Research On Block-node Based Topology Control Algorithm For Optical Wireless Communication Networks

Due to high bandwidth, high security, flexible networking and other advantages, Optical Wireless Communication(OWC) has become one of the most important research topics in the field of communications. With the expansion of network scale, the increase of user needs and the arrival of the big data era, simple point-to-point OWC has not been able to meet the requirements of large-scale network applications. OWC Networks(OWCN) are more and more urgent.Firstly, the features of OWC, the research significance and the development status and trends around the world are discussed in this paper. The key technologies are introduced, including the precise beam control, efficient optical signal transceiver, fast and accurate APT, the influence of atmospheric channel on OWC and topology control. On one hand, these key technologies boost the development of OWC; on the other hand, they become the obstacles of mobile OWC networking. Especially, its networking becomes more and more difficult with the increase of node speed.At present, researches on OWC networking technology for high speed mobile nodes are relatively little. APT technology required by OWC increases the difficulty of high dynamic topology networking. OWC node carries the limited antennas, so its maximum degree constraint is low. Therefore, a Block-Node Based Topology Control Algorithm(BNBTCA) which is referred to as BNB Algorithm is proposed. The algorithm is designed for multi nodes topology formation in high speed movement, which aims to make connectivity as high as possible and maintain the topology as stable as possible in low maximum degree constraint. Realization of BNB algorithm is divided into two steps: the first step is to form Block-Node which has high internal stability using the prediction values of contact time as weights. The second step is to form multi-connection topology between Block-Nodes according to the quantitative link weights. Eventually, a connected topology graph forms.The BNB algorithm includes three sub algorithms: contact time prediction algorithm, BlockNode formation algorithm and multi-connection between Bock-Nodes formation algorithm. In addition, the algorithm design and simulation are based on Smooth Random Mobility(SRM) model, which is more complex. In SRM model, the movement direction and speed jump of nodes do not exist, which approaches to a realistic environment and can reflect the effectiveness more accurately.Finally, the BNB algorithm for the planar structure OWCN is simulated in SRM model and is compared with Minimum Spanning Tree(MST) algorithm. The results show that the topology formed by BNB algorithm has higher network connectivity and reliability than that of MST algorithm. And by changing the nodes and network parameters, the influences of maximum degree constraint and topology update period on BNB algorithm are analyzed. Results show that the higher maximum degree constraint or the shorter topology update period makes the network performance better. Theoretical analysis and simulation results show that the BNB algorithm has obvious advantages on topology stability and connectivity under low maximum degree constraint of high-speed mobile node, and can effectively solve the non-uniform distribution problem of topology connectivity.