정지궤도 위성통신 환경모의를 위한 100 MHz 대역폭의 위성링크 시뮬레이터 개발

With the rapid development of vehicular sensor networks (VSNs) technology, the potential use of networked real-time control and automation is enormous and appealing. However, closed-loop control VSNs via the Internet are very difficult to implement practically because of their stochastic nature. One of the biggest challenges in VSNs is how to deal with sensor networks time delay and data loss. The authors investigate the potential of using the predictive control scheme for VSNs based on round-trip time (RTT) delay prediction to overcome the VSNs transmission delay and data loss. The predicted RTT delay is taken as the sampling interval reference for variable-period sampling approach. Modelling the time delay of networked control systems as a non-linear time series, the least mean square (LMS) filter algorithm is adopted to predict online the time delay induced in VSNs. The simulation results show that the LMS algorithm can achieve ideal efficacy if time delay has no variety abnormally. The predictive compensation strategy is proposed to reduce the detrimental effect of stochastic time delays induced by communication networks on control performance. The results of offline simulations via the Internet illustrate that the predictive control scheme based on RTT delay prediction has the potential to overcome the VSNs time delay and data loss.

The pulse-wave velocity (PWV) is inversely related to arterial compliance, and provides a useful measure of vascular function. In this study, the PWV was measured non-invasively in the mouse carotid artery using the time-delay (TD) and flow-area (QA) methods. The TD technique determines the distributed PWV from the time-delay between Doppler-derived upstrokes at two locations a known distance apart. The QA method estimates the local PWV as the ratio between the change in volume flow and the change in cross-sectional area during the reflection-free period of the cardiac cycle. Our new QA approach measures the cross-sectional area and flow through the vessel using a high- frame-rate retrospective colour flow imaging (RCFI) technique. The cross-sectional area is determined by integrating over the region of flow in each frame of the RCFI dataset, while the volume flow is calculated by averaging the velocities over the vessel in each frame and multiplying by the corresponding area. The TD method was compared with the flow-area method in the carotid artery of 7 young CD-1 mice, anesthetized with isoflurane. The average TD PWV was found to be 3.03±0.17 m/s. The average QA PWV was found to be 2.97±0.18 m/s. The TD method was found to correlate well with the QA method (r=0.91, p<0.001). The mean difference between the TD method and the QA method was 0.06±0.08 m/s, and 95% of the differences fell within ±0.41±0.20 m/s of the mean difference. These results indicate that the QA method should be capable of distinguishing between changes to PWV caused by vascular disease. It was found that the QA method permits the measurement of the local PWV. The TD method offered superior reliability to the QA method for PWV determination in the mouse carotid artery because it was affected by fewer contextual factors. However, the QA method is useful for situations in which the TD method is unsuitable due to the geometry of the vessel. In this study, we compared a QA method of measuring the PWV with an image-guided TD method in the carotid artery of seven CD-1 mice. The TD technique was used to measure a distributed PWV over the carotid artery from the aortic arch to the bifurcation. The QA method was applied to determine the local PWV at the midsection of the carotid. The objective of this study was to assess the potential of the QA method against the TD method and to demonstrate a simple image-based methodology for performing PWV measurements. Determination of the most reliable PWV estimation method will be useful in a future longitudinal study of vascular development in transgenic mice.

Neural network based adaptive dynamic surface control of nonaffine nonlinear systems with time delay and input hysteresis nonlinearities

The role of commercial services within a military satellite communication system and their ability to support the communication requirements of the fixed and mobile military users has been the subject of considerable interest. Although commercial services are currently employed in the UK military communication systems, their implementation is typically restricted to the leasing of point to point circuits, on an as required basis. This paper considers the potential application of commercial satellite and terrestrial services for the next generation military communication systems. In considering the relative benefits of commercial satcom, it is important to assess not only the provision of in orbit transponders, but also the impact on ground management systems and user terminals, to support an integrated architecture.

In this paper, a new technique of time-delay compensation is proposed for active control of a flexible hub–beam system. The first-order approximation coupling (FOAC) model proposed recently for dynamics of hub–beam systems is used to verify the applicability of this technique. The FOAC model is first linearized to obtain a linearized equation. The linearized equation with time delay is then transformed into a standard form with no time delay by a particular integral transformation. The time-delay controller is designed based on this standard equation using the classical optimal tracking control theory. Since the controller is a function of modal coordinates, a modal filter is presented to estimate the modal coordinates from physical sensor measurements. The effectiveness of the proposed technique for time delay is demonstrated by numerical simulations. Simulation results indicate that a very small time delay may result in instability of the control system if it is not compensated in control design. The proposed time-delay controller is effective in controlling the system even when the maximum time delay for stability without time-delay compensation is greatly exceeded. Moreover, for the system without time delay, the proposed time-delay controller may possibly obtain much better control effectiveness than the controller without time delay.

This paper involved the design and analysis of multi-threshold voltage CMOS (MTCMOS) current sense amplifier focusing on optimizing power and time delay. In this work the basic 6T SRAM structure was chosen and the simulation is implemented using ADS programs. The key to low power operation in the SRAM data path is to reduce the signal swings on the bit lines and the data lines. The power dissipation and delay of the sense amplifier circuit can be further reduced by using several low power and high speed techniques like MTCMOS. This technique can be used for solving the leakage power dissipation problem in the higher technology design. Simulated results show the current mode sense amplifier with MTCMOS technology has 0.82ns time delay and 0.395μW power dissipation. The designs and simulations in 0.25μm CMOS technology with supply voltage equal to 1.8 V have been carried out to evaluate the efficiency of the current mode sense amplifier with MTCMOS technique proposed.

한국군은 미래 군 위성통신의 요구 사항에 걸맞은 한국형 군 위성통신 체계 구축을 위하여 고속대용량, 생존성 보장, All IP 통신, 기동성 보장과 같은 발전 방향을 목표로 차기 군 위성통신 체계를 개발하고 있다. 본 논문은 차기 군 위성통신 체계의 최적 자원 할당과 IP 네트워킹 기술에 집중하여, MF-TDMA 자원 할당, 랜덤 액세스, 위성/지상 연동망 구조, 그리고 PEP의 세부 연구 분야에 대하여 연구 내용 조사 및 분석을 실시하였다. 각 연구분야에 대한 기존 연구는 채널 효율 및 처리량의 증가를 위한 연구가 주를 이루고 있다. 이에 더하여 차기 군 위성통신 체계를 위한 연구는 이기종 단말, Full Mesh 환경, 분산망, 위성/지상 연동망, 항재밍 등의 특성 들을 고려해야 한다. 본 논문에서는 이러한 특수성을 고려하여 각 분야 별 핵심 연구 이슈들을 제시하고, 주요 이슈에 대하여는 모의실험을 통한 결과를 제시하였다. Korean military is developing the next generation military satellite communications system in order to achieve the requirements of future military satellite communication such as high speed, high capacity, survivability, all IP networking, and on-the-move. In this paper, we survey and analyze the research interests about optimal resource allocation and IP networking such as MF-TDMA, random access, satellite IP routing, and PEP. Conventional researches have focused on the increase in channel throughput and efficiency. In addition to these measurements, we consider heterogeneous satellite terminals, full mesh topology, distributed network, anti-jamming, and the like which are the special characteristics of the next generation military satellite communications system. Based on this, we present key research issues and evaluation on the issues by simulation.

For the high speed substrate design, the synchronization of the signals is one of the most important concerns. Time delay control methodologies that are based on high speed substrate design rules which include equalizing differences between the same group high speed transmission lines, maximizing time balance between different high speed transmission lines and balancing over all nets difference between every high speed transmission lines. In this paper, we consider approaches that include ground trace impacts, near by differential pairs, and reference ground plane edging to minimize the time delay between traveling signals through different high speed propagation paths. We also propose the design guidelines to minimize the time delay of signal paths. The rules are applied to high speed differential pair design FCBGA, and the time delay is controlled within 3 pico seconds.

Limited resources of nodes in MAMETs force the extensive studies for energy-aware multipath routing protocols, which should provide the fault tolerance for broken links and the load balance for extending bandwidth and equalizing energy consumption. This paper proposes a novel energy-aware multipath ad hoc routing protocol to equalize the energy consumption, thus, to extend the network lifetime of each node in MANETs. The proposed Time Delay On-demand Multipath (TIDOM) routing protocol accommodates the time delay function in flooding RREQ packets. The time delay function is inversely proportional to the residual battery capacity of intermediate nodes themselves. This function avoids nodes with poor residual battery capacity, and promotes nodes with good residual battery capacity joining the routes. Simulation results show that TIDOM improves the network lifetime, energy consumption, and additionally packet delivery ratio over the Ad hoc On-demand Multipath Distance Vector (AOMDV).

Solar wind control of spacecraft charging conditions in geostationary orbit during magnetic storms

This paper is concerned with an intelligent application of Moving Picture Expert Group (MPEG) video transmission in a Bluetooth link. MPEG Variable Bit Rate (VBR) video is data hungry and results in excessive data loss and time delay over wireless networks. In a Bluetooth channel transmission rate is unpredictable as result of interferences by channel noises or other close by wireless devices. Therefore, it is difficult to transmit MPEG VBR video in Bluetooth without data loss and/or time delay. A buffer entitled ‘traffic regulating buffer’ is introduced before the Bluetooth protocol stack to prevent excessive overflow of MPEG video data over the network. Two novel neural fuzzy schemes are presented in this paper to monitor the traffic regulating buffer input and output rates, in order to ensure the video stream conforms to the traffic conditions of Bluetooth. The computer simulation results demonstrate that the two supervised neural fuzzy schemes reduce standard deviation and data loss, when compared with a traditional MPEG VBR video transmission over Bluetooth.KeywordsVideo TransmissionInternal Model ControlGeneral Packet Radio ServiceAdaptive Neural Fuzzy Inference SystemMove Picture Expert GroupThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

McDonnell Douglas Helicopter Company recently undertook a study to determine the actual simulator hardware time delay in all the simulators, It also investigated the effect of time delay on pilot performance and his aircraft evaluaiion in- an engineering design environment. This paper describes the system architecture, techniques -of measuring thruput delays, and initial study results. It was found that the average total system delay was about 87 milliseconds, well below values reported in open literature for most of the training and engineering simulators. The second phase of the study involved systematically varying the simulator delays so that data on the effect of time delay could be collected and used as a useful parameter in aircraft /simulator design. Pilot performance was recorded and subjective evalua- tions in the form of Cooper-Harper ratings were also obtained. Analysis of pilot performance did not provide any dramatic changes due to increased simulator delays but did show that the pilot control activity increased in the low speed, high gain tasks. It was found that with increased time delay the Cooper-Harper rating increased indicating degradation in perceived handling qualities. However, for the type of helicopter simulated, there was not a definite time delay at which the ratings changed abruptly. This indicates that for engineering design purposes while it is desirable to keep the delay to the absolute minimum, there may be sufficient flexibil- ity in the design of the simulator to permit cost/ capability trade offs. However, this needs to be further validated by additional tests that introduce pilot dis- tractions (such as gusts) and force the pilot to increase his closed loop gain. Abbreviations

Line-of-sight communications links between satellites allow data to be transmitted directly from one satellite to another. The different types of links which can be implemented between satellites in geostationary orbit (GSO) and low Earth orbit (LEO), are illustrated. There are two main classes, interorbit links between LEO and GSO satellites, and intersatellite links (ISLs) between satellites which are both in GSO or LEO orbit. This paper is primarily concerned with ISLs between GSO satellites for military communications.

Efficiency of area-concentrated searching behaviour in a continuous patchy environment

Dry sliding wear behaviors of La 2O 3–WSi 2–MoSi 2 composite against alloy steel