Age of Information Study in Energy Harvesting Dual-sensor Network Based on HARQ

Oriented toward energy harvesting dual sensors and a destination wireless sensor state update system, wherein sensors with finite size batteries collect energy to transmit sensed state updates to the destination. A two-stage communication strategy that integrates the transmission of sensing and control data is proposed to ensure the freshness of data at the receiving end. Specifically, the target transmits control data to the sensor using a selective combination of Hybrid Automatic Repeat Requests (HARQs), and the sensor is triggered to synchronize sensing and send the corresponding state updates to the destination using a maximum proportional combination of truncated HARQs. The system focuses not only on the latest sensed data but also on steadily collected energy. First, the stochastic energy reach model is investigated, and the corresponding energy transfer matrix and its steady-state probability distribution are obtained. Second, the maximum ratio merging and selective merging retransmission techniques are adopted for sensing data and control data, respectively. Preemptive and nonpreemptive transmission schemes are considered, and the explicit expressions of the Age of Information (AoI) with respect to the probability of sensing, the probability of energy reach, and the maximum number of transmissions are derived. The numerical simulation results demonstrate the effects of different network parameters on the AoI of the system. Additionally, the performance of the preemptive and nonpreemptive transmission schemes are compared. The results reveal that the preemptive transmission scheme can achieve a lower AoI to some extent compared to that achieved by the nonpreemptive transmission scheme.