# Research on Networking Protocols for Large-Scale Mobile Ultraviolet Communication Networks
## 2 LSM-UVCN
### Networking Protocol  
Protocols based on competition-free mechanisms can ensure the normal transmission of the highest-priority data during channel competition, adhering to the \"one frame per time slot\" principle even under intense competition [15; 16; 17; 18; 19; 20]. This approach significantly enhances channel utilization while preserving network flexibility. However, in large-scale network scenarios with exponentially increasing channel resources, such protocols remain constrained to transmitting a single frame per time slot. This limitation prevents performance scaling with resource expansion and may even degrade efficiency due to increased inter-node distances.  
Through in-depth analysis, we identified that competition-free protocols require full network connectivity, necessitating the broadcast of data to all nodes. Nevertheless, only the competition segment (priority segment) of the frame is critical for achieving competition-free transmission. Once this segment is transmitted and the winning node is determined, other nodes cease transmission. Hence, the root cause of channel resource wastage lies in the continued broadcast of subsequent frame segments across the network after competition resolution.  
LSM-UVCN addresses this inefficiency by decoupling channel competition from data transmission. It establishes multiple non-interfering data transmission paths through successive competition rounds, followed by simultaneous data transmission from multiple source nodes to achieve spatial division multiplexing, as illustrated in Figure 3.  
Figure 3: The complete workflow of the networking protocol.  
First, the network enters the neighbor discovery stage, during which a connection matrix is established in each node. Subsequently, the network proceeds to the transmission stage, which comprises multiple complete transmission cycles. Each complete transmission cycle includes several channel competition time slots and one data transmission time slot.  
In the channel competition time slots, nodes engage in competition-free competition with other nodes by broadcasting short frames that contain only the source node ID, destination node ID, and priority field. Eventually, the node with the highest priority successfully wins the competition. Then, a transmission path is established by traversing the connection matrix.  
The proposed protocol employs a shortest path selection algorithm prioritizing high-priority nodes to establish transmission paths. Taking the network topology shown in Figure 1a as an example, when Node 3 needs to transmit data to Node 1 and successfully wins the competition, each node uses Node 3 as the source and generates a hop-by-hop neighbor table by traversing the connection matrix, as shown in Figure 4. Subsequently, each node determines a unique transmission path in Figure 4 according to the strategy of selecting the shortest path via high-priority nodes, thereby completing path establishment.  
During the data transmission time slot, instead of broadcasting data across the entire network, only the relay nodes on the transmission path perform relay forwarding. Through simultaneous data transmission along multiple transmission paths, SDM can be achieved, enabling the full utilization of channel resources and enhancing network performance.