Multi-Dimensional Polarized Modulation for Land Mobile Satellite Communications

In this article, a novel multiple-input multiple-out (MIMO) transmission scheme, called generalized polarized enhanced spatial modulation (GPESM), is proposed for dual-polarized land mobile satellite (LMS) communications. We first introduce the enhanced spatial modulation (ESM) technique for dual-polarized LMS communications, in which polarization dimension, spatial dimension and multiple signal constellations are used to transmit information and obtain substantial performance gain. Meanwhile, the theoretical upper bound for the average bit error probability (ABEP) of the proposed GPESM scheme is derived. In order to further improve the reliability of the system, we also propose two novel power allocation (PA) algorithms for GPESM system, which are the optimization-driven approximated max-min distance (AMMD)-based PA algorithm and the data-driven deep neural network (DNN)-based PA algorithm. To achieve an enhanced spatial diversity gain, we consider to apply a reconfigurable intelligent surface (RIS) to the GPESM system as a relay to assist in transmitting information. In this way, the user can receive the information transmitted by the satellite on one hand, and the information sent by the satellite via the RIS relay on the other hand. We also extend the above-mentioned two PA algorithms to the RIS-assisted GPESM systems. Our simulation results show that the RIS-assisted GPESM systems are capable of obtaining high bit error rate (BER) performance gain (up to 10 dB) compared to the standard GPESM system and two PA algorithms can further improve the performance to the systems.

I. Introduction

As the fifth generation mobile networks (5G) becomes commercially available, the research community has started to investigate the 6G. The latter will be not only limited to the ground, but also extended to the space and the sea to achieve ubiquitous and seamless connections between the ground, satellite and airborne networks [1]–[3]. Driven by this trend, in recent years, satellite communications have gained renewed interest with reduced satellite deployment costs and breakthroughs in materials and antenna technology [2]. Space-earth integration network has become a key issue in future 6G wireless networks. While the existing terrestrial cellular network technologies may be vulnerable to disasters and terrorist attacks, satellite platforms have a wide range of coverage and broadcast capabilities and can compensate the weakness of terrestrial platforms [2]–[4]. More notably, with commercial satellite companies investing heavily in the satellite industry, satellite platforms have become an important part of the Internet-to-Things (IoT) [1], [5]. In [3], unmanned aerial vehicle (UAV)-based low-altitude platforms (LAP) can be quickly deployed and flexibly adjusted to the optimal communication environment to achieve better bit error rate (BER) performance and energy efficiency in short-range communications. To address the large amount of data satellites in future, edge intelligent computing has been proposed in [5] for satellite IoT.