# Advanced Progress of Optical Wireless Technologies for Power Industry: An Overview
## 2 Classification and Progress of Power Industry Optical Wireless Communications
### Channel Characteristics between Power Line and Indoor Wireless Optical Communications
#### 2.1.2 Channel Characteristics of Outdoor Wireless Optical Communications
Small-scale fading is mainly due to the multipath signal at the receiving end passing through different paths during transmission, which leads to different amplitudes, delays, and phases. When the signal arriving at the receiving end has no LOS transmission, it is regarded as to obey the Rayleigh distribution. In the part of PLC, researchers usually follow the adaptive echo model put forward by [PERSON] [10]. This model comprehensively reflects the attenuation characteristics of multipath propagation, dependent frequency, and line length in a dynamic line network. In the IWOC part, for the convenience of modeling and analysis, researchers usually use the wireless optical integrator model to represent the frequency response of IWOC channel. Unlike the traditional OW non-parametric modeling scheme that requires data estimation to obtain the density distribution form, the channel gain of channel irradiance component can be obtained directly only by the surface area of the light receiver and the room and the average reflective of the room, and the modeling complexity is significantly reduced. By changing PLC channel parameters, the researchers simulated different PLC environments and frequency responses. With the increase in the number of PLC channel taps, the frequency response grooves of PLC and IWOC joint channels will need to be further increased. The results of different PLC network with IWOC-PLC channel are shown in Figure 5[11]. Figure 5a indicates the frequency response to IWOC-PLC channel. It evaluates a bad PLC network environment with six taps and bandwidth in excess of 10 MHz. The parameters of IWOC environment are a room with an area of about 25 m\({}^{2}\), the effective surface area of IWOC receiver is 3 cm\({}^{2}\), and the distance from the LED transmitter is about 3 m [11]. Figure 5 shows the PLC channel and the resulting IWOC-PLC channel. From the results, the PLC-IWOC channel has a notch characterized which varies throughout the entire frequency band. We have likewise observed the effect of the IWOC channel, which weakens frequency response  
Figure 5: The results of different PLC network with their resulting IWOC-PLC channel: (**a**) 6 PLC taps network [11]; (**b**) 12 PLC taps network [11]. of the PLC channel. IWOC-PLC channel also simulates and approximates the low-pass frequency characteristics of the PLC channel. Specifically, Figure 5b shows the joint channel characteristics of PLC and IWOC with 12 PLC taps. In particular, the VLC in Figure 5a,b represented by IWOC in this paper. [PERSON] et al. studied the random channel generator of the hybrid PLC and IWOC system, and a set of variable parameters in [25] is used to describe the complex transfer function of the general typical apartment complex system network. The power line (with branch) is the backbone network. IWOC LED is used as a visible light modulator for electrical signal scheduling, as shown in Figure 6a. In [26], the CFR of the indoor power line channel is presented as the sum of all propagation paths under low-voltage conditions. APD is a photoelectric converter that demodulates an optical signal into an electrical signal and is generally considered to be an all-pass filter because of its broadband properties. Figure 6b shows the measured pure power line channels and integrated channels. It can be seen from the figure that, compared to pure PLC channel, the attenuation of the integrated channel is large and the channel performance is poor [25]. To characterize the influence of LED modulation bandwidth on the frequency response of integrated PLC and IWOC channel, the researchers measured part of the frequency response of IWOC  
Figure 6: The integrated PLC and IWOC: (**a**) Channel structure of the integrated PLC and IWOC; (**b**) measured pure PLC channel and integrated channel [25]. and the overall frequency response characteristics of the mixed system in the laboratory environment, as shown in Figure 7.  
The measurement results are demonstrated that the attenuation introduced by the LED light source near 50 MHz is only 10 dB.