs can offer a better SER performance than the proposed single-mode JGSM (SM-JGSM) and the conventional SM-JGSM, which are validated through the analytical bounds.

Performance analysis of gain ratio power allocation strategies for non-orthogonal multiple access in indoor visible light communication networks

Non-orthogonal multiple access (NOMA) is a promising method for enhancing the throughput in visible light communication (VLC) networks. In NOMA, signal power domain control, called gain ratio power allocation (GRPA), can significantly improve the user sum rate with full-time frequency resource utilization. In indoor NOMA-VLC networks, the scenario in which users are covered by VLC illuminants on the ceiling is typical. First, this paper proposes a novel GRPA strategy for a single VLC cell. Second, due to the difficulty of direct comparisons between our and previously reported GRPA strategies, this paper presents an alternative lower bound for comparability. Third, in two- and three- user cases, this paper analytically demonstrates that our NOMA-VLC GRPA strategy outperforms the aforementioned strategy, when successive interference cancellation (SIC) is used. Moreover, in the multi-user case, experimental results show that the average user data rate (AUDR) of multi-user cases under our strategy is better than that under the previous strategy. Finally, our paper provides both analytic and numerical results to prove that VLC single-cell system throughput under our strategy is better than that under the previous strategy. The proposed alternative lower bound is also proved to fit the original NOMA-VLC GRPA target asymptotically based on indoor VLC channels. Furthermore, to achieve the same AUDR, our strategy supports worse received conditions than does the previous strategy.

Coded color shift keying with frequency domain equalization for low complexity energy efficient indoor visible light communications

The adaptive tri-chromatic color shift keying (CSK) modulation standardized in IEEE 802.15.7 and the advanced quad-chromatic CSK are unable to utilize their entire spectral efficiency range over dispersive indoor VLC channels and incur large power penalties without the use of channel equalization and forward error correction. This degrades the energy efficiency and limits the throughput capability of CSK schemes to approximately half of the data-rates specified in the IEEE standard for multimedia services in wireless personal area networks. To comply with the desire for low latency and minimal implementation complexity in the CSK standardization framework, we consider an industry standard binary convolutional code and frequency domain equalization (FDE) which provide one-shot data packet processing. Our results show that when operating over hybrid indoor visible light communication (VLC) links, the FDE based rate-adaptive coded modulation CSK scheme achieves a significant 11 dB SNR gain over an uncoded, unequalized system.

Achievable Rate Region of the Zero-Forcing Precoder in a $2\times 2$ MU-MISO Broadcast VLC Channel With Per-LED Peak Power Constraint and Dimming Control

In this paper, we consider the 2 X 2 multi-user multiple-input-single-output (MU-MISO) broadcast visible light communication (VLC) channel with two light emitting diodes (LEDs) at the transmitter and a single photo diode (PD) at each of the two users. We propose an achievable rate region of the Zero-Forcing (ZF) precoder in this 2 X 2 MU-MISO VLC channel under a per-LED peak and average power constraint, where the average optical power emitted from each LED is fixed for constant lighting, but is controllable (referred to as dimming control in IEEE 802.15.7 standard on VLC). We analytically characterize the proposed rate region boundary and show that it is Pareto-optimal. Further analysis reveals that the largest rate region is achieved when the fixed per-LED average optical power is half of the allowed per-LED peak optical power. We also propose a novel transceiver architecture where the channel encoder and dimming control are separated which greatly simplifies the complexity of the transceiver. A case study of an indoor VLC channel with the proposed transceiver reveals that the achievable information rates are sensitive to the placement of the LEDs and the PDs. An interesting observation is that for a given placement of LEDs in a 5 m X 5 m X 3 m room, even with a substantial displacement of the users from their optimum placement, reduction in the achievable rates is not significant. This observation could therefore be used to define "coverage zones" within a room where the reduction in the information rates to the two users is within an acceptable tolerance limit.

Research of LED Emission Cross-Section on Light Communication Systems

Visible light communication (VLC) is an optical wireless communication technology that uses visible light emitting diodes (LEDs) as a communication source. Since the LEDs are also used for illumination, the cross-section emission effects of the LEDs need to be analyzed as they apply to indoor VLC channels. In order to evaluate the illumination and communication performance according to the emission cross-section pattern, a simple LED model with a quasi-elliptic emission cross-section is proposed and compared to a circular LED model. The LEDs with a quasi-elliptic emission cross-section provide less fluctuation in the illumination and optical power distribution at the receiving plane. The four-transmitter VLC system is found to support at least at 30 and 33 Mb/s for circular and quasi-elliptic emission cross-section LEDs for the entire receiving plane, respectively.