关键词： cooperation   data management   transaction   mobility   disconnection   history merging  

摘要： Mobile computing and workgroup computing are emerging technologies which have so far been treated independently. Current approaches to support cooperative work neglect the special characteristics of mobile environments like limited bandwidth or temporary disconnection. On the other hand, approaches to support disconnected operation rely on the assumption that the degree of data-sharing is low which is obviously not appropriate for cooperative work. In this paper, we utilize the COACT cooperative transaction model to provide support for parallel activities in mobile environments. We present a system architecture that is able to cope with the special characteristics of mobile environments and a formal framework for the consistent information exchange between mobile users. The paper shows how the COACT history merge algorithm reduces conflicts by exploiting operation semantics and offering consistent sequences of operations. We believe that our new approach is a viable solution to the growing demand for cooperation in mobile environments.

关键词： Mobile computing  

摘要： Mobile computing is a component that will be included in many future computing environments. This paper presents a scheme that will allow the addition of a mobile component to an existing distributed deductive database. This scheme allows for the following features: 1 ) data replication on the mobile unit, 2) transaction logging to log changes both in the mobile user's database and in the network's database, 3) concurrency control to prevent both copies from updating the same record, and 4) reconnection procedures to update both copies upon reconnection. To facilitate data replication and reconnection updates, we have established 'Proxy Nodes' in the network database to keep track of data of interest to the mobile user. © Springer-Verlag London Ltd.

关键词： Antennas  

摘要： Based on a recent remarkable development of digital beamforming (DBF) antenna technologies, we propose a new concept of kaleidoscopic antenna, we call it `software antenna,' which is a more general one extending DBF schemes. The software antenna instantly reconfigures itself adapting its software and hardware to changes in the radio-environment. To realize the software antenna, the development of high-speed reconfigurable FPGAs is indispensable. As an intelligent antenna, we believe the software antenna could play a key role in the days of software radio having a function of mobile computing.

关键词： Mobile radio systems  

摘要： This paper proposes a novel FEC (forward error correction) scheme for high-speed wireless systems aiming at mobile computing applications. The proposed scheme combines inner nonredundant error correction with outer parallel encoding random FEC for differentially detected QPSK (quadrature phase shift keying) signals. This paper, first, examines error patterns after the differential detection with nonredundant error correction and reveals that particular double symbol errors occur with relatively high probability. To improve the outer FEC performance degradation due to the double symbol errors, the proposed scheme uses I and Q channel serial to parallel conversion in the transmission side and parallel to serial conversion in the receiving side. As a result, it enables to use simple FEC for the outer parallel encoding random FEC without interleaving. Computer simulation results show the proposed scheme employing one bit correction BCH coding obtains a required Eb/No improvement of 1.2 dB at a Pe of 10-5 compared to that with the same memory size interleaving in an AWGN environment. Moreover, in a Rician fading environment where directional beam antennas are assumed to be used to improve the degradation due to severe multipath signals, an overall Eb/No improvement at Pe of 10-5 of 3.0 dB is achieved compared to simple differential detection when the condition of delay spread of 5 nsec, carrier to multipath signal power ratio of 20 dB and Doppler frequency at 20 GHz band of 150 Hz.

关键词： MOBILE computing   COMPUTER industry  

摘要： Presents developments in mobile computing for the week ending July 28, 1997. Data General Corp.'s release of a docking station and communications software called Serial Docking Station for its DataGenie III/Li handheld terminal; Hewlett-Packard's plans to ship three lines of smaller and lighter portable personal computers; Apple Computer's upgrade of the processor in its PowerBook 1400 family of Macintosh notebooks.

关键词： cluster   structure   perturbation   lineshift   SF6   UF6  

摘要： A new site-site intermolecular potential for UF6, featuring exchange, dispersion, electrostatic and induction terms, is presented. The new potential is used to determine UF6 cluster structures up to the hexamer and, by means of a second order line shift formalism, to calculate the corresponding IR spectra in the region of the nu(3) vibrational mode. (C) 1997 Elsevier Science B.V.

关键词： 北大方正   计算机   多媒体创作工具   移动计算   服务器   新产品   笔记本电脑   多能奔腾处理器   中国市场   新技术  

摘要： 一年一度的京交会是国内主要计算机厂商向社会各界展示技术、展示产品、展现实力的一次盛会。正在举办全国性全系列新产品发布、技术展示以及电脑普及活动的方正电脑,挟覆盖移动计算、办公商用计算、多媒体网络计算直至高级工程与图形计算领域的全系列新品亮相京交会。以方正电脑新品为平台,方正向电脑爱好者、普通电脑用户展示了包括MMX多能奔腾处理器技术、In-ternet可视电话、数字影像技术、3维图形加速技术在内的电脑科技最新发展。随着巡展的顺利进行,方正携在全国范围内形成的方正电脑九七“创新、精彩、领先”的这股清新的风飨宴京城百姓。展会上。

关键词： Communication   Multicast   Implement   Systems   Time   multicast communication   Messages   Network topology   algorithms   Communication Research   Mobile Computing   bandwidth requirement   Multicast  

摘要： Causal message ordering is required for several distributed applications, In order to preserve causal ordering, only direct dependency information between messages, with respect to the destination process(es), need be sent with each message. By eliminating other kinds of control information from the messages, the communication overheads can be significantly reduced, In this paper we present an algorithm that uses this knowledge to efficiently enforce causal ordering of messages, The proposed algorithm does not require any prior knowledge of the network topology or communication pattern, As computation proceeds, it acquires knowledge of the communication pattern and is capable of handling dynamically changing multicast communication groups, and minimizing the communication overheads, With regard to communication overheads, the algorithm is optimal for the broadcast communication case, Extensive simulation experiments demonstrate that the algorithm imposes lower communication overheads than previous causal ordering algorithms, The algorithm can be employed in a variety of distributed computing environments, Its energy efficiency and low bandwidth requirement make it especially suitable for mobile computing systems, We show how to employ the algorithm for causally ordered multicasting of messages in mobile computing environments. (C) 1997 Academic Press.

关键词： 移动计算环境   移动数据库   移动计算机  

摘要： 1引言目前,越来越多的用户开始拥有积各种便隽计算设备,例如笔记本心脑PDA等。