Hybrid Analog/Digital Precoding for Downlink Massive MIMO LEO Satellite Communications

TL;DR

This paper proposes hybrid analog/digital precoding methods for downlink LEO satellite massive MIMO systems, optimizing energy efficiency using statistical CSI and addressing implementation complexity, with algorithms tailored for different architectures.

Contribution

It introduces energy-efficient hybrid precoding algorithms for LEO satellite MIMO, considering both fully and partially connected architectures with discrete phase shifts.

Findings

Significant energy efficiency gains over existing methods.

Effective algorithms for both fully and partially connected architectures.

Discrete phase shift networks enhance precoding performance.

Abstract

Massive multiple-input multiple-output (MIMO) is promising for low earth orbit (LEO) satellite communications due to the potential in enhancing the spectral efficiency. However, the conventional fully digital precoding architectures might lead to high implementation complexity and energy consumption. In this paper, hybrid analog/digital precoding solutions are developed for the downlink operation in LEO massive MIMO satellite communications, by exploiting the slow-varying statistical channel state information (CSI) at the transmitter. First, we formulate the hybrid precoder design as an energy efficiency (EE) maximization problem by considering both the continuous and discrete phase shift networks for implementing the analog precoder. The cases of both the fully and the partially connected architectures are considered. Since the EE optimization problem is nonconvex, it is in general difficult to solve. To make the EE maximization problem tractable, we apply a closed-form tight upper bound to approximate the ergodic rate. Then, we develop an efficient algorithm to obtain the fully digital precoders. Based on which, we further develop two different efficient algorithmic solutions to compute the hybrid precoders for the fully and the partially connected architectures, respectively. Simulation results show that the proposed approaches achieve significant EE performance gains over the existing baselines, especially when the discrete phase shift network is employed for analog precoding.