# Channel Characteristics and Link Adaption for Visible Light Communication in an Industrial Scenario
###### Abstract  
Visible light communication (VLC) is one of the key technologies for the sixth generation (6G) to support the connection and throughput of the Industrial Internet of Things (IIoT). Furthermore, VLC channel modeling is the foundation for designing efficient and robust VLC systems. In this paper, the ray-tracing simulation method is adopted to investigate the VLC channel in IIoT scenarios. The main contributions of this paper are divided into three aspects. Firstly, based on the simulated data, large-scale fading and multipath-related characteristics, including the channel impulse response (CIR), optical path loss (OPL), delay spread (DS), and angular spread (AS), are analyzed and modeled through the distance-dependent and statistical distribution models. The modeling results indicate that the channel characteristics under the single transmitter (TX) are proportional to the propagation distance. It is also found that the degree of time domain and spatial domain dispersion is higher than that in the typical rooms (conference room and corridor). Secondly, the density of surrounding objects and the effects of user heights on these channel characteristics are also investigated. Through the analysis, it can be observed that the denser objects can contribute to the smaller OPL and the larger RMS DS under the single TX case. Furthermore, due to the blocking effect of surrounding objects, the larger OPL and the smaller RMS DS can be observed at the receiver with a low height. Thirdly, due to the distance dependence of the channel characteristics and large time-domain dispersion, the link adaption method is further proposed to optimize the multipath interference problem. This method combines a luminary adaptive selection and delay adaption technique. Then, the performance of the link adaption method is verified from four aspects through simulation, including the signal-to-noise (SNR), the RMS DS, the CIRs, and the bit-error rate (BER) of a direct-current-biased optical orthogonal frequency division multiplexing (DCO-OFDM) system. The verification results indicate that our proposed method has a significant optimization for multipath interference. 18 March 202323 March 20232  
The ultimate performance limits of a communication system are determined by the channel in which it operates [5]. VLC channel modeling is the foundation of designing and optimizing VLC communication systems, which can evaluate the performance limit of the VLC system [6]. Therefore, the realistic channel models for IIoT scenarios are of critical importance to accurately predict the propagation characteristics. There are already indoor VLC channel models in existing standards. However, the IIoT scenario has a larger physical size, with many more metal machine tools and production lines in it [7] than in an indoor office. Thus, the IIoT scenario exhibits many new channel characteristics, e.g., a dense multipath reflected by the abundance of metallic scatterers. Moreover, the light rays cannot penetrate the walls and will experience greater blocking caused by the equipment during propagation. Hence, modeling the VLC channel in the IIoT scenario is necessary for industrial applications, and the existing channel models for typical indoor scenarios are not applicable in factories [7]. In addition, the channel characteristics (e.g., path loss and delay spread) might vary significantly [5] due to the larger physical size in the IIoT scenario. Furthermore, the severe multipath fading caused by the scatterers will also contribute to inter-code interference (ICI), leading to the difficulty of the VLC communication system. Therefore, a link adaptation method should be proposed to optimize the multipath interference. This manuscript mainly focuses on the VLC channel characterization in the IIoT scenario and the designing of the link adaption method. In the state of the art, several works have been conducted on these two aspects.