## 1 Introduction
The study explores various network topologies, performance analyses, and system-level simulations of hybrid RF/VLC systems, showcasing their potential benefits in terms of connectivity, throughput, coverage, and energy efficiency. By discussing research directions and emerging applications, the authors highlight the significance of hybrid RF/VLC systems in improving user rates, mobility, network capacity, and overall network optimization. In [11], the researchers developed an indoor hybrid PLC/VLC/infrared (IR) communication system based on the TCP/IP model. The system integrates PLC, VLC, and IR to enable full-duplex communication between two personal computers. By utilizing a virtual network interface and implementing Carrier-Sense Multiple Access (CSMA) as a medium access technique, the system achieves a latency of 2.85 ms and a bandwidth of 29 kbps. The integration with the TCP/IP model was facilitated through software written in Python, and Universal Software Radio Peripheral (USRP) software was used to define radio platforms with the GNU radio program for physical layer implementation. The experimental setup included a PLC link, a VLC downlink, and an IR uplink, showcasing the feasibility and performance of the hybrid communication system in indoor environments.The authors in [12] investigated the physical layer security of hybrid PLC and VLC networks, addressing a gap in the current research, which had previously largely focused on communication reliability and resource allocation. The study examined secure communication in a two-hop PLC/VLC network with two legitimate users employing non-orthogonal multiple access (NOMA), and considered the threats posed by eavesdroppers on both the PLC and VLC links. By analyzing the channel statistical characteristics influenced by the randomness of impulsive noise in the PLC link and user positions in the VLC link, the authors derived approximate closed-form expressions for secrecy outage probability (SOP). Their simulations validated the theoretical findings, highlighting the necessity of a joint parameter design for both links to achieve optimal secrecy performance. Their results demonstrated that the worst-case SOP scenario occurs when eavesdropping is possible on both the PLC and VLC links, compared to eavesdropping on a single link. The study in [10] presents a hybrid optical wireless network that integrates FSO and VLC to address the needs of space-air-ground-ocean communication architectures, particularly in RF-sensitive or security-requiring environments. The study defines the functional modules of the network coordinator and outlines the implementation and deployment details. Key network-layer mechanisms--user identification and localization, user mobility and handoff control, and routing and traffic management--are designed within the coordinator. An experimental platform evaluates the transmission performance of the hybrid network, demonstrating a complete data aggregation, transmission, and distribution procedure using heterogeneous interconnections. This includes a two-segment 1.0 m 450 Mb/s VLC transmission interconnected by a one-segment 430 m 0.96 Gb/s FSO transmission, maintaining a BER within the forward-error-correction limit. The study also experimentally assesses VLC performance at three speed levels and FSO performance under five air-quality conditions, confirming the feasibility and reliability of the proposed hybrid optical wireless network for high-data-rate, secure communication in various environments. In terms of THz, similar to VLC, several studies have been conducted that combine it with either RF or FSO [13; 14]. Some studies have been conducted on performance improvement that combine all three of them into one system; for example, in [6], the authors propose a hybrid FSO/RF-THz DF relay link. Here, an adaptive combining-based approach is used for the backhaul network by combining FSO and RF, and then, through the DF relay, the end user receives the information using a THz link.