Age of Synchronization Minimization in Wireless Networks with Random Updates and Hybrid ARQ under Power Constraints

This work considers a wireless network transmitting status updates arriving randomly using the Hybrid Automatic Repeat Request (HARQ) protocol under average power con-straints. We measure the information freshness by the Age of Synchronization, which is defined as the time elapsed since the last synchronization. The updates transmitted unsuccessfully can be retransmitted with a higher success probability by the HARQ. However, there is a trade-off between retransmitting the old update with a high success probability and transmitting the new update with a low success probability. We model the time-average AoS minimization problem as a constrained Markov decision process (CMDP) and solve the problem by a relative value iteration algorithm. Numerical simulations show that our scheduling policy outperforms traditional ARQ and HARQ policies on the AoS performance and indicates the stability of our scheduling policy under different channel parameters.