Massive MIMO Transmission for LEO Satellite Communications

TLDR

LEO satellite communications are poised to become integral to future 5G and beyond networks, offering global high‑rate access, yet massive MIMO techniques—widely used on Earth—have not yet been applied to these systems. This work proposes a massive MIMO transmission scheme with full frequency reuse for LEO satellites that leverages statistical channel state information to replace infeasible instantaneous CSI. The scheme models the LEO MIMO channel, applies Doppler and delay compensation at user terminals, and derives closed‑form low‑complexity sCSI‑based downlink precoders and uplink receivers that maximize ASLNR and ASINR, followed by a space‑angle user‑grouping algorithm to schedule users. The proposed design achieves upper‑bound DL ASLNRs and UL ASINRs under certain conditions, is asymptotically optimal as antenna or group counts grow, and numerical results show substantial data‑rate gains with sCSI‑based precoders matching the performance of impractical iCSI schemes.

Abstract

Low earth orbit (LEO) satellite communications are expected to be incorporated in future wireless networks, in particular 5G and beyond networks, to provide global wireless access with enhanced data rates. Massive multiple-input multiple-output (MIMO) techniques, though widely used in terrestrial communication systems, have not been applied to LEO satellite communication systems. In this paper, we propose a massive MIMO transmission scheme with full frequency reuse (FFR) for LEO satellite communication systems and exploit statistical channel state information (sCSI) to address the difficulty of obtaining instantaneous CSI (iCSI) at the transmitter. We first establish the massive MIMO channel model for LEO satellite communications and simplify the transmission designs via performing Doppler and delay compensations at user terminals (UTs). Then, we develop the low-complexity sCSI based downlink (DL) precoder and uplink (UL) receiver in closed-form, aiming to maximize the average signal-to-leakage-plus-noise ratio (ASLNR) and the average signal-to-interference-plus-noise ratio (ASINR), respectively. It is shown that the DL ASLNRs and UL ASINRs of all UTs reach their upper bounds under some channel condition. Motivated by this, we propose a space angle based user grouping (SAUG) algorithm to schedule the served UTs into different groups, where each group of UTs use the same time and frequency resource. The proposed algorithm is asymptotically optimal in the sense that the lower and upper bounds of the achievable rate coincide when the number of satellite antennas or UT groups is sufficiently large. Numerical results demonstrate that the proposed massive MIMO transmission scheme with FFR significantly enhances the data rate of LEO satellite communication systems. Notably, the proposed sCSI based precoder and receiver achieve the similar performance with the iCSI based ones that are often infeasible in practice.