Design Of Information Transmission Scheme And Evaluation Of Information Timeliness Characteristics Of Satellite Internet Of Things Syste

Under the fact that the fifth generation(5G)mobile communications system has been commercially deployed in worldwide and the research of the sixth one(6G)has been launched,as one of critical derivers for 5G/6G,the internet of things(Io T)has been developed quickly.Today,the application of Io T can be found in various scenarios,such as agriculture,industry,medicine,vehicle,smart furniture,and so on.In terrestrial communications,because of low power of sensors and complicated environment,the signals of Io T systems are degraded greatly and the coverage is heavily limited.The freshness of status update of sensors can not be satisfied.Recently,as another main direction of Io T,the satellite Internet of Things(S-Io T)has been proposed and investigated widely.However,the S-Io T is characterized by large distance between transmitter and receiver and non-trivial propagation latency.This results in the low throughput in classical hybrid automatic repeat request(HARQ)policy.Therefore,it is a key to design an effective status update delivery scheme for S-Io T system with high throughput and information freshness.This thesis focuses on the problem.The main contributions are as follows.(1)To achieve the simultaneous improvement on throughput and information freshness of the S-Io T,a novel scheme is proposed for the timely delivery of status update packets,which perfectly integrates adaptive Modulation and Coding(AMC)and Layer-coded hybrid automatic repeat request(L-HARQ)policies.With AMC policy,the transmitter adaptively selects the transmission rate of packets based on the feedback of channel status information(CSI)at receiver.At the same time,in L-HARQ policy,a mixing packet is retransmitted in each round,which consists of the new packet and the one that is not successfully decoded in previous round.The retransmission policy overcomes the disadvantage of the classical HARQ.Both feedforward and backtrack decoding policies are used at receiver.In addition,the truncated HARQ is used to satisfy the timeliness of state updates,where the maximum number of retransmissions is limited.Considering the large delay of signal propagation,the difference of CSIs between transmitter and receiver is specially exploited.As a result,the packet error ratios of both feedforward and backtrack decoding are derived under Rayleigh fading channel model.(2)In proposed novel scheme,both feedforward and backtrack decoding policies are simultaneously employed.In the feedforward decoding,the last packet is obtained.However,in the backtrack decoding,the system obtains the time instant at which the receiver lastly successfully recovers a status update.This makes that it is vague to calculate the age of information(Ao I)by using its classical definition.Motivated by this observation,this thesis proposes the idea of age of error information(Ao EI),which is defined as the time since the generation instant of the status update that is lastly and successfully decoded at receiver during backtrack decoding.The concept of Ao EI shows the trade off between throughput and information freshness.Then,the Ao EI evolution model is established by defining the related variables of time durations.By charactering the statistical descriptions of theses time duration variables,the precise mathematics model of Ao EI is proposed.In the established Ao EI model,it is found that the key parameters are coupled.This yields that it is hard to find the optimal Ao EI.With this fact,under the throughput constraint,an Markov Decision Process(MDP)is established for the AOEI optimization problem as well as the value iteration algorithm.The presented numerical results validate the analysis ones.(3)Aming at the space-ground communication systems,a general status update system with probability preemption of bufferless M/PH/1/1 queueing is established by using queuing theory.The distribution expressions of Ao I and PAo I(Peak Age of Information)of each information source are obtained by using matrix analysis algorithms such as Markov fluid queue theory and sample path parameters.Firstly,the accuracy of the proposed method is verified by simulation and theoretical analysis.Secondly,by comparing with the traditional non-preemptive strategy,self-preemptive strategy,global preemptive strategy and preemptive strategy,the probability-based preemptive strategy is the best Ao I strategy.