Effect of Conductive Propellers on VHF UAV-based Antenna Measurements: Experimental Results

Professional Unmanned Aerial Vehicles (UAVs) are generally equipped with carbon fiber propellers. Their conductivity and significant size can potentially increase both noise and systematics of UAV-based antenna measurement systems operating in the VHF band. A set of alternative fiberglass propellers has been manufactured and tested. This paper present measured results on the signal stability achieved with both fiberglass and carbon-fiber propellers at 175 MHz

Channel Model and Performance Analysis of Millimetre-wave UAV Air-to-Ground Link under UAV Wobbling

Fifth-generation (5G) and beyond mobile communication networks are expected to meet an explosion of data traffic usage and a fast-varying environment. The millimetre-wave communications and unmanned aerial vehicles (UAVs) communications are two important methods to tackle these challenges. To thoroughly investigate millimetre-wave UAV communications, it is essential to have a good understanding of electromagnetic wave propagation in the millimetre-wave band between the UAV-carried aerial base station or the mobile relay node and ground nodes, which is known as the UAV air-to-ground (A2G) channel model. To support the millimetre-wave UAV A2G network design, it is vital to have a deep cognition of the network performance evaluation parameters of the UAV A2G link, e.g., throughput and energy efficiency. This thesis discusses three problems related to millimetre-wave UAV A2G communications. In this study, the effect of the inevitable UAV wobbling on the millimetre-wave UAV A2G channel is first investigated. The wobbling process of a hovering UAV, which is affected by wind gusts and the high vibration frequency of its propellers and rotors, is modelled. The analytical temporal autocorrelation function (ACF) for the millimetre-wave UAV A2G link is derived. With the derived temporal ACF equation, the Doppler power spectrum density for the millimetre-wave UAV A2G link is investigated. The numerical results show that the temporal ACF decreases quickly with time and the impact of the Doppler effect caused by UAV wobbling is significant on bit error probability (BEP) for the millimetre-wave A2G link. Then, the problem of throughput for the millimetre-wave UAV A2G link under UAV wobbling is investigated. Two types of detectors at the receiver to demodulate the received signal and get the instantaneous BEP of a millimetre-wave UAV A2G link under UAV wobbling are introduced. Based on the designed detectors, an adaptive modulation scheme maximising the average transmission rate under UAV wobbling by optimizing the data transmission time subject to the maximum tolerable BEP is proposed. The numerical results show that the proposed adaptive modulation maximises the temporally averaged transmission rate of the millimetre-wave UAV A2G link compared with other transmission policies under UAV wobbling. After proposing the adaptive modulation, the power control to minimise the power consumption is investigated considering the limited on-board energy of a UAV. A power control policy that minimises the transmission power while maintaining both the BEP under the threshold and the maximised average transmission rate is proposed for the millimetre-wave UAV A2G link under UAV wobbling. The energy efficiency of the UAV A2G link is evaluated to show how effective this power control policy is. The numerical results show that the power control policy reduces the power consumption by up to 50% for wobbling millimetre-wave UAV A2G links and the energy efficiency of the system under power control is higher than that of the adaptive modulation scheme without the power control policy. In summary, the thesis studies the channel characteristics and evaluates the performance of the millimetre-wave UAV A2G link under wobbling to support the future millimetre-wave UAV communication network deployment. A key observation is that even for weak UAV wobbling, the temporal ACF of the UAV A2G link deteriorates quickly, making the link difficult to establish a reliable communication link. To keep the reliable A2G link and achieve high throughput, the adaptive modulation scheme of the millimetre-wave UAV A2G link under wobbling is proposed. The power control policy for the adaptive modulation of the millimetre-wave UAV A2G link could save power by over 50% and support the green UAV A2G link

A survey on fractional order control techniques for unmanned aerial and ground vehicles

In recent years, numerous applications of science and engineering for modeling and control of unmanned aerial vehicles (UAVs) and unmanned ground vehicles (UGVs) systems based on fractional calculus have been realized. The extra fractional order derivative terms allow to optimizing the performance of the systems. The review presented in this paper focuses on the control problems of the UAVs and UGVs that have been addressed by the fractional order techniques over the last decade

Unmanned aerial vehicles (UAVs) for wireless communication and networks : potentials and design challenges

Unmanned aerial vehicles (UAVs) are mostly considered by the military for surveillance and reconnaissance operations, and by hobbyists for aerial photography. However, in recent years, the UAV operations have been extended for civilian and commercial purposes due to their agile and cost-effective deployment. UAVs appear to be more prolific platforms to enable wireless communication due to their better line-of-sight (LOS) channel conditions as compared with the fixed base stations (BSs) in terrestrial communication which suffer from severe path loss, shadowing, and multipath fading in more challenging propagation environments. In UAV-enabled wireless communications, the UAV can either act as a complementary aerial BS to provide on-demand communication or as an aerial user equipment (UE) which is operated by the existing cellular network. Several challenges exist in the design of UAV communications which include but not limited to channel modeling, optimal deployment, interference generation, performance analysis, limited on-board battery lifetime, trajectory optimization, and unavailability of regulations and standards which are specific for UAV communication and networking. This thesis particularly investigates some important design challenges for safe and reliable functionalities of UAV for wireless communication and networking. UAV communication has its own distinctive channel characteristics compared to the widely used cellular or satellite systems. However, several challenges exist in UAV channel modeling. For example, the propagation characteristics of UAV channels are under explored for spatial and temporal variations in non-stationary channels. Therefore, first and foremost, this thesis provides an extensive review of the measurement methods proposed for UAV channel modeling and discusses channel modeling efforts for air-to-ground and air-to-air channels. Furthermore, knowledge-gaps are identified to realize accurate UAV channel models. The efficient deployment strategy is imperative to compensate the adverse impact of interference on the coverage area performance of multiple UAVs. As a result, this thesis proposes an optimal deployment strategy for multiple UAVs in presence of downlink co-channel interference in the worst-case scenario. In particular, this work presents coordinated multi-UAV strategy in two schemes. In the first scheme, symmetric placement of UAVs is assumed at a common optimal altitude and transmit power. In the second scheme, asymmetric deployment of UAVs with different altitudes and transmit powers is assumed. The impact of various system parameters, such as signal-to interference-plus-noise ratio (SINR) threshold, separation distance between UAVs, and the number of UAVs and their formations are carefully studied to achieve the maximum coverage area inside and to reduce the unnecessary coverage expansion outside the target area. Fundamental analysis is required to obtain the optimal trade-off between the design parameters and performance metrics of any communication systems. This thesis particularly considers two emerging scenarios for evaluating performance of UAV communication systems. In the first scenario, the uplink UAV communication system is considered where the ground user follows the random waypoint (RWP) model for user mobility, the small-scale channel fading follows the Nakagami-m model, and the uplink interference is modeled by Gamma approximation. Specifically, the closed-form expressions for the probability density function (PDF), the cumulative distribution function (CDF), the outage probability, and the average bit error rate (BER) of the considered UAV system are derived as performance metrics. In the second scenario, the downlink hybrid caching system is considered where UAVs and ground small-cell BSs (SBSs) are distributed according to two independent homogeneous Poisson point processes (PPPs), and downlink interference is modeled by the Laplace transforms. Specifically, the analytical expressions of the successful content delivery probability and energy efficiency of the considered network are derived as performance metrics. In both scenarios, results are presented to demonstrate the interplay between the communication performance and the design parameters

Systems approach to model the conceptual design process of vertical take-off unmanned aerial vehicle

The development and induction in-service of Unmanned Air Vehicles (UAV) systems in a variety of civil, paramilitary and military roles have proven valuable on high-risk missions. These UAVs based on fixed wing configuration concept have demonstrated their operational effectiveness in recent operations. New UAVs based on rotary wing configuration concept have received major attention worldwide, with major resources committed for its research and development. In this thesis, the design process of a rotary-wing aircraft was re-visualised from an unmanned perspective to address the requirements of rotary-wing UAVs – Vertical Take-off UAVs (VTUAV). It investigates the conventional helicopter design methodology for application in UAV design. It further develops a modified design process for VTUAV addressing the requirements of unmanned missions by providing remote command-and-control capabilities. The modified design methodology is automated to address the complex design evaluations and optimisation process. An illustration of the automated design process developed for VTUAVs is provided through a series of inputs of the requirements and specifications, resulting in an output of a proposed VTUAV design configuration for “design decision support”. The VTUAV automated design process has been developed to pioneer an aerospace design tool for further detailed development and application as a – Design Decision Support System