# Advanced Progress of Optical Wireless Technologies for Power Industry: An Overview
## 2 Classification and Progress of Power Industry Optical Wireless Communications
### Integrated Transmission Schemes of Power Line and Indoor Wireless Optical Communications
Paper [37] studies the link of relaying cascade PLC and IWOC with amplify and forward (AF) relay, based on that AF relay has not been considered to connect PLC and IWOC links before. In the first stage, the source transmits the information to the relay through the PLC link. In the second stage, AF relay amplifies the received signal and forwards it to the target node via IWOC channel. Setting the total capacity of a hybrid IWOC/PLC system provides the opportunity to examine the performance of such a system and the effect of different system parameters such as relay position and relay distance to the target. The accuracy of the results is verified by Monte Carlo simulation. Figure 17: Demo and Android APP for indoor localization based on IWOC: (**a**) demo [12]; (**b**) receiver (back and front) [12]; (**c**) signal detection in the Android APP [16]; (**d**) map localization in the Android APP [19]. For comparison, the performance of the hybrid system is compared with that of the hybrid/PLC, in which a linear combination is used to maximize the overall capacity of the system. In [67], the coordination between the light sources and how to improve the performance of the IWOC system are studied. The author verifies that the implementation of decode and forward (DF) relay has better performance than AF relay, as shown in Figure 18. To further improve the performance of PLC and IWOC cooperative system, researchers introduced relay technology into such IWOC indoor broadcast communication system [37; 38; 68; 69; 70]. In [69], PLC link is connected with IWOC link through DF relay and becomes the backbone of IWOC link. This paper investigates both AF and DF protocols for IWOC-based uplink transmissions. In traditional cellular mobile networks, relay technology can significantly improve network throughput and extend coverage. Inspired by this, PLC and IWOC system can also be regarded as relay-assisted dual-hop communication systems. At the signal transmission level, there are two main relay technologies to choose from, namely decoding and forwarding and amplifying and forwarding. In the decoding, forwarding, and relay scheme, PLC signals need to be demodulated and decoded for PLC transmission before being loaded into LED light source, and then re-coded and re-modulated for IWOC transmission [38]. At the same time, in the amplification code forwarding and relay scheme, the analog PLC signals superimposed with noise components are directly amplified and sent when loaded onto the LED light source, without any coding operation [66]. Specifically, The PLC subsystem assumes part of the return link of IWOC link, which is susceptible to log-normal distribution fading and additive noise. The former method can completely eliminate the cumulative effect of the above noise by DF, but the implementation complexity is relatively high. Although the latter scheme cannot eliminate the influence of noise, it does not involve complex decoding and encoding operation, and the implementation complexity is very low, which is beneficial to significantly reduce the implementation cost of the system. At present, international research teams have proposed to provide services for users through multiple IWOC access points in IWOC link, as shown in Figure 18. The simulation indicates that the overall characteristics of system depend on the random distribution of the multi-user in the end terminal. By selecting the diversity combination technology, the appropriate access point can be  
Figure 18: System model for the DF relaying hybrid IWOC/PLC network for indoor communication applications [67]. selected for the user, and then the maximum instantaneous SNR can be provided for the user. On the basis of a single relay node, the performance gain can be further introduced into the system. For the sake of enhance the throughput performance of integrated PLC and IWOC systems, more and more researchers are engaged in related research work.