Non-Orthogonal Multiple Access-Based Average Age of Information Minimization in LEO Satellite-Terrestrial Integrated Networks

In this paper, we investigate non-orthogonal multiple access (NOMA) based average age of information (AoI) in LEO satellite-terrestrial integrated networks. Two-user NOMA scheme is used in terrestrial networks and several satellites provide orthogonal access for the rest of users to update status packets. Firstly, the closed-form expressions of average AoI in terrestrial networks and satellite channels are derived with average block error rate. Then, the average AoI minimization problem is decomposed into two parts: 1) average AoI minimization in terrestrial networks and 2) average AoI minimization among satellites. In the first part, a base station-terrestrial user selection and transmit power optimization algorithm is proposed for choosing the optimal NOMA pair and transmit power to minimize average AoI in each BS. A coalition formation game (CFG) is formulated to minimize average AoI among satellites in second part. With the proposed Min-AoI order, the CFG is theoretically proven to be an exact potential game, which can achieve total average AoI minimization of all satellite users. A distributed CFG-based algorithm is proposed for SUs grouping with low complexity. Finally, numerical results are provided to verify the correctness of theoretical analysis and evaluate our proposed algorithms, compared with other schemes.