Lifang Feng

Visible light positioning (VLP) is one of the effective solutions for low-cost and high-precision indoor positioning in the emerging wireless communication ecosystem, particularly in the context of 6G networks, due to its advantages of low latency, high data transmission rates, and immunity from radio frequency induced electromagnetic interference. However, severe performance limitations, including line-of-sight dependency, signal attenuation caused by obstacles, and restricted coverage, present a major challenge for the development of VLP. This article constructs an LED array-based hybrid indoor positioning system. An innovative LED array beacon is developed to simultaneously transmit coordinate and graphical information. A hybrid receiving structure, comprising an image sensor (IS) and a photodetector (PD), is constructed along with a dedicated hybrid positioning algorithm. This algorithm leverages image processing techniques to track the target trajectory, converts light intensity to identify the identification of LED, which finally resolves the target's precise world coordinates. The system's performance was validated through three experimental trials. The results demonstrate that the proposed beacon effectively covers the entire positioning area, achieving an average positioning error of 8.32 cm and a maximum positioning distance of 6.8 m. These results suggest that the proposed system provides a robust and efficient solution for precise indoor positioning applications in next-generation wireless communication networks.

This study introduces a comprehensive physical layer security (PLS) scheme in visible light communication (VLC) systems using non-Lambertian beamforming and intelligent reflecting surfaces (IRSs). It withstands eavesdropping and attacks to secure indoor VLCs, even with imperfect channel state information (CSI). In conventional VLC systems, the required illuminance maintaining normal communication is about 80 lux. The proposed scheme reduces the illuminance in a potential eavesdropping area to 5.2 lux by manipulating the direction and intensity of the optical signals, which leads to eavesdropping failure. Meanwhile, the proposed scheme is jamming-resistant. Simulations demonstrate that the system adopting the proposed security scheme has a SINR of 40.32 dB with jamming attacks, compared to 26.13 dB in typical VLC systems, so the resisting interference ability is improved by 54%. Eavesdropping resistance and attack resilience make VLC security in sensitive contexts more robust.

In visible light imaging positioning systems, the design of light-emitting diode identification (LED-ID) plays a crucial role in enhancing the system access capacity. The frequency feature based on frequency division multiplexing (FDM) is widely used for distinguishing LED-ID owing to its simplicity of deployment. Appropriately assigning frequency bands to each LED and designing effective recognition algorithms can support more available addresses. We derived a formula for the influencing factors of LED imaging stripes in the FDM scenario. The formula indicates that, if the LED-ID is distinguished by stripe width, the driving frequency interval of LEDs should be inversely proportional to the distribution of the driving frequency. On this basis, we derive the upper and lower bounds and the minimum resolution of frequency and give the theoretical maximum number of LED access and the corresponding optimal LED-driven frequency distribution. To ensure a high recognition accuracy when the number of LEDs in the system reaches the theoretical limit, two corresponding image processing algorithms are proposed: a local binarization method based on the Lambertian model and an improved stripe width recognition algorithm. Results show that the proposed method reduces the system recognition error rate to 1.1% within the applicable frequency range. The feasibility of the proposed scheme is introduced through hardware implementation.

This study investigates the optimization of energy efficiency in robust visible light communication (VLC)—intelligent reflecting surface (IRS) systems through a novel resource allocation strategy based on coalitional game theory. By employing coalitional game theory, the proposed strategy optimizes LED power and IRS energy consumption within practical constraints. IRS elements form coalitions centered around a central unit or units, enhancing the system performance through coordinated element management. Simulation results demonstrate significant improvements in energy efficiency and signal quality compared to conventional methods, validating the effectiveness of the proposed strategy.

Due to the inherent tendency to be blocked by obstacles, reliability is a major challenge for visible light communication (VLC). The intelligent reflective surface (IRS) is an effective way to reduce or eliminate the influence of blockage in the VLC system. However, the complexity increases correspondingly due to complex shadow analysis when access points (APs), IRSs, and obstacles coexist. We proposed a robust layout optimization scheme for the IRS-VLC system to resist blockages. First, we model the random obstructions based on spatial geometry methods. Second, we build the optimization problem model considering consistent illumination, achievable data rate (ADR), the positions of the APs, and the directions of the IRS array. In order to achieve this objective, we develop an anti-occlusion method based on the non-dominated sorting genetic algorithm-II (NSGA-II) to get the Pareto front and use enhanced measurement functions (ASFs) to extract the best solution. Simulation results show that the proposed scheme works well in the IRS-VLC system. It is noteworthy that the rectangle layout has always demonstrated superior performance in the IRS-VLC system compared to other traditional layouts.

In this paper, a positioning algorithm based on the combination of K-means clustering and deep neural networks (DNNs) is first presented for multiple light emitting diodes (LEDs) integrated with visible light positioning (VLP) systems. We extracted the maximum value from the collected optical power of LEDs, utilizing the ratio of each optical power to this maximum optical power as the input training data. The experimental results demonstrate that the proposed algorithm outperformed the conventional DNN algorithm in terms of anti-jamming capability and positioning accuracy. In addition, the positioning accuracy of the proposed system reached a millimeter level, which is the highest experimental VLP accuracy, to the best of our knowledge.

In this paper, an integrated visible light communication and positioning (VLCP) code division multiple access (CDMA) system is proposed for recovering original user data and obtaining positioning information simultaneously. A generalized modification method for balanced bipolar code set is presented, which can be applied to VLCP-CDMA system with intensity modulation. Both modified bipolar code sets, zero correlation zone (ZCZ) code set and Walsh code set, are employed and evaluated in VLCP-CDMA systems. When considering synchronous and quasi-synchronous (QS) systems, it is demonstrated that the modified ZCZ code set with ideal zero correlation zone properties performs better communication and positioning performance than the modified Walsh code set by system simulations and experiments. As a result, a bit error rate (BER) of 1.8×10⁻³ and an average positioning error of 1.50 cm are successfully obtained by adopting modified ZCZ code set in a 4-user real-time VLCP-CDMA system. It will offer a promising solution to meet both communication and positioning requirements of future intelligent systems.

In this paper, a novel adaptive feedback threshold (AFT) based demodulation for mobile visible light communication and positioning (VLCP) integrated system is proposed. The AFT can vary with the received signal without excessive fluctuation and support communication and positioning in mobile environment. For the VLCP integrated system with single light emitting diodes (LED) and multiple photodetectors (PDs), maximal ratio combining (MRC) and received optical power ratio (ROPR) based on the AFT is further achieved for communication and positioning with high performance, respectively. It is demonstrated that high credible communication and high accuracy positioning for the mobile integrated VLCP system can be realized by using the proposed AFT based demodulation. As a result, the implemented VLCP system with a moving speed of 1 m/s is evaluated experimentally. Average positioning error of 3.43 cm with 800 mA current and the bit error ratio (BER) with different currents are also obtained.