Research On Random Access Under The Constraint Of Transmission Time Limit

The class of random access protocols has been a widely used solution to the channel-sharing problem for uncoordinated or asynchronous users,owing to its simple and distributed nature.Considering that some data services in WSNs,VANETs or SATNETs require a strict delivery deadline,this thesis aims to develop deadline-constrained performance analysis and optimization for ALOHA and CSMA type schemes.First,based on multichannel slotted ALOHA without retransmissions,in order to maximize the deadline-constrained system reliability of the unicast service,this thesis derives the optimal channel selection probabilities and the optimal transmission probability.Moreover,the optimal schedule subject to a throughput constraint is further obtained.Second,considering the coding-based slotted ALOHA for broadcasting systems,this thesis derives closed-form expressions for deadline-constrained performance metrics,such as system reliability,throughput and delay.In particular,a simple closed-form sub-optimal transmission probability for maximizing reliability is proposed and the minimum value of the coding packets is given.Third,for the retransmission-based CSMA used in broadcasting systems,this thesis proposes a 2-D Markov model to analyze the reliability,throughput and delay performance and verifies it under different network conditions.