OFDM-Based Massive Connectivity for LEO Satellite Internet of Things

Low earth orbit (LEO) satellite has been considered as a potential supplement for the terrestrial Internet of Things (IoT). In this paper, we consider grant-free non-orthogonal random access (GF-NORA) in orthogonal frequency division multiplexing (OFDM) system to increase capacity and reduce latency LEO satellite-IoT. We focus on joint device activity detection (DAD) channel estimation (CE) problem at point. The delay Doppler effect are assumed be partially compensated. propose an OFDM-symbol repetition technique better distinguish residual shifts, present grid-based parametric probability model characterize sparsity delay-Doppler-user domain, well relationship between states activity. Based that, develop robust Bay esian message-passing algorithm named modified variance state propagation (MVSP) DAD CE. Moreover, tackle mismatch real its on-grid representation, expectation–maximization (EM) framework is proposed learn grid parameters. Simulation results demonstrate that our algorithms significantly outperform existing approaches both accuracy.