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UAV-Involved Wireless Physical-Layer Secure Communications: Overview and Research Directions
Hui-Ming Wang, Xu Zhang, Jia-Cheng Jiang
TL;DR
UAV communication security is challenged by eavesdropping, and the article surveys physical-layer approaches across UAV roles and their design freedoms. It concludes that position, trajectory, and power design are central considerations, while identifying practical channel modeling and multi-UAV configuration as research directions.
Problem
The article surveys UAV-involved secure communications and the design freedoms introduced by UAV mobility, organizing research that had lacked a well-organized overview.
Source: §I · p. 3, §II · p. 5Method
The article categorizes UAV secure communications by UAV role and reviews transmission design around 3D position, trajectory, and transmit power.
Source: §I · p. 3, §II · p. 5, §VII · p. 15Results
The overview concludes that UAV-enabled secure communications and UAV-aided cooperation can be analyzed through these roles and secrecy-oriented design considerations.
Source: §VII · p. 15Takeaways & Limitations
The article identifies practical research directions intended to encourage more significant and practical UAV-involved secure communications research.
Source: §VII · p. 15Dominant-LoS channel assumptions are described as oversimplified for suburban, urban, and metropolitan environments, motivating probabilistic LoS/NLoS models and obstacle-aware trajectory constraints.
Source: §VI · p. 14
Abstract
from arXiv · showhide
Due to their flexible deployment and on-demand mobility, small-scale unmanned aerial vehicles (UAVs) are anticipated to be involved in widespread communication applications in the forthcoming fifth-generation (5G) networks. However, the confidentiality of UAV communication applications is vulnerable to security threats due to the broadcast nature and dominant line-of-sight (LoS) channel conditions, and physical-layer security (PLS) technique can be applied for secrecy performance enhancement in such a context. On the other hand, it is also promising to exploit UAVs to cooperatively protect secure communications. This article provides an overview of the recent research efforts on UAV-involved secure communications at the physical layer. We focus on the design of secure transmission schemes according to different roles of UAVs and the optimization of introduced degrees of freedom (DoFs) by the unique characteristics of UAVs. We also propose some future research directions on this topic.
I. INTRODUCTION
UAVs’ flexible deployment and on-demand mobility make them promising for communication applications, but broadcast transmissions and LoS channels expose them to eavesdropping. The article motivates physical-layer security and surveys UAV roles and design freedoms for secure communications.
I. INTRODUCTION
- UAVs’ flexible deployment and on-demand mobility offer channel advantages and new position-related degrees of freedom for communication links.The introduction also distinguishes payload communication from control and non-payload communication, whose requirements can differ.Source: §I · p. 2
- UAV communications face confidentiality threats from the broadcast medium and strong LoS channels, while cryptographic key management and processing delay pose challenges for mobile UAVs.PLS exploits wireless-channel randomness without shared keys, complementing cryptography for this setting.Source: §I · pp. 2–3
- The survey organizes secure UAV communications into UAV-enabled links and UAV-aided cooperation, and identifies a need for an organized overview of recent progress.It frames joint optimization of static 3D position, mobile trajectory, and transmit power as security degrees of freedom.Source: §I · p. 3
II. TYPICAL APPLICATION SCENARIOS AND MAIN DESIGN CONSIDERATIONS
UAVs can provide direct secure communications or cooperate through relaying and jamming. Their mobility introduces position and trajectory choices that can be optimized alongside transmit power to improve secrecy.
II. TYPICAL APPLICATION SCENARIOS AND MAIN DESIGN CONSIDERATIONS
- UAV-enabled scenarios use UAVs as direct-link aerial base stations or aerial terminals, while UAV-aided cooperation uses relaying or friendly jamming.A hybrid scheme may combine the two scenario types.Source: §II · pp. 3–4
- On-demand mobility introduces security degrees of freedom through static UAV 3D position and mobile UAV trajectory design, alongside transmit power.The article proposes optimizing these choices jointly for secrecy performance.Source: §II · p. 5
- Static UAV positioning balances horizontal proximity to legitimate users or eavesdroppers with altitude-dependent path loss and LoS blockage, so an optimal altitude generally exists.For friendly jamming, the preferred horizontal placement reverses relative to communication-service or relaying roles.Source: §II · p. 5
- Mobile UAV trajectory design discretizes flight into time slots, with shorter slots improving the static-per-slot approximation but increasing design complexity.Transmit power should also account for time-varying legitimate and wiretap channel quality.Source: §II · p. 5
III. UAV-ENABLED SECURE COMMUNICATIONS
The section surveys UAV-enabled secure communications by distinguishing aerial base stations from aerial legitimate terminals. It introduces these as the two application categories discussed next.
III. UAV-ENABLED SECURE COMMUNICATIONS
- The section organizes UAV-enabled secure communications into two application categories based on the UAV’s role.The categories are aerial base stations and aerial legitimate terminals.Source: §III · p. 6
- Aerial base stations are one of the two categories used to structure the section’s review of recent research efforts.The section addresses them in a separate following part.Source: §III · p. 6
- Aerial legitimate terminals form the other category in the section’s organization of UAV-enabled secure communications.They are discussed in a separate following part.Source: §III · p. 6
A. UAV Aerial Base Stations
Aerial base stations can use UAV mobility to improve legitimate channels relative to wiretap channels. Research surveyed here jointly designs their trajectory and transmit power, including under uncertain eavesdropper locations.
A. UAV Aerial Base Stations
- Aerial base-station mobility can be positioned to strengthen legitimate channels and weaken wiretap channels, addressing eavesdropping risks from broadcast transmissions and strong LoS links.The deployment can provide temporary service to an area.Source: A. UAV Aerial Base Stations · p. 6
- A sufficiently long flight period enables the optimal fly-hover-fly trajectory, with the UAV flying at maximum speed to an optimal position before hovering for secrecy performance.The study jointly optimizes trajectory and transmit power to maximize average achievable secrecy rate; Fig. 3 shows trajectories and rates across flight periods.Source: A. UAV Aerial Base Stations · pp. 6–7, Figure 3 · p. 7
- A robust transmission scheme in significantly improves secrecy performance when eavesdropper locations are imperfectly estimated.The design maximizes average worst-case secrecy rate over locations within a bounded estimation-error area.Source: A. UAV Aerial Base Stations · pp. 7–8
- For static aerial base stations in, increasing transmit power raises both legitimate-user and eavesdropper achievable rates, while an optimal power can maximize average secrecy rate under certain conditions.The analysis considers mmWave transmission with mixed LoS/NLoS A2G channels and friendly jamming.Source: A. UAV Aerial Base Stations · p. 8
B. UAV Aerial Legitimate Terminals
UAV aerial terminals require communication security while carrying out special tasks under wireless control links. Research covers both static terminal design and trajectory planning against malicious jamming.
B. UAV Aerial Legitimate Terminals
- Aerial terminals carry out special tasks and operate automatically under associated GCS control via wireless links, making their communication security a concern.Source: B. UAV Aerial Legitimate Terminals · p. 8
- Under statistical eavesdropper CSI, null-space artificial noise and power allocation improve G2A secrecy, with an optimal UAV height varying by conditions.The work derives a hybrid outage probability and obtains the power allocation by bisection search.Source: B. UAV Aerial Legitimate Terminals · p. 8
- With fixed ground attacker positions and jamming powers, trajectory planning maximizes flight-period throughput; SCA addresses non-convexity, and a static deployment is derived as the unlimited-speed case.The optimal hovering position is relatively close to the optimal static deployment.Source: B. UAV Aerial Legitimate Terminals · pp. 8–9
IV. UAV-AIDED SECURE COOPERATION
UAV-aided secure cooperation uses UAVs to protect communications in two application scenarios: mobile relaying and friendly jamming.
IV. UAV-AIDED SECURE COOPERATION
- UAV-aided secure cooperation is categorized by UAV role into mobile relaying and friendly jamming.Source: §IV · p. 9
- Mobile relaying is one of the two identified UAV-aided secure cooperation applications.Source: §IV · p. 9
- Friendly jamming is the other identified UAV-aided secure cooperation application.Source: §IV · p. 9
A. UAV-Enabled Mobile Relaying
UAV mobile relays can adapt their positions to dynamic environments, strengthening legitimate channels relative to wiretap channels. Relay mode choice involves trade-offs, and mobility-aware multi-relay design remains an open area.
A. UAV-Enabled Mobile Relaying
- Traditional fixed ground relays adapt poorly to dynamic environments, motivating mobile UAV relays for secure cooperation.Source: A. UAV-Enabled Mobile Relaying · pp. 9–10
- UAV mobility lets relays move near communication nodes, potentially improving legitimate A2G channels while degrading wiretap channels,.Earlier work optimized transmit-power allocation, then extended the design to dynamic UAV trajectories.Source: A. UAV-Enabled Mobile Relaying · p. 10
- DF relaying can offer better decoding capability near GBSs but limited UAV speed implies large buffers and delay; AF reduces processing complexity and delay but amplifies noise, losing relative performance at high SNR,.The best mode depends on the application scenario; AF is also appropriate for untrusted relays.Source: A. UAV-Enabled Mobile Relaying · p. 10
- In multiple-relay settings, selects the UAV maximizing end-to-end SNR, appearing random to eavesdroppers, but does not exploit relay mobility.Cooperative beamforming is identified as a missing research direction.Source: A. UAV-Enabled Mobile Relaying · p. 10
B. UAV-Enabled Friendly Jamming
UAV friendly jamming uses mobile aerial platforms to transmit artificial noise against eavesdroppers. Design must account for time-varying trajectories, the risk of harming legitimate channels, and uncertain eavesdropper locations.
B. UAV-Enabled Friendly Jamming
- UAV jammers can adjust power with relative positions, while strong LoS A2G links degrade wiretap channels and make jamming-channel CSI easier to obtain [12].Source: B. UAV-Enabled Friendly Jamming · p. 11
- Joint trajectory and power design maximizes average secrecy rate, but improper jamming power can harm secrecy by degrading legitimate channels.The jammer's time-varying positions depend on its flight period and affect trajectory design.Source: B. UAV-Enabled Friendly Jamming · p. 11
- Because eavesdropper locations are difficult to estimate exactly, models a target area and optimizes static 3D jammer deployment to maximize coverage subject to legitimate-user outage constraints.The design uses discrete location samples and alternating optimization; different coverage definitions lead to different transmission schemes.Source: B. UAV-Enabled Friendly Jamming · pp. 11–12
V. UAV-ENABLED HYBRID SECURE TRANSMISSION SCHEME
The section reviews hybrid secure transmission using multiple UAVs with different roles, including aerial base stations and friendly jammers. It reports that UAV mobility improves secrecy performance over schemes with a static friendly jammer or base station.
V. UAV-ENABLED HYBRID SECURE TRANSMISSION SCHEME
- In, dual UAVs combine an aerial base station and friendly jamming, scheduling one legitimate user per TDMA slot while treating unscheduled users as potential eavesdroppers.The design maximizes the worst-case average secrecy rate through alternating optimization, using closed-form scheduling updates and SCA for other non-convex subproblems.Source: §V · p. 12
- In, a related design considers multiple external ground eavesdroppers and adds collision avoidance for the dual UAVs.It transforms binary scheduling constraints using auxiliary continuous variables and applies P-CCCP with penalty terms; the design can extend to multiple UAV jammers.Source: §V · pp. 12–13
- The hybrid transmission scheme significantly improves secrecy performance over schemes with a static friendly jammer or base station.Fig. 6 plots achievable secrecy rate against flight period for the scheduled legitimate user facing potential internal eavesdropping.Source: Figure 6 · p. 13, §V · p. 13
VI. RESEARCH CHALLENGES AND FUTURE DIRECTIONS
The section identifies open challenges in practical UAV trajectory design, multi-UAV configuration, multi-antenna transmission, energy management, and covert communications. It highlights constraints and unresolved research needs in each area.
Trajectory design
- Practical trajectory design must address dynamic environments, probabilistic LoS/NLoS channels, obstacle distributions, and the complexity of realistic constraints.Existing work often uses static 3D deployment under mixed LoS/NLoS conditions or horizontal trajectories under dominant LoS assumptions; these approaches have practical limitations.Source: §VI · pp. 13–14
Multi-UAV communications
- Multi-UAV systems need scenario-specific joint distributed processing and configuration, while CR and NOMA may improve spectral efficiency but bring security issues to consider.Optimal configurations may differ with transmission environments, terminal and attacker distributions, and the security objective.Source: §VI · p. 14
Multi-antenna transmission
- Multi-antenna spatial diversity can support beamforming and compensate for UAV location-dependent DoFs, but high mobility makes accurate channel estimation difficult.The discussion especially notes potential benefits for low-altitude UAVs with probabilistic multipath NLoS transmissions.Source: §VI · p. 14
Energy issues
- UAV energy limits make joint secrecy and energy performance important, while movement-dependent energy use complicates trajectory design.Wireless energy harvesting can extend endurance, and information-independent energy-bearing signals can be designed as jamming signals to degrade wiretap channels and improve secrecy.Source: §VI · p. 15
Covert communications
- UAV-involved covert communication research remains limited, with design opportunities in UAV configuration, transmit power, and trajectory.The stated objective is to prevent message interception because hiding UAVs is difficult; covert communication has higher requirements than preventing successful decoding by eavesdroppers.Source: §VI · p. 15
VII. CONCLUSION
The conclusion recaps the overview's scenario categories and design considerations, then points to future research directions for UAV-involved secure communications.
VII. CONCLUSION
- The article categorizes UAV-involved secure communications as UAV-enabled secure communications and UAV-aided secure cooperation, based on UAV roles.Source: §VII · p. 15
- It reviews static UAV 3D position, mobile UAV trajectory, and transmit power design as considerations for secrecy enhancement.Source: §VII · p. 15
- The article offers research directions intended to encourage more significant and practical work on UAV-involved secure communications.Source: §VII · p. 15