Since the channel propagation model for Vehicular Ad Hoc NETwork (VANET) is unrealistic in the urban environment, an propagation model considering the impact of obstacle was proposed. Firstly, using the position of the vehicle in the digital map, the propagation of the signal was classified into three types: Line Of Sight (LOS), Not Line Of Sight with one (NLOS-1) turn and prohibitive propagation. Secondly, the expression of the received signal power was introduced under the conditions of LOS and NLOS-1. Finally, the packet delivery ratio with Nakagami distribution was deduced. Theoretical analysis and simulation results show that the model can reflect an realistic propagation of the signal which is hindered by the obstacles at roadside, the reachability is decreased by 31.4 percentage points in light load and sparse network, while it is increased by 13.32 percentage points in heavy load and dense network. The rectilinear propagation effect of the high frequency 5.9 GHz signal was simulated by the proposed model, which provides a basis for the communication protocol design and the realistic simulation of VANET.

Through the cryptanalysis of a signcryption scheme without bilinear pairing proposed by Gao et al. (GAO J, WU X, QIN Y. Secure certificateless signcryption scheme without bilinear pairing.Application Research of Computers,2014,31(4):1195-1198) recently, the scheme could not resist public-key substitute attacks. Then a new ID-based signcryption scheme without bilinear pairing was proposed and the proposed scheme was proved to be secure in the random oracle model under the first type attacker. Finally, a contrast analysis of efficiency was made between the new scheme and other schemes. Compared with other signcryption schemes, the new scheme uses only 3 Hash operations and 7 point multiplication operations, so it has higher computational efficiency.