摘要:

This paper surveys some past and present principles of speech coding. The advent of digital logic systems and integrated circuit components is seen as a major turning point in the implementation of effective coding principles that could not previously be used satisfactorily.Various coding methods are discussed, covering frequency domain, time domain and analogue and digital output systems. The problems of key generator integrity, synchronization, received voice quality and recognizability, and channel bandwidth restrictions, and the security offered by different systems are considered.The author concludes that in the immediate future high security speech encipherment systems will be of the digital output crypto-vocoder type, with audio bandwidth analogue output coders offering an increasingly secure alternative for the majority of applications. Digital output coders will continue to be used effectively in those applications where the communication equipment and transmission path have the necessary characteristics to carry low-error-rate digital signals. Advances in analogue-to-digital speech conversion providing acceptable quality at bit rates below 9.6 k bit/s should eventually enable a simple digital output coder to be as effective as a cryptovocoder for audio band high security applications.

DOI:10.1049/ree.1980.0022

出版商:IERE    

年代:1980

数据来源: IET

摘要:

A circuit is proposed which transforms a delta sequence (d.s.) of a signal into another delta sequence of a double amplitude signal. With the proposed circuit, it is possible to transform the d.s. of half-sums obtained from the conventional delta-adders into a d.s. of the corresponding full sums. This increases the flexibility of the realization of digital filters with delta input-output sequences.

DOI:10.1049/ree.1980.0023

出版商:IERE    

年代:1980

数据来源: IET

摘要:

A radio receiver system for frequency-modulated signals is described which uses a direct conversion (zero intermediate frequency) technique. The characteristics of the system are developed especially in areas of difference from conventional methods.The realization is shown of the complete receiver in two integrated circuits which form part of a synthesized 30 to 88 MHz equipment. The conclusion is drawn that the combination of direct conversion and large-scale integration is a very powerful means for future development of radio receiver techniques.

DOI:10.1049/ree.1980.0024

出版商:IERE    

年代:1980

数据来源: IET

摘要:

The paper is concerned with the problem of generating complex patterns on two-dimensional liquid-crystal arrays, without either an excessive number of control terminals or prohibitively complex control circuits. Following a brief introduction to the operating principles of liquid-crystal displays, the initial Section indicates how the problem could be solved using a two-dimensional shift-register/liquid-crystal sandwich—if the technology were available. Succeeding Sections then derive and analyse efficient ways of arranging and driving sets of parallelXandYconductors to generate desired display patterns. Particular attention is given to the examples of generating arrays of 7×5 dot matrix symbols, and of generating single two- or three-valued waveform displays. Drive sequences within the response speed of the liquid crystals are shown to be feasible for character displays, and to have the advantage of simplicity and tolerance to variations in operating conditions. Mean-squared, slow-response drives are shown to be more widely applicable and to provide superior visual performance in certain conditions, providing that the ratio of the mean-squared white-to-black voltages is adequate.

DOI:10.1049/ree.1980.0025

出版商:IERE    

年代:1980

数据来源: IET

摘要:

A detailed comparison of recording codes, using superposition, is used to show that there is little to choose between the popular ones, as regards maximum achievable data density. It is shown that relatively few general classifications are necessary to encompass all the codes, and that, within each classification, it is often possible to say which code is optimum. A guide to the selection of an efficient code for some common conditions of use is presented.

DOI:10.1049/ree.1980.0026

出版商:IERE    

年代:1980

数据来源: IET