## 4 OWC Technologies for the 5G, 6G, and IoT Solutions
### Fulfilling the Network and Infrastructure Characteristics
for outdoor applications, the hybrid system can overcome the atmospheric effect. Figure 5 illustrates a few possible means of connectivity in the RF/optical hybrid systems. The RF and optical links work together for connectivity. Connectivity from a source to a destination is established directly or through relay. The optical link in the relay system can be established either from source-to-relay or relay-to-destination in a hybrid system. In any or both of these, the links can also be established with the presence of optical and RF links simultaneously. The forward and return communication links may be different or the same on the basis of the application scenario and the hybrid type. Another possibility is the sharing of forward and return paths. The optical links can be used for the forward path, and the RF link can be used for the return path. Hence, the OWC technologies can play an important role in designing hybrid systems to mitigate the limitations and bring a proper solution in the 5G/6G networks. _Massive device connectivity:_ Massive connectivity is a crucial characteristic of future communication systems. The IoT in 5G is predicted to connect up to 50 billion heterogeneous devices. These devices will be used in not only mobile phones but also in other devices, such as vehicles, household electronics, and medical equipment, to build a smart society [46]. Through the massive connectivity, the IoT supports an integration of various sensors and physical devices, which can monitor and communicate directly with one another without human intervention [47]. In addition, it is expected that the IoT in the 6G paradigm will connect more devices with the capability of being intelligent in nature. The OWC can play a vital role in providing massive connectivity. The usage of LEDs for different purposes is exponentially increasing because of LEDs' low price, low-energy consumption, and longer life span. The OCC has especially attracted much interest in the area of IoT. Using an existing or a slightly modified infrastructure, the OCC facilitates the development of economically attractive solutions for a wide range of IoT applications. Hence, the OWC technology can provide an enormous number of connections through low-power LEDs to achieve the goals of the 5G/6G and IoT networks. Figure 6 illustrates only a few examples of massive connectivity in different environments through different OWC technologies. The OWC technologies support massive connectivity in homes, healthcare, transportation systems, remote connectivity, and smart grid systems. A smart grid comprises different operational and energy-measuring devices, such as smart meters, smart appliances, renewable energy resources, and energy-efficient resources. Through the massive connectivity among these, smart grids serve as building blocks for energy management of a sustainable environment [47]. Figure 5: Few possible ways of connectivity using optical and RF hybrid systems. The IoT networks have some important characteristics. Some key requirements of the IoT are low device cost, low deployment cost, high energy efficiency, high security and privacy, and support for a large number of devices. The LED-based OWC systems have all the great features required to support the IoT. The key technologies currently used for the IoT connectivity are Zigbee, Bluetooth Low Energy (BLE), and WiFi. Zigbee is a low-cost, low-power, wireless mesh network standard that has been widely used for IoT applications [48]. Zigbee only supports a low transmission rate, and its security level is not good. The interference is a concern in dense Zigbee networks. The BLE is a smart low-energy version of Bluetooth designed for short-range communication. The BLE currently only supports a single-hop topology, namely piconet, with one master device communicating with several slave nodes, and a broadcast group topology with an advertiser node broadcasting to several scanners [48].