GaAs Monolithic MIC's for Direct Broadcast Satellite Receivers

A 12-GHz low-noise amplifier (LNA), a 1-GHz IF amplifier (IFA), and an 11-GHz dielectric resonator oscillator (DRO) have been developed for DBS home receiver applications by using GaAs monolithic microwave integrated circuit (MMIC) technology. Each MMIC chip contains FET's as active elements and self-biasing source resistors and bypass capacitors for a single power supply operation. It also contairns dc-block and RF-bypass capacitors. The three-stage LNA exhibits a 3.4-dB noise figure and a 19.5-dB gain over 11.7-12.2 GHz. The negative-feedback-type three-stage IFA shows a 3.9-dB noise figure and a 23-dB gain over 0.5-1.5 GHz. The DRO gives 10.mW output power at 10.67 GHz, with a frequency stability of 1.5 MHz over a temperature range from -40-80°C. A direct broadcast satellite (DBS) receiver incorporating these MMIC's exhibits an overafl noise figure of /spl les/ 4.0 dB for frequencies from 11.7-12.2 GHz.     

Potential Interference from Terrestrial Sources into Direct Broadcast Satellite Home Receiving Systems

Potential interference sources into direct broadcast satellite (DBS) home receiving equipment and the means of reducing the effects are discussed in this paper. Interference sources are divided into two categories: those that enter at the receiving antenna microwave equipment, and those that enter at the indoor unit or at the coaxial cable connecting the antenna to indoor equipment. The results of the analysis show that good design practice will control this kind of interference to an acceptable degree. Recommendations to reduce the interference are given.     

Multiple Sound Channel Tradeoffs for Satellite TV Broadcast Systems

The state of the art of geostationary satellites makes it feasible to provide direct community broadcasts to convey tional Television (ITV) and Educational Television (ETV) programs. The wide coverage provided by such satellites makes it imperative to provide multiple sound channels along with a common video program.     

Adaptive Rate Control and QoS Provisioning in Direct Broadcast Satellite Networks

Adaptive rate control, if properly employed, is an effective mechanism to sustain acceptable levels of Quality of Service (QoS) in wireless networks where channel and traffic conditions vary over time. In this paper we present an adaptive rate (source and channel) control mechanism, developed as part of an Adaptive Resource Allocation and Management (ARAM) algorithm, for use in Direct Broadcast Satellite (DBS) networks. The algorithm performs admission control and dynamically adjusts traffic source rate and Forward Error Correction (FEC) rate in a co-ordinated fashion to satisfy QoS requirements. To analyze its performance, we have simulated the adaptive algorithm with varying traffic flows and channel conditions. The traffic flow is based on a variable bit rate (VBR) source model that represents Motion Picture Expert Group (MPEG) traffic fluctuations while the DBS channel model is based on a two-state Additive White Gaussian Noise (AWGN) channel. For measures of performance, the simulator quantifies throughput, frame loss due to congestion during transmission as well as QoS variations due to channel (FEC) and source (MPEG compression and data transmission) rate changes. To show the advantage of the adaptive FEC mechanism, we also present the performance results when fixed FEC rates are employed. The results indicate significant throughput and/or quality gains are possible when the FEC/source pairs are adjusted properly in co-ordination with source rate changes.     

中国第一颗直播卫星频率/轨位资源的回顾与展望

广播卫星频率资源是稀缺性宝贵资源。本文回顾了国家广电总局与国家相关部门长期努力为我国争取BSS规划频率/轨位资源的历程。我国直播卫星的实施必将进一步促进我国广播电视的覆盖与发展,同时有效地利用了卫星广播资源。     

An Assessment of the Potential Terrestrial Interference Due to Direct Broadcast Satellite Television Receivers

The potential interference of spurious, radiation from the local oscillators of direct broadcast satellite (DBS) television receivers to terrestrial 11 GHz microwave radio services is examined. Typical parameters for DBS receivers are identified and used in a computer simulation to calculate the aggregate effect of a large number of units distributed about a terrestrial repeater site. The results of the analysis show that for a local oscillator frequency of 11.2 GHz, DBS LO leakage of -70 dBW/unit, and a density of 2600/km²(1000/mi²) the cumulative interference power would be comparable to the thermal noise level of a terrestrial radio system under realistic conditions. Methods of scaling the results for other system parameters are also presented.     

美国研制的高能激光武器系统

综述了美国研制的机载、车载和舰载激光武器系统以及地基激光反卫星武器和未来的天基激光武器系统,并给出了武器的性能和有关的技术参数。     

The energy outlook for the United States

In addition to reporting on prevailing trends in U.S. energy production and consumption, this article makes a number of statements concerning the outlook for the future. For example, the growth of underground distribution and control over the sulfur content of fuels and stack emissions may possibly halt or reverse the long-term downtrend in the cost of electricity. Although nuclear power is beginning to emerge as a competitor of fossil fuels, it is still too early to predict its eventual impact on the overall picture.     

Factors Affecting the Choice of Frequency Band for DBS Systems in the United States

The prospective operator of a system intended primarily for broadcasting directly to homes in the United States (as opposed to distributing programming to CATV head ends or terrestrial broadcasting stations) must choose between two frequency bands: 12.2-12.7 GHz and 11.7-12.2 GHz. The first of these bands is allocated to the broadcasting-satellite service (BSS) with the assignment of frequencies, orbital positions, sense of polarization, and maximum radiated power to service areas governed by an international plan. The other band is allocated to the fixed-satellite service (FSS), but with a footnote permitting use of transponders already authorized in the FSS to be used for BSS transmissions under certain constraints on maximum radiated power and mutual interference. This paper examines the differences between the two frequency bands in terms of their impact on a number of factors of practical interest to a DBS system operator.     

The United States in space

The US program is examined in three contexts: its position internationally, its role domestically, and NASA's workings internally. Some of the principal issues explored are: what it means for NASA to be simply a lead agency instead of the sole agency charged with implementing the US space program; whether the types of technical and managerial troubles NASA has recently experienced are different in quality from the troubles it had during the Apollo era; how the various pressures to which it is being subjected are effecting its internal ways of doing business; and whether there are lessons from the experiences of other nations' space programs and their ways of overseeing projects are doing business that could be useful to the US space program, and vice versa     

美国机载激光武器发展-ABL计划

介绍了美国机载激光武器(ABL)计划,分析了ABL武器的组成、工作原理、战技指标和作战运用设计,进而从概念设计、技术验证、分系统集成测试和全系统综合试验四个阶段总结回顾了ABL计划的发展历程,最后从技术制约、作战运用、政策变化、运营管理四个方面探讨了ABL计划失败的原因,并从风险控制、关键技术评估、全寿命需求论证与考核等方面给出了研制发展高新技术武器的启示。     

基于卫星广播的虚拟课堂系统的设计与实现

本文介绍的是基于卫星广播的虚拟课堂系统。在互联网接入带宽受限的前提下,为了满足点对多点传送大量数据的需要,采用IP卫星广播方式传送多媒体课件。本系统主要针对师资力量薄弱,教学水平低下的偏远山区,实现了把名校名师授课的真实课堂通过卫星广播的方式传输到卫星所覆盖的任何区域,使接收端可以很方便快捷的接收到远程授课端的真实而系统的教学过程,重现了一个虚拟课堂。对于提高教学质量,师资力量,促进远程教育的发展有着重大而深远的意义。     

The technological dilemma of the United States

The rapid growth of federally supported research and development during and following World War II, and particularly between 1950 and 1960, appears to have had several major effects on the technological activity of the United States and its industry. However, the most important effect of this growth was the rise in the cost of research and development, including the cost of the technical personnel involved in it. In an assessment of the U.S. investment in R&D for space and defense versus civilian-oriented research and development, it is seen that the United States lags behind the eight European nations studied, and trails Japan even further. With this in mind, it is clear that if both the social and material needs of the people are to be met, new policies and new directions are required of governmental, industrial, and academic institutions.     

卫星地球站播出网管系统广播风暴的产生及应对措施

随着各省卫星地球站网络化的发展,网管系统逐渐成为整个播出系统的重要组成部分,而广播风暴是导致网管系统故障的重要原因之一,从实际工作中观察播出网管系统的广播风暴是如何产生的,并思考如何应对它。