Source-linked AI summary
Enabling Smart Reflection in Integrated Air-Ground Wireless Network: IRS Meets UAV
Changsheng You, Zhenyu Kang, Yong Zeng, Rui Zhang
TL;DR
UAVs and IRSs can proactively alter wireless channels through maneuver control and smart reflection, but each has practical limitations. The article jointly uses terrestrial IRS for UAV-ground links and UAV-mounted IRS for terrestrial communication, finding benefits from deploying both in 3D networks.
Problem
UAV and IRS communication technologies face different practical limitations despite their ability to alter wireless channels through maneuver control and smart reflection.
Method
The article proposes IRS-assisted UAV communication and UAV-mounted IRS-assisted terrestrial communication, examining use cases, design issues, and potential solutions.
Results
4.8 s versus 11.2 s: terrestrial IRS enables the UAV to achieve the same max-min rate with less flying time and propulsion energy than without IRS.
Takeaways & Limitations
Deploying both terrestrial and aerial IRSs is promising for optimizing wireless-network performance by exploiting smart reflections in 3D space.
Abstract
from arXiv · showhide
Intelligent reflecting surface (IRS) and unmanned aerial vehicle (UAV) have emerged as two promising technologies to boost the performance of wireless communication networks, by proactively altering the wireless communication channels via smart signal reflection and maneuver control, respectively. However, they face different limitations in practice, which restrain their future applications. In this article, we propose new methods to jointly apply IRS and UAV in integrated air-ground wireless networks by exploiting their complementary advantages. Specifically, terrestrial IRS is used to enhance the UAV-ground communication performance, while UAV-mounted IRS is employed to assist in the terrestrial communication. We present their promising application scenarios, new communication design issues as well as potential solutions. In particular, we show that it is practically beneficial to deploy both the terrestrial and aerial IRSs in future wireless networks to reap the benefits of smart reflections in three-dimensional (3D) space.
I. INTRODUCTION
Future 6G networks need controllable wireless environments for reliable, high-capacity 3D connectivity. The article proposes integrating terrestrial and aerial IRSs with UAVs to exploit their complementary advantages despite practical limitations.
- 6G must address random, time-varying channels while targeting global coverage, ubiquitous 3D connectivity, and ultra-high data rates.
- UAV mobility can create favorable channels, while IRS dynamically tunes reflections to control channel realizations and statistics.
- UAVs face SWAP, propulsion-energy, endurance, and blockage constraints, whereas terrestrial IRSs have fixed, limited coverage and may incur severe product-distance path loss.
- Terrestrial IRS can create reflected LoS links for blocked users and let UAVs serve nearby users without flying as close, reducing propulsion energy and access delay.
- The article investigates IRS-assisted UAV communication and UAV-mounted IRS-assisted terrestrial communication, covering applications, design issues, solutions, and numerical effectiveness.
II. IRS-ASSISTED UAV COMMUNICATION
The article introduces IRS-assisted UAV communication as one of two integrated air-ground methods. It revisits UAV communication design issues and presents solutions that account for terrestrial IRS effects.
- IRS-assisted UAV communication is presented as a method for integrating terrestrial access with aerial UAV communication.
- The section revisits key UAV communication design issues while incorporating the effects of IRS.
A. Typical Use Cases
Terrestrial IRS can support UAV data collection, relaying, security, SWIPT, and cellular-connected UAV communication. Its deployment and passive beamforming add degrees of freedom for balancing communication objectives.
- A. Typical Use Cases: IRS near distributed ground nodes can increase UAV data-collection rates at fixed transmit power or reduce node power for a required rate.
- A. Typical Use Cases: IRS deployment and passive beamforming provide degrees of freedom to balance UAV throughput, delay, and propulsion-energy consumption.
- A. Typical Use Cases: IRS near a ground gateway can enhance UAV relay backhaul capacity, while IRS can also support physical-layer security and UAV-enabled SWIPT.
- A. Typical Use Cases: IRS can assist cellular-connected UAV communication where the UAV is supported by cellular networks as an aerial user.
B. New Design Issues
IRS-assisted UAV communication creates joint placement, trajectory, passive-beamforming, and channel-estimation challenges. Terrestrial IRS can reduce UAV altitude or flight time, but UAV mobility makes CSI acquisition more demanding.
- B. New Design Issues: UAV placement and trajectory must be jointly optimized with IRS passive beamforming, creating a new design challenge.
- B. New Design Issues: In dense urban areas, increasing UAV altitude improves LoS probability but increases path loss, creating a placement trade-off.
- B. New Design Issues: An IRS near cell-edge users can reduce UAV altitude while maintaining their rate through passive-beamforming gain, thereby shortening other links and reducing path loss.
- B. New Design Issues: IRS channel estimation is harder because it adds UAV-IRS and IRS-user coefficients, while UAV mobility makes the UAV-IRS channel dynamic and can require frequent pilots.
- B. New Design Issues: For LoS UAV-IRS channels, tracking can use the UAV’s elevation and azimuth angles, with Kalman-filter-based methods offered as an efficient approach.
III. U-IRS-ASSISTED TERRESTRIAL COMMUNICATION
This section discusses U-IRS-assisted terrestrial communication and its main applications and design challenges.
- U-IRS is considered for assisting terrestrial communication.
- The section focuses on applications of U-IRS-assisted terrestrial communication.
- It also identifies communication design challenges for this setting.
A. U-IRS Enhanced Coverage
U-IRS is used as a passive aerial relay for ground-node data forwarding and is expected to provide broader coverage more cost-effectively than active relays or terrestrial IRS.
- A. U-IRS Enhanced Coverage: U-IRS serves as a passive aerial relay that forwards data for ground nodes.
- A. U-IRS Enhanced Coverage: U-IRS is expected to offer superior coverage performance compared with conventional active-relay and terrestrial-IRS systems.
- A. U-IRS Enhanced Coverage: The expected coverage advantage is described as more cost-effective than conventional alternatives.
B. New Design Issues
U-IRS deployment and beamforming introduce coverage, alignment, placement, and element-allocation challenges requiring specialized designs.
- B. New Design Issues: U-IRS beamforming must balance gains across users over its large coverage area, unlike terrestrial IRS with local coverage.
- B. New Design Issues: Figure 4 concerns U-IRS enhanced coverage relative to active relay and terrestrial IRS.
- B. New Design Issues: Sub-array partitioning can enable 3D beam broadening and flattening for multi-beam coverage, while aerial drift and vibration create beam-misalignment concerns.
- B. New Design Issues: U-IRS deployment must balance high-altitude line-of-sight access against the resulting path loss to ground users.
- B. New Design Issues: Allocating reflecting elements between BS-side U-IRS and user-side terrestrial IRSs is combinatoric and requires low-complexity algorithms.
IV. NUMERICAL RESULTS
The numerical-results section presents evaluations intended to demonstrate the effectiveness of methods jointly applying IRS and UAV in integrated air-ground wireless networks.
- IV. NUMERICAL RESULTS: Numerical results are presented to demonstrate the effectiveness of the proposed joint IRS–UAV methods.
- IV. NUMERICAL RESULTS: Figure 5 compares optimized UAV trajectories with and without terrestrial IRS.
- IV. NUMERICAL RESULTS: The evaluated methods jointly apply IRS and UAV in integrated air-ground wireless networks.
A. IRS-Assisted UAV Communication
Terrestrial IRSs can reduce UAV flight demands for uncovered ground nodes, while hybrid aerial–terrestrial IRS deployment improves fairness in two-user relaying.
- IRS-assisted UAV communication: 4.8 s versus 11.2 s: terrestrial IRS reduces UAV flying time for achieving the same common target max-min rate among all sensor nodes.The UAV only flies around sensor nodes outside the IRS coverage, rather than visiting every node sequentially.
- U-IRS-assisted terrestrial communication: With a total budget of N = 600 reflecting elements, the optimized hybrid allocation uses N1 = 325 aerial and N2 = 275 terrestrial elements.The U-IRS is deployed at 30 m to establish an LoS link with user 1 only, while the terrestrial IRS serves user 2.
- U-IRS-assisted terrestrial communication: Hybrid IRS deployment further improves the BS-side U-IRS strategy's rate performance more fairly between the two users.The additional terrestrial IRS serves user 2, allowing the U-IRS to lower its altitude and the element allocation to balance the users' rates.
- U-IRS-assisted terrestrial communication: The BS-side U-IRS achieves a higher max-min rate than the user-side terrestrial IRS, whose fixed local coverage leaves user 1 with a very low rate.The BS-side strategy covers both users from sufficient altitude, but user 2's rate decreases because of the resulting longer link distance.
V. CONCLUSION
The article proposes two complementary IRS–UAV integration methods and discusses their applications, design issues, and numerical benefits in integrated aerial and terrestrial access.
- The article introduces IRS-assisted UAV communication and U-IRS-assisted terrestrial communication for future wireless networks with integrated aerial and terrestrial access.
- It examines UAV placement and trajectory optimization, IRS passive beamforming, channel estimation, and deployment as associated communication design issues.
- Numerical results demonstrate benefits from exploiting the complementary advantages of IRS and UAV, supporting deployment of both terrestrial and aerial IRSs.
BIOGRAPHIES
The biography identifies the researcher as a Singapore-based Ph.D. candidate whose interests include UAV communications, intelligent reflecting surfaces, and convex optimization.
- The researcher has been in Singapore since 2019 and is pursuing a Ph.D. in Electrical and Computer Engineering.
- The stated research interests include UAV communications and intelligent reflecting surfaces.
- Convex optimization is also listed among the research interests.