Graph-based conflict-free MAC protocol and conflict analysis for a two-layer ultraviolet communication network

Abstract

To efficiently exploit the space division multiplexing of ultraviolet (UV) communication, we apply link coverage characteristics to construct a conflict graph and design conflict-free protocols for a two-layer UV communication network. The network is divided into two layers: the first-layer network forms a backbone and the second-layer network serves as local access. We construct a routing model and medium-access control (MAC) model. Then we propose Routing-MAC joint scheduling for the first-layer network based on the conflict graph. We investigate the system throughput and delay of joint scheduling under different node intensities. For second-layer networks, we propose a multi-link conflict-free protocol adopting protocol frames of carrier sense multiple access with collision avoidance (CSMA/CA). Numerical results show that the multi-link conflict-free protocol can improve the system throughput by more than 100% compared with CSMA/CA. Moreover, we perform a conflict analysis on the proposed protocols to investigate the influence of conflict intensity. According to the conflict analysis, we optimize the path planning of Routing-MAC joint scheduling to reduce the average delay of the network. Numerical results show that the optimized Routing-MAC joint scheduling leads to larger system throughput and lower delay.