Fine-grained oriented object recognition (FGO ² R) is a practical need for intellectually interpreting remote sensing images. It aims at realizing fine-grained classification and precise localization with oriented bounding boxes, simultaneously. Our considerations for the task are general but decisive: (i) the extraction of subtle differences carries a big weight in differentiating fine-grained classes, and (ii) oriented localization prefers rotation-sensitive features. In this article, we propose a network with separate feature refinement (SFRNet), in which two transformer-based branches are designed to perform function-specific feature refinement for fine-grained classification and oriented localization, separately. To highlight the discriminative information advantageous to fine-grained classification, we propose a spatial and channel transformer (SC-Former) to capture both the long-range spatial interactions and the key correlations hidden in the feature channels. Besides, we design a Multi-RoI loss (MRL) following the protocol of deep metric learning to enhance the separability of fine-grained classes further. For oriented localization, we integrate the oriented response convolution with the transformer structure (namely, OR-Former) to assist in encoding rotation information during regression. Extensive experimental results validate the effectiveness and robustness of our SFRNet. Without bells and whistles, our SFRNet achieves state-of-the-art performance on the large-scale FAIR1M datasets (FAIR1M-1.0 and FAIR1M-2.0). Code will be available at https://github.com/Ranchosky/SFRNet.

In this paper, a novel reconfigurable intelligent surface (RIS)-assisted HAP-UAV secure multi-user mixed radio frequency (RF)/free space optical (FSO) system is proposed. Specifically, the Gamma-Gamma distribution is utilized to characterize the atmospheric turbulence effect for the FSO link from UAV to HAP, while the Rayleigh and Nakagami- m distribution fading are applied to simulate the legitimate and wiretap RF links, respectively. We present the closed-form expressions for the probability density functions, the cumulative distribution functions, and the secrecy outage probability (SOP) of the end-to-end signal-to-noise ratio (SNR) in terms of Meijer’s G-function. To gain more insight into secrecy performance, we further obtain the closed-form expressions for the asymptotic SOP, the asymptotic probability of positive secrecy capacity (PPSC), the diversity gain, and the coding gain at high SNR regions. We can observe that the secrecy performance depends on the weaker channel between the RF and FSO, and is closely related to the number of RIS elements, the number of terrestrial users, the atmospheric turbulence factor, pointing error parameters, and the fading parameter of Nakagami- m distributed wiretap link. Finally, numerical results validate the derived results and demonstrate that the proposed design achieves superior secrecy performance over the benchmarks.

Object detection for remote sensing is a fundamental task in image processing of remote sensing; as one of the core components, small or tiny object detection plays an important role. Despite the considerable advancements achieved in small object detection with the integration of CNN and transformer networks, there remains untapped potential for enhancing the extraction and utilization of information associated with small objects. Particularly within transformer structures, this potential arises from the disregard of the complex and the intertwined interplay between spatial context information and channel information during the global modeling of pixel-level information within small objects. As a result, valuable information is prone to being obfuscated and annihilated. To mitigate this limitation, we propose an innovative framework, YOLO-DCTI, that capitalizes on the Contextual Transformer (CoT) framework for the detection of small or tiny objects. Specifically, within CoT, we seamlessly incorporate global residuals and local fusion mechanisms throughout the entire input-to-output pipeline. This integration facilitates a profound investigation into the network’s intrinsic representations at deeper levels and fosters the fusion of spatial contextual attributes with channel characteristics. Moreover, we propose an improved decoupled contextual transformer detection head structure, denoted as DCTI, to effectively resolve the feature conflicts that ensue from the concurrent classification and regression tasks. The experimental results on the Dota, VISDrone, and NWPU VHR-10 datasets show that, on the powerful real-time detection network YOLOv7, the speed and accuracy of tiny targets are better balanced.

Unmanned aerial vehicle mounted base stations (UAV-BSs) are expected to become an integral component of future intelligent transportation systems, which can provide seamless coverage for vehicles on highways with poor cellular infrastructures. Motivated by the above, this paper proposes an aerial-ground integrated vehicular networking architecture, based on which a UAV-vehicle collaboration perspective is proposed. Specifically, an emerging vehicle-to-UAV (V2U) and vehicle-to-vehicle (V2V) collaboration framework is first presented to facilitate diverse vehicular applications. Next, we investigate the coverage radius maximization problem by optimizing the UAV-BS altitude. Meanwhile, by taking the channel state information (CSI) feedback delay into account, we formulate a V2U communication sum rate maximization problem by optimizing the power control and spectrum allocation, which is constrained by the capacity and reliability requirements. Then, we derive the closed-form expression of optimal UAV-BS altitude. Afterwards, we decouple the formulated sum rate maximization problem, and devise an efficient algorithm with polynomial complexity, where the optimal power control and spectrum sharing are solved. Finally, simulation results demonstrate that the maximum coverage radius and optimal UAV-BS altitude can be achieved by our proposed scheme in different urban environments. In addition, our designed scheme can effectively improve the V2U communication sum rate in comparison with the current works.

Urban sensing is a rapidly growing field that involves gathering real-time data from urban environments. These smart sensing systems are pivotal in enhancing urban planning, resource management, and overall quality of life in cities. However, in the context of data collection and network congestion, non-negligible latency can be experienced in urban environments. Recently, federated learning (FL) has emerged as an attractive approach to address network latency concerns. FL achieves distributing data processing tasks in urban sensing by uploading training results rather than raw data to a central server. In light of this, our paper proposes a wireless sensor air-ground integrated federated learning (AGIFL) network with covert communication. The AGIFL system utilizes a high-altitude platform (HAP) as a parameter server to provide mobility and sustainability of urban sensors and a friendly jammer unmanned aerial vehicle (UAV) to enhance information security. Our main objective is to minimize FL latency for the urban sensor network and ensure secure transmission. To achieve this, we jointly optimize the local training accuracy, interference power, and transmit power of FL sensors. To tackle the nonconvexity of the problem, we decompose the original nonconvex problem into subproblems and solve it using successive convex approximation (SCA) with alternating iterations. Simulation results show that the proposed scheme reduces latency in urban sensor networks significantly and ensures the secure transmission of information compared to benchmarks.

Ship detection is essential for both military and civilian applications. Existing ship detection methods focus on prominent offshore ships, paying less attention to complex nearshore ships, which are easily confused with the intricate background. Utilizing contextual information, such as location and shape, can enhance ship detection and classification in complex environments. In this paper, we propose a Context Modulated Representation Learning-based detection method termed as CM-YOLO. It adopts the classical detector design framework, which includes the backbone, neck, and head. The input image is sequentially processed through these components to obtain the detection results. Our method specifically optimizes ship detection in complex scenarios. To achieve this, we propose a Dual Path Context Enhancement Neck (DCEN) to extract contextual information for ship detection. The neck builds on the path augmentation feature pyramid network with the proposed Dual Path Context Enhancement Module (DCE), which is designed to enhance feature representations by incorporating high-level semantic information. It captures long-range dependencies across both channel and spatial dimensions while suppressing irrelevant features. Additionally, to enhance the scale-aware capability of the head for detecting multi-scale ships in complex environments, we introduce the Multi-Context Boosted Detection Head (MCB). The MCB can flexibly adjust the receptive field and extracts relevant context for ships of various scales using multiple large-kernel convolutions.We conduct experiments on three commonly-used ship datasets: Seaships7000, ShipRSImageNet, DIOR-ship, and HRSC2016. Experiment results demonstrate that CM-YOLO achieves excellent performance compared with other leading ship detection methods.