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The NASA Advanced Communications Technology Satellite (ACTS) program will conduct high-data-rate experiments that will be applicable to the emerging broadband services of the telephony market. The existing broadband integrated services digital network (BISDN) services and delivery method as defined by the International Consultative Committee for Telephone and Telegraph (CCITT) and satellites' role in provisioning those services are discussed. The ACTS experimental efforts are summarized 相似文献
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Otsu T. Nagayama K. Kurokawa A. Nakashima H. Umehira M. 《IEEE transactions on aerospace and electronic systems》2000,36(4):1047-1057
This paper presents an advanced satellite communication system named DYANET II. This system uses satellite channels as subscriber lines for ISDN customers as well as trunk circuits for overflow traffic. The system can offer the same ISDN services to satellite customers as those available to terrestrial subscribers in terms of numbering, signaling, and charging systems as well as user-network interfaces. It can also set up satellite channels on a demand assignment basis to achieve efficient satellite channel utilization, and to connect customers by single-hop satellite connections. A compact, lightweight Earth station has been developed for remote customers and temporary demands such as exhibitions. 相似文献
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IEEE Standards for Prognostics and Health Management 总被引:1,自引:0,他引:1
Sheppard J.W. Kaufman M.A. Wilmer T.J. 《Aerospace and Electronic Systems Magazine, IEEE》2009,24(9):34-41
Recently operators of complex systems such as aircraft, power plants, and networks have been emphasizing the need for on-line health monitoring for purposes of maximizing operational availability and safety. The discipline of prognostics and health management (PHM) is being formalized to address the information management and prediction requirements for addressing these needs. Herein, we will explore how standards currently under development within the IEEE can be used to support PHM applications. Particular emphasis will be placed on the role of PHM and PHM-related standards with Department of Defense (DOD) automatic test systems-related research. 相似文献
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根据标校卫星的用途及所需提供的高精度比较标准等技术要求,针对星载比较标准及靶场数据处理状况,提出了改进和提高测控系统精度鉴定的技术途径.探讨和提出了4种类型的数据处理技术和方法,简述了它们的思路和关键技术,分析了应用条件和特点.其中.第1种方法是目前使用的经典鉴定方法;后3种方法(自鉴定方法、精确标准鉴定方法和融合处理鉴定方法)都充分利用了星上测量资源、卫星轨道运动特性以及优良的差分、自校准等融合处理技术,它们都明显优于经典鉴定方法.可以使标校卫星提供更精确的比较标准,扩大其目前的功能和用途.特别是融合处理鉴定方法,不仅可以精确地评定定位系统测量精度,而且可以为测速系统精度评定提供一种良好的技术途径. 相似文献
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黏度是液体的重要理化性能指标。工程上常用Zahn黏度杯快速检查不同液体的黏度。不同的制造商生产出来的Zahn黏度杯有一定的差异,企业在使用Zahn黏度杯时有其具体引用的规范或标准。目前,国际通用的Zahn黏度杯的规范标准为ASTM D4212,而波音等国外飞机制造商的Zahn黏度杯规范中关于液体黏度和流出时间特性转换公式与通用标准存在差异。基于同一种标准黏度液体,系统地比较了两种规范中特性转换公式的差异,并分析产生差异的原因,同时给出了这些差异可能造成的影响。 相似文献
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A career development program for information systems practitioners currently being used widely by employers in the UK and now becoming available in North America is described. The program, called the Professional Development Scheme (PDS), was developed by the British Computer Society to address the lack of structure and quality control generally present in the way computing professionals were being trained. The performance standards underpinning the program (The British Computer Society Industry Structure Model) have been thoroughly updated and now include material specific to the development, maintenance, and management of software for safety-critical applications. The use of the program for this purpose and potential developments in the field of training and registration for safety-critical software specialists are discussed 相似文献
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Weinberger H.L. Kanehira E.M. 《IEEE transactions on aerospace and electronic systems》1977,(2):188-196
This paper analyzes the performance of a number of speech processing techniques that have been considered for single voice channel per carrier transmissions via satellite. This transmission mode is applicable to demand assigiment systems, which make possible the most efficient loading of the satellite transponder applications where the traffic at individual earth terminals is not sufficient to justify a substantial number of dedicated channels. The analysis basically determines the operating point for the satellite transponder which minimizes the required earth terminal G/T. Both analog and digital modulation techniques are considered, and the effects of syllabic companding and voice actuation of carriers are demonstrated. The results are presented in general analytic form, applicable to any modulation technique for which carrier-to-noise density ratio, channel width, and guardband width may be specified. Full carrier modulation is assumed. Curves are also furnished showing the required G/T and uplink per carrier EIRP as a function of the number of voice channels per transponder and the transponder gain. "CCIR/CCITT type" speech quality is assumed, together with a transponder El RP and bandwidth typical of current domestic satellite configurations. 相似文献
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比较分析了2000版ISO9000族标准与94版标准的差别,提出了经94版标准认证注册的组织在实施转换时必须做好的几项工作和应注意的问题. 相似文献
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Harlisya Harun Kaharudin Dimyati Ungku Azmi Ungku Chulan 《Aerospace Science and Technology》2013,24(1):136-140
Multiple antenna transmission methods are currently being developed all around the world for evolving 3G wireless standards. Space–Time Trellis Code (STTC) has been proven to use transmit diversity efficiently. It effectively exploits the effects of multipath fading to increase the information capacity of the multiple antenna transmission systems. STTC is a channel coding technique that maximises the ‘distance’ between different symbol matrices such that the probability of transmission errors are decreased when transmitting redundant symbol or in other words, to maximise the minimum determinant. Maximising the minimum determinant is equivalent to obtaining optimal generator matrix G. Instead of using state diagrams, optimal generator matrix G discussed in this paper is obtained using an improved algorithm which is based on Lisya tree structure. Optimal generator matrix G in this paper has a minimum determinant of 48 which is the highest coding gain obtained so far. 相似文献
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民机驾驶舱显示触控系统人机工效综合评价 总被引:1,自引:0,他引:1
未来民机驾驶舱将广泛采用触控技术,但目前尚未形成针对民机驾驶舱显示触控系统的人机工效评价体系与评价方法。针对上述问题,首先梳理民机驾驶舱显示触控系统相关的现行标准与规范,结合适航规章中人为因素考察项,提出民机驾驶舱显示触控系统人机工效评价指标体系。其次,考虑到评价指标的模糊性与灰色性,基于灰色关联分析,对传统模糊层次综合评价算法从数据集结处理和指标权重确定两个方向进行改进,通过构造专家信度系数修正秩次矩阵,实现专家认知特性的定量描述,建立民机驾驶舱显示触控系统人机工效综合评价模型。最后,结合ACROSS项目下的民机驾驶舱显示触控系统人机工效评价试验案例,分析驾驶舱显示触控系统配置策略对系统人机工效的影响,验证了评价体系与评价方法的适用性和合理性。 相似文献
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With the advent of automatic dependent surveillance (ADS), a detailed probability model of aircraft cross-track deviations is required to determine the impact of ADS. A suitable causal probability model is presented where normal navigation, degradation, pilot blunder, and failure are each modeled by Gaussian density functions with mean and standard deviations defined by the physics of the event. The overall model is a weighted sum of the Gaussian error probabilities and is thus amenable to extrapolation. Overlap and encroachment probabilities are derived,and the effect of ADS on this is model determined. It is shown that by using a simple form of ADS separation standards can be reduced, and transmitting a figure of merit (FOM) providing information on failures and degradations can further reduce separation standards. The results suggest an improvement by a factor of two from current separation standards 相似文献
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Geren W. Murphy T. Pankaskie T. 《IEEE transactions on aerospace and electronic systems》2008,44(2):711-723
Airborne GPS systems are being upgraded to provide sufficient positioning accuracy to support automatic landing operations in low visibility conditions. This is made possible by differential GPS (DGPS), in which the errors common to the airborne receiver and ground station are removed by knowledge of the latter's precise location. However, errors specific to the airborne system remain, of which the dominant components are receiver noise and multipath. To support the assessment of the integrity of the signal in space, these residual errors are incorporated in a statistically based error model, designated as the "standard model." The standard model is defined as the standard deviation of a Gaussian distribution that overbounds the residual pseudo-range (PR) error. It relates the standard deviation of the overbounding distribution to the elevation angle of the satellite relative to the local level coordinate system. The international community is currently developing improved standards to enable DGPS systems to support landings in the worst visibility conditions (i.e., CAT III). As a part of this development, the standard model for multipath is being re-evaluated and an improved model is sought. In order to better characterize the residual multipath errors, tools for accurate calculation of the airframe scattering effects are needed. Development of such tools is the subject of this paper. A new method for accurately computing pseudo-range error, based on the use of high-fidelity EM models, is described. This approach provides new insight into the mechanisms causing multipath error. 相似文献
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北斗卫星导航系统(简称北斗)在民用航空器中安装应用的前提是明确和符合北斗机载设备的适航要求。但由于全球定位系统(GPS)与北斗在星座结构、信号体制及功能上的不同,导致目前国际上全球卫星导航系统(GNSS)相关适航标准不适用于北斗设备。标准的缺失严重制约北斗民航产业发展,急需进行自主研究与制定。针对北斗在民用航空器中应用第一阶段的功能及场景,即仅用作航空器追踪,分析当前可参考标准的适用性,明确适航要求的制订策略及框架,综合考虑适航安全性、民航对北斗机载设备的紧迫需求,未来机载设备的发展方向,以及当前工业水平,提出一套仅用作航空器追踪的北斗机载设备适航要求,形成审定要素及评审要求,可支持工业方对适航标准的理解。 相似文献
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李现宗 《郑州航空工业管理学院学报(管理科学版)》1992,(3)
本文就国际审计准则的产生与发展、制定主体、目的与性质,对各国的影响及利用情况等方面作了概括论述,以求为研究国际审计准则的进程与发展趋势,及对我国制定审计准则提供有益经验。 相似文献
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利用CAD软件绘制工程图样更应加强国标意识,采用可编程对话框技术可以实现国家制图标准或其它相关标准的实时服务,从而减少不符国标的图样表达。 相似文献