DOI:10.1049/ecej:19900046

出版商:IEE    

年代:1990

数据来源: IET

摘要:

Not long after the discovery of error-control coding (codes for error detection and correction) in about 1950, the subject was officially declared dead: codes of adequate performance were too complicated to implement, and few real applications could be envisaged. Fortunately, this official pronouncement, like many others, proved to be quite wrong. Because of the enormous progress that has occurred in the design and manufacture of microelectronic circuits for digital processing and storage, coding practice has been revolutionised. Error control codes are now used to detect and correct the errors which inevitably occur, caused by noise, interference, imperfections and other deleterious effects, in a very wide range of communications, control, processing and information storage applications.

DOI:10.1049/ecej:19900047

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The location of radio transmitters through direction finding (DF) has been required almost since the earliest days of radio communications. The two world wars have, not unexpectedly, given impetus to major advances in DF technology. The only major advance in DF technology since World War II has been in the field of wavefront analysis and it is only now that the supporting technologies have made these techniques a practical proposition. Superresolution DF techniques potentially offer the user not only the capability to operate in multiple and unfriendly signal environments but also flexibility of antenna deployment and fast operation. The paper attempts to explain how this enhanced DF performance is obtained aided by comparison with other DF techniques. Results obtained with the Siemens - Plessey SR DF demonstrator are also presented to outline the practical performance of superresolution DF techniques.

DOI:10.1049/ecej:19900048

出版商:IEE    

年代:1990

数据来源: IET

摘要:

Gallium arsenide monolithic microwave integrated circuits (GaAs MMICs) are a means of utilising the high-mobility, high-frequency aspects of the GaAs MESFET together with the semi-insultaing properties of gallium arsenide to form a low-loss integrated circuit with active elements. Novel semiconductor growth structures allow devices with cut-off frequencies well into the millimetre wave ranges to be fabricated, with dramatic improvements in gain and noise figure. Multilevel structures also permit very high circuit densities, so complete receivers and phased-array radar multifunction circuits can be made with high repeatability in a few square millimetres. Such advances, however, are only possible because of major investments in component characterisation and product consistency.

DOI:10.1049/ecej:19900049

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The introduction of dramatically new technologies, the extension of radio utilisation to higher and higher frequencies and the increased use of satellite systems has necessitated the restructuring and reorganisation of the CCIR. In an endeavour to streamline the working methods and to reduce the costs of the Geneva secretariat, Study Groups will establish working parties and task groups which will have a continuing existence between Study Group meetings. Changes are also being made to CCIR publications.

DOI:10.1049/ecej:19900050

出版商:IEE    

年代:1990

数据来源: IET

摘要:

New technology is needed by digital transmission networks for the increased bandwidth, performance and reliability requirements of existing and future telecommunication services, such as broadband ISDN. Increased flexibility, automation and control are also major issues being addressed. The combination of these factors has led to the development of synchronous digital heirarchy (SDH) networks to replace existing asynchronous networks during the 1990s. These issues are reviewed and further developments to bandwidth-transparent optical networks indicated for the twenty-first century.

DOI:10.1049/ecej:19900054

出版商:IEE    

年代:1990

数据来源: IET