Study On Scheduling Methods Based On Age Of Information For Wireless Networks With Retransmission Condition

Ao I(Age of Information)is a novel metric used to measure the timeliness of data transmission in wireless communication field.Ao I reveals a more accurate freshness of the data than delay by measuring the time interval from the generation of latest received data to the current time stamp from the perspective of receiver.Optimizing Ao I in the wireless networks has become an effective way to improve the real-time transmission performance.Besides,considering the error-prone characteristic of the wireless network channels,data retransmission has been used in diverse wireless communication scenarios to improve the reliability of networks effectively.However,how to promote both the reliability and data timeliness by optimizing network's Ao Is under retransmission conditions still becomes an unsolved problem.Therefore,this thesis focuses on constructing scheduling methods to solve Ao I optimization problem under the specific retransmission conditions in the wireless network.According to whether the ACK/NACK confirmation mechanism is adopted,the retransmission mechanism can be divided into a pre-scheduled fixed retransmission mechanism without transmission confirmation and a continuous retransmission mechanism with transmission confirmation,which generate different optimizing problems.The main contributions of the thesis include:1.This thesis analyzes the basic theories for Ao I optimization problem in wireless networks,including relevant Ao I theoretical analysis based on queue model,the analysis of updating Ao I in wireless networks and the analysis of partial retransmission mechanisms in wireless networks.2.Considering an asymmetric updating network with prearranged fixed retransmission mechanism,a scheduling method based on the policy of minimizing the system's expected decision loss is proposed.In first,a switch-type property of the optimal scheduling policy in symmetric updating network is proven,and the convergence state of the network Ao Is in this case is derived.Next,this thesis analyzes the scheduling process of the asymmetric updating network with prearranged fixed retransmission mechanism.By constructing the system's expected decision loss expression,this thesis proposes a policy named minimizing the system's expected decision loss policy,which forms the proposed scheduling method.3.Considering an asymmetric updating network with continuous retransmission mechanism,three scheduling methods are proposed in this case.In first,two novel policies are proposed by improving the policy of minimizing the system's expected decision loss.Then,the Lyapunov optimization framework is used to decouple the Ao I optimization problem and thus the original optimization problem is transformed into the problem of minimizing the frame based Lyapunov Drift.By solving the transformed problem,a scheduling policy named slot based max-weight policy is proposed.Finally,three scheduling methods are formed based on above policies.Simulation results show that the proposed methods can outperform the existed scheduling methods in terms of frame size,user's number,and maximum allowable retransmission times.In conclusion,the Ao I optimization problems under two different retransmission mechanisms are studied in this thesis,and four policies are proposed to improve the timeliness of data transmission while ensuring the high reliability of wireless network communications at the same time.All these works provide a great value for the development of Ao I optimization theory in wireless communication field.