# A Review-Unguided Optical Communications: Developments, Technology Evolution, and Challenges
## 5 Advancements in Optical Wireless Communications
### Optical Camera Communication (OCC)  
The growing use of smart devices equipped with a flashlight, LED screens, and multiple cameras, means they can also be used as a data Tx and receiver, to establish VLC links without the need for the additional hardware for the emerging IOT [332]. In VLC systems, two main decoders (photodetectors (PDs) and cameras (an image sensor designed with multiple PDs)) with a wide bandwidth (MHz to >GHz) are more commonly used. The PDs used for VLC normally have a high data rate, typically up to 4.81 Gbps, but have limited mobility, and increased blocking and shadowing [333; 334; 335]. A high-speed camera typically has much lower data rates, i.e., \(\approx\)200 kbps [336; 337]. In indoor contexts, however, multi-array Tx/Rx and/or NLoS VLC systems can resolve both shadowing and mobility, albeit at substantially lower data rates due to multipath generated dispersion [333]. In contrast, in outdoor contexts, PD-based VLC systems will be subjected to high levels of ambient light, particularly sunlight-induced noise, resulting in significant degradation of the link's performance in terms of SNR and BER [338]. Cameras based on CMOS technology offer spatial separation of multiple optical sources such as sunlight, streetlight, and vehicle lights. These cameras are used for vision, photography, surveillance, augmented reality [339], motion detection, virtual reality [340], localization [341], and data communications [342]. This feature led to the development of VLC with a camera, also known as OCC, which has piqued the interest of the research community [333; 343], and it has been examined as a part of the OWC framework and considered as an option in the IEEE 802.15.7\(\pi\) standard [344]. The use of PDs, or array-based image sensors, gives a large field of view to VLC-OCC with the spatial and wavelength separation of the lights [345]. VLC-OCC also offer MIMO capability [346] for use in indoor [347] and outdoor [348] applications such as device/machine to device/machine, communications, display-based transmissions, indoor positioning, etc., with no additional hardware [349]. In addition, unlike PD-based VLCs, VLC-OCC cameras capture two-dimensional (2D) data as image sequences, which allows for more information to be transmitted. Vision, surveillance, biometric facial recognition [350], scene change detection [351], augmented reality [352], positioning [353], digital signage [354], lighthouse-to-ship/ship-to-ship communications [355], and drone-to-drone communications for collision avoidance are all possible applications of VLC-OCC technology as a part of the fourth industrial revolution. However, one of the most interesting application areas for VLC-OCC is ITS for broadcasting traffic and safety-related information between road-side infrastructure and vehicles to improve traffic guidance [356], reduce pollution and energy usage, reduce road fatalities [357], improve economical productivity, and quality of life [358]. Every year, globally, road accidents result in \(\approx\)1.3 million deaths [359]. The information between vehicles and vehicle to road-side infrastructure can be established with the supports of ITS. The recent ITS developments use specific short-range communication (DSRC) infrastructure that mainly uses RF wireless technologies, where communications between vehicles can be established without using cellular wireless base stations [360].