Joint Device Identification, Channel Estimation, and Signal Detection for LEO Satellite-Enabled Random Access

This paper investigates joint device identification, channel estimation, and
signal detection for LEO satellite-enabled grant-free random access, where a
multiple-input multipleoutput (MIMO) system with orthogonal time-frequency
space modulation (OTFS) is utilized to combat the dynamics of the
terrestrial-satellite link (TSL). We divide the receiver structure into three
modules: first, a linear module for identifying active devices, which leverages
the generalized approximate message passing (GAMP) algorithm to eliminate
inter-user interference in the delay-Doppler domain; second, a non-linear
module adopting the message passing algorithm to jointly estimate channel and
detect transmit signals; the third aided by Markov random field (MRF) aims to
explore the three dimensional block sparsity of channel in the
delay-Doppler-angle domain. The soft information is exchanged iteratively
between these three modules by careful scheduling. Furthermore, the
expectation-maximization algorithm is embedded to learn the hyperparameters in
prior distributions. Simulation results demonstrate that the proposed scheme
outperforms the conventional methods significantly in terms of activity error
rate, channel estimation accuracy, and symbol error rate.