Design, Technologies and Applications of High Power Vacuum Electronic Devices from Microwave to THz Band

The last decade has contributed to the rapid progress in developing high-power microwave sources. This Special Issue aims to bring together information about the most striking theoretical and experimental results, new trends in development, remarkable modern applications, new demands in parameter enhancement, and future goals. Although only a tiny part of the achievements of recent years is included in this Issue, we hope that the presented articles will be useful for experts and students focusing on modern vacuum electronics

Performance enhancement for LTE and beyond systems

A thesis submitted to the University of Bedfordshire, in partial fulfilment of the requirements for the degree of Doctor of PhilosophyWireless communication systems have undergone fast development in recent years. Based on GSM/EDGE and UMTS/HSPA, the 3rd Generation Partnership Project (3GPP) specified the Long Term Evolution (LTE) standard to cope with rapidly increasing demands, including capacity, coverage, and data rate. To achieve this goal, several key techniques have been adopted by LTE, such as Multiple-Input and Multiple-Output (MIMO), Orthogonal Frequency-Division Multiplexing (OFDM), and heterogeneous network (HetNet). However, there are some inherent drawbacks regarding these techniques. Direct conversion architecture is adopted to provide a simple, low cost transmitter solution. The problem of I/Q imbalance arises due to the imperfection of circuit components; the orthogonality of OFDM is vulnerable to carrier frequency offset (CFO) and sampling frequency offset (SFO). The doubly selective channel can also severely deteriorate the receiver performance. In addition, the deployment of Heterogeneous Network (HetNet), which permits the co-existence of macro and pico cells, incurs inter-cell interference for cell edge users. The impact of these factors then results in significant degradation in relation to system performance. This dissertation aims to investigate the key techniques which can be used to mitigate the above problems. First, I/Q imbalance for the wideband transmitter is studied and a self-IQ-demodulation based compensation scheme for frequencydependent (FD) I/Q imbalance is proposed. This combats the FD I/Q imbalance by using the internal diode of the transmitter and a specially designed test signal without any external calibration instruments or internal low-IF feedback path. The instrument test results show that the proposed scheme can enhance signal quality by 10 dB in terms of image rejection ratio (IRR). In addition to the I/Q imbalance, the system suffers from CFO, SFO and frequency-time selective channel. To mitigate this, a hybrid optimum OFDM receiver with decision feedback equalizer (DFE) to cope with the CFO, SFO and doubly selective channel. The algorithm firstly estimates the CFO and channel frequency response (CFR) in the coarse estimation, with the help of hybrid classical timing and frequency synchronization algorithms. Afterwards, a pilot-aided polynomial interpolation channel estimation, combined with a low complexity DFE scheme, based on minimum mean squared error (MMSE) criteria, is developed to alleviate the impact of the residual SFO, CFO, and Doppler effect. A subspace-based signal-to-noise ratio (SNR) estimation algorithm is proposed to estimate the SNR in the doubly selective channel. This provides prior knowledge for MMSE-DFE and automatic modulation and coding (AMC). Simulation results show that this proposed estimation algorithm significantly improves the system performance. In order to speed up algorithm verification process, an FPGA based co-simulation is developed. Inter-cell interference caused by the co-existence of macro and pico cells has a big impact on system performance. Although an almost blank subframe (ABS) is proposed to mitigate this problem, the residual control signal in the ABS still inevitably causes interference. Hence, a cell-specific reference signal (CRS) interference cancellation algorithm, utilizing the information in the ABS, is proposed. First, the timing and carrier frequency offset of the interference signal is compensated by utilizing the cross-correlation properties of the synchronization signal. Afterwards, the reference signal is generated locally and channel response is estimated by making use of channel statistics. Then, the interference signal is reconstructed based on the previous estimate of the channel, timing and carrier frequency offset. The interference is mitigated by subtracting the estimation of the interference signal and LLR puncturing. The block error rate (BLER) performance of the signal is notably improved by this algorithm, according to the simulation results of different channel scenarios. The proposed techniques provide low cost, low complexity solutions for LTE and beyond systems. The simulation and measurements show good overall system performance can be achieved

Marshall Space Flight Center Research and Technology Report 2018

Many of NASAs missions would not be possible if it were not for the investments made in research advancements and technology development efforts. The technologies developed at Marshall Space Flight Center contribute to NASAs strategic array of missions through technology development and accomplishments. The scientists, researchers, and technologists of Marshall Space Flight Center who are working these enabling technology efforts are facilitating NASAs ability to fulfill the ambitious goals of innovation, exploration, and discovery

Radio Communications

In the last decades the restless evolution of information and communication technologies (ICT) brought to a deep transformation of our habits. The growth of the Internet and the advances in hardware and software implementations modified our way to communicate and to share information. In this book, an overview of the major issues faced today by researchers in the field of radio communications is given through 35 high quality chapters written by specialists working in universities and research centers all over the world. Various aspects will be deeply discussed: channel modeling, beamforming, multiple antennas, cooperative networks, opportunistic scheduling, advanced admission control, handover management, systems performance assessment, routing issues in mobility conditions, localization, web security. Advanced techniques for the radio resource management will be discussed both in single and multiple radio technologies; either in infrastructure, mesh or ad hoc networks

On the design, implementation and experimental evaluation of a novel gateway architecture for the GSM Short Message Service

Congestion and capacity pi'ohIens of the existing mobile communication networks of the late eighties resulted in the demand for a brand new mobile telephony standard. Competition amongst the various existing standards implementation was fierce and lead to the availability of a plethora of incompatible networks and very little hope for the establishment of a global technology geared up to the expectancy of the users. Paging network were widely used as a cheaper alternative to voice enabled networks and were Offering users the ability to receive textual information while on the move. Bridging the gap between the paging world and the mobile communication world was essential. The Global System for Mobile communications was designed as the European answer. The European alternative was promising a feature rich, secure and truly global system with the added ability to handle two-way paging like functionalities with the Short Message Service (SMS). The success of a new service such as SMS relies heavily on its adoption by a majority of users. which in turn is mainly a consequence of the availability of software application gateways. In the mid nineties a Sheffield based software company realising the market needs teamed up with the University's research department to produce the first commercially available gateway architecture for the SMS. The resulting work is described in this thesis. The first part of the analysis examines the architecture of' a (ISM network and the building blocks of the SMS. The technical implementation is described and the fundamental properties examined such as roaming. routing, protocol limitations, usability and interoperahility problems. The specification and design of the gateway architecture is then addressed with an emphasis on character set conversion, routing and queLicing issues. The implementation details are then examined with a description of each of' the modules. The performance of the gateway is examined with the implenientation of a test bed fed by traffic generated by customers. The issues examined were: identification of bottlenecks, protocol efficiencies and an analysis of the chosen queueing model implementation. The second part of the analysis presents the results obtained from the measurements taken for a period of a year. Arm analytical model was formulated to validate the results from the measurements. The comparison revealed the ability of the model to simulate the behaviour of the gateway under medium to heavy loads and highlighted the areas that would be most affected by optimisation. The important factors limiting throughput and quality of service were di scoverecl in the capacity of the connections to network operators and policy chosen for the message queues. An alternative queueing discipline is proposed that would lead to increased fairness offered to the wide variety of applications connected to the gateway and the network operators through a single link of' known capacity. Interactive conversations such as quizzes and gaines based are offered low latency while more bandwidth demanding ones such as mass voting applications benefit from very high throughput. The overall gateway,architecture described was the first one of its kind and consequently each of its module was designed and implemented from scratch. As a result Dialogue (Tommnunicatmons benefited l'i'omn the novelty and head start needed in a fierce competitive market to position itself as a market leader ]it mobile applications and services, competing with global companies such as Logica. Ericcson or Microsoft

Desarrollo de un esquema de enrutamiento dinámico basado en matrices de tráfico para garantizar calidad de servicio en redes definidas por software usando el protocolo OpenFlow

RESUMEN: Las redes definidas por software permiten separar los planos de control y de datos, migrando el control a un ente central, capaz de indicar a los dispositivos de red sobre cómo manejar los flujos de datos, lo que abre un rango de posibilidades para la implementación de estrategias novedosas para la gestión de las redes de datos. En este trabajo se presenta un esquema de enrutamiento din´mico que monitoriza periódicamente el estado de la red, utilizando el protocolo OpenFlow, para calcular su matriz de tráfico y tomar acciones que permitan transmitir las demandas extremo a extremo garantizando la calidad de servicio (QoS, Quality of Service) en los caminos establecidos y ahorrar la mayor cantidad posible de energía. El esquema es probado en un escenario de telemedicina, específicamente de monitorización de pacientes con enfermedades crónicas en hospitalización domiciliaria, como parte del esfuerzo de la Alianza Regional en Tecnologías de la Información y la Comunicación Aplicadas (Artica) por ofrecer soluciones a los problemas que se presentan en el sistema de salud Colombiano. Para la evaluación en este escenario, se buscó minimizar el consumo energético total de la red, y los resultados obtenidos se comparan con los de otras dos propuestas que tienen objetivos similares, GreenMST y MdST. Los resultados obtenidos muestran que el esquema planteado satisface holgadamente las restricciones para tráfico de telemedicina, para en escenario de evaluación seleccionado, y mejora tanto el consumo energético como el retraso de las rutas establecidas los resultados de las otras dos estrategias analizadas, logrando mejoras de hasta 66.67 % respecto de GreenMST y 30.77 % respecto de MdST. También se logró establecer que a medida que el retraso mínimo permitido disminuye, aumenta el consumo energético, y disminuye el retraso observado en las rutas. A partir de los resultados obtenidos para el caso de uso seleccionado para la evaluación inicial se desprende que el esquema puede ser aplicado para otros escenarios, como juegos en línea o transmisión de video en tiempo real, y buscando otros objetivos en su modelo de optimización

Human-sensor dialogue in participatory sensing

Participatory sensing is an emerging field that uses pervasive technology to create new forms of sensing networks combining people, personal devices, and other sensors. Pervasive computing technology forms an essential component, used to report data and coordinate activities. This thesis reviews research in participatory sensing and key fields related to it: pervasive computing, observation networks and public engagement with science. After examining wider issues in sensor-based interaction from pervasive computing literature, this thesis investigates human-sensor dialogue; specifically how to develop new forms of dialogue in future participatory sensing experiences. The term 'dialogue' is used in broad sense, encompassing affordances and ongoing relationships between sensors and users. The thesis examines participatory sensing activities centring on two studies involving groups of young people collecting and visualising environmental sensor data using automatic and manual sensors. Participant observation methods are used for in-situ, naturalistic evaluation using observations, video footage and system logs and data. A framework for human-sensor dialogue is developed as a tool to help analyse the dialogue in participatory sensing experiences and inspire new forms of dialogue in future experiences. It highlights five activities to which dialogue can relate: planning, testing, navigation, capture and reflection. These are interleaved throughout an experience, affecting how it takes shape and resulting from the design of the devices and the whole experience. The framework is demonstrated by applying it to the experiences in the previous two studies. The framework is used to prototype a new experience intended for longer term engagement. It is used to elicit requirements for the new experience, structuring the activity and highlighting the desired transitions. The resulting prototype application is described, outlining the activity setup, key features and technical details. This application uses handheld devices as mobile sensors, wirelessly connected to fixed environmental sensors, which collect, process, and store the restating data

Key management in mobile ad hoc networks.

Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2005.Mobile ad hoc networks (MANETs) eliminate the need for pre-existing infrastructure by relying on the nodes to perform all network services. The connectivity between the nodes is sporadic due to the shared, error-prone wireless medium and frequent route failures caused by node mobility. Fully self-organized MANETs are created solely by the end-users for a common purpose in an ad hoc fashion. Forming peer-to-peer security associations in MANETs is more challenging than in conventional networks due to the lack of central authority. This thesis is mainly concerned with peer- t o-peer key management in fully self-organized M ANETs. A key management protocol’s primary function is to bootstrap and maintain the security associations in the network, hence to create, distribute and revocate (symmetric or asymmetric) keying material as needed by the network security services. The fully self-organized feature means that t he key management protocol cannot rely on any form of off-line or on-line trusted third party (TTP). The first part of the thesis gives an introduction to MANETs and highlights MANETs' main characteristics and applications. The thesis follows with an overall perspective on the security issues in MANETs and motivates the importance of solving the key management problem in MANETs. The second part gives a comprehensive survey on the existing key management protocols in MANETs. The protocols are subdivided into groups based on their main characteristic or design strategy. Discussion and comments are provided on the strategy of each group. The discussions give insight into the state of the art and show researchers the way forward. The third part of the thesis proposes a novel peer- to-peer key management scheme for fully self-organized MANETs, called Self-Organized Peer-to-Peer Key Management (SelfOrgPKM). The scheme has low implementation complexity and provides self-organized mechanisms for certificate dissemination and key renewal without the need for any form of off-line or on-line authority. The fully distributed scheme is superior in communication and computational overhead with respect to its counterparts. All nodes send and receive the same number of messages and complete the same amount of computation. ScifOrgPKM therefore preserves the symmetric relationship between the nodes. Each node is its own authority domain which provides an adversary with no convenient point of attack. SelfOrgPKM solves t he classical routing-security interdependency problem and mitigates impersonation attacks by providing a strong one-to-one binding between a user’s certificate information and public key. The proposed scheme uses a novel certificate exchange mechanism t hat exploits user mobility but does not rely on mobility in anyway. The proposed certificate exchange mechanism is ideally suited for bootstraping the routing security. It enables nodes to setup security associations on the network layer in a localized fashion without any noticeable time delay. The thesis also introduces two generic cryptographic building blocks as the basis of SelfOrgPKM: 1) A variant on the ElGamal type signature scheme developed from the generalized ElGamal signature scheme introduced by Horster et al. The modified scheme is one of the most efficient ElGamal variants, outperforming most other variant s; and 2) A subordinate public key generation scheme. The thesis introduces t he novel notion of subordinate public keys, which allows the users of SelfOrgPKM to perform self-organized, self-certificate revocation without changing their network identifiers / addresses. Subordinate public keys therefore eliminate the main weakness of previous efforts to solve the address ownership problem in Mobile IPv6. Furthermore, the main weakness of previous efforts to break t he routing-security interdependence cycle in MANETs is also eliminated by a subordinate public key mechanism. The presented EIGamal signature variant is proved secure in t he Random Oracle and Generic Security Model (ROM+ GM ) without making any unrealistic assumptions . It is shown how the strong security of the signature scheme supports t he security of t he proposed subordinate key generation scheme. Based on the secure signature scheme a security argument for SelfOrgPKM is provided with respect to a genera l, active insider adversary model. The only operation of SelfOrgPKM affecting the network is the pairwise exchange of certificates. The cryptographic correctness, low implementation complexity and effectiveness of SelfOrgPKM were verified though extensive simulations using ns-2 and OpenSSL. Thorough analysis of the simulation results shows t hat t he localized certificate exchange mechanism on the network layer has negligible impact on network performance. The simulation results also correlate with efficiency analysis of SelfOrgPKM in an ideal network setting, hence assuming guaranteed connectivity. The simulation results furthermore demonstrate that network layer certificate exchanges can be triggered without extending routing protocol control packet

Inverse Dynamics Problems

The inverse dynamics problem was developed in order to provide researchers with the state of the art in inverse problems for dynamic and vibrational systems. Contrasted with a forward problem, which solves for the system output in a straightforward manner, an inverse problem searches for the system input through a procedure contaminated with errors and uncertainties. An inverse problem, with a focus on structural dynamics, determines the changes made to the system and estimates the inputs, including forces and moments, to the system, utilizing measurements of structural vibration responses only. With its complex mathematical structure and need for more reliable input estimations, the inverse problem is still a fundamental subject of research among mathematicians and engineering scientists. This book contains 11 articles that touch upon various aspects of inverse dynamic problems