Information Freshness in Truncated Layer-HARQ Based Satellite-IoT Systems

To achieve the simultaneous improvement on throughput and information freshness of the satellite-based Internet of Things (S-IoT), this paper firstly proposes a method based on the adaptive modulation and coding (AMC) and truncated layer-HARQ (L-HARQ) strategies. Secondly, considering the fact that the improved backtrack decoding is used in the L-HARQ, the original definition of age of information (AoI) be insufficient to quantify the status update delivery, this paper proposes the age of error information (AoEI), which is defined as the elapsed time since the generation of the last successfully backtrack-decoded status update. Thirdly, the closed-form expression of average AoEI is derived under the assumption of independent and identically distributed fading channels. Finally, the Markova Decision Process (MDP) is used to optimize the packet parameters in each round of L-HARQ process under the general fading scenario. Thereby, the optimized transmission scheme that minimizes AoEI is solved. The simulations investigate the effect of system parameters on the average AoEI.