The scenario the researchers envision is compelling: a UAV base station hovering at a predetermined altitude above a service area, connecting cellular users and D2D pairs distributed at random throughout the region. Cellular users employ frequency division multiple access to connect to the UAV in the uplink, while D2D pairs exchange data directly with each other by multiplexing the sub-channels of multiple cellular subscribers. This many-to-many spectrum reuse mode allows a single cellular user’s frequency resources to be shared with several D2D pairs, and vice versa. While this sharing inevitably creates co-channel interference, the researchers discovered that with appropriate spectrum reuse and power control techniques, this interference can actually be mitigated—and the distance between legitimate and eavesdropping channels can be widened, leading to more secure communication.

The vulnerability is real. The very characteristics that make UAV-assisted communication so powerful—strong concealment, flexibility, mobility, and the ability to establish line-of-sight links—also make these networks susceptible to eavesdropping by malicious ground nodes. The line-of-sight transmission and wireless broadcasting nature of UAV communication networks means that signals can be intercepted by passive eavesdroppers who simultaneously monitor both the cellular network and the D2D communications. Traditional encryption technology, which has been the primary information secrecy protection measure, requires high computing power and power consumption—resources that are limited for UAVs deployed in the open, easily captured, and operating under severe energy constraints.

Physical layer secure transmission technology offers a potent alternative. This approach leverages the physical properties of the channel itself to accomplish secure transmission, without requiring complex encryption algorithms. It has inherent secrecy attributes, low computational complexity, and low power consumption, making it well adapted to large-scale, distributed network architectures. The theoretical foundation traces back to the wiretap channel model, and subsequent research has demonstrated that when the legitimate channel’s capacity exceeds that of the eavesdropping channel, there always exists an encoding technique that enables the legitimate receiver to receive confidential information with nearly no errors while the eavesdropper cannot obtain any of it.

What distinguishes this new work from existing research is its focus on the total secrecy energy efficiency (TSEE)—the ratio of secrecy rate to power consumption for both D2D pairings and cellular users combined. Most existing studies on UAV-assisted wireless networks under passive eavesdropping have focused either on optimizing flight trajectories or on mode selection and cooperative interference strategies, without considering the total power consumption of UAVs and ground users. Others have concentrated on maximizing energy efficiency without considering the presence of eavesdroppers at all. The researchers identified this gap and designed their framework to simultaneously meet the requirements of secure communication, mitigation of co-channel interference, and power saving.

The mathematical challenge is formidable. The optimization problem the researchers formulated is nonlinear and nonconvex, making it extremely difficult to find a direct analytical solution. To overcome this, they proposed an internal and external iterative optimization technique that combines two powerful algorithms. The Dinkelbach algorithm, which has strong convergence properties and is frequently used to address nonlinear fractional programming issues, ensures that the original problem converges to the optimal solution. Meanwhile, the convex approximation algorithm transforms the nonconvex optimization problem into a geometric programming problem that can be solved efficiently using the CVX toolbox in MATLAB, which converts geometric programming problems into convex geometric programming problems through variable substitution and transformation of objective and constraint functions.

The system model incorporates realistic channel characteristics. Both the channels between D2D transmitters and UAVs and the channels between cellular users and UAVs are air-to-ground channels, represented using a probability-weighted sum of line-of-sight and non-line-of-sight components. For ground users, the channel gains incorporate path loss constants, path loss exponents, and shadowing fading that follows a log-normal distribution. The researchers also accounted for the influence of circuit power consumption, including the power consumed by mixers, filters, analog-to-digital converters, and baseband processing units, as well as the efficiency factor of the power amplifier. Constraints ensure that the secrecy rate for cellular users and D2D pairs does not fall below minimum thresholds, and that transmit power does not exceed maximum limits.

Simulation results demonstrate the effectiveness of the proposed approach. When compared against benchmark algorithms including particle swarm optimization (PSO), random spectrum and power allocation (RSPA), and existing methods focused on D2D communication efficiency or cellular user secrecy efficiency maximization, the proposed algorithm consistently performed better in improving network secrecy efficiency. The PSO method performed poorly because it is dependent on parameter values and is prone to becoming caught in local optima. The algorithm focused on D2D communication efficiency was somewhat less effective because D2D has a shorter communication distance and higher transmission rate, meaning D2D communication efficiency has a greater impact on TSEE. The approach based on cellular user secrecy efficiency maximization demonstrated that increasing cellular user secrecy efficiency comes at the expense of significantly lowering D2D transmission and secrecy rates.

The researchers also evaluated the impact of UAV altitude on network performance, varying the altitude from 100 to 1,000 meters with different numbers of cellular users and D2D pairings. They found that the total secrecy energy efficiency exhibits complex trends—sometimes expanding first then decreasing, sometimes dropping then growing before stabilizing—because variations in UAV altitude have distinct effects on different locations. The cellular communication secrecy efficiency often exhibits a tendency of initially rising, then falling, and eventually stabilizing, because the air-to-ground channel gain initially rises and then falls as UAV altitude increases. When the channel gain rises, cellular users can fulfill the minimum secrecy rate requirement with lower transmit power, improving efficiency. The D2D communication secrecy efficiency variation was not significant, because the fast transmission rate and small distance of D2D communication make it relatively resilient to interference changes from cellular users.

This research represents a meaningful step toward practical, secure, energy-efficient wireless networks for the 6G era. By optimizing spectrum reuse and power control strategies simultaneously, the framework achieves a balance between network energy consumption and secure communication performance while effectively reducing co-channel interference. The implications extend to disaster communication scenarios, hot areas with limited terrestrial infrastructure, and any environment where fixed infrastructure is destroyed or unavailable. However, the researchers acknowledge that their work was based on optimal channel state information and accurate user location information—conditions that are very difficult to obtain in practical UAV communication networks due to link latency, the dynamic flight of UAVs, and the passive nature of eavesdroppers. Future research will focus on UAV-assisted network secrecy communication technologies under conditions of imperfect channel state information and user location information, bringing this promising framework closer to real-world deployment.

Subject of Research: Novel framework for physical-layer secrecy and network secrecy energy efficiency of UAV-assisted device-to-device communication

Article Title: Novel framework for physical-layer secrecy and network secrecy energy efficiency of UAV-assisted device-to-device communication

Article References: Alalmaei, S., Hinov, N., Al-Turjman, F., Salama, R., González López, H. A., Aristizábal, L. F., Neira-Rodado, D., Escorcia-Gutierrez, J., & Andriukaitis, D. (2026). Novel framework for physical-layer secrecy and network secrecy energy efficiency of UAV-assisted device-to-device communication. Frontiers in Physics, 14, Article 1964844. https://doi.org/10.3389/fphy.2026.1964844

Image Credits: AI Generated

DOI: 10.3389/fphy.2026.1964844

Keywords: Novel, framework, physical-layer, secrecy, network, energy, efficiency, UAV-assisted, device-to-device, communication, scientific research