## 4 OWC Technologies for the 5G, 6G, and IoT Solutions
### Fulfilling the Network and Infrastructure Characteristics
WiFi does not offer any guaranteed QoS and is affected by high interference caused by sharing the unlicensed band with Zigbee, Bluetooth, and many other ISM (industrial, scientific, and medical) band devices. The OWC technologies have a superior capability of meeting the requirements of the IoT networks compared to other existing wireless technologies. _Small-cell networks_: An effective method of increasing the area spectral efficiency is to shrink the cell size where a small number of users are served by a cell [49]. To support the cellular connectivity and cope with the demand, the third generation communication system contains only the macrocellular networks; the 4G system added small-cell and microcell along with macrocellular networks, whereas the 5G system will contain ultra-dense small-cells along with macrocellular networks [50]. The shrinking creates an opportunity to provide more spectra to each user. The introduction of indoor small-cell or femtocell has opened a lot of opportunities. The cell radius of an indoor small-cell is around 10 m to serve five to six users [51]. The small-cell deployment is a cost-effective and energy-efficient solution of meeting the coverage and capacity requirement [45]. The peak user data rates of the 5G and 6G communication systems are expected to be 10 Gbs and 1 Tbps, respectively. Heavy data traffic must be handled by indoor small-cell networks because large data are generated indoors. Hence, one of the most important characteristics of the 5 GB communication systems will be the deployment of highly dense small-cell networks. The indoor VLC and LiFi create highly dense small cells. Each of the networks under one light source is considered a small cell. Even hundreds of VLC/LiFi-based small cells can be found in a large room. Hence, the OWC networks can fulfill the criteria for the 5G/6G networks. _Seamless movement_: Seamless movement is an essential criterion for considering any kind of technology in the 5 GB networks. The LiFi system offers complete mobility support to meet the demand of 5G and 6G communication systems. Figure 6: Few examples of massive connectivity using the OWC technologies. High-capacity backhaul networkA backhaul is a network that connects the access network to the core network. Current backhaul networks mostly comprise dedicated fiber, copper, microwave, mmWave, and, occasionally, satellite links [8; 52]. Backhaul connectivity using satellite link depends on the availability of other options. A high-capacity backhaul network is an essential part in the 5 GB systems' ability to exchange a large volume of data traffic between the access and core networks. Without a high-capacity backhaul network, the communication system will not be completed, even though the access networks support the Gbps communication link between the access network and the user equipment. A low-capacity backhaul network will create a bottleneck in the system. Along with the wired optical fiber networks, optical wireless networks, such as the FSO, can effectively solve this issue. The FSO system has excellent features to establish a high-capacity and long-range outdoor backhaul link. Figure 7 presents a few scenarios of the high-capacity backhaul connectivity using FSO communications. High-capacity backhaul networks using the FSO provide connectivity in remote areas, such as underwater, sea, space, and an isolated island. Even the FSO can be used to establish excellent quality connectivity with the macrocellar base stations (MBSs), instead of the existing backhaul network technologies. Table 4 presents a comparison of the achieved data rates and latencies in a few important existing backhaul technologies. The throughput in optical fiber is the highest among all the technologies up until now. However, the throughput in FSO system is comparable with optical fiber. Both the optical fiber and FSO systems use a similar type of transmitter and receiver, and, hence, it will possible to achieve similar throughput in FSO as is the case with the optical fiber system in near future.