Department Publications

This paper addresses the problem of high energy consumption in the standard take-off mode of quad-plane unmanned aerial vehicles (UAV). In the standard mode, the quad-plane takes-off vertically using the quad mode, and when the predefined altitude is reached the plane mode kicks in. However, the" bird" mode, where both quad and plane modes kick in together, the UAV could achieve altitude and airspeed while consuming lower energy. This paper presents the energy consumption and comparison in standard and bird take-off modes with actual experimental results obtained through flight tests of a small 1.35 kg quad-plane. The experiments showed that as much as 22% energy can be saved if the bird take-off mode is used.

Unmanned aerial vehicles (UAVs) commonly referred to as drones are becoming the attractive solution that provides wireless connectivity in a situation wherever the standard terrestrial base station is burden with high data traffic or unreachable in a disaster scenario. Our work examines the problem of best deployment of the UAVs as an aerial base station to empower wireless coverage to the users in the coverage less area. The foremost contributions of this study incorporate couple of strategies to deploy the ABSs and associate the UEs to the best ABS, where the total spectral efficiency of the network is maximized. Approaches will be chosen considering the prevailing environmental condition and system constraints. The first strategy uses an unsupervised clustering algorithm to determine the 2D positioning of the UAV ((x, y) coordinates) and a stable marriage approach is used for UE assignment by …

Deployment of unmanned aerial vehicles (UAVs) as aerial base stations (ABSs) has been considered to be a feasible solution to provide network coverage in scenarios where the conventional terrestrial network is overloaded or inaccessible due to an emergency situation. This article studies the problem of optimal placement of the UAVs as ABSs to enable network connectivity for the users in such a scenario. The main contributions of this work include a less complex approach to optimally position the UAVs and to assign user equipment (UE) to each ABS, such that the total spectral efficiency (TSE) of the network is maximized, while maintaining a minimum QoS requirement for the UEs. The main advantage of the proposed approach is that it only requires the knowledge of UE and ABS locations and statistical channel state information. The optimal 2-dimensional (2D) positions of the ABSs and the UE assignments are found using K-means clustering and a stable marriage approach, considering the characteristics of the air-to-ground propagation channels, the impact of co-channel interference from other ABSs, and the energy constraints of the ABSs. Two approaches are proposed to find the optimal altitudes of the ABSs, using search space constrained exhaustive search and particle swarm optimization (PSO). The numerical results show that the PSO-based approach results in higher TSE compared to the exhaustive search-based approach in dense networks, consuming similar amount of energy for ABS movements. Both approaches lead up to approximately 8-fold energy savings compared to ABS placement using naive exhaustive search.

The potential of drone based services is enormous with applications ranging from consumer product delivery to health services. When meeting this demand, one of the major challenges we face is the noise produced by drones, which not only contributes to listener discomfort, but also hinders the device's ability to effectively communicate via audio. Thus, there exists a pressing need for understanding the characteristics of drone related noise, which can then be suppressed using suitable methods. This paper presents a preliminary study on modeling the relationship between input motor current and acoustic noise produced by a drone. An experimental study is conducted indoors for a drone under hovering manoeuvre with a single active motor and propeller. The drone noise was measured by a single on-board microphone. We identify multiple tones or harmonics in the drone noise spectrum that vary proportionally …

We present a novel low cost time-of-flight (ToF) sensor deck for micro UAVs capable of sparse range measurements for localisation and mapping. In disaster scenarios such as building collapses, the larger UAVs equipped with highfidelity sensors such as lidars, structured light cameras and stereo cameras to perceive the environment with high resolution, may have difficulties when navigating through cluttered confined spaces. Micro UAVs are ideal for providing vital data in the aftermath of a disaster scenario but does not have the payload capacity for such sensors. Miniature low cost ToF sensors can provide range measurements albeit with low range and resolution. The proposed solution includes the design and implementation of a novel sensing deck for a commercially available micro UAV with 13 miniature ToF sensors, a low resolution thermal camera and a method to generate reliable 2D maps of GPS denied areas. The sparse observations obtained from range sensors are combined in a Rao-Blackwellized particle filter to create a reliable map. The ToF sensors are arranged to capture a maximum number of points in the horizontal plane at the flying height despite fluctuations in altitude and orientation. Particle weighting and resampling are only performed in a loop closure or when moving through a known area. Importance weight for the particles are computed by an Iterative Closest Point based method by calculating the error between nearest scan points. The proposed method has been tested in indoor environments and verified as a robust method to generate reliable maps of unknown environments.

The paper considers physical layer security (PLS) of an untrusted unmanned aerial vehicle (UAV) network, where a multitude of UAVs communicate in full-duplex (FD) mode. A source-based jamming (SBJ) scheme is exploited for secure communication without utilizing any external jammers. Firstly, the optimal power allocation between the confidential signal and the jamming signal is derived to maximize the secrecy rate of each link between the source and the destination. Then, the best UAV selection scheme is proposed to maximize the overall secrecy rate of the network. The corresponding secrecy outage probability (SOP) and the average secrecy rate (ASR) of the network are analyzed based on the proposed UAV selection and the optimal power allocation schemes. Asymptotic results are also obtained to derive the achievable diversity order. Results are validated through numerical evaluations while …

This paper presents a method for localizing an Unmanned Aerial Vehicle (UAV) using geo-referenced aerial images, in case of GPS failure. When flying in urban environments in low altitudes the inaccurate GPS localization has become a major problem. The proposed method fuses measurements from inertial sensors and visual odometer and perform image registration process using the images captured by the onboard down looking camera. A pre-built local orthomosaic map with geotagged aerial images is used for the registration. The problem of unreliable matches caused by the dynamic objects is addressed in our approach. The experiment results show that it is possible to localize the UAV in urban environments with a low margin of error by using our method.

This paper describes the development of a quadrotor fixed-wing hybrid unmanned aerial vehicle (UAV). By combining the flying qualities of quadrotor UAV and that of fixed-wing UAVs it is possible to achieve superior flying qualities. This way, the vertical take-off and landing capability of quadrotors and the long endurance of fixed-wing UAVs have been put together, while eliminating the disadvantages of both of these UAV types. The proposed hybrid drone has shown exciting performance in taking-off, cruising and landing fully autonomously. Control transition from quadrotor to fixed-wing and backwards have been analyzed. Sky Scout fixed-wing drone has been used to build the hybrid UAV, and the performance has been successfully demonstrated through flight tests. This paper precent the complete design of a quadrotor fixed-wing hybrid aerial vehicle with modelling, simulation and experimental verification.

In this paper, a feasibility study for construction and control of a novel design of a Multi-quadrotor unmanned aerial vehicle (UAV) is presented. This novel concept tests four identical Quadrotors assembled in a bigger cross structure. And, it also tests the ability of using the same controller that is used to control a single quadrotor to fly the novel design of cross assembled four quadrotor UAV. The main objective here is to improve redundancy and robustness and load carrying capacity of quadrotor UAVs. Even though there are four quadrotors, there is only one controller involves. When each individual Quadrotor works on a certain flight maneuver, it is expected that the assembled UAV of four of these in a cross structure to also be able to demonstrate the same maneuver. The prototype of the novel UAV was designed and built, and has been experimentally tested for a proof of concept where it was able to stabilize the …

Accurate attitude estimation in high dynamic motion scenarios like unmanned aerial vehicle navigation or human motion and magnetically disturbed indoor environments requires compensation of accelerometer disturbances as well as magnetometer disturbances. This paper proposes a novel algorithm for accelerometer disturbance rejection by adaptive estimation of accelerometer measurement covariance matrix online. Magnetic disturbances are generally lasting long compared to accelerometer disturbances which are generally short term in indoor navigation environments. Novel two step Kalman filter update method is proposed to separate attitude correction from heading correction. The magnetometer is used only for heading update such that the attitude estimation is not affected by errors in magnetometer measurement. Performances of the proposed algorithms are shown by using real world sensor data.

This paper presents on the stability analysis for RAVAN twin boom H-Tail Medium Scale UAV which has been developed by University of Moratuwa. It is required to understand the UAV behavior for the small perturbations in high altitudes while it is flying to be invisible. Indeed, without doing a proper stability analysis in different flying conditions, there is a high risk to fail the UAV for perturbations. Not only that but also it will help to optimize aerodynamic behavior for prolonging the flight endurance and effective deployment. The proper stability analysis will facilitate to increase the control flexibility.XFLR5 computational fluid dynamic software is used to do this stability analysis.

Since recently, UAVs (Unmanned Aerial Vehicles) have increasingly been recognized as a reliable, and effective means of aerial surveillance. Deployment of UAVs in disaster management for aerial surveillance and real-time video feed, when land access is cut off, is one of the most prominent applications. The ability of small, lightweight UAVs in aerial access and gathering data, in areas that are insecure or impossible for humans to reach has significantly improved remote accessibility. In this research, a new low cost small scale UAV with fully-fledged autopilot system on board the aircraft with the capabilities of following a predefined path and returning home autonomously has been designed, built, and tested successfully. This small-scale UAV is capable of navigating through given GPS coordinates at given altitude, while providing real-time flying status back to the ground control station.

Pitch and airspeed responses of a medium scale UAV were identified using the prediction error method. Data collection was conducted with an active closed loop autopilot control system. A naive SISO open loop transfer function was estimated using the parametric direct approach. Since its predictability was not significant, better estimators were developed using MISO parametric direct, and SISO parametric indirect method. The model validations were done to quantify their predictability.

Flying and handling qualities are substantially dependent on, and this paper is described it, in terms of the stability and control characteristics of UAV. It is essential to be able to describe and quantify the stability and control parameters completely. It is absolutely essential to understand the relationship between the aerodynamics of the airframe and its stability characteristics to prolong the flight endurance and effective deployment. And this paper is described the stability analysis based on the dynamic model of the twin boom double vertical stabilizer UAV.

This paper presents modelling, simulation and implementation of a quadrotor Unmanned Ariel Vehicle (UAV) Focus of this work is to gain in-depth understanding of quadrotor dynamics to develop a simulator and a laboratory platform to facilitate future development of control algorithms, automatic navigation systems, and trajectory planning for quadrotors. Quadrotor dynamics is modeled using Newton-Euler method. The model predicts the effects of the forces and torques generated by the four propellers on the quadrotor motion. Based on the model, a quadrotor simulator was developed in MATLAB® Simulink, on which various control algorithms can be developed and tested. A quadrotor prototype was built on which some of the control algorithms were tested experimentally in different environments to evaluate the stability and controllability of the platform. Experimental flight data and simulation results were …

quadrotor microaerial vehicles (MAVs) are simple robotic platforms with regard to their construction. In their basic form, they are no more than two counterrotating propeller pairs attached symmetrically to a rigid crosslike frame, along with the means to control the speed of each individual propeller. This symmetric design has enabled the quadrotor to become a simple but powerful vertical takeoff and landing aerial platform popular among the robotics community.

This paper describes the synthesis and evaluation of a "virtual odometer" for a Quadrotor Micro Aerial Vehicle. Availability of a velocity estimate has the potential to enhance the accuracy of mapping, estimation and control algorithms used with quadrotors, increasing the effectiveness of their applications. As a result of the unique dynamic characteristics of the quadrotor, a dual axis accelerometer mounted parallel to the propeller plane provides measurements that are directly proportional to vehicle velocities in that plane. Exploiting this insight, we encapsulate quadrotor dynamic equations which relate acceleration, attitude and the aerodynamic propeller drag in an extended Kalman filter framework for the purpose of state estimation. The result is a drift free estimation of lateral and longitudinal components of translational velocity and roll and pitch components of attitude of the quadrotor. Real world data sets gathered from two different quadrotor platforms, together with ground truth data from a Vicon system, are used to evaluate the effectiveness of the proposed algorithm and demonstrate that drift free estimates for the velocity and attitude can be obtained.

This paper analyzes the performance of an Extended Kalman Filter (EKF) based attitude estimator for a Quad Rotor Unmanned Aerial Vehicle (QRUAV). A non-linear dynamic model of the QRUAV, simulated in Matlab was complemented with an EKF based attitude estimator. The estimator fuses measurements obtained from simulated accelerometers and gyroscopes onboard the QRUAV. It is then shown that this estimator only results in adequate representation of the attitude when the translational velocity is large. This behavior is explained considering the dynamics of the vehicle and the onboard accelerometers. Also a possible method of exploiting this behavior for improving the estimation accuracy is suggested.

Quad Rotor unmanned aerial vehicle (UAV) is an aerial vehicle platform which has drawn much attention in the recent past due to its simple yet unique design. Despite the simplicity in the hardware, the vehicle is inherently unstable, and many control strategies have been proposed to achieve stability and control of the quad rotor platform. This paper presents a Fuzzy Logic based design to stabilize and control the quad rotor UAV. The fuzzy controller was designed and simulated along with a non-linear dynamic model of the quad rotor UAV. The fuzzy controller was then used to achieve stable hovering of the quad rotor UAV, amidst velocity disturbances. The simulation results show that stable hovering conditions can be achieved with the designed controller.

This paper presents a real time non linear automatic UAV simulation test-bed and autonomous control implementation with way point navigation. This UAV simulator is an integrated product that combines a vehicle operator station with a synthetic environment to support UAV research, training and operations while providing the operators (Internal Pilot) with a consistent interface. the simulated air vehicle operates against simulated terrain, weather, and computer generated forces In the synthetic mission space. External pilot also interact into synthetic simulation test-bed. The autonomous control system is based on the Aerosonde UAV and major considerations of controller performance and minimum instability within manual and autonomous switching have been evaluated with full software simulation. Major requirements for the good control system are minimum overshoot, minimum setting time without undesirable …

This paper presents non linear automatic unmanned aerial vehicle (UAV) control simulation with high maneuverability and precise tracking. Major considerations of flight performance and precise tracking have been evaluated with software simulation by aerosonde UAV. The autonomous control system is based on the Aerosonde UAV with control theory previously developed and implemented into aircraft. Major requirements for the high maneuverability are good path following with minimum overshoot, settling time without oscillation and low coupling between high level commands. High maneuverability leads to precise tracking for any kind of application. A MATLAB reg standard configuration environment and the Aerosim reg Aeronautical Simulation Block Set are utilized for simulation studies and presented through a Flightgear reg interface.

Flying and handling qualities are substantially dependent on, and this paper is described it, in terms of the stability and control characteristics of UAV. It is essential to be able to describe and quantify the stability and control parameters completely. It is absolutely essential to understand the relationship between the aerodynamics of the airframe and its stability characteristics to prolong the flight endurance and effective deployment. And this paper is described the stability analysis based on the dynamic model of the twin boom double vertical stabilizer UAV.