Research On Timeliness Of Wireless Sensor Networks Based On Random Multiple Acces

The Internet of Things applications would increasingly rely on the exchange of latencysensitive information for state monitoring and control.Applications such as command and control systems,industrial control,virtual reality,and sensor networks,for example,rely heavily on the distribution of time-sensitive information.In sensor networks,sensors need to send their observations to control centers to ensure operational safety.In vehicular networks,vehicles need to exchange safety-critical information with other vehicles around them,and this requirement would increase with the advent of driverless cars.Likewise,unmanned aerial vehicles are required to exchange position,speed,and other control information to avoid collisions in the air.In such applications,it is important to keep the information fresh,otherwise outdated information would be less valuable to use.To characterize the freshness of information,the age of information(AoI)comes into existence.In this thesis,we investigate the timeliness of wireless sensing networks based on random multiple access.The thesis mainly contains the following work:1.The timeliness of the CSMA/CA and slotted Aloha based wireless networks are investigated.For each of the two protocols,equivalent operational transmission models are developed.Based on this new developed model,the transmission probability,collision probability,service rate,and average AoI of the networks are derived,respectively.In the process of deriving the average AoI,it is found that the packet arrival interval and the packet waiting time are correlated.To this end,the auxiliary function is constructed to calculate the expectation of the product of the packet arrival interval and the packet waiting time.It calculates the maximum packet rate that the network can allow and the number of nodes that can be contained.Finally,the correctness of the theoretical analysis is verified through simulations,and it explores the impact of packet rate and number of nodes on the timeliness performance of the network,as well as the advantages and disadvantages of AoI performance using CSMA/CA and slotted Aloha based networks.2.The timeliness of the slotted Aloha based wireless broadcast network is investigated.First,an analyzable transmission model is developed for analyzing the whole network broadcasting and forwarding process of the slotted Aloha based wireless broadcast network.Based on this model,the transmission probability,collision probability,and service rate are derived.Second,a traffic model for operational analysis is developed by using an approximation between the Poisson process and the Bernoulli process at low traffic rates.Based on these two models,from the transmitter perspective,the timeliness and speed of the broadcasting process and the forwarding process are investigated,which are called the broadcast age of information(bAoI)and the spread velocity,respectively.The broadcast capacity,the packet spread velocity,and the average bAoI of the network are given explicitly.Therefore,the temporal metric of bAoI and the spatial index of spreading velocity exhibit a kind of duality and can be optimized by adjusting traffic rate and transmission range,respectively.Finally,the correctness of the theoretical analysis is verified by simulations,and parameters such as traffic rate,node density,and transmission range are explored on the timesensitive performance.