Research On Safety Messages Delivery With Power Control In VANET

Vehicular Ad-Hoc Network(VANET) refers to a wireless ad hoc network between vehicles and vehicles. vehicles and roadside unit establish connection and transmission information with each other. Vehicles can get the surrounding road traffic conditions from other vehicles or RSU to ensure traffic safety and reliability. Therefore, how to ensure the effective delivery of safety message is an important topic in VANET.Safety messages in VANET usually deliver by broadcast. It can be further divided into single-hop delivery and multi-hop delivery depanding on the type of the message. The basic safety messages(BSM) usually deliver by single-hop broadcast which contains location,speed and other basic status of vehicle. The event driven message generally deliver by multi-hop broadcast which contains the information of accident and traffic condition. This thesis will both research single-hop broadcast and multi-hop broadcast with the point of power control in VANET.The target of power control in VANET is following: 1)If vehicles were sparse in road, distance between vehicles is farther. In this case, increasing transmission power of vehicles can enhance the connectivity of the network; 2)If vehicles were intensive in the road, a lot of vehicles contend the channel in the collision domain. It can achieve congestion control if vehicles decreased transimission in this situation. In order to solve these problem, this thesis propose a power dynamic adjustment method based on local vehicle density. Firstly, in order to get the local density, this thesis propose a distributed local density estimation algorithm DLDE. Every vehicles estimate the density based on the basic safety message receive in this period. Then, we propose a distributed power control algorithm DPDA which adjust transmission power with the local density from DLDE. Meanwhile, this thesis will describes the iteration between two algorithms: DLDE provides real-time node density information and DPDA can promote the success rate of BSM messages which cause density estimation result more accurate. The results of two algorithms will finally tend to converge. We use NS-3 network simulator simulate above two algorithm under multi scene to verify the accuracy of our achievement. Meanwhile, we simulate the process of iteration over several periods and verify that the result of DLDE after iteration is more acurrate than the result which use fixed transmission power.On the basis of above algorithms, we research multi-hop delivery strategy. This thesis proposed PDBV multi-hop broadcast protocol based on distance-based broadcasting strategy. To solve existing problems in tradition distance-based strategy, PDBV protocol propose a series of improvement measure. Since PDBV protocol will also use DPDA to adjust the transmission power, so the traditional one-hop-distance-base relay selection is no longer applicable. PDBV based on two-hop distance(last hop distance and next hop expected distance) to select relay node. This thesis will also use NS-3 network simulator simulate PDBV protocol and compared with the traditional distance-based broadcasting strategy. Simulation results shows, at least in reliability, real-time and low redundancy three dimensions, the PDBV protocol is better than traditional distance-based broadcasting strategy.