Energy-Age Tradeoff in Status Update Communication Systems Based on HARQ

The development of the Internet of Things (IoT) has given birth to many real-time applications, which have strict requirements for fresh data. Therefore, a new indicator, age-of-information (AoI), is defined to measure data freshness. On the other hand, the IoT devices such as remote sensors are usually energy-constrained. In this paper, we study the energy-age tradeoff in a state update system. In this system, a source node senses the status data and transmits to a receiver through an error-prone channel. When the transmission fails, the source may either retransmits the existing data to save energy, or sense and transmits new data to reduce the age-of-information. Hybrid Automatic Repeat request (HARQ) and threshold-based retransmission strategy are adopted. Then, we derive the expressions of the average information age and average energy consumption of the system. Finally, the theoretical results are verified via simulations, and the energy-age tradeoff relationship is analyzed. In addition, it is shown that HARQ strategy is more efficient than Automatic Repeat request (ARQ) when the channel condition is very poor.