# Channel Characteristics and Link Adaption for Visible Light Communication in an Industrial Scenario
###### Abstract
In terms of VLC channel modeling in indoor scenarios, the works can be divided into two groups, i.e., simulations and measurements. In the first group, theoretical VLC channel models (e.g., recursive and iterative models) and ray-tracing simulations are usually used to characterize indoor VLC channels. For example, the optical path loss (OPL) of non-Line-of-sight (NLOS) components with different reflection orders was analyzed in [8] by using simulations with the iterative model. Other configurations, e.g., the room size and transceiver deployment, were also considered in [9] through simulations. However, some simplifying assumptions such as empty rooms and fixed reflectance were considered in these works. Therefore, the most realistic indoor VLC channel modeling is presented in [10; 11], where accelerated ray tracing features of Zemax(r) are used to obtain channel impulse responses (CIRs) for various indoor environments. In [12], the VLC channel characteristics based on the flexible OLED are investigated in shopping malls by using ray-tracing simulations. Numerical models for the delay spread and optical path loss are derived, which followed a 2-term power series model for both empty and furnished rooms. Authors in [13] propose a realistic channel model for VLC assuming a mobile user. The CIRs for each point over the user movement trajectories are obtained and the path loss and delay spread are further proposed as a function of distance through curve fitting. Furthermore, a ray tracing-based channel modeling method is adopted to characterize the effect of user mobility on the VLC channel parameters in [14]. Statistical models for path loss and RMS DS are further proposed in the simulated 3D environments, where the user, upon which three MBSN nodes are placed, walks over extensive realistic random trajectories. Authors in the [15] compared the propagation characteristics between mmWave and VLC bands in a conference room by using ray-tracing simulations. The OPL model was further proposed as a function of the distance and physical size of photodetectors (PDs). In [11], four different real-life-based hospital scenarios were designed to model and characterize the downlink VLC-based MBSN channels. Generally, simulation results should be validated by experimental investigations. In the second group, [16] presented channel measurement campaigns with an empty room, including LOS and NLOS cases. Then, the large-scale OPL and channel impulse responses were investigated. In [17], the wavelength dependence of the optical path loss was experimentally analyzed and modeled in the conference room and corridor. In terms of the designing of the link adaption method, authors in [13] proposed a simple adaptive VLC transmission scheme that selects both optimal combinations of light emitting diodes (LEDs) and modulation orders to maximize the signal-to-noise (SNR) and spectral efficiency (SE), while satisfying a targeted value of the bit-error-rate (BER). Furthermore, in [18], the effects of the user-mobility were mitigated by an adaptive VLC transmission technique, which varies the modulation order under a specified BER constraint. An adaptive modulation scheme that aims to maximize the data rate under the constraint of a targeted bit error rate was also considered in [5]. However, these methods cannot solve the problem of the co-channel interference (CCI) under multiple LED cases. Hence, in [19], a novel delay adaptation technique is proposed to mitigate CCI. The authors controlled the time of transmitting the effective signal so that the LOS components from variable transmitters arrive at the receiver side at the same time. Generally, the existing works regarded to the indoor VLC channel characterization are mainly limited to typical indoor scenarios, such as the conference room, the living room, and the underground mining environment. To the best of our knowledge, almost no existing literature focuses on characterizing and modeling the VLC channel characteristics in the IIoT scenarios.