Holographic Metasurface-Based Beamforming for Multi-Altitude LEO Satellite Networks

TL;DR

The paper tackles the problem of delivering global Internet access via dense multi-altitude LEO satellite networks, addressing inter-satellite interference and the prohibitive overhead of acquiring full CSI.It introduces a holographic metasurface-based hybrid beamforming architecture, featuring a holographic beamformer at the terrestrial user and two MMSE-based digital beamformers, one using full CSI and another leveraging the distribution of visible satellites via stochastic geometry.A closed-form solution for the holographic phase design is derived, and the digital beamformers are analyzed with respect to throughput, including a complexity comparison that favors the distribution-based approach in dense constellations.Simulations show that when mutual coupling is accounted for, the holographic metasurface design outperforms state-of-the-art antenna arrays at the same hardware size, and the distribution-based MMSE RC closely matches full-CSI performance in dense deployments, reducing CSI overhead substantially.

Abstract

Low Earth Orbit (LEO) satellite networks are capable of improving the global Internet service coverage. In this context, we propose a hybrid beamforming design for holographic metasurface based terrestrial users in multi-altitude LEO satellite networks. Firstly, the holographic beamformer is optimized by maximizing the downlink channel gain from the serving satellite to the terrestrial user. Then, the digital beamformer is designed by conceiving a minimum mean square error (MMSE) based detection algorithm for mitigating the interference arriving from other satellites. To dispense with excessive overhead of full channel state information (CSI) acquisition of all satellites, we propose a low-complexity MMSE beamforming algorithm that only relies on the distribution of the LEO satellite constellation harnessing stochastic geometry, which can achieve comparable throughput to that of the algorithm based on the full CSI in the case of a dense LEO satellite deployment. Furthermore, it outperforms the maximum ratio combining (MRC) algorithm, thanks to its inter-satellite interference mitigation capacity. The simulation results show that our proposed holographic metasurface based hybrid beamforming architecture is capable of outperforming the state-of-the-art antenna array architecture in terms of its throughput, given the same physical size of the transceivers. Moreover, we demonstrate that the beamforming performance attained can be substantially improved by taking into account the mutual coupling effect, imposed by the dense placement of the holographic metasurface elements.

Figures (9)

• Figure 1: System model of holographic metasurface-based multi-altitude LEO satellite networks.
• Figure 2: Holographic metasurface-based hybrid beamforming architecture.
• Figure 3: Throughput $R$ versus the number of holographic metasurface elements in each microstrip $N$, with the fixed holographic metasurface element spacing $\delta_N=\frac{\lambda}{4}$ in each microstrip, i.e. the physical dimension of each microstrip being $\frac{\lambda}{4}N$.
• Figure 4: Throughput $R$ versus the number of holographic metasurface elements in each microstrip $N$, with the fixed physical dimension of $4\lambda$ for each microstrip, i.e. for the holographic metasurface element spacing of $\delta_N=\frac{4\lambda}{N}$.
• Figure 5: The throughput $R$ versus the physical size of the microstrip.