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51.
无线数据通信网发展趋势 总被引:1,自引:0,他引:1
无线数据通信具有两大发展趋势,即低速的广域移动数据网及高速的局域无线数据网。本文介绍了其技术特点、应用情况和市场前景,分析了无线数据通信传输技术、网络结构和媒质接入控制等问题。 相似文献
52.
53.
无线接入系统凭借其建设速度快、运营成本低、提交成本回收快等特点,越来越受到电信运营商的青睐。目前,宽带城域网和宽带小区的建设正如火如荼,具有广阔的发展前景。中国无线接入技术与市场呈现多元化。介绍了中国电信的“天翼通”、中国移动的“移动梦网”以及中国联通的“联通无限”。这三种业务即存在竞争又相互补充。 相似文献
54.
内嵌闪存MCU的高性能多通道24位采集系统ADuC845 总被引:6,自引:0,他引:6
ADuC845是ADI公司新推出的嵌有单指令周期8052闪存MCU、带两路24位∑ -△A/D、双12位D/A以及两个灵活脉宽调制输出的高性能24位数据采集与处理系统芯片。该芯片的数据处理速度达12MIPS,且设计简单 ,噪声低 ,非常适用于精密仪器仪表。文中详细介绍了该芯片的功能特点和工作原理 ,给出了该芯片的应用方法。 相似文献
55.
Giovanni Giambene Enrico Zoli 《International Journal of Satellite Communications and Networking》2003,21(2):199-225
In this paper, we investigate a packet access scheme that is able to support mixed traffics in the presence of high propagation delays. Referring to a Time‐Code Division Multiple Access air interface, we propose a Medium Access Control (MAC) protocol based on a random access scheme. A successful attempt grants the use of a slot‐code resource. This protocol is named Adaptive Time Code‐Packet Reservation Multiple Access (ATC‐PRMA), since the access parameters are changed, depending on the traffic load conditions, so as to fulfil Quality of Service requirements. Numerical examples are carried out for the Low Earth Orbit (LEO)‐Mobile Satellite System (MSS) scenario, but all these considerations could be applied to High‐Altitude Platform Stations (HAPSs) as well. In both cases, high propagation delays prevent an immediate feedback to users. An analytical approach is proposed to study the stability of our MAC scheme. Accordingly, we define a criterion for optimizing system performance. The predicted ATC‐PRMA behaviour is supported by simulation results. Finally, we show the performance improvement of ATC‐PRMA with respect to a MAC protocol not employing adaptive parameters. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
56.
EPON技术具有大带宽、高性价比、结构简单和一定服务质量保证等特点,被业界普遍看好,成为 下一代接入网的最佳候选技术.本文主要介绍了EPON的工作原理、分层结构、接入控制和组帧方式,最后给出 了实现EPON的关键技术和难点以及EPON的发展近况. 相似文献
57.
Snell-Johns Jessica; Mendez Julia L.; Smith Bradley H. 《Canadian Metallurgical Quarterly》2004,18(1):19
Various definitions exist for what constitutes family therapy. In this article, we consider family therapy to encompass any intervention that targets family interactions and conceptualizes problems as existing beyond individual clients. Numerous individual studies and several quantitative reviews have established family therapy as an effective treatment modality and the treatment of choice for many disorders. However, critiques of existing service provision highlight the unfortunate fact that numerous barriers to treatment exist at multiple levels of the broader ecology, preventing many families from benefiting from these services. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
58.
D. Twigger M. Byard S. Draper R. Driver R. Hartley S. Hennessy C. Mallen R. Mohamed‡ C. O'Malley§ T. O'Shea‡ E. Scanlon‡ 《Journal of Computer Assisted Learning》1991,7(2):144-155
Abstract This paper outlines the work of the Conceptual Change in Science project, funded as part of the ESRC InTER programme. The aims of this research project are to clarify and describe the process of change in learners' conceptual understandings of natural phenomena. The domain of reasoning selected for study is that of mechanics. Computer software which may be useful in exploring and developing pupils' reasoning and promoting conceptual change in this domain is being developed and evaluated. The group that is carrying out the research is based at the Universities of Leeds, Glasgow and the Open University. 相似文献
59.
In this paper, we consider a method (splitting) for calculating the auto- covariances of fractional integrated processes (ARFIMA) and generalized integrated processes (GARMA). The splitting method does not require any restriction on the autoregressive roots, and allows fast calculation of the autocovariances of these processes. 相似文献
60.
Gathercole Susan E.; Pickering Susan J.; Ambridge Benjamin; Wearing Hannah 《Canadian Metallurgical Quarterly》2004,40(2):177
The structure of working memory and its development across the childhood years were investigated in children 4-15 years of age. The children were given multiple assessments of each component of the A. D. Baddeley and G. Hitch (1974) working memory model. Broadly similar linear functions characterized performance on all measures as a function of age. From 6 years onward, a model consisting of 3 distinct but correlated factors corresponding to the working memory model provided a good fit to the data. The results indicate that the basic modular structure of working memory is present from 6 years of age and possibly earlier, with each component undergoing sizable expansion in functional capacity throughout the early and middle school years to adolescence. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献