Embracing Beam-Squint Effects for Wideband LEO Satellite Communications: A 3D Rainbow Beamforming Approach

2025-12-21

AI Summary

In low-Earth-orbit (LEO) satellite broadband communications, beam squint induces intra-band beam misalignment, while conventional beam-hopping techniques suffer from uplink throughput bottlenecks and high latency due to time-domain switching. To address these challenges, this paper proposes a novel three-dimensional (3D) “rainbow beamforming” paradigm. It pioneers the reconfiguration of beam squint—from a detrimental interference source into an actively programmable resource—leveraging true-time-delay (TTD) and joint phase–time array (JPTA) antennas. Through 3D geometric modeling and a non-convex alternating optimization framework, the approach achieves full-coverage single-slot transmission and massive-user concurrent uplink reception. Experimental results demonstrate a 2.8× improvement in uplink throughput and significant latency reduction, establishing a key enabler for 6G global real-time broadband access.

Technology Category

• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Search and Optimization: Sampling/Simulation-based Search
• Machine Learning: Large Multimodal Models (LMMs)

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Data management and stream processing for Web, mobile and wireless applications
• Search and Retrieval-Augmented AI: Personalized, context-aware and across-device search
• User Modeling, Personalization and Recommendation: On-Device user modeling, personalization, and recommendation

Abstract

Low Earth Orbit (LEO) satellite communications (SATCOM) offers high-throughput, low-latency global connectivity to a very large number of users. To accommodate this demand with limited hardware resources, beam hopping (BH) has emerged as a prominent approach in LEO SATCOM. However, its time-domain switching mechanism confines coverage to a small fraction of the service area during each time slot, exacerbating uplink throughput bottlenecks and latency issues as the user density increases. Meanwhile, wideband systems experience the beam-squint effect, where analog beamforming (BF) directions vary with subcarrier frequencies, potentially causing misalignment at certain frequencies, thereby hindering the performance of wideband SATCOM. In this paper, we aim to shift the paradigm in wideband LEO SATCOM from beam-squint as an impairment to beam-squint as an asset. Specifically, we put forth 3D rainbow BF employing a joint phase-time array (JPTA) antenna with true time delay (TTD) to intentionally widen the beam-squint angle, steering frequency-dependent beams toward distributed directions. This novel approach enables the satellite to serve its entire coverage area in a single time slot. By doing so, the satellite simultaneously receives uplink signals from a massive number of users, significantly boosting throughput and reducing latency. To realize 3D rainbow BF, we formulate a JPTA beamformer optimization problem and address the non-convex nature of the optimization problem through a novel joint alternating and decomposition-based optimization framework. Through numerical evaluations incorporating realistic 3D LEO SATCOM geometry, our numerical results demonstrate that the proposed rainbow BF-empowered LEO SATCOM achieves up to 2.8-fold increase in uplink throughput compared to conventional BH systems. These results mark a significant breakthrough for 6G wideband LEO SATCOM.

Problem

• Addresses uplink throughput and latency bottlenecks in LEO satellite communications.
• Leverages beam-squint effects to serve entire coverage areas simultaneously.
• Optimizes joint phase-time array beamforming for wideband satellite systems.

Innovation

• Employs 3D rainbow beamforming with joint phase-time array
• Uses true time delay to intentionally widen beam-squint angle
• Serves entire coverage area in single time slot via frequency-dependent beams