Transformer based Collaborative Reinforcement Learning for Fluid Antenna System (FAS)-enabled 3D UAV Positioning

In this paper, the problem of using one active unmanned aerial vehicle (UAV) and four passive UAVs to localize a 3D target UAV in real time is investigated. In the considered model, each passive UAV receives reflection signals from the target UAV, which are initially transmitted by the active UAV. The received reflection signals allow each passive UAV to estimate the signal transmission distance which will be transmitted to a base station (BS) for the estimation of the position of the target UAV. Due to the movement of the target UAV, each active/passive UAV must optimize its trajectory to continuously localize the target UAV. Meanwhile, since the accuracy of the distance estimation depends on the signal-to-noise ratio of the transmission signals, the active UAV must optimize its transmit power. This problem is formulated as an optimization problem whose goal is to jointly optimize the transmit power of the active UAV and trajectories of both active and passive UAVs so as to maximize the target UAV positioning accuracy. To solve this problem, a Z function decomposition based reinforcement learning (ZD-RL) method is proposed. Compared to value function decomposition based RL (VD-RL), the proposed method can find the probability distribution of the sum of future rewards to accurately estimate the expected value of the sum of future rewards thus finding better transmit power of the active UAV and trajectories for both active and passive UAVs and improving target UAV positioning accuracy. Simulation results show that the proposed ZD-RL method can reduce the positioning errors by up to 39.4% and 64.6%, compared to VD-RL and independent deep RL methods, respectively.

Unmanned aerial vehicles (UAVs) have been considered as a solution to extend coverage for disaster-resilient communication networks in a disaster area when the communication infrastructure which is known as the base station (BS) cannot afford the service as usual. However, when the link between the UAV and the serving BS is constrained, the UAV must keep the appropriate distance for reliable transmission. In addition, the altitude of the UAV may significantly affect the link quality between the UAV and the BS, as well as the link between the UAV and the users/rescuers. In this paper, we analyze the coverage of the disaster-resilient communication network with a UAV for guaranteeing the reliability of all links. We show that the position of UAV can be a function of the BS's and user's elevation angle. The simulation results show that the maximum radius of coverage in the high-rise urban environment can be 5.25 km and 2.46 km for downlink and uplink, respectively. Moreover, this paper can provide a principle for the central emergency operation center (CEOC) to immediately deploy the disaster-resilient communication network.

In response to the challenges of posture diversity, motion blur and small target detection in unmanned aerial vehicle (UAV) target detection in long-distance and complex scenarios, this paper proposes an improved UAV target detection model:YOLO11n-SMSH. This model significantly improves the detection performance through four core mechanisms: Firstly, a CRIE module with edge perception integration is introduced in the backbone network to enhance the ability of extracting target edge features; Secondly, a SRA-DFF network with semantic association enhancement capability is used as the neck network to achieve high-quality feature interaction and fusion; Furthermore, the NTTAA detection head is finely designed, and through the weight sharing mechanism and bidirectional parallel task alignment path, the collaboration between classification and localization tasks is effectively strengthened; Finally, the GIoU loss function is introduced, and the boundary box regression is optimized using spatial coverage, improving the model's adaptability to UAV targets. Experimental results on the DUT Anti-UAV dataset show that YOLO11n-SMSH performs excellently. Compared with the baseline model, the accuracy (P), recall rate (R), mAP50 and mAP50-95 have significantly increased by 1.5%, 3.9%, 2.6% and 2.5%, respectively. The experimental results verify the effectiveness of the multi-module collaborative optimization strategy and provide a high-performance solution for UAV target detection tasks in practical applications.

This paper describes an accurate attitude determination technique using multiple global navigation satellite system (GNSS) receivers and antennas for small unmanned aerial vehicles (UAVs). A laser survey using a small UAV needs highly accurate position and attitude information for reconstructing 3D models. The proposed technique uses the multiple GNSS antenna's positions computed by the GNSS carrier phase measurements to estimate the UAV's position and attitude. To solve the GNSS carrier phase ambiguity, the reliable ambiguity search is performed with a couple of constraints for the base line vector. The performance of the proposed technique is evaluated in the static test. From the test, the proposed technique could estimate UAV's attitude in 0.1 degree accuracy. Furthermore, the accurate UAV's position could be estimated in almost 100 % availability.

With technological development of multi sensors, UAV (unmanned aerial vehicle) can identify and locate key targets in essential monitoring areas or geological disaster-prone areas by taking video sequence images, and precise positioning of the video sequence images is constantly a matter of great concern. In recent years, precise positioning of aerial images has been widely studied. But it is still a challenge to simultaneously realize precise, robust and dynamic positioning of UAV’s patrolling video sequence images in real time. In order to solve this problem, a visual positioning model for patrolling video sequence images based on DOM rectification is proposed, including a robust block-matching algorithm and a precise polynomial-rectifying algorithm. First, the robust block-matching algorithm is used to obtain the best matching area for UAV’s video sequence image on DOM (Digital Orthophoto Map), a pre-acquired digital orthophoto map covering the whole UAV’s patrolling region. Second, the precise polynomial-rectifying algorithm is used to calculate accurate rectification parameters of mapping UAV’s video sequence image to the best matching area obtained above, and then real time positioning of UAV’s patrolling video sequence images can be realized. Finally, the above two algorithms are analyzed and verified by three practical experiments, and results indicate that even if spatial resolution, surface specific features, illumination condition and topographic relief are significantly different between DOM and UAV’s patrolling video sequence images, proposed algorithms can still steadily realize positioning of each UAV’s patrolling video sequence image with about 2.5 m level accuracy in 1 s. To some extent, this study has improved precise positioning effects of UAV’s patrolling video sequence images in real time, and the proposed mathematical model can be directly incorporated into UAV’s patrolling system without any hardware overhead.

This paper considers the problem of fault detection and identification (FDI) in applications carried out by a group of unmanned aerial vehicles (UAVs) with visual cameras. In many cases, the UAVs have cameras mounted onboard for other applications, and these cameras can be used as bearing-only sensors to estimate the relative orientation of another UAV. The idea is to exploit the redundant information provided by these sensors onboard each of the UAVs to increase safety and reliability, detecting faults on UAV internal sensors that cannot be detected by the UAVs themselves. Fault detection is based on the generation of residuals which compare the expected position of a UAV, considered as target, with the measurements taken by one or more UAVs acting as observers that are tracking the target UAV with their cameras. Depending on the available number of observers and the way they are used, a set of strategies and policies for fault detection are defined. When the target UAV is being visually tracked by two or more observers, it is possible to obtain an estimation of its 3D position that could replace damaged sensors. Accuracy and reliability of this vision-based cooperative virtual sensor (CVS) have been evaluated experimentally in a multivehicle indoor testbed with quadrotors, injecting faults on data to validate the proposed fault detection methods.

Manipulating objects using arms mounted to unmanned aerial vehicles (UAVs) is attractive because UAVs may access many locations that are otherwise inaccessible to traditional mobile manipulation platforms such as ground vehicles. Historically, UAVs have been employed in ways that avoid interaction with the environment at all costs. The recent trend of increasing small UAV lift capacity and the reduction of the weight of manipulator components make the realization of mobile manipulating UAVs imminent. Despite recent work, several major challenges remain to be overcome before it will be common practice to manipulate objects from UAVs. Among these challenges, the constantly moving UAV platform and compliance of manipulator arms make it difficult to position the UAV and end-effector relative to an object of interest precisely enough for reliable manipulation. Solving this challenge will bring UAVs one step closer to being able to perform meaningful tasks such as infrastructure repair, disaster response, law enforcement, and personal assistance. Toward a solution to this challenge, this thesis describes a way forward that uses the UAV as a means to crudely position a manipulator within reach of the end-effector's goal position in the world. The manipulator then performs the fine positioning of the end-effector, rejecting position perturbations caused by UAV motions. An algorithm to coordinate the redundant degrees of freedom of an aerial manipulation system is described that allows the motions of the manipulator to serve as inputs to the UAV's position controller. To demonstrate this algorithm, the manipulator's six degrees of freedom are servoed using visual sensing to drive an eye-in-hand camera to a specified pose relative to a target while treating motions of the host platform as perturbations. Simultaneously, the host platform's degrees of freedom are regulated using kinematic information from the manipulator. This ultimately drives the UAV to a position that allows the manipulator to assume a pose relative to the UAV that maximizes reachability, thus facilitating the arm's ability to compensate for undesired UAV motions. Maintaining this loose kinematic coupling between the redundant degrees of freedom of the host UAV and manipulator allows this type of controller to be applied to a wide variety of platforms, including manned aircraft, rather than a single instance of a purpose-built system. As a result of this loose coupling, careful consideration must be given to the manipulator design so that it can achieve useful poses while minimally influencing the stability of the host UAV. Accordingly, the novel application of a parallel manipulator mechanism is described.

This paper shows the design and development of a truly low cost attitude determination and navigation system based primarily on non-dedicated mass market GNSS receivers and antennas, aided by MEMS inertial sensors. GNSS/INS integration combines the advantages of absolute satellite-based positioning with the high dynamic performance and data rates of inertial sensors, having become the standard approach in navigation systems for Unmanned Aerial Vehicles (UAV) among other applications. We have used a Tightly-Coupled (TC) algorithm aimed at the integration of GPS and INS devices, designed to exploit the measurements provided by four GNSS receivers and a MEMS IMU. This task is accomplished by forming double differences (DD) of carrier-phase measurements and properly solving the ambiguities on-the-fly. The robustness of the algorithm is enhanced by exploiting unambiguous DD of code-phase observables or un-differenced pseudoranges when carrier phase ambiguity fix is not reliable. In order to limit the unwanted effects of vibration, the INS raw samples (i.e. gyro and accelerometer measurements) are passed through a proper low-pass filter before being used by the fusion algorithm. Furthermore, we have constrained the TC algorithm with the heading information obtained from the DD carrier-phase measurements of four GNSS receivers that are available in the final system. These carrier-phase measurements need to be processed and their ambiguities solved before becoming usable, for which proper integer ambiguity resolution methods are described too. Achieving the realization of the first prototype relies on advances beyond the state-of-the-art in the fields of multi-receiver GNSS-based attitude determination, inertial MEMS/GNSS data fusion and precise calibration of properly selected GNSS antennas. All these advances aim at optimizing the cost, weight, size and power consumption of the overall system to enable its use in one of the most demanding applications as is the control and navigation of small UAV. The feasibility of a real-time implementation has been demonstrated. We have run the designed TC algorithm first onboard a car for validating the implementation by gathering real data in different user configurations (i.e. static and dynamic) and environmental scenarios (open-sky, urban canyon, etc.). For performance evaluation of the real-time system the prototype was mounted onboard the target UAV as a sample case of aerial applications.

The unmanned aerial vehicle (UAV) base station plays a significant role in enhancing the terrestrial network, when the ground base station (GBS) is destroyed in emergent cases or its load exceeds the capacity of the terrestrial network. Presently, many papers focus on optimizing the UAV position deployment and user access, while ignoring the optimization about the spectrum resource management. To solve this problem, we formulate a joint optimization problem of the spectrum resource management and the position placement for UAVs with the constraint of the limited backhaul capacity. Later, the joint optimization problem is modeled as a hierarchical game decision architecture comprised of a UAV position placement game and a spectrum resource management game. Further, we analyze the equilibrium property of the two games and propose two best response- (BR) based optimization algorithms to reach the Nash Equilibriums (NEs) of the two games, respectively. Specifically, the proposed algorithm about the UAV deployment considers the variable granularity local exploration and global random exploration. Simulation results show that the proposed UAV deployment algorithm can improve the total throughput by 7% and 20% at least in comparison with the K-means deployment algorithm and the fixed granularity exploration algorithm, respectively.

In the unmanned aerial vehicle (UAV) based localization of slow-moving radio frequency (RF) sources with unknown transmitted strength of signal, such as a person with a cell phone in a search and rescue mission, the UAV navigation errors are significant sources of localization error. Although the use of a global positioning system (GPS) can reduce the UAV’s localization error significantly resulting in more accurate RF source localization, if the GPS signal is lost temporarily or permanently, the accuracy of the UAV-based localization decreases rapidly. In this paper, a simultaneous localization and mapping (SLAM)-inspired approach for simultaneous localization of UAV and RF sources (SLUS) is proposed. The proposed approach solves these two connected problems, i.e. the UAV localization and RF source localization, simultaneously to decrease the error of the UAV position estimation and the error of the RF source localization. In the proposed approach, beside the UAV position prediction, the RF source position prediction is also performed. Then the predicted states are augmented and the augmented predicted state information is corrected using range-ratio and bearing observations, i.e. RF source features, considering the unknown transmitted power. The proposed approach is simulated and the results show that the normal divergence of a target localization and the divergence of the UAV navigation in latitude and longitude channels have been eliminated using this approach. In other words, simultaneous localization of the UAV and RF sources uses the RF sources, as features in the environment, to aid the navigation system. Although the approach is similar to the mapping of RF sources in the environment, the created map would be useless after finding the RF sources. That is why SLUS has been used instead of SLAM. The main contributions of this work are: 1) performing simultaneous localization of a UAV and targets using RF signals, especially in a non-line of sight (NLOS) condition; 2) using difference of signal strength, i.e. differential received strength signal indicator (DRSSI), to eliminate the impact of unknown target signal power; and 3) simultaneous multi-target localization and tracking.

This paper considers unmanned aerial vehicle (UAV)-assisted infrastructure-to-vehicle (I2V) communication employing UAVs as relays to increase the throughput between a roadside unit (RSU) and a vehicular user equipment (VUE). We investigate the UAV position planning problem under both single UAV and multiple cooperative UAVs scenarios while considering the mobility of the VUE, aiming to maximize the data rate of the system. We first consider using a single UAV and prove that the single UAV position planning can be formulated as a convex optimization problem, and then obtain the optimal position of the UAV. Next, we investigate the multiple cooperative UAVs scenario and formulate the joint power control and position planning problem to improve the data rate of the system under a fixed total power consumption. Numerical simulations are provided to verify our theoretical results. Our findings highlight the effects of important system parameters, such as height, transmit power, and the number of UAVs, on the optimal UAV positioning and system performance.

Aiming at the problem that the unmanned aerial vehicle (UAV) cannot complete the positioning and ranging in the complex background and the signal is interfered, we proposed a monocular measurement scheme of assigning 4 LED fiducials (also called landmarks) with 3 colors in total on the target UAV. Firstly, feature areas are screened out by using high saturation, high brightness and specific hue range of LED in HSV (Hue, Saturation, Value) color space. After morphological processing, the background that does not meet the features is removed. Then, the mapping relationship between target LED fiducials and image fiducials is established by using the average hue of connected domain and special geometric layout. The improved Lambda-Twist is used to find the distance from the target UAV to the center of the camera, and the performance of the UAV recognition and ranging from 90m to 245m is tested. The experimental results show that the method can quickly and accurately measure the distance to the target, and can be used for UAV auxiliary measurement.

In recent years, unmanned aerial vehicle (UAV) has been widely used in target tracking tasks such as security, anti-terrorism, tracking and monitoring because of its wide and flexible perspective. At the same time, deep learning creates new conditions for UAV visual recognition and motion tracking because it has high recognition accuracy and fast recognition speed. This paper presents an UAV dynamic tracking algorithm based on deep learning. The algorithm mainly includes three parts: the PTZ control, relative position calculation and the UAV control. The main work includes: 1. The tracking target is identified through the deep learning network based on YOLOv3, and the PTZ angle is adjusted in real time by using the control method of combining the PID control with the time-delay control to reduce the impact of image transmission delay; 2. The relative position between the UAV and the target is calculated by combining the UAV flight altitude, UAV attitude, PTZ angle and the coordinate of the target in the image. At the same time, the relative position prediction is added to estimate the relative distance between the UAV and the target at the next frame time as a reference value of the UAV speed, so as to improve the dynamic tracking ability; 3. The relative position information is fed back to the flight control function, and the linear velocity of UAV is output by the PID controller. Through the simulation test in Airsim, it is proved that the proposed algorithm can effectively improve the stability and robustness of the UAV tracking system.

U-turn is a common and typical turn process in area coverage of Unmanned Aerial Vehicle (UAV) in which the flying path of UAV projection and motion path of camera footprint center do not coincide with each other. This paper investigates the U-turn optimization for three-dimensional area coverage of UAV. Firstly, the relationship between UAV attitude and camera footprint is studied. And some related formulas concerning the camera footprint of UAV are given for different maneuvers which can be used to obtain the parameters of camera footprint and coordinate transformation between UAV centroid and footprint center. Then the differences paths of UAV projection and camera footprint are discussed in line sweep coverage approach. Finally, The U-turn optimization of UAV which contains the distances and duration is analyzed in three different cases.

소형 및 저가형 CCD 카메라의 성능은 소형 쿼드콥터의 정밀 추적기능을 구현하는데 있어서 충분한 성능을 갖추고 있지 못하는데 본 연구에서는 덜 정확한 GPS 보다 CCD 카메라를 이용한 보행자와 같은 대상물의 상공에서 강건한 호버링을 유지시키기 위한 방법을 제시하였다. 기존의 연구 대상이었던 고정된 물체가 아닌 보행자를 타깃으로 이용한 UAV의 절대 위치를 추정하는 방법을 제시하였다. 이는 UAV가 산악이나 사람들이 붐비는 공공지역에서 이동할 때 UAV의 절대위치를 인식할 수 있는 방법이 없을 경우 UAV 주변에서 움직이는 물체의 정보를 활용하여 UAV의 절대위치를 보정하는 방법으로 매우 유용하다. 연구를 위해서 보행자의 위치를 알고 있는 것으로 가정하나 실제적인 상황 속에서는 영상매칭을 통하여 그 정보를 수신하는 것으로 해석한다. 본 연구를 위하여 UAV의 위치 추정 불확실성을 정량적으로 나타내었으며, 좌표계 변환을 통한 영상기반의 기하학적 구속 식을 유도하여, 칼만 필터를 적용하여 로봇의 위치를 보정하여 위치 추정 불확실성을 줄일 수 있음을 보였다. The accuracy of small and low cost CCD camera is insufficient to provide data for precisely tracking unmanned aerial vehicles(UAVs). This study shows how UAV can hover on a human targeted tracking object by using CCD camera rather than imprecise GPS data. To realize this, UAVs need to recognize their attitude and position in known environment as well as unknown environment. Moreover, it is necessary for their localization to occur naturally. It is desirable for an UAV to estimate of his attitude by environment recognition for UAV hovering, as one of the best important problems. In this paper, we describe a method for the attitude of an UAV using image information of a maker on the floor. This method combines the observed position from GPS sensors and the estimated attitude from the images captured by a fixed camera to estimate an UAV. Using the a priori known path of an UAV in the world coordinates and a perspective camera model, we derive the geometric constraint equations which represent the relation between image frame coordinates for a marker on the floor and the estimated UAV's attitude. Since the equations are based on the estimated position, the measurement error may exist all the time. The proposed method utilizes the error between the observed and estimated image coordinates to localize the UAV. The Kalman filter scheme is applied for this method. its performance is verified by the image processing results and the experiment.