# A Review of Hybrid VLC/RF Networks: Features, Applications, and Future Directions
## 5 Challenges and Future Directions for Hybrid VLC/RF Networks  
This section discusses important issues facing hybrid VLC/RF networks as well as their future directions, including the use of Software Defined Networking (SDN) platforms, multiple access techniques, the development of new modulation and coding schemes, the design of efficient resource allocation and handover algorithms, the development of security mechanisms, the hybrid channel model, load balancing, uplink communication in VLC, outdoor scenarios, and Optical Camera Communication (OCC). The use of SDN platforms has been booming in recent years due to their ability to efficiently manage all access points in the network. Several papers have been presented on SDN [177] in which the advantages of its use in resource allocation and network scalability have been demonstrated. The use of SDN platforms in hybrid VLC/Femtocell networks remains in its infancy, and it remains necessary to study this topic in greater depth. The use of SDN platforms in hybrid VLC/RF networks must overcome challenges such as the coexistence of technologies and hybrid topology management [178]. Hybrid VLC/RF networks must be able to interoperate efficiently with existing technologies, which can pose compatibility and interference management challenges. In addition, the management of hybrid topologies may require a more dynamic and flexible approach to ensure optimal connectivity between the two technologies. Therefore, new standards and algorithms for VLC/RF networks on SDN platforms that facilitate interoperability and coexistence of the technologies are required. This can help minimize compatibility issues and manage interference effectively [179]. Supporting user mobility is vital in hybrid networks. The user may move in the scenario with multiple obstacles, which makes the location of the mobile receiver and the coordination mechanism between the LED transmitter and the RF base station a key challenge for multiple access techniques [51]. The CSMA/CA access technique has been presented separately for single network scenarios instead of hybrid networks [180] making a CSMA/CA access technique especially designed for hybrid VLC/RF networks required in order to support user mobility. On the other hand, non-orthogonal multiple access (NOMA) techniques have been presented in recent works as a promising option for multiple access between users via power multiplexing [97; 118]. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Applications** & **VLC/RF Systems** & **RF Network** \\ \hline IoT Home [161] & \(\bigstar\) (Bandwidth, Latency) & \(\star\) \\ IoT Factory [162] & \(\bigstar\) (Bandwidth, Latency) & \(\bigstar\) (Coverage) \\ Vehicle Control [163] & \(\bigstar\) (Latency, Coverage) & \(\star\) \\ Security [119] & \(\bigstar\) (Security, Reliability) & \(\star\) \\ System Capacity [166] & \(\bigstar\) (Energy efficiency) & \(\star\) \\ Mining Systems [168] & \(\bigstar\) (Interference, Connectivity) & \(\bigstar\) (Coverage) \\ agriculture [170] & \(\bigstar\) (Interference, Connectivity) & \(\star\) \\ localization [172] & \(\bigstar\) (Underground connectivity) & \(\bigstar\) (Coverage, Precision) \\ Power Transfer [118] & \(\bigstar\) (Bandwidth, Latency) & \(\star\) \\ IoT City [131] & \(\bigstar\) (Bandwidth, Latency) & \(\star\) \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Summary of VLC/RF network performance for different applications. The \(\star\) and \(\bigstar\) marks indicate good and excellent performance, respectively. The communication channel is the medium responsible for transmitting information between the transmitter and receiver. Efficient channel modeling is vital because it reduces multi-project and interference effects [40]. It is necessary to optimally design a hybrid channel model that integrates VLC and RF technologies and takes advantage of the benefits provided by each channel independently.