A Novel VLC Channel Model Based on Beam Steering Considering the Impact of Obstacle
Abstract: In this letter, a novel channel model of visible light communication (VLC) system was proposed with the impact of position, size and shape of the obstacle taken into account. The illumination area of the light-emitting diode (LED) was divided into independent solid angles and the ray was transmitted in every solid angle by beam steering, then the point cloud of the obstacle was determined by the received rays in photo detector (PD). Further, the convex hull model was used to represent the point cloud for simplification, the complex VLC channel model was set up and the expression of the channel impulse response (CIR) was derived. Five scenarios with different obstacles were simulated for analysis and results revealed that the position, shape and size of the obstacle have deeply impact on channel characteristics of the VLC system. Besides, beam steering increased the uniformity of the signal-to-noise ratio (SNR) distribution and the available bandwidth. Monte Carlo (MC) simulation was also provided to confirm the correctness of the proposed channel model. Existing system:
The existing infrared communication by the recursive methodnd the modified Monte Carlo algorithm (MMCA) . To improve the speed of the algorithm, M. L. Zhang et al. proposed a photon-tracing algorithm (PTA) on the basis of MMCA. J. P. Ding et al. presented a rigorous and efficient channel modeling scheme named independent reflection interaction characterization (IRIC) by recursive method. Actually, these methods are all based on an empty room; by contrast, the real scenario contains certain obstacles, whose impact on the channel characteristics should be considered. Z. Y. Dong et al. used the Poisson process to describe a rectangular obstacle, but this method might lead to deviation when the number of obstacles is small. Y. Xiang et al. investigated the human shadowing effect on the indoor VLC channel property, and the obstacle was modeled as cuboid objects. Actually, for a real scenario, the obstacle would be at random positions with any shape and size. Therefore, a proper channel model including an accurate obstacle model would be in great need for high reliable VLC system design. Recently, beam steering technology has been applied in VLC to enhance system performance by focusing light on the desired target, and it could be also considered to detect the obstacle as laser radar does in unmanned technology. Proposed system: Motivated by the aforementioned facts, a novel channel model for indoor VLC is proposed in which LEDs are adopted to make a detection of the obstacle by beam steering, and then, the obstacle is described as a convex hull. The expression of the CIR is derived on the basis of recursive calculation, and beam steering is used to increase the received energy of the area whose line-of-sight (LOS) links are blocked through NLOS links. The scenarios are simulated with random obstacles, which are then verified by PTA, an MC method. Further, the characteristics of this complex channel are analyzed in detail. Advantages: In recent years, visible light communication (VLC), using light-emitting diode (LED) for both illumination and data transmission, has gained magnified attention due to its advantages such as high transmission rate, unlicensed spectrum, enhanced security, high modulation bandwidth, low energy consumption and low cost.
However, in the VLC system, the light ray arriving at the photo detector (PD) through non-line-of-sight (NLOS) path suffers multiple reflections through different reflecting surfaces, such as walls, floor, and ceiling, thereby leading to inter-symbol interference (ISI) and becoming a hindrance for high bit rate communication system. For overcoming this problem and obtaining an efficient, reliable, and robust VLC system, a proper channel model is quite essential for determining the channel characteristics that could provide a good description for the multipath interference. Disadvantages:
However, in the VLC system, the light ray arriving at the photo detector (PD) through non-line-of-sight (NLOS) path suffers multiple reflections through different reflecting surfaces, such as walls, floor, and ceiling, thereby leading to inter-symbol interference (ISI) and becoming a hindrance for high bit rate communication system. For overcoming this problem and obtaining an efficient, reliable, and robust VLC system, a proper channel model is quite essential for determining the channel characteristics that could provide a good description for the multipath interference. Modules: Visible light communication: In recent years, visible light communication (VLC), using light-emitting diode (LED) for both illumination and data transmission, has gained magnified attention due to its advantages such as high transmission rate, unlicensed spectrum, enhanced security, high modulation bandwidth, low energy consumption and low cost. However, in the VLC system, the light ray arriving at the photo detector (PD) through non-line-of-sight (NLOS) path suffers multiple reflections through different reflecting surfaces, such as walls, floor, and ceiling, thereby leading to inter-symbol interference (ISI) and becoming a hindrance for high bit rate communication system. For overcoming this problem and obtaining an efficient,
reliable, and robust VLC system, a proper channel model is quite essential for determining the channel characteristics that could provide a good description for the multipath interference. Photon- tracing algorithm: The existing infrared communication by the recursive method and the modified Monte Carlo algorithm (MMCA). To improve the speed of the algorithm, M. L. Zhang et al. proposed a photon-tracing algorithm (PTA) on the basis of MMCA in J. P. Ding et al. presented a rigorous and efficient channel modeling scheme named independent reflection interaction characterization (IRIC) by recursive method . Actually, these methods are all based on an empty room; by contrast, the real scenario contains certain obstacles, whose impact on the channel characteristics should be considered. Z. Y. Dong et al. used the Poisson process to describe a rectangular obstacle, but this method might lead to deviation when the number of obstacles is small. Y. Xiang et al. investigated the human shadowing effect on the indoor VLC channel property, and the obstacle was modeled as cuboid objects. Actually, for a real scenario, the obstacle would be at random positions with any shape and size. Therefore, a proper channel model including an accurate obstacle model would be in great need for high reliable VLC system design. Recently, beam steering technology has been applied in VLC to enhance system performance by focusing light on the desired target, and it could be also considered to detect the obstacle as laser radar does in unmanned technology. Recursive method: The one-bounce and two-bounce CIRs are calculated in all scenarios by a recursive method, which are verified by PTA, an MC method. The impact of obstacle is shown by comparing scenario 1 and scenarios 2-5 in Fig.6. It can be seen that the received energy is significantly decreased due to the existence of obstacle in VLC channel. Besides, the obstacles with varying sizes, shapes, and positions have different impacts on the CIRs. Table 2 shows the obtained time dispersion parameters of the five different scenarios. As can be found, for one-bounce, optical links with uniform time delays are blocked by the obstacles, and the time dispersion parameters show minimal difference. On the contrary, a lot of optical links with time delays in 25-35ns are blocked by the obstacle in two-bounce,
especially in Scenarios 3 and 5, which leads to increased variance and RMS delay spread.