Tomlinson-Harashima Precoding for MU-MISO ODDM-Based Satellite Communications

The high mobility in low-earth-orbit (LEO) satellite communications results in severe Doppler spreads, for which orthogonal delay-Doppler (DD) division multiplexing (ODDM) modulation has emerged as a promising solution. In this paper, we investigate the Tomlinson-Harashima precoding (THP) scheme for downlink multi-user (MU) multiple-input single-output (MISO) ODDM transmissions. This scheme facilitates simplified equalization, and numerical results confirm its superior performance in mitigating the inter-symbol coupling in the DD domain. In addition, we characterize the achievable sum-rate of the proposed scheme by establishing an information-theoretic equivalent model. In particular, we derive the scaling laws for the achievable rate with respect to the number of antennas and users. Numerical simulations corroborate the accuracy of our theoretical derivation.