AoI Analysis in Energy Harvesting IoT Systems With ARQ and TARQ

Ensuring timely information delivery is of paramount importance for mission-critical applications in the Internet of Things (IoT). The age of information (AoI), which measures the time elapsed from data generation to reception, is critical for assessing information freshness in time-sensitive scenarios. This work focuses on the AoI analysis of cooperative IoT systems with decode-and-forward relaying mode, where automatic repeat request (ARQ) and truncated ARQ (TARQ) protocols are employed to enhance the reliability of short packet communications. The source and relay nodes have limited battery capacity, thereby harvesting energy from the charging towers. We derive analytical expressions for the average AoI and the average peak AoI for the proposed ARQ-assisted and TARQ-assisted protocols. Simulation results validate our theoretical analysis and explore the impact of system parameters on AoI performance. Our findings highlight the existence of the optimal packet length and retransmission time that minimize AoI, providing valuable insights for designing efficient IoT systems.