Age of Information in Ultra-Dense IoT Systems with Noisy Channels: With and Without Feedback

摘要

In this paper, a dense Internet of Things (IoT) monitoring system is studied in which a large number of devices contend for transmitting timely status packets to their corresponding receivers over wireless noisy channels, using a carrier sense multiple access (CSMA) scheme. When each device completes one transmission, due to possible transmission failure, two cases with and without transmission feedback must be considered. Particularly, for the case without feedback, the device uses policy (I): It goes to an idle state and releases the channel regardless of the outcome of the transmission. For the case with perfect feedback, if the transmission succeeds, the device goes to an idle state, otherwise it uses either policy (W), i.e., it goes to a waiting state and re-contends for channel access; or it uses policy (S), i.e., it stays at a service state and occupies this channel to attempt another transmission. For those three policies under schemes with and without preemption in service, the closed- form expressions of the average age of information (AoI) are characterized. It is shown that, for each policy, the scheme with preemption in service always achieves a smaller average AoI, compared with the scheme without preemption. Then, a mean-field approximation approach with guaranteed accuracy is developed to analyze the asymptotic performance for the considered system with an infinite number of devices. Simulation results show that the proposed mean-field approximation is accurate even for a small number of devices and policy (S) achieves the smallest average AoI among the three policies.