DOI:10.1049/ecej:19920012

出版商:IEE    

年代:1992

数据来源: IET

摘要:

Personal communication networks (PCNs) capture the concept of low-cost, mobile communications for the mass market and are seen as a major growth area for public telecommunications, offering new areas of choice and flexibility to the customer. With commercial PCN service due to be offered in the first half of 1993, the availability of infrastructure equipment and handsets, complying with internationally agreed standards, together with novel design methods to meet the special needs of PCN are important ingredients for a successful system implementation. The article examines the technical requirements of PCN and explains the factors which influenced the development of the DCS 1800 standard.

DOI:10.1049/ecej:19920013

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The bandwidth capability of optical communication networks continues to increase. Optical fibres have low attenuation windows of many thousands of gigahertz and individual optical sources can now be modulated at rates well above 20 GHz. This is much faster than the switching rates of the electronic components needed to achieve multiplexing in applications such as time division multiplexing (TDM). Subcarrier multiplexing, which uses analogue intensity modulation of optical sources with readily available microwave components, can provide an elegant method of using the optical bandwidth and is capable of graceful evolution for future networks.

DOI:10.1049/ecej:19920014

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The paper describes the design of a digitally implemented modem for use over HF (2-30 MHz) radio channels. As a completely digital approach offers the prospect of a number of significant improvements, a new digital multifrequency-shift-keying (MFSK) modem has been developed that employs a novel digital processing procedure termed code-assisted bit synchronisation (CABS). Signal detection is achieved via a set of noncoherent correlators, whilst symbol synchronisation and error correction are performed using a soft-decision Viterbi decoder. Practical tests of the modem show that it operates effectively under both additive white Gaussian noise and real HF channel conditions.

DOI:10.1049/ecej:19920015

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The fundamentals of radio receiver design have changed little over the last twenty years. The same, however, cannot be said for the technology used for implementation. The performance of both analogue and digital technology has revolutionised the way in which receiver design can be approached. In particular, the advent of low-cost analogue to- digital convertors and digital signal-processing devices has made possible, for the first time, the implementation of architectures once considered as unrealistic. The article addresses the design of an HF band receiver using commercially available technology, with the aim of producing a receiver whose performance is better than that available with current purely analogue designs and which incorporates a significant element of digital signal processing.

DOI:10.1049/ecej:19920016

出版商:IEE    

年代:1992

数据来源: IET

摘要:

Devices constructed from thin polymer films with randomly dispersed liquid crystal droplets (PDLC films) are reviewed. PDLC films have already been researched in some detail and materials in the form of tough flexible films are available commercially. The materials used in their manufacture are available in commercial quantities and can be processed by standard film-forming techniques rendering large-area, environmentally robust displays and light shutters easy and inexpensive to manufacture. Single-piece light valves of up to 3 m2 are relatively common. PDLC shutters do not require polarisers, so that light loss through the cell in the clear state is reduced. The article describes the operating principle of PDLC films and discusses their electro-optic properties with emphasis on their influence on device performance. Finally, an assessment of present and future applications of this technology is presented.

DOI:10.1049/ecej:19920017

出版商:IEE    

年代:1992

数据来源: IET