# Optical Wireless Fronthaul-Enhanced High-Throughput FC-AE-1553 Space Networks
## 3 System Model of Optical Wireless Fronthaul-Enhanced Hybrid Space Network
### HSN Layered Architecture  
When the FC-AE-1553 terminal node is enhanced with wireless capabilities, it extends the existing multi-layer Fiber Channel protocol architecture to incorporate a multi-layer Ethernet protocol architecture (Figure 4). This integration occurs at the application layer, enabling the seamless coexistence of wired FC-AE-1553 communication and wireless Ethernet communication within the terminal node. This optimized architecture offers enhanced flexibility and efficiency in communication, empowering the terminal node to effectively adapt to diverse communication requirements while achieving superior capabilities in data transmission and task processing.  
**Physical Layer and Data link Layer**  
The physical and data link layers are responsible for bit synchronization recovery, channel coding and decoding, link establishment, disconnection, and link recovery. In this hybrid architecture, the Li-Fi physical channel is separated from the FC-AE-1553 physical channel. The FC-AE-1553 network is connected by a fiber or copper cable with an optical module or high-speed electrical transceivers. The Li-Fi network is connected by free space with an LED transmitter and photo-detector receiver. The physical and data link layers of the FC-AE-1553 network follow FC-PI-2 [56] and FC-PH [57] standard protocols. The physical and data link layers of the Li-Fi network follow the IEEE 802.11 bb standard protocol.  
**Transport Layer**  
The transport layer is responsible for end-to-end communication, flow control, segmentation of data, error correction, multiplexing, and demultiplexing. In this hybrid architecture, the transport layers of Li-Fi and FC-AE-1553 are used independently. The transport layer of the FC-AE-1553 network follows FC-FS [58] and FC-AE-1553 [32] standard protocols, and the transport layer of the Li-Fi network follows UDP [59] and TCP [60] standard protocols.  
The FC-AE-1553 protocol varies across different terminals, as each terminal has a distinct role in the multi-hierarchical FC-AE-1553 system. In the root terminal, the NC protocol is followed. In the gateway terminal, both the NT and NC protocols are used, with the NT protocol belonging to the higher-level network and the NC protocol to the lower-level network. In the user terminal, the NT protocol is employed.  
In addition to the FC-AE-1553 and Li-Fi channels, there is an alternative option for data transmission within an independent terminal. The bridge module serves as a connection  
Figure 4: Hybrid layered architecture.  
between FC-AE-1553 and Li-Fi in the transport layer. It enables data to be received from the FC and forwarded to the Li-Fi or received from the Li-Fi and directly forwarded to the FC without requiring control from the application layer.  
**Application Layer**  
The application layer is responsible for upper-layer network scheduling, data security, reliability, and privacy, and controls the processing of tasks. It serves as the direct interface for user interactions, with user behavior influencing traffic transfer and offloading requirements. In this hybrid network, the application layer comprises four key modules: the user application module, traffic management module, network management module, and time-slot management module. The user application module facilitates user access and system configuration interactions, whereas the traffic management module handles the scheduling and selection of multi-priority traffic. The network management module monitors, collects, and calculates network parameters, and the time-slot management module is responsible for effectively partitioning time slots for pending tasks.