Unequal Timeliness NOMA Downlink Scheme for Mission Critical Communications in Satellite-Integrated Internet

The satellite-Integrated Internet can provide unequal timeliness protection multicast (UTM) for various mission critical communications (MCC) in the upcoming sixth-generation (6G) network. In this paper, we propose two UTM non-orthogonal multiple access (NOMA) downlink schemes for three types MCC user equipments (UEs) in satellite-Integrated Internet, named independent successive UTM (IS-UTM) and cognitive offloading UTM (CO-UTM). First, in the IS-UTM scheme, we utilize age of information (AoI) to capture the timeliness requirements of information, and classify three types MCC UEs into three groups and specify their transmission stages in the transmission frame according to their AoI requirements. To further enhance timeliness and reliability for MCC UEs, we propose CO-UTM scheme to allow timeliness critical group to share redundant resources to timeliness tolerable group. Then, in order to meet the reliability and AoI requirements of MCC for the above ISand CO-UTM schemes, we adopt a proximal policy optimization (PPO)-based dynamic power allocation (PDPA) algorithm to minimize the long-term average packet error rate (PER) of MCC groups within a transmission stage. Simulation results show that the CO-UTM scheme has better AoI performance compared to the IS-UTM scheme when the timeliness critical group has redundant resources.