Visible Light Communication Channel Research Articles

Distortion-tolerant on–off keying preemphasis signal transmission for a 10 Gbps indoor visible light communications

Abstract The design and simulation of indoor visible light communication (VLC) system with preemphasis is proposed for 5 m transmission of signal at the data rate of 10 Gbps for receiving only applications like smart TV, smart speaker, and smart home appliance control. The preemphasis driver circuit is designed to reduce the intersymbol interference by pulse shaping the signal and transimpedance amplifier is used to amplify the signal for longer distance transmission. Intensity modulation at the sender side and direct detection at the receiver-side are adopted in this work for the improvement of the system’s overall performance and to decrease its implementation cost. The system performance is analyzed in terms of BER, data-rate, Q-factor, and eye diagrams. The setup is developed, which includes a nonreturn-to-zero (NRZ) generator, preemphasis driver, light-emitting-diode, VLC channel, and receiver with an avalanche photodiode and Gaussian LPF. At 10 Gbps data rate, the maximum transmission distance that can be obtained is 5 m with a BER of less than 10−31.

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.

On the physical layer security of visible light communications empowered by gold nanoparticles

Visible light is a proper spectrum for secure wireless communications because of its high directivity and impermeability in indoor scenarios. However, if an eavesdropper is located very close to a legitimate receiver, secure communications become highly risky. In this paper, to further increase the level of security of visible light communication (VLC) and increase its resilience to malicious attacks, we propose to capitalize on the recently synthesized gold nanoparticles (GNPs) with chiroptical properties for circularly polarized light resulting in the phase retardation that interacts with the linear polarizer angle. GNP plates made by judiciously stacking many GNPs perform as physical secret keys. Transmitters send both the intended symbol and artificial noise to exploit the channel variation effect by the GNP plates, which is highly effective when an eavesdropper is located close to the legitimate receiver. A new, to our knowledge, VLC channel model is first developed by representing the effect of GNP plates and linear polarizers in the circular polarization domain. Based on the new channel model, the angles of linear polarizers at the transmitters and legitimate receiver are optimized considering the effect of GNP plates to increase the secrecy rate in wiretapping scenarios. Simulations verify that, when the transmitters are equipped with GNP plates, even if the eavesdropper is located right next to the legitimate receiver, insightful results on the physical layer security metrics are gained as follows: (1) the secrecy rate is significantly improved, and (2) the symbol error rate gap between the legitimate receiver and eavesdropper becomes much larger due to the chiroptical properties of GNP plates.

Simplified channel model for indoor VLC systems

The channel model of indoor visible light communication (VLC) is primarily influenced by the receiver’s position and orientation. In this study, we decouple the effects of receiver position and orientation, treating them as independent random variables. This decoupling enables a clearer understanding of how each factor independently influences the channel model. Specifically, we focus on the impact of the azimuth angle, a critical component of orientation, on the VLC channel. We present a simplified channel model for indoor VLC systems based on partial orientation information. Theoretical analysis and simulation results collectively indicate that the accuracy of the simplified channel model is influenced by the field-of-view (FOV), with higher accuracy achieved at narrower FOVs. To evaluate practical performance, we compare our simplified model with the existing complete channel model in a two-user precoding system. Results show that our proposed simplified channel model maintains value, particularly in narrow-FOV scenarios. The research findings indicate that this simplified model is suitable for applications with high demands for channel accuracy in narrow-FOV indoor VLC systems, and can be extended to applications in wide-FOV systems where perfect channel information is not required.

VLC channel model in underground mining scenarios with the extinction effect and shadowing effect

In this work, a novel, to our knowledge, visible light communication (VLC) channel model is proposed for underground mining scenarios taking into account the impact of coal dust particles and obstacles. Specifically, the extinction effect of the coal dust particles is analyzed on the basis of the Mie theory, and the quantitative formula of the influence on channel direct current (DC) gain is derived. Meanwhile, the effect of a random shadowing phenomenon is investigated and quantified with the geometric and statistical model considering the position, size, and shape of the obstacles. The channel impulse response, path loss, root mean square delay spread, and bit error rate (BER) are further investigated in two different underground mining scenarios, namely, a mining roadway and coal mine working face. Simulation results show that the shadowing effect plays a major role in the influence of DC gain attenuation. Furthermore, the BER performance is noticeably degraded due to the presence of coal dust particles and obstacles, especially when the receiver is located far from the transmitter. This work will benefit the design of the VLC systems in underground mines.

Method for evaluation of the optical uniformity distribution in the white LEDs-based visible light communication applications

The uniformity characteristic of emitted radiation in VLC applications is a factor that can affect the efficiency of a detector and the overall efficiency of the VLC system. In this paper, we theoretically investigate the optical uniformity characteristic of using LEDs in VLC applications in terms of the parameter of the emission angle of LEDs and the spatial distribution of LEDs. The result indicates that the optical uniformity can be controlled at a high level by controlling the emission angle of the LED or distributing the LEDs in the room's space. Full Text: PDF References E.-F. Schubert, J.-K. Kim, "Solid-State Light Sources Getting Smart", Science 308, 1274 (2005). CrossRef N. Narendran, Y. Gu, "Life of LED-based white light sources", J. Display Technol. 1, 167 (2005). CrossRef E. Schubert, Light-Emitting Diodes (Cambridge, Cambridge Univ. Press 2006). CrossRef C.C. Sun, Q.K. Nguyen, T.X. Lee, S.K. Lin, C.S. Wu, T.H. Yang, Y.W. Yu, "Active thermal-fuse for stopping blue light leakage of white light-emitting diodes driven by constant current", Sci. Reports 12, 12433 (2022). CrossRef Z. Ghassemlooy, W. Popoola, S. Rajbhandari. Optical Wireless Communications System and Channel Modelling with MATLAB (Florida, CRC Press, Taylor & Francis Group, 2013). CrossRef A. Burton, H. Le Minh, Z. Ghasemlooy, S. Rajbhandari, "A study of LED lumination uniformity with mobility for visible light communications", IEEE 2012 Int. Workshop on Opt. Wireless Comm. (IWOW), Pisa, Italy, 2012. CrossRef M.S.M. Gismalla, M.F.L. Abdullah, M.I. Niass, B. Das, W.A. Mabrouk. "Effect of optical attocells deployment on the RMSD spread in indoor visible light communication systems", Int. J. Commun Syst. e4349 (2020). CrossRef C. Wang, J. Wang, J. Zhang, J. Wang, H. Du, J. Wang, "Research on uniform illumination distribution of indoor visible light communication", Proc. SPIE 12062, AOPC 2021: Optoelectronics and Nanophotonics (2021). CrossRef M.V. Bhalerao, M. Sumathi, S.S. Sonavane. "Line of sight model for visible light communication using Lambertian radiation pattern of LED", Int. J. Comm. Systems (2016). CrossRef J.F. Zang, Y. Piao. "Research on visible light communication system based on white LEDs", Proc. SPIE 10255, (2016). CrossRef M. Oliveira, F.C.B. Tosta, D.E.F. Guillen, P.P. Monteiro, A.A.P. Poh, "Theoretical and Experimental Analysis of LED Lamp for Visible Light Communications", Wireless Personal Communications 125, 3461(2022). CrossRef J.P. Ding, C. Lin, J.T. Wang, H. Yang, "Effects of Optical Beams on MIMO Visible Light Communication Channel Characteristics", Sensors 22, 216 (2022). CrossRef X. Zhang , N. Zhao, F. Al-Turjman, M.B. Khan, X. Yang. "An Optimization of the Signal-to-Noise Ratio Distribution of an Indoor Visible Light Communication System Based on the Conventional Layout Model", Sustainability 12, 9006 (2020). CrossRef A. Kaewpukdee, P. Uthansakul, "Characteristic of Line-of-Sight in Infrastructure-to-Vehicle Visible Light Communication Using MIMO Technique", Materials Continua 74, 1026 (2023). CrossRef

Multi-Wavelength Path Loss Model for Indoor VLC with Mobile Human Blockage

Visible light communication (VLC) is one of the candidate technologies for the sixth generation (6G) networks. The path loss model is particularly important for link budget estimation and network planning in VLC. Due to the wideband nature and the extremely poor diffraction capacity of light, the path loss of the VLC channel is susceptible to wavelength dependence and blockage effect. In this paper, we propose a novel path loss model which can characterize the impact of wavelength dependence combined with mobile human blockage for both the single-LED (light emitting diode) and the multi-LED scenario. When there is no blockage in the channel, the multi-wavelength path loss under free space propagation is modeled with a small standard deviation of 0.262 in the single-LED scenario and a small root mean square error of 0.009 in the multi-LED scenario which indicates the high accuracy of the model. When considering the mobile human blockage, the blockage probability (BP) is modeled with full consideration of realistic human mobility and human body shadowing. The results indicate that the BP in single-LED scenario can reach 0.08, while the BP in multi-LED scenario is 0.022. This demonstrates that the distributed deployment of transmitters can effectively reduce the occurrence of the blockage state in VLC.

CNN neural network temporal feature storage structure fusion for the visible channel equalization algorithm

The visible light communication channel has time-varying characteristics and is difficult to predict. This paper proposes an equalization algorithm based on the structure of a convolutional neural network (CNN), combining time series feature length and long short-term memory (LSTM), and adding a residual structure. It can be seen that the equalization coefficient vector of the optical channel is a time series, which can reflect the noise characteristics of the channel and has storage characteristics. The equalizer algorithm can accurately learn the complex channel characteristics and calculate the compensation coefficient according to the channel characteristics. It can also restore the original transmission signal. At the same time, this paper also examines the compensation method of the receiver in the mobile state. The long-term memory parameters of LSTM are used to represent the sequence causality in the memory channel, and CNN and residual structure are used to refine the results and improve the accuracy of the reconstruction. The simulation results show that the algorithm can effectively eliminate the influence of the fading characteristics of the visible optical channel, improve the bit error rate performance of system transmission, solve the overall problem of channel corruption, and precisely restore the original transmission signal with fast convergence speed. In addition, this method can achieve a better balance between performance and complexity compared to the traditional contention balancing method, which proves the potential and effectiveness of the proposed channel balancing method.

On the performance of delta sigma modulators for DCO-OFDM based NOMA visible light communication systems

The revolution of the solid-state lighting technology and the looming radio frequency (RF) spectrum crisis enabled the rapid evolution of visible light communication (VLC) in the recent times. To furnish contemporaneous illumination and communication, VLC relies on white light emitting diodes (WLEDs). However, the limited modulation bandwidth of WLEDs poses a threat to VLC as the achievable data rates are drastically minimized. Eventually, to enhance the achievable throughput, the pre-eminent way is to apply orthogonal frequency division multiplexing (OFDM) to a VLC system. Furthermore, a VLC system can also exploit non-orthogonal multiple access (NOMA) scheme to bestow with seamless services to the multiple users. However, much similar to the RF-based OFDM system, the OFDM-VLC system also inherits one of the serious disadvantages like the high peak to average power ratio (PAPR). In addition, the rapid fluctuations of the continuous time-domain signal amplitude in DC-biased optical OFDM (DCO-OFDM) results in much complicated design of the LED driver circuitry for driving the LED. Thus, to overcome such drawbacks, we incorporate delta-sigma modulators (DSM) to the NOMA-VLC system which is making use of DCO-OFDM, and we analyze its performance over VLC channel environment. The stunning advantage imparted by the proposed DSM-based DCO-OFDM-NOMA-VLC system is that the continuous amplitude of the time-domain transmitted signal is converted into two levels for driving the LED. Additionally, with the major goal to maximize the sum throughput of the proposed multiuser VLC system by taking into consideration both the user fairness as well as the intensity constraints, we derived the optimal values for the power allocation coefficients corresponding to the fair power allocation algorithm. Furthermore, the dynamically varying fair power allocation algorithm is compared with the fixed/static power allocation algorithm. The major contribution of this work is of two-fold: firstly, the proposed DCO-OFDM-NOMA-VLC system which is making use of DSM exhibits a remarkable reduction in PAPR when compared with the conventional system without the application of DSM, where the proposed system demonstrates a significant gain of 4.78 dB in terms of PAPR reduction. Secondly, from the simulated results it can affirmed that the proposed system not only achieves enhanced sum rates and better outage performance but also imparts a better bit error ratio (BER) performance corresponding to the far user.

Capacity and Achievable Rate Analysis for Visible Light Communication Channels

Capacity and Achievable Rate Analysis for Visible Light Communication Channels

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.

Vector Coding Optical Wireless Links

The quasi-static nature of the optical wireless channel means that the channel state information (CSI) can be readily available at the transmitter and receiver prior to data transmission. This implies that electrically band-limited optical wireless communication (OWC) systems can make use of optimal channel partitioning or vector coding based multi-channel modulation (MCM) to achieve high throughput by mitigating the non-linearities arising from the optical and electrical channel. This paper proposes a pulse amplitude modulation (PAM) based DC-biased optical vector coding (DCO-VC) MCM scheme for OWC. The throughput performance of DCO-VC is evaluated and compared to the well known DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM) over hybrid (line-of-sight and diffuse) and diffuse (non line-of-sight only) visible light communication (VLC) channels with additive white Gaussian noise. For the completeness of the VLC physical layer, the performance comparison is based on an uncoded and a forward error correction transmission mode using well-known convolutional codes with Viterbi decoder. The results show that the coded DCO-VC outperforms DCO-OFDM system by achieving up to 2 and 3 dB signal to noise ratio gains over hybrid and diffuse VLC channels, respectively.

SLIPT-Enabled Multi-LED MU-MISO VLC Networks: Joint Beamforming and DC Bias Optimization

This paper studies a simultaneous lightwave information and power transfer (SLIPT)-enabled multi-user (MU) multiple input single output (MISO) visible light communication (VLC) network, where multiple user equipments (UEs) are simultaneously allowed to receive information by the photodiode (PD) and harvest energy by the solar panel, respectively. To improve the system spectral efficiency, an achievable sum rate maximization problem is formulated subject to the minimum energy harvesting (EH) requirement of each UE, the total transmit power constraint of the LEDs and the dimming control constraint of the LEDs, by jointly optimizing the beamforming vector and the direct current (DC) bias vector of the LEDs. To be general, the practical non-linear EH model and the information capacity model of the VLC channel are adopted. To solve the non-convex optimization problem, the objective function is equivalently transformed at first by using the epigraph reformulation, and then the transformed problem is relaxed with the semi-definite relaxation (SDR) method. Based on this, an iterative algorithm is designed to approximately obtain the maximal achievable sum rate based on the successive convex approximation (SCA). Simulation results indicate that there exists a non-trivial trade-off between the achievable sum rate and the harvested energy, and that DC bias vector dominates the amount of the harvested energy compared with the beamforming vector. Besides, for a given relatively high EH requirement, the achievable sum rate increases with the increment of the dimming level, especially for relatively small dimming level. Once the dimming level is larger than a specific value, with the increment of the dimming level, more transmit power will be allocated for illumination, resulting in the decrement of the achievable sum rate.

Joint precoding and power allocation in a FSO channel with signal-dependent noise.

To enhance the throughput of visible light communication (VLC), this paper investigates precoding and power allocation jointly in a free space optical channel with signal-dependent noise (SDN-FSO). With the presence of SDN from a light source, a more realistic multi-user multiple-input single-output (MU-MISO) VLC channel model is introduced. First, based on the entropy power inequality, a capacity bound for the SDN-FSO channel is derived under a MU-MISO scenario. Second, due to the nonnegativity of SDN-FSO input, a zero forcing constraint is introduced to alleviate multi-user interference. Third, from the perspective of resource allocation, min-max and total power budget constraints are taken into consideration. A non-convex joint optimization problem is formulated and divided into two subproblems, i.e.,the precoding subproblem and power allocation subproblem. Moreover, an iterative algorithm based on a concave and convex program and a simplified high signal-to-noise ratio approximation method are iteratively implemented in the precoding subproblem. For the power allocation subproblem, successive convex approximation is employed to ensure its optimality. Simulation results indicate that the proposed joint optimization methods can converge after about two iterations and accomplish a throughput improvement of up to 1∼3n a t s/s/H z as compared with the benchmarks for four different spacing scenarios. When channel state information is interfered with noise, the proposed methods still demonstrate their superior performance with varying degrees of noise.

Distortion managed directly modulated on-off keying signal transmission for 10 Gbps visible light communications using electrical filtration

Abstract In this research, a communication system that uses visible light as a carrier and is designed for high-throughput interior applications. In order to lower the overall system cost, this work uses intensity modulation at the transmitter and direct detection with electrical filtering at the receiver. Various low-pass filtration techniques (Gaussian, Butterworth, Bessel, and Chebyshev) have been proposed in his paper to mitigate the effect of channel distortion in visible light communication (VLC) systems. The achieved transmission range is up to 3 m in addition to the supported data rate of 10 Gbps with a bit error rate of less than 10−9. Simulations are carried out using optisystem software that includes PRBS OOK optical signal generation at LED output in the transmitter, VLC channel, and APD with LPF in the receiver.

Visible Light Communications for Unmanned Aerial Vehicle: Channel Modeling and Experimental Validation

Unmanned aerial vehicles (UAVs) have been widely applied for their high mobility and low cost, and the visible light communication (VLC) aided UAV can combine the flexibility of UAV and the high transmission rate of VLC. However, the VLC links of a UAV are inevitably affected by the jittering effects, which were rarely characterized. In this letter, the channel between a light emitting diode (LED) and a hovering UAV is modeled considering the random orientation error of the UAV. Closed-form expressions are derived for the probability density function (PDF) and the cumulative distribution function (CDF) of the orientation error, which also leads to closed-form asymptotic PDF and CDF expressions of the UAV’s VLC channel gain. Simulation and experimental results are demonstrated to verify the theoretical derivations. The work lays a theoretical foundation for VLC-aided UAVs, providing insightful suggestions for the system design.

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.

R-AP's position-domain model for an RO-receiver and AP placement strategy for an uninterrupted link between the robotic arm and AP in the VLC network.

In the visible light communication (VLC) network, the optical link between the robotic arm and the access point (AP) is easily interrupted due to the random orientation of the receiver on the robotic arm. First, based on the VLC channel model, a position-domain model of reliable AP (R-AP) for a random-orientation receiver (RO-receiver) is proposed. The channel gain of the VLC link between the receiver and the R-AP is non-zero. The tilt-angle range of the RO-receiver is [0,π]. Given the field of view (FOV) angle and the orientation of the receiver, the R-AP's position domain of the receiver can be obtained by this model. Then, based on the R-AP's position-domain model for the RO-receiver, a novel AP placement strategy is proposed. Under this AP placement strategy, the number of R-APs for the RO-receiver is not less than 1, thereby effectively avoiding link interruption caused by the random orientation of receivers. Finally, it is proved by the Monte Carlo method that, under the AP placement strategy proposed in this paper, the VLC link of the receiver on the robotic arm can remain uninterrupted during the movement of the robotic arm.