Communications and the personal computer

Communication between personal computers and other computers is a rapidly developing area of computing. The paper provides an overview of the many alternatives currently available for implementing communications on personal computers. The techniques covered include asynchronous and synchronous techniques, terminal emulations, workstation replacement, disc emulators, data concentrators and techniques peculiar to personal computers themselves. Consideration is also given to some of the advantages and disadvantages of each technique, the problems of using imported personal computer software and hardware, and of attaching personal computers to British Telecom lines. The likely factors affecting the future development of personal computer communications are also discussed.     

Frequency recovery techniques for TM/TC satellite modem in critical scenarios

Reliability and effectiveness are essential features of satellite transceivers for telemetry and telecommand applications. Modem performance has a strong impact on the success of a satellite mission, in particular, during critical scenarios as the early operation phase, the disposal of a satellite at the end of its life, or the deep‐space missions. In these specific mission critical scenarios, fast and correct data reception is even more important than high channel capacity. An unknown and fast variable channel condition, which can be caused by uncertain spacecraft attitude and large Doppler shift with respect to the data rate, requires efficient and innovative receiver architecture. This paper introduces a complete digital implementation of a transceiver for TM/TC application in low Earth orbit mission that is perfectly compliant with aforementioned requirements. Particular attention is dedicated to the definition and selection of the most appropriate frequency recovery technique; 2 open‐loop techniques that are derived from ML optimal estimator are presented and compared. Additionally, the performance of the proposed receiver is extensively studied and compared with an incoherent technique that is based on the double differential PSK modulation and is known to be suitable for sat‐com in critical scenarios.     

基于短波电台的无线数据传输系统的设计与实现

针对现行石油钻井生产管理体制，提出了钻井信息无线数据传输的方案和结构。对TKM-707短波电台进行计算机技术改造，使之具有数字传输功能，对包含生产技术数据、报表和文档等内容的混合数据进行压缩和调制，通过电台的无线传输，接入到钻井公司企业网。在钻井公司及其下属钻井队的推广应用，有效提高钻井技术和现场管理水平。     

直升机实时指挥监控系统

为了满足某部队对某直升机监控的特殊要求，根据GPS全球卫星定位系统和数传电台及PC104嵌入式计算机的工作原理，研制了集差分GPS信息获取和处理、数据信息流通控制与传输、监控信息的动态图像和参数刷新显示的监控系统，即直升机实时指挥与监控系统．阐述了监控系统的硬件结构组成、系统工作及软件模块的功能．试飞报告鉴定结果证明，该监控系统运行稳定可靠，完全满足设计要求，并成功配备于某军用直升机中．     

Square‐root Nyquist FIR filter synthesis for QAM modems

An optimal joint method for digital FIR filters synthesis used in PSK and QAM modulators and demodulators is proposed. It is based on the criterion of demodulation energy loss minimization (bit‐error rate minimization). The analysis of energy loss of demodulation is developed and the objective function for energy loss minimization is obtained. The synthesis is carried out for fixed filter lengths, signal‐to‐noise ratio at the input of demodulator, carrier spacing between adjacent channels, and relative powers between considered and adjacent channels. This method does not require the introduction of any other weighting coefficients or functions for synthesis. Copyright © 2000 John Wiley & Sons, Ltd.     

双向电力线网报警通信系统的研制

本文根据主控机、前置机和终端机构成的分布式微机自动报警系统,分析其中的通信系统。具体阐述了利用电力线传输报警信号的可行性,以及实现前置机与终端机之间双向通信的机理,并且还介绍了软、硬件相结合进行调制解调的方法和系统的自动复位技术。     

Using a multiple priority reservation MAC to support differentiated services over HFC systems

The successful commercial deployment of Hybrid Fibre/Coaxial (HFC) access networks in the residential market has so far been driven by demand for faster Internet access and the prospects of a host of new services based on real‐time voice and video. To sustain their growth rates and compete with alternative approaches, such as ADSL, they must be enhanced with the capability to efficiently handle quality‐intensive real‐time services. The new multi‐service paradigm mandates isolation of traffic classes, conditioning of entering traffic and preventive control in addition to traditional closed‐loop control. The differentiated services (DiffServ) architecture with its relevant traffic control tools and the bundling of behaviour aggregates is particularly suited to the H/W‐based MAC of HFC systems. It constitutes a suitable framework enabling the support of proliferating real‐time voice‐ and video‐based services while aligning the system to the emerging Internet strategy of scalable service differentiation. The implementation of such a solution in the ACTS 327AROMA research project is presented in this paper. The performance of the system is evaluated using computer simulation. Copyright © 2002 John Wiley & Sons, Ltd.     

Multilevel signals and trellis coding for data communication modems

The special bandwidth efficiency features of coded single carrier multilevel data communication signals pave the way for implementation of high speed data transmission via public analogue telephone networks. The minimum distance of nonredundant coded signals and the minimum free-distance of redundant coded signals are discussed and their influence on error rates is analysed. Security of data on public networks, where it is subject to noise and interference, is improved by advanced trellis coding. Combining the trellis with multilevel signalling provides high speed data modems with security against nearly all spurious signals, transient noise and circuit impairments. The signal structure and coding algorithm of CCITT's recent recommendations on 9600 bit/s and 14 400 bit/s modems for PSTN and leased lines are also discussed.