In this paper the solar-blind ultraviolet (UV) light is used as communication medium for wireless sensor networks (WSNs). Three types of single scattering UV communication models are introduced and a directional flooding model is proposed, which are based on the directionality of the UV communication and the traditional flooding routing model. The delay, delay jitter, throughput and energy consumption of the three types of communications of the new model are simulated and compared. The results indicate that the proposed directional flooding model can effectively avoid the unidirectionality and the blindness of the traditional flooding broadcast messages. The energy consumption of nodes in the network is reduced and the life cycle of the network is extended.The ultraviolet light communication is a kind of wireless optical communication by the scattering, which can realize the non-line-of-sight (NLOS) communication [1] . And it is suitable for short distance communication, and is not easily interfered and captured [2][3][4] , since the attenuation of ultraviolet light in the atmosphere is high.The research on routing protocol is important in the wireless sensor network (WSN). At present, the routing protocols in WSNs can be divided into flat-based routing protocol and hierarchical routing protocol. The flooding routing protocol is one of the flat routing protocols, and it does not need to maintain routing information, distributes data rapidly, and can guarantee the robustness of the network. However, there are extensive unusable duplicate messages in the flooding process of the traditional flooding routing protocol. Some improved schemes are presented [5][6][7][8] . The modified arithmetic can enhance energy availability, and can effectively reduce the redundant data packets, but it increases the time delay, transmission cost or arithmetic complexity. Based on the location information of the node, a directional flooding routing arithmetic is proposed by using the directionality of ultraviolet light wireless communication. The realization of it is easy, and the transmission cost is small. Hence, it can curb * This work has been supported by the the redundant information of flooding broadcast, save the node's energy and prolong the life cycle of the entire network.Because of the Rayleigh scattering and the Mie scattering, the "solar-blind" ultraviolet light is attenuated rapidly in the atmospheric transmission. However, the scattering transmission path can bypass the artificial and natural obstacles, realizing the no-line-of-sight communication [9][10][11] .There are three types of communication modes, depending on the angle between the optical axis and the horizontal axis ( Fig.1). They are NLOS (a), NLOS (b) and NLOS (c), respectively. Fig.1 NLOS communication modes of the ultraviolet light [11]Tab.1 indicates the performance comparison of the three types of communication modes.The traditional flooding model [5] has a serious waste of

Duty-cycled technology has been introduced as an efficient way to preserve node energy and prolong network lifetime for wireless sensor networks (WSNs). However, many applications with real-time feature require that some message must be sent to the sink node within a limited time. The authors propose a novel data collecting scheme-MTDR which aims to minimise transmission delay in low-duty-cycle WSNs. In MTDR, all the nodes are assigned to the corresponding levels according to the hop count to the sink node, and calculate their minimum transmission delay to the sink node based on the shortest path structure. Finally, simulation results show that their proposed algorithm can achieve better performance compared with some related works.