Deadline-Aware Adaptive Packet Scheduling And Transmission In Multi-hop Cooperative Wireless Networks

The past decades have witnessed the rapid growth of computational capability and various breakthroughs in wireless technologies.Based on these developments,a variety of services with strict delay requirements have emerged in commercial wireless networks,such as the streaming multimedia applications in mobile cellular systems,the real-time sensing and control in wireless sensor networks and so on.In these applications,packets have strict deadline constraints and must arrive at their destinations before their deadlines.Otherwise,they become invalid and are dropped,which degrade the quality of service.Therefore,how to meet the strict delay requirements in wireless networks has drawn increasing attention in recent years.In cooperative wireless networks,multiple transmission methods can be used in packet transmission,including network coding.On one hand,network coding can reduce transmission time by permitting a relay to encode at least two packets received separately from different source nodes.On the other hand,network coding can also bring coding delay.Therefore,it is necessary to develop a deadline-aware adaptive packet scheduling and transmission scheme to minimize the packet dropping probability in multi-rate cooperative wireless networks.This thesis first briefly introduces conventional network coding and physical network coding.Then how to calculate the transmission time of four kinds of transmission methods is presented.The delay constraint packet transmission is formulated into an optimization problem and an exhaustive search based method is proposed to obtain the optimum scheme.To reduce the computational complexity,a Markov approximation approach based method is proposed,in which the original optimization problem is approximated as a convex optimization problem and a Markov chain is constructed to obtain the approximate solution.To further reduce the computational complexity,a dynamic graph model based method is introduced by the observation of the optimal solution.Simulation results show that the two heuristic methods perform closely to the optimal solution.Finally,the two heuristic methods are compared in aspects of simulation time,packet dropping probability and different channel conditions.Simulation results show that the proposed heuristic methods achieve suboptimal results with low computational complexity,and each method can be applied indifferent scenarios.