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Rotatable Antenna-Enabled Space-Air-Ground Integrated Networks: Opportunities and Challenges

Yanhua Tan, Beixiong Zheng, Tiantian Ma, Qingjie Wu, Lipeng Zhu, Wenyan Ma, Cheng-Xiang Wang, Robert Schober, Rui Zhang

arXiv:2609.37338v1cs.ITeess.SPmath.IT

TL;DR

Fixed-boresight antennas have limited spatial adaptability as SAGIN service regions, link directions, and sensing tasks change. This article examines rotatable antennas (RAs), which adjust boresight while keeping antenna positions fixed, and discusses their roles, challenges, and implementation tradeoffs. A prototype and two simulations illustrate feasibility and potential benefits for air-ground ISAC and ground-satellite communication.

Abstract

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Space-air-ground integrated networks (SAGINs) are expected to support ubiquitous three-dimensional (3D) communication and sensing services in future sixth-generation (6G) wireless networks. However, heterogeneous mobility and service requirements across the space, air, and ground segments challenge fixed-boresight or fixed-sector antennas in supporting wide-area coverage, maintaining directional alignment over time-varying communication links, and flexibly adjusting observation directions for sensing tasks. To address these limitations, rotatable antenna (RA) technology has emerged as a promising solution by enabling mechanical or electronic boresight adjustment while keeping the antenna positions fixed. This article investigates the roles of RA technology in enabling communication and sensing in SAGINs. Specifically, we first explain how RA boresight control complements platform mobility and supports wide-area coverage, dynamic directional transmission, cross-segment cooperative operation, and cooperative sensing. We then discuss the main design challenges, potential approaches, and future research directions, including channel acquisition and predictive tracking, joint orientation control and access/handover coordination, cross-segment coordination and resource management, as well as deployment tradeoffs and practical implementation. Finally, an RA array prototype and two representative simulation studies are presented to illustrate the feasibility and potential performance gains of RA-enabled SAGINs.

I. INTRODUCTION

SAGINs address terrestrial infrastructure limits by combining satellite, aerial, and ground segments, but their heterogeneous mobility and service demands challenge fixed-antenna designs. Rotatable antennas offer fixed-position boresight adjustment, while coordinated flexible-antenna operation across all three segments remains relatively unexplored.

I. INTRODUCTION

  • SAGINs combine satellite, aerial, and terrestrial infrastructure to support services in remote and infrastructure-limited scenarios.Their segments have complementary capabilities, but differ in coverage, mobility, and propagation environments.Source: §I · p. 1
  • Fixed boresights or service areas limit spatial adaptability as service regions, link directions, and sensing tasks change over time.Compensation may require larger arrays, denser deployment, or more frequent updates, increasing hardware complexity, control overhead, and energy consumption.Source: §I · p. 1
  • RA adjusts boresight mechanically or electronically while keeping antenna position fixed, offering compact reconfigurability with lower hardware and control complexity.Prior FAS, MA, and 6DMA studies largely address individual links or specific segments; coordinated flexible-antenna operation across space, air, and ground remains relatively unexplored.Source: §I · p. 1

GEO (35786 km)

The article presents RA-enabled SAGINs as a unified 3D framework for diverse future 6G services. It outlines RA roles and challenges, then uses a prototype and simulations to illustrate feasibility and potential gains.

GEO (35786 km)

  • RA boresight adaptability complements platform mobility, enabling scanning across regions or tracking selected links and targets while nodes retain planned trajectories.This separates antenna orientation from platform trajectory and attitude control.Source: GEO (35786 km) · p. 2
  • The article frames RA-enabled SAGINs as a unified 3D framework for remote-area, aerial, maritime, transportation, and emergency services.Fig. 1 presents an architecture for RA-enabled SAGINs.Source: GEO (35786 km) · p. 2, Figure 1 · p. 2
  • An RA array prototype and two representative simulation studies illustrate implementation feasibility and potential performance gains for RA-enabled SAGINs.The article identifies air-ground ISAC and dynamic ground-satellite communication as the simulation settings.Source: GEO (35786 km) · p. 2

II. RA-ENABLED COMMUNICATION AND SENSING IN SAGINS

RA boresight control adds spatial adaptability to mobile SAGIN platforms while keeping antenna positions fixed. It complements platform motion through scanning or tracking, supporting service and observation within the regions that platform trajectories make accessible.

A. RA Boresight Control for Mobile SAGIN Platforms

  • RA boresight control adds spatial degrees of freedom that complement signal-domain beamforming as link directions vary across mobile SAGINs.This is useful when mission-constrained platform trajectories and attitudes cannot be adjusted solely to maintain alignment.Source: A. RA Boresight Control for Mobile… · pp. 2–3
  • Platform motion determines the accessible service or observation region, while RA provides finer directional adaptation within it.A UAV can follow its intended path while redirecting its antenna toward a link or sensing target; satellites can likewise retain their orbits while directing boresights.Source: A. RA Boresight Control for Mobile… · p. 3
  • Boresight scanning expands service or observation coverage, while boresight tracking maintains directional alignment with selected links or targets.The article introduces these modes as the basis for the communication and sensing functions discussed next.Source: §II · p. 2, A. RA Boresight Control for Mobile… · p. 3

B. RA-Enabled Communication in SAGINs

RA scanning and tracking support communication and sensing across mobile SAGINs. Scanning broadens service or observation coverage over time, while tracking and cross-segment coordination support directional links, target observation, and complementary sensing.

B. RA-Enabled Communication in SAGINs

  • Sequential boresight scanning extends the service region over time and can mitigate persistent coverage holes, but wider scans or more regions increase revisit intervals and reduce dwell time.Scan range and region count should reflect user distribution, traffic demand, service priority, and delay requirements.Source: B. RA-Enabled Communication in SAGINs · p. 3
  • RA tracking can maintain directional support as inter-node and cross-segment link directions change, with satellite ephemeris and planned UAV trajectories informing updates.Nodes can coordinate boresights along a satellite-backhaul, aerial-relay, and ground-access path.Source: B. RA-Enabled Communication in SAGINs · p. 3

C. RA-Enabled Sensing in SAGINs

  • For sensing, RA scanning supports target discovery and monitoring, and boresight redirection tracks identified targets as platforms or targets move.Positioning, localization, and navigation assistance also depend on reference-node geometry, synchronization, and signal processing.Source: C. RA-Enabled Sensing in SAGINs · p. 3
  • Coordinated satellite, aerial, and ground sensing can provide complementary observations of a target from different altitudes and directions, improving robustness to blockage.Sensing results such as target locations and blockage information can assist communication coverage adaptation, tracking, and relay selection; user and link information can also guide sensing direction.Source: C. RA-Enabled Sensing in SAGINs · pp. 3–4

III. MAIN DESIGN CHALLENGES, POTENTIAL APPROACHES, AND FUTURE DIRECTIONS

This section identifies channel acquisition and predictive tracking as key challenges in RA-enabled SAGINs. It describes using stable geometry and prior observations to guide boresight updates while accounting for channel change and reconfiguration delay.

A. Channel Acquisition and Predictive Tracking

  • In highly dynamic SAGINs, channel conditions and link geometry can change during boresight adjustment, making acquired information stale and degrading link performance.Dominant geometric information often evolves more smoothly than small-scale fading, particularly on LoS-dominant satellite and aerial links.Source: A. Channel Acquisition and Predictive… · p. 4
  • Satellite ephemeris, planned trajectories, node locations, and prior observations can predict link directions and narrow the directional search range.Local angular observations can refine predictions after trajectory deviations or blockage changes; the prediction horizon should include RA reconfiguration delay.Source: A. Channel Acquisition and Predictive… · p. 4
  • Adaptive acquisition and tracking must balance prediction accuracy, observation overhead, and RA reconfiguration latency.The section identifies deciding when to trust a prediction versus triggering additional observations as an open challenge.Source: A. Channel Acquisition and Predictive… · p. 4

B. Joint Orientation Control and Access/Handover Coordination

In RA-enabled SAGINs, access, handover, and antenna orientation are interdependent: link availability alone is insufficient without boresight alignment. The section proposes coordinating these decisions across timescales and identifies seamless handover under limited antenna resources as an open problem.

B. Joint Orientation Control and Access/Handover Coordination

  • A new serving link may suffer transient degradation or service interruption if handover precedes boresight alignment.Coordination may be needed across affected access, relay, and backhaul links.Source: B. Joint Orientation Control and… · p. 4
  • At slower timescales, large-scale network information can select candidate nodes, relay paths, and coarse boresight settings; faster adjustments maintain alignment and support handover.The proposed timescale split is intended to maintain directional support while limiting handover overhead and interruption risk.Source: B. Joint Orientation Control and… · p. 4
  • Using some RAs to maintain the current link while others align with a candidate node is one proposed route to seamless handover, but resource coordination remains open.The challenge is supporting both links with limited antenna resources as link geometry changes rapidly.Source: B. Joint Orientation Control and… · p. 4

C. Cross-Segment Coordination and Resource Management

Cross-segment resource management must account for how RA orientation affects link gain, interference, and competition for antenna resources. Practical deployment also entails platform-specific hardware tradeoffs and choices about deployment scale and update frequency.

C. Cross-Segment Coordination and Resource Management

  • Resource allocation across access, relay, and backhaul links must account for orientation-dependent directional gain, interference, and competition for limited RAs, subarrays, or orientation states.Orientation acts as an additional spatial resource affecting both desired-link enhancement and interference coupling.Source: C. Cross-Segment Coordination and… · pp. 4–5
  • Boresight adjustment can steer gain toward desired links and away from dominant interferers, facilitating spectrum reuse when directions are sufficiently separated.Otherwise, power control, orthogonal spectrum allocation, or time-domain separation may still be needed; limited directional support can also be addressed through subarray reassignment or traffic redirection.Source: C. Cross-Segment Coordination and… · p. 5

D. Deployment Tradeoffs and Practical Implementation

  • Mechanical RA offers wide steering for coarse pointing and slow tracking but may incur latency, wear, and maintenance; electronic adjustment is faster and compact but often has discrete directions and calibration needs.Hybrid designs combine wide-angle mechanical pointing with fast electronic refinement while increasing hardware complexity and calibration overhead.Source: D. Deployment Tradeoffs and Practical… · p. 5
  • Deployment scale and update frequency trade coverage flexibility and directional support against calibration, coordination, signaling, and reconfiguration overhead.The section suggests stable coarse orientations with finer adjustments triggered by significant changes in geometry, demand, blockage, or interference; platform-specific budgets and constraints also shape design choices.Source: D. Deployment Tradeoffs and Practical… · p. 5

IV. CASE STUDIES

The case studies include an air-ground cooperative ISAC prototype in which a ground base station uses grouped rotatable antennas for UAV and UGV links, with UAV-assisted sensing when ground sensing is blocked. The reported prototype hardware cost is 297.22 USD.

A. RA Array Prototype for Air-Ground Cooperative ISAC

  • A 3×3 RA array at a ground base station groups antennas toward a UAV and UGV, while the UAV can assist in locating the UGV when ground-side sensing is blocked.The prototype integrates RA grouping, boresight adjustment, and UAV-assisted sensing for air-ground communication and sensing tasks.Source: A. RA Array Prototype for Air-Ground… · p. 5, Figure 2 · p. 6
  • 297.22 USD is the reported total hardware cost for the prototype, including directional antennas, servo gimbals, an FPGA, a PWM controller, and a power adapter.The authors present the cost as indicating potential for low-cost RA-array implementation.Source: A. RA Array Prototype for Air-Ground… · pp. 5–6, Figure 2 · p. 6

B. Simulation Results for RA-Enabled Air-Ground ISAC

In the emergency-response scenario, RA-enabled ISAC achieves higher minimum echo signal power than random-orientation and fixed-boresight designs under the same communication-rate requirement. Adaptive boresights help illuminate the aerial sensing region while maintaining vehicle links.

B. Simulation Results for RA-Enabled Air-Ground ISAC

  • The simulated LAP is at 50 m and uses a 3×3 RA array with half-wavelength antenna spacing.Source: B. Simulation Results for RA-Enabled… · p. 6
  • At the same communication-rate requirement, RA-enabled ISAC achieves higher minimum echo signal power than random-orientation and fixed-boresight designs.The scenario has an RA-equipped LAP communicating with two emergency-response vehicles while sensing an aerial region where a rescue UAV may be located.Source: B. Simulation Results for RA-Enabled… · p. 6
  • RA boresights adapt to vehicle and possible rescue-UAV locations, supporting aerial-region illumination while maintaining the two vehicle links.Source: B. Simulation Results for RA-Enabled… · p. 7

C. Simulation Results for RA-Enabled Ground-Satellite Communication

For a representative LEO pass, RA with boresight tracking yields a more favorable achievable-rate distribution than no-tracking and fixed-boresight designs, while remaining close to the perfect-CSI upper bound. The study compares four update strategies in a ground-satellite link scenario.

C. Simulation Results for RA-Enabled Ground-Satellite Communication

  • The representative pass uses 3 × 3 RA arrays at the ground node and satellite, a 2 GHz carrier, and 15 s data-transmission frames.Source: C. Simulation Results for RA-Enabled… · p. 7
  • The four strategies are tracking estimated satellite direction, updating only during training, fixed boresights, and perfect CSI as an upper bound.Source: C. Simulation Results for RA-Enabled… · p. 7
  • RA with boresight tracking achieves a more favorable rate distribution than no-tracking and fixed-boresight designs, remaining close to the perfect-CSI upper bound.The result is attributed to following the predictable evolution of the ground-satellite link direction, reducing directional mismatch during transmission.Source: C. Simulation Results for RA-Enabled… · p. 7

V. CONCLUSION

The article examines controllable RA boresight adjustment as a complement to platform mobility in SAGIN communication and sensing. A prototype and two simulations illustrate implementation feasibility and potential benefits.

V. CONCLUSION

  • The article investigates how controllable RA boresight adjustment complements platform mobility for communication and sensing in SAGINs.Source: §V · p. 7
  • It discusses design challenges and future directions in channel acquisition and predictive tracking, orientation and handover coordination, cross-segment resource management, and practical implementation.Source: §V · p. 7
  • An RA array prototype and two simulation studies illustrate feasibility and potential benefits for air-ground ISAC and dynamic ground-satellite communication.Source: §V · p. 7
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