Research On Content Transmission Algorithms In Dense Deployment Based Vehicular Networks

With the rapid development of wireless communication technique,vehicular networks have been well recognized to provide increasing convenience and entertainment to drivers and passengers.In order to facilitate a more pleasant journey,vehicular networks promise a large number of applications including safety auxiliary driving system and in-vehicle entertainment.In recent years,the demand for content service is increasing.As a result,content dissemination is one of the most important applications in vehicular networks,such as web browsing,video and audio content download.Unlike the traditional wireless networks,vehicles are often moving very fast and suffer from the harsh channel conditions.Therefore,the achieved data rate is difficult to satisfy the requirement.Densely deploying RSUs is a potential technique to increase the transmission rate by decreasing the distance between an RSU and a vehicle.However,densely deploying RSUs increases the interference at each vehicle,such that the transmission rate varies significantly when vehicles move along the road.This paper mainly studies the latency-constrained content dissemination scheme in dense small cell based vehicular networks.We consider that each vehicle requests content with a predefined deadline.The server should schedule to transmit the content to the requesting vehicle before its expiration time.Otherwise,the download fails.By exploiting the deadline characteristic of content,if the vehicle suffers from the harsh channel condition because of interference,the server can postpone to schedule it until the achieved data rate is increased,so as to improve the system throughput.On the other hand,always scheduling the packet with high transmission rate would cause some packet to be dropped due to expiration.Therefore,designing an efficient scheduling scheme for latency-constrained content dissemination in vehicular networks is not trivial.Firstly,we propose a scheduling algorithm based on time expended graph.We formulate the scheduling problem with the objective of minimizing the spectrum resource consumption while satisfying the delay requirement of content.Upon receiving a content download request,the server constructs the corresponding TEG according to the deadline demand and the existing flows in the system.Based on TEG,the scheduling problem can be converted into a minimum cost flow problem.We can solve it by the existing algorithm with low computational complexity.The simulation results show that the proposed algorithm can minimize the consumption of system spectrum resources and meet the delay requirement compared with the existing earliest due date algorithm.Besides,another scheduling algorithm based on lyapunov optimization for the latencyconstrained content dissemination in vehicular networks is proposed.The proposed scheduling algorithm exploits the explicit delay information from the head-of-line packet at each vehicle to stabilize the network.By proper packet dropping,the delay requirement can be ensured.Simulation results show that the proposed algorithm can guarantee the demand of delay and improve the throughput of the system compared with the earliest due date algorithm.