IA-OPD : an optimized orthogonal pulse design scheme for waveform division multiple access UWB systems

A new design scheme of orthogonal pulses is proposed for waveform division multiple access ultra-wideband (WDMA-UWB) systems. In order to achieve WDMA and to improve user capacity, the proposed method, termed as interference alignment based orthogonal pulse design (IA-OPD), employs combined orthogonal wavelet functions in the pulse design. The combination coefficients are optimized by using interference alignment. Due to the reciprocity between transmitted and local template signals, the iterative process based on maximum signal to interference plus noise ratio (Max-SINR) criterion can be used to solve the optimization problem in interference alignment. Numerical results demonstrate that the optimized orthogonal pulses provide excellent performances in terms of multiple access interference (MAI) suppression, user capacity and near-far resistance without using any multiuser detection (MUD) techniques. Thus, the IA-OPD scheme can be used to efficiently design a large number of orthogonal pulses for multiuser WDMA-UWB systems with low computational complexity and simple transceiver structure

Hierarchical Decentralized LQR Control for Formation-Keeping of Cooperative Mobile Robots in Material Transport Tasks

This study provides a formation-keeping method based on consensus for mobile robots used in cooperative transport applications that prevents accidental damage to the objects being carried. The algorithm can be used to move both rigid and elastic materials, where the desired formation geometry is predefined. The cooperative mobile robots must maintain formation even when encountering unknown obstacles, which are detected using each robot's on-board sensors. Local actions would then be taken by the robot to avoid collision. However, the obstacles may not be detected by other robots in the formation due to line-of-sight or range limitations. Without sufficient communication or coordination between robots, local collision avoidance protocols may lead to the loss of formation geometry. This problem is most notable when the object being transported is deformable, which reduces the physical force interaction between robots when compared to rigid materials. Thus, a decentralized, hierarchical LQR control scheme is proposed that guarantees formation-keeping despite local collision avoidance actions, for both rigid and elastic objects. Representing the cooperative robot formation using multi-agent system framework, graph Laplacian potential and Lyapunov stability analysis are used to guarantee tracking performance and consensus. The effectiveness and scalability of the proposed method are illustrated by computer simulations of line (2 robots) and quadrilateral (4 robots) formations. Different communication topologies are evaluated and provide insights into the minimum bandwidth required to maintain formation consensus

Issue Small Satellites

Small satellite is a disruptive technology in space industries. Traditionally, space industries were dominated by satellites which have thousands of kilograms and are bulky and expensive. Small satellites denote a new generation of miniaturized satellites which, by taking advantages of modern technologies (e.g., integrated circuits, digital signal processing, MEMS, and additive manufacturing), can achieve a significant reduction in volume, mass, development time, and cost of satellites. During recent decades, small satellites, including CubeSats, NanoSats, MiniSats, and MicroSats, have undergone rapid developments, and are playing an increasingly larger role in exploration, technology demonstration, scientific research, and education. These miniature satellites provide a low-cost platform for missions, including planetary space exploration, Earth observations, fundamental Earth and space science, and developing precursor science instruments like laser communications and millimeter-wave communications for intersatellite and intrasatellite links, and autonomous movement capabilities. They also allow educators an inexpensive means to engage students in all phases of satellite development, operation, and exploitation through real-world, hands-on research and development experience on rideshare launch opportunities. A number of miniaturized satellites can form spaceborne wireless sensor networks in the space, which are also going to play an important role in Internet of Space (IoS) of the futur

Maneuvering formations of mobile agents using designed mismatched angles

This paper investigates how to maneuver a planar formation of mobile agents using designed mismatched angles. The desired formation shape is specified by a set of interior angle constraints. To realize the maneuver of translation, rotation and scaling of the formation as a whole, we intentionally force the agents to maintain mismatched desired angles by introducing a pair of mismatch parameters for each angle constraint. To allow different information requirements in the design and implementation stages, we consider both measurement-dependent and 10 measurement-independent mismatches. Starting from a triangular formation, we consider generically angle rigid formations that can be constructed from the triangular formation by adding new agents in sequence, each having two angle constraints associated with some existing three agents. The control law for each newly added agent arises naturally from the angle constraints and makes full use of the angle mismatch parameters. We show that the control can effectively stabilize the formations while simultaneously realizing maneuvering. Simulations are conducted to validate the theoretical results

A review of optimization techniques in spacecraft flight trajectory design

For most atmospheric or exo-atmospheric spacecraft flight scenarios, a well-designed trajectory is usually a key for stable flight and for improved guidance and control of the vehicle. Although extensive research work has been carried out on the design of spacecraft trajectories for different mission profiles and many effective tools were successfully developed for optimizing the flight path, it is only in the recent five years that there has been a growing interest in planning the flight trajectories with the consideration of multiple mission objectives and various model errors/uncertainties. It is worth noting that in many practical spacecraft guidance, navigation and control systems, multiple performance indices and different types of uncertainties must frequently be considered during the path planning phase. As a result, these requirements bring the development of multi-objective spacecraft trajectory optimization methods as well as stochastic spacecraft trajectory optimization algorithms. This paper aims to broadly review the state-of-the-art development in numerical multi-objective trajectory optimization algorithms and stochastic trajectory planning techniques for spacecraft flight operations. A brief description of the mathematical formulation of the problem is firstly introduced. Following that, various optimization methods that can be effective for solving spacecraft trajectory planning problems are reviewed, including the gradient-based methods, the convexification-based methods, and the evolutionary/metaheuristic methods. The multi-objective spacecraft trajectory optimization formulation, together with different class of multi-objective optimization algorithms, is then overviewed. The key features such as the advantages and disadvantages of these recently-developed multi-objective techniques are summarised. Moreover, attentions are given to extend the original deterministic problem to a stochastic version. Some robust optimization strategies are also outlined to deal with the stochastic trajectory planning formulation. In addition, a special focus will be given on the recent applications of the optimized trajectory. Finally, some conclusions are drawn and future research on the development of multi-objective and stochastic trajectory optimization techniques is discussed

Hierarchical Decentralized LQR Control for Formation-Keeping of Cooperative Mobile Robots in Material Transport Tasks

This study provides a formation-keeping method based on consensus for mobile robots used in cooperative transport applications that prevents accidental damage to the objects being carried. The algorithm can be used to move both rigid and elastic materials, where the desired formation geometry is predefined. The cooperative mobile robots must maintain formation even when encountering unknown obstacles, which are detected using each robot's on-board sensors. Local actions would then be taken by the robot to avoid collision. However, the obstacles may not be detected by other robots in the formation due to line-of-sight or range limitations. Without sufficient communication or coordination between robots, local collision avoidance protocols may lead to the loss of formation geometry. This problem is most notable when the object being transported is deformable, which reduces the physical force interaction between robots when compared to rigid materials. Thus, a decentralized, hierarchical LQR control scheme is proposed that guarantees formation-keeping despite local collision avoidance actions, for both rigid and elastic objects. Representing the cooperative robot formation using multi-agent system framework, graph Laplacian potential and Lyapunov stability analysis are used to guarantee tracking performance and consensus. The effectiveness and scalability of the proposed method are illustrated by computer simulations of line (2 robots) and quadrilateral (4 robots) formations. Different communication topologies are evaluated and provide insights into the minimum bandwidth required to maintain formation consensus

Development of control architectures in multi-agent satellite systems for Earth observation services

ilustraciones, fotografías, graficas, mapasLas necesidades de apropiación tecnológica y la estructuración de misiones espaciales en el contexto colombiano traen consigo la demanda de servicios y trabajos colaborativos y especializados, para los diferentes segmentos de un sistema espacial, como bien se está identificando en la estructuración del Programa Espacial Colombiano. Frente a estos derroteros, la presente investigación aborda el reto de apropiación del conocimiento en el diseño de misión, el control del segmento espacial y en especial el reto de proponer estrategias de control a sistemas satelitales multiagente, ya que los sistemas convencionales por su costo, centralización y modos de control conservadores, restringen el desempeño individual y grupal para las nuevas alternativas de sistemas en red que se presentan con los satélites de pequeña escala. En este sentido y mediante el uso de la metodología en V, se abordan los procesos de diseño de misión, así como el diseño de controladores individuales y grupales para la orientación y traslación de satélites en misiones de observación terrestre. Lo anterior con el fin de aprovechar la reducción de costos y flexibilidad operacional que brinda el uso de satélites de pequeña escala; a pesar de su limitada capacidad operacional/física, la cual hace necesario disponer de más de un agente para lograr los objetivos de servicio. Esta necesidad inherente, demanda la posibilidad de interconectar agentes en red y explorar arquitecturas de control con estrategias de cooperación, consenso y técnicas robustas de control en red, que permitan afrontar las no linealidades, incertidumbres y errores que limitan su coordinación y cooperación. Según lo expuesto, se definen diferentes arquitecturas de control frente a perturbaciones, limitaciones de actuación e incertidumbres, donde se identifican y caracterizan parámetros de desempeño individual y grupal ante diferentes tipos de misión, comportamientos adaptativos, políticas de consenso y cooperación, en dos etapas: La primera con el análisis, diseño y desarrollo de misiones, modelos y controladores, útiles para la definición del sistema y las arquitecturas de control formuladas; y la segunda mediante la evaluación e integración de algoritmos de control y consenso, validados con el método de Montecarlo y la aplicación de los índices propuestos como métricas de desempeño de la red. Adicionalmente, se incluye el diseño e implementación de una interfaz gráfica para la instrucción y entrenamiento en el diseño de misión y configuración de agentes, como complemento a los controladores y arquitecturas propuestas para la apropiación de tecnologías de control modernas y el manejo de sistemas satelitales de pequeña escala, como medios para la democratización y el despliegue del concepto del New Space en el territorio colombiano. (Texto tomado de la fuente)The needs for technological appropriation and structuration of space missions in the Colombian context bring with them the demand for collaborative and specialized services and works, for the different segments of a space system, as is being well identified in the structuration of the Colombian Space Program. Facing these objectives, this research addresses the challenge of knowledge appropriation in mission design, space segment control, and especially the challenge of proposing control strategies for multi-agent satellite systems, since conventional systems due to their cost, centralization, and conservative control modes, restrict individual and group performance for the new network system alternatives that come with small-scale satellites. In this sense and using the V methodology, the mission design processes are addressed, as well as the design of individual and group controllers for the orientation and translation of satellites in terrestrial observation missions. The foregoing to take advantage of the cost reduction and operational flexibility provided using small-scale satellites; despite its limited operational / physical capacity, which makes it necessary to have more than one agent to achieve service objectives. This inherent need demands the possibility of interconnecting agents in the network and exploring control architectures with cooperation strategies, consensus, and robust network control techniques, which allow facing the non-linearities, uncertainties and errors that limit their coordination and cooperation. According to the above, different control architectures are defined against disturbances, actuation limitations and uncertainties, where individual and group performance parameters are identified and characterized in front of different types of mission, adaptive behaviors, consensus and cooperation policies, in two stages: The first with the analysis, design and development of missions, models and controllers, useful for defining the system and formulated control architectures; and the second through the evaluation and integration of control and consensus algorithms, validated with the Montecarlo method and the application of the indexes proposed as network performance metrics. Further, the design and implementation of a graphical interface for instruction and training in mission design and agent configuration is included, as a complement to the controllers and architectures proposed for the appropriation of modern control technologies and the management of small-scale satellite systems, as means for the democratization and deployment of the New Space concept in Colombian territory.DoctoradoDoctor en IngenieríaIngeniería de Automatización, Control y Mecatrónic