摘要:

The paper provides an introductory tutorial and review, directed at scientists, system designers and engineers on the edges of laser device research, about the extensive influence of Bragg gratings in the current design of semiconductor lasers along with the attempts to improve frequency selection, reduce linewidth, lower frequency chirp on modulation of lasers and reduce threshold currents. Future laser designs for communication systems will incorporate many of the generic features outlined in this paper.

DOI:10.1049/ecej:19930066

出版商:IEE    

年代:1993

数据来源: IET

摘要:

Pulse width modulation (PWM) has found application in various situations where efficient delivery of high power is required. In this paper its use in the conversion of signals from digital to analogue representations is addressed, i.e. as a digital-to-analogue converter (DAC), and it is shown that there are many advantages in using PWM over conventional DAC methods and that high resolution and accuracy can be achieved. One advantage is that, provided a suitable output stage can be provided, a complete, high-power, high-resolution digital-to-analogue power converter can be constructed. Because this work was motivated by the author's interest in digital audio, such a device has come to be known as a digital (power) amplifier. The article describes PWM, particularly in its digital forms, and shows how to make it practical for use as a DAC. This involves various digital signal processing stages prior to the final modulator. Results are presented from simulations and from demonstrator hardware.

DOI:10.1049/ecej:19930068

出版商:IEE    

年代:1993

数据来源: IET

摘要:

Both the Navstar GPS and GLONASS satellite navigation systems, developed respectively by the United States and the Soviet Union (now the Commonwealth of Independent States), are now planned to become operational by the year 1994/95. Both systems are capable of providing the civil community with high-precision position-fixes and/or timing references on a continuous, world-wide basis. For many years both systems have had satellites in orbit in order for pre-operational testing to be conducted. The paper discusses (a) the widely-differing launch histories of both systems, (b) developments in the planned use of orbits, (c) the deliberate degradation of accuracy by the use of selective availability and (d) progress in plans to provide a joint Navstar GPS/GLONASS civil satellite navigation system, possibly integrated with other satellite ranging systems.

DOI:10.1049/ecej:19930069

出版商:IEE    

年代:1993

数据来源: IET

摘要:

Much of the excitement in both research and practical engineering lies in the exploration of the ‘margins’, or boundaries and limits, between what is just feasible and what is impossible. Electronics has a particular fascination because, unlike other branches of engineering, its workings are almost invisible, and its power to perform useful tasks is so great as to be almost magical. A good understanding of the fundamental limits of the laws of science and of the rules of thumb or design rules of current technology are needed for the margins of engineering achievement to be pushed forward safely and effectively. The paper contains a personal selection of laws and rules and their application in the fields of radio, control, digital electronics and speculative future communications.

DOI:10.1049/ecej:19930070

出版商:IEE    

年代:1993

数据来源: IET

摘要:

This paper summarises the consolidated results of the collaborative research carried out within the workpackage ‘Evolution prospects and framework’ (EPF) of the Project RACE 1044: IBC development and implementation strategies. The workpackage has provided pointers to the most suitable paths for evolution towards the target IBC (integrated broadband communications) reference configuration based on detailed analysis of the relevant demand-cost models. The work carried out within the workpackage is described and an overview given of the results achieved and of their exploitation within and outside the RACE community.

DOI:10.1049/ecej:19930071

出版商:IEE    

年代:1993

数据来源: IET