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51.
52.
A method for determining the scattering matrix of the junction between smooth and corrugated cylindrical waveguides is developed. The model is based on expanding the modal fields for the corrugated waveguide into eigenfunctions of the transmission matrix of a waveguide unit cell. This method, used in conjunction with usual techniques for evaluating the scattering matrix of mode converters, is shown to improve the precision of results obtained by rendering uniform the accuracy of the models applied in the calculations. The analysis is now valid for any size of corrugation depth, and the frequency band, of applicability is enlarged accordingly 相似文献
53.
Jorge Granjal Edmundo Monteiro Jorge Sá Silva 《International Journal of Communication Systems》2014,27(10):1938-1963
The design of standard communications and security mechanisms for resource‐constrained sensing applications and devices may provide an important contribution for its integration with the Internet and consequently towards the realization of what we nowadays identify as the Internet of Things. This vision will only be realizable if appropriate security mechanisms are available, and in this context we target the design and experimental evaluation of security mechanisms for communications at the network‐layer with sensing devices (smart objects) using the standard IPv6 protocol. Our work proposes and evaluates the usage of new compressed security headers for the network layer with smart objects. We implement and evaluate what is, as far as we know, the first proposal of security at the network layer experimentally evaluated using the TinyOS operating system and its networking stack. As we verify in the course of our evaluation study, various scenarios employing network‐layer secure communications involving smart objects are feasible, particularly when security mechanisms are designed to benefit from cross‐layer interactions that allow the optimization of expensive cryptographic operations. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
54.
Ícaro L. J. da Silva André L. F. de Almeida Robert Baldemair Sorour Falahati F. Rodrigo P. Cavalcanti 《Wireless Personal Communications》2014,75(4):2523-2547
In 3rd generation partnership project (3GPP) long term evolution (LTE) systems, when no resources has been assigned in the uplink to a given user equipment (UE), the control information associated with layers 1 and 2 in the protocol stack is conveyed back to the base station through the so-called physical uplink control channel (PUCCH). In PUCCH, the data streams transmitted by multiple UEs are multiplexed in the time-domain and in the frequency-domain with the aid of spreading codes. Although the spreading codes associated with UEs within the same cell can be assumed to be orthogonal, the presence of inter-cell interference (ICI) in multi-cell scenarios severely limits receiver performance. In particular, the Format 1 of PUCCH, which is associated with the transmission of hybrid automatic repeat request acknowledgements (ACK/NACK) and scheduling requests, has a major impact on system performance, since an incorrectly decoded ACK/NACK message may introduce significant delay in data transmission. In this contribution, we propose a new multi-user receiver for ICI reduction in PUCCH LTE that operates both in cooperative and non-cooperative multi-cell architectures. The proposed receiver relies on a constrained tensor modeling of the received signal in PUCCH signaling, and affords an iterative joint channel estimation and symbol detection by simultaneously exploiting the energy of the data symbols and the pilot tones present in PUCCH. The formulation of the proposed algebraic receiver model incorporates symbol-basis hopping and slot-basis hopping signaling schemes, which are interference randomization techniques existing in the 3GPP specifications of LTE system. Computer simulation results show the remarkable performance gains of the proposed receiver compared to the conventional time-frequency decorrelator based receiver. 相似文献
55.
Eduardo Pompeo da Silva Mineiro Débora Christina Muchaluat-Saade 《International Journal of Wireless Information Networks》2014,21(3):223-237
This work presents an admission control mechanism for multi-hop wireless mesh networks based on the IEEE 802.11 standard and the OLSR routing protocol. This mechanism, called CAC-OLSR, aims at ensuring that traffic flows with quality of service (QoS) requirements, especially voice and video, are only admitted in the mesh network if it has available resources in order to provide flow requirements. In addition, QoS requirements of previously admitted traffic flows cannot be violated. The proposal was evaluated with NS-2 and Evalvid simulations. 相似文献
56.
Vodonos Y.I. Conroy B.L. Losh D.L. Silva A. 《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》2007,95(10):1947-1957
The Deep Space Network (DSN), managed by the Jet Propulsion Laboratory for NASA, is equipped with multiple microwave transmitters ranging in average radiated power from 200 W to 400 kW. The transmitters are used for routine or emergency communication with spacecraft, for navigation, and for radio science tasks. The latest advances in transmitter engineering were implemented in a new generation of 20-kW dual-band transmitters developed for the DSN 34-m beam waveguide antennas. Innovations include additional X-band communication capability for near Earth missions, new c, automated calibration, improved and expanded computerized monitoring and diagnostics, reduced cabling, and improved maintainability. The innovations were very beneficial for the DSN ldquooverloadrdquo during the Mars 2003/2004 missions and will benefit other missions throughout the next decade. This paper describes the current design of the new transmitters and possible future developments. 相似文献
57.
A concurrent, integrated, and multicriteria methodology is presented for the conceptual design of mechatronic systems. It uses an evaluation model called mechatronic design quotient (MDQ) to facilitate decision-making in the design process. A nonlinear fuzzy integral is used for the aggregation of criteria in MDQ, thereby accommodating possible correlations among them. The performance of the developed methodology is validated by applying it to an industrial fish cutting machine called Iron Butcher-an electromechanical system that falls into the class of mixed or multidomain systems 相似文献
58.
Concepts of mechatronics are applicable in the design of complex and multi-domain dynamic systems. This paper presents an approach based on the mechatronic design quotient (MDQ) for systematic design of a mechatronic system. Traditional procedures of design are hierarchically separated into topological design and parametric design. Extending this concept, an MDQ may be “structured” into a multi-layered hierarchy. The approach and significance of the application of MDQ in mechatronic design are indicated using illustrative examples. 相似文献
59.
Constant-frequency sliding-mode and linear proportional integral (PI) cascaded controllers (internal current loop and external output voltage control loop) for 12-pulse thyristor rectifiers are designed, using new models and convenient assumptions, and their performances compared. The use of sliding-mode control on line-commutated power converters implies the use of fixed-frequency sliding-mode design, originating steady-state errors. These are eliminated using a higher order switching function, with fourth-order Bessel polynomial coefficients, to minimize the response time and to eliminate the overshoot in the reaching mode. Comparisons are made using simulations (MATLAB/SIMULINK blocks) and experimental results. The sliding-mode controllers, as well as the PI controllers, need almost the same hardware and present no steady-state errors and no output voltage overshoots. Besides allowing a faster dynamics than the PI controllers, the proposed sliding-mode approach provides a new, nonlinear theoretical frame for solving the control problem of power rectifiers with output filters 相似文献
60.
dos Reis Barbosa L. Vieira J.B. Jr. de Freitas L.C. da Silva Vilela M. Farias V.J. 《Power Electronics, IEEE Transactions on》1999,14(3):445-453
High-switching frequency associated with soft commutation techniques is a trend in switching converters. Following this trend, a buck pulsewidth modulation (PWM) converter is presented. The DC voltage conversion ratio of this converter has a quadratic dependence on duty cycle, providing a large stepdown. This new buck quadratic PWM soft-single-switched converter, having only a single active switch, provides a high efficient operating condition for a wide load range at high-switching frequency. In order to illustrate the operating principle of this new converter, a detailed study including theoretical analysis, relevant equations and simulation, and experimental results is carried out 相似文献