In this article, we consider the secure uplink transmissions from ground nodes to an unmanned aerial vehicle (UAV) receiver through analog collaborative beamforming (ACB). When the location information of the UAV receiver is available, ACB can be realized in a fully distributed manner, since each transmitting node can locally adjust its phase. ACB-based physical layer security (PLS) algorithm, where the virtual antenna array (VAA) elements are randomly selected at each transmit time unit, can effectively protect against eavesdropping attacks by creating artificial noise to the directions except the legitimate receiver (Bob). However, when Bob is mounted on the UAV, it can suffer from array gain loss due to jittering effects caused by airflow turbulence and mechanical vibration. Motivated by this issue, in this article, we investigate the impact of the UAV jitter on the secrecy performance. We derive the theoretical expressions of the secrecy rate both in the absence and presence of the jittering effects. Further, the simulation results show that the ACB-based PLS cannot guarantee non-zero secrecy rate even with the radial distance perturbations on the order of a few centimeters, especially when an eavesdropper (Eve) exists in close proximity to Bob.
In this article, we consider the secure uplink transmissions from ground nodes to an unmanned aerial vehicle (UAV) receiver through analog collaborative beamforming (ACB). When the location information of the UAV receiver is available, ACB can be realized in a fully distributed manner, since each transmitting node can locally adjust its phase. ACB-based physical layer security (PLS) algorithm, where the virtual antenna array (VAA) elements are randomly selected at each transmit time unit, can effectively protect against eavesdropping attacks by creating artificial noise to the directions except the legitimate receiver (Bob). However, when Bob is mounted on the UAV, it can suffer from array gain loss due to jittering effects caused by airflow turbulence and mechanical vibration. Motivated by this issue, in this article, we investigate the impact of the UAV jitter on the secrecy performance. We derive the theoretical expressions of the secrecy rate both in the absence and presence of the jittering effects. Further, the simulation results show that the ACB-based PLS cannot guarantee non-zero secrecy rate even with the radial distance perturbations on the order of a few centimeters, especially when an eavesdropper (Eve) exists in close proximity to Bob.
Physical-layer security (PLS) is a promising alternative or complement to cryptography-based solutions, because security key management and distribution required in such schemes are challenging in future wireless technologies with a distributed nature (e.g., Internet-of-Things (IoT) and massive machine-type communication). Motivated by this fact, in this paper, we investigate a PLS algorithm using linear virtual antenna array (VAA) constructed by multiple single-antenna nodes in mobile ad hoc networks such as unmanned aerial vehicles (UAVs) and mobile robots. Digital cooperative beamforming (CB) has been extensively explored such as cooperative null-steering or jamming. However, in spite of their effectiveness, the digital CB-based schemes incur prohibitive overhead and complexity, which creates difficulty in networks with limited hardware (e.g., IoT). To overcome this issue, we consider an analog CB-based PLS with linearly distributed VAA, which can be implemented in a fully distributed manner. In the proposed scheme, the received signal at the intended receiver is co-phased, while other receivers capture noise-like signals through randomized radiation patterns using the linear VAA. Assuming Rician channels, we derive secrecy rate of the proposed algorithm in a closed-from expression for an arbitrary K-factor, which is not available in previous work on the analog CB-based PLS. Furthermore, we show that the random location perturbations of the VAA elements following Gaussian distributions can enhance the secrecy performance by resolving the angle-of-departure ambiguity issue in linear arrays.
As the importance to guarantee confidentiality against security attacks by eavesdroppers has attracted significant attention, there has been much effort to enhance the security performance through cooperative beamforming (CB) in the context of physical layer security (PLS). In particular, analog CB (ACB), which requires vastly lower overhead compared to digital CB, can provide significantly higher secrecy rate compared to the PLS methods with co-located array. In this letter, we focus on ACB with open-loop architecture that requires low complexity, and consider phase offsets across multiple virtual antenna array (VAA) elements for ACB, which are caused by position estimation error of VAA. We investigate the impact of the phase offsets in ACB in terms of the secrecy throughput loss.
Uncrewed aerial vehicles (UAVs) are expected to play a crucial role in future sixth-generation systems and low-altitude communication networks owing to their mobility, flexibility, and wide-range coverage capability. However, the predominance of line-of-sight channels makes UAV communications highly susceptible to eavesdropping, posing significant challenges for secure transmission. Distributed collaborative beamforming has emerged as a promising physical layer security technique for the UAV networks, but its performance is fundamentally constrained by the intrinsic jitter of UAV platforms, which is unavoidable in practical systems. In this paper, a physical layer security scheme is proposed for UAV networks based on collaborative beamforming technologies, within which distinct algorithms are designed according to whether the location of the eavesdropper (EAV) is known or unknown. When the location of the EAV is unknown, the theoretical secrecy performance of the proposed method is derived, and a beamforming strategy is constructed based on the properties of the generalized Rayleigh quotient for the situation of known location. Then, the average secrecy rate of the proposed collaborative beamforming scheme is derived under jitter conditions, and a robust beamforming method is further developed for the scenario in which the location of the EAV is known. Simulation results demonstrate that the average secrecy rate is dramatically improved by the proposed collaborative beamforming scheme compared to the conventional approaches, and a substantial secrecy performance gain is maintained in the presence of UAV jitter.
A wireless sensor network (WSN) refers to a network of sensor nodes that collaboratively work to sense, monitor, and control their surrounding environments. As WSNs are integrated into the Internet of Things, it is crucial to protect the network against malicious security attacks considering its wide applicability, such as military monitoring, healthcare, and civilian applications. Thus, in this paper, we consider a physical-layer security technique exploiting analog cooperative beamforming (ACB), where multiple sensor nodes create a virtual antenna array (VAA) and locally adapt their phases. As WSNs inherently have clustered topology, we model the VAA elements' locations by Gaussian distributions. The secrecy capacity of the ACB with the Gaussian-distributed elements is derived in a closed-form expression. The theoretical and numerical results indicate that the ACB-based schemes provide a better secrecy rate compared to the conventional co-located antenna array-based schemes. In addition, the ACB with Gaussian-distributed elements can better suppress side-lobe, which causes undesired information leakage to certain directions, compared to the ACB with uniformly distributed elements. Furthermore, we investigate the impacts of fading channel and phase estimation error in the ACB.
Owing to flexible management and low overhead, wireless physical layer security (PLS) has been applied to support many critical applications (e.g., data dissemination) of unmanned aerial vehicles (UAVs)-based mobile communication networks in emergency scenarios. Although the impact of static network scenarios or receiver mobility on PLS has been well studied, there is no much work that studies the impact of UAV-based transmitter mobility on PLS. To fill this gap, in this paper, we investigate PLS of a scenario, where a random mobile UAV-based transmitter transmits information to a static ground entity under Rayleigh fading channel. More specifically, we consider a communication system, in which a mobile UAV hovers over a region to collect information and then disseminates this information to a static ground network entity in a confidential manner under the presence of an eavesdropper. Because of popularity and practicality, the UAV is assumed to hover following the random way point (RWP) mobility model. We investigate the secrecy characteristics of the UAV under steady running state in terms of ergodic secrecy capacity (ESC), positive secrecy capacity probability (PSCP) and secrecy outage probability (SOP) for the communication between the UAV and the receiver. We then investigate the secrecy performance of the proposed system while considering the pause time of the RWP mobility model adopted by the UAV. We further extend our proposed theoretical model to other realistic scenarios, including the presence of multiple cooperative and non-cooperative eavesdroppers, and study the PSCP and SOP metrics of the corresponding system. Furthermore, we propose three types of secrecy improvement strategies for the considered communication model. We strike a good trade-off between the secrecy improvement and transmit outage probability. Extensive simulations have been conducted to validate our theoretical analysis as well as the effectiveness of the proposed secrecy improvement strategies.
In this paper, physical layer security issue for a down-link wireless communication system is examined, composed of an unmanned aerial vehicle (UAV), a legitimate receiver and a passive eavesdropper. The destination is equipped with two antennas and applies the full-duplex (FD) Bob-based jamming (FD-BBJ) strategy to achieve secure transmission. Considering that practical air-to-ground (A2G) channels experience Nakagami-m fading and the FD legitimate receiver is affected by self-interference (SI), closed-form expressions of approximate ergodic achievable secrecy rate (EASR) with help of Gauss-Laguerre Quadrature (GLQ) and compact secrecy outage probability (SOP) expression are derived, respectively. To gain more insights, asymptotic secrecy performance is analysed in the case of extreme total system transmit power, via deriving closed-form expression for asymptotic EASR and compact expression for asymptotic SOP. Numerical results have verified the correctness of our theoretical analysis and proved that the FD-BBJ strategy applied in the UAV-aided wireless communication system can help achieve considerable secrecy performance gain.