| In recent years,with the rapid development of time-sensitive Internet of Things(Io T)applications in the 5G and 6G wireless era,such as industrial control,smart home systems,Unmanned Aerial Vehicles control,and other time-sensitive applications,people begin to pay attention to different time-related performance metrics,namely delay,and age,to provide time-sensitive services.However,these problems become increasingly challenging in wireless environments due to the inherent unreliability of wireless channels.Age of Information(Ao I)is a new performance metric proposed in recent years,which captures the freshness of information from the perspective of the destination.Under the unreliable wireless scenarios,by focusing on multi-user applications,this thesis studies comprehensively Ao I models and transmission scheduling strategies and designs actual network control mechanisms.By using system implementation,the performance of these mechanisms in actual operating scenarios is evaluated.The specific research contents are as follows:(1)For the multi-access wireless sensor networks with limited channel resources,in order to realize real-time information transmission,it is required to consider channel environment,spectrum utilization,and freshness of information.Firstly,the thesis proposes a cognitive radio network model in which Secondary Users(SU)share the spectrum of Primary Users(PU)through the underlying scheme.Sensor node with Energy Harvesting(EH)function dynamically monitors changes in the surrounding environment and transfers status updates to common secondary target nodes.Considering the stability of the data queue in SU,the working state of PU,and the stable service interference constraints,an optimization problem is proposed to minimize the average Ao I and the average Peak Ao I(PAo I)of EH nodes.Secondly,the Probabilistic Random Access(PRA)strategy and the Drift Plus Penalty(DPP)strategy are used to solve the probabilistic random access strategy.The simulation results show that the DPP strategy is more significant than the PRA strategy in Ao I optimization,and can effectively improve the timeliness and freshness of data packets.(2)In general,due to the small size of sensors,the Wireless Sensor Network(WSN)is characterized by the limited coverage of communications and a limited energy supply.In addition,in WSN the packet size is small,which yields that it is difficult to accurately describe the achievable rate and reliability of signal transmission by using the conventional assumptions with an infinite length of codes with the help of Shannon theory.With this inspiration,a multi-access relay-assisted WSN based on Short Packet Communications(SPC)is introduced.By considering the channel transmission failure and node throughput constraints,the optimal scheduling strategy is studied to optimize the transmission sequence of source-destination node pairs,so as to obtain the overall average optimal Ao I performance.Finally,an improved stationary random access strategy is proposed.The correctness of the derivation is verified by comparative analysis.In addition,the simulation results show that the improved stationary random access method not only improves the freshness of information but also imposes a remarkable effect on the system throughput,which provides a clear line for the system design.(3)The sensors in WSN are usually deployed in remote locations with complicated working environments.This yields that it is difficult to realize the direct transmission of signals from source to destination.Inspired by this fact,this thesis proposes a multi-relayassisted large-scale multi-source multi-destination Io T system by designing a hybrid timedivision and frequency-division transmission scheme and introducing the idea of partial optimal terminal reception.Based on the Round-Robin scheduling strategy,to obtain subpackets transmitted on multiple parallel sub-channels,a Random Linear Network Coding(RLNC)scheme is used for the multiple information packets of each heterogeneous sensor source so that multiple network-coded packets are achieved.After channel coding,these resulting sub-packet signals are parallelly transmitted to multiple relays that work on a single frequency point.At relays,a partial earliest reception relay selection scheme is proposed.Only these selected relays that work on a single point,forward the received packets to the information-receiving destinations by using the decode-and-forward protocol.In order to meet the information timeliness,for the considered large-scale information delivery and reception system,an evolution model of instantaneous Ao I is first introduced.Using mathematical ordering theory,the statistical characterizations of the number and time duration of transmissions are derived.As a result,this thesis achieves the average Ao I at a given information receive destination from a sensor source.At the same time,the average Ao I is investigated with the help of multi-source scheduling. |
