摘要:

The paper describes the application of some statistical estimation techniques to the problem of evaluating the probability of error of (digital) communication systems. The usefulness of an estimator is governed by the variance of the estimate, which, in this case, is the measured probability of error. It is shown that, for the low values of probability of error considered to be practically useful, simple sample-mean estimation requires somewhat large numbers of statistical trials to give results of low variance. The number of statistical trials, however, may be decreased by the use of simple control or antithetic estimators.

DOI:10.1049/piee.1971.0073

出版商:IEE    

年代:1971

数据来源: IET

摘要:

The paper describes an experiment to measure the subjective effect of unsuppressed echo to determine the improvement in echo return loss required of echo cancellers in long-delay telephone communications. Using a simulated long-delay telephone connection of 16.5 dB nominal overall reference equivalent, tests were carried out over a range of conditions in which the 1-way delay varied between 50ms and 600ms, and the echo return loss between 15 dB and 50 dB. Echo-path frequency characteristics which an echo canceller might cause in practice were represented by a flat characteristic and a charactereistic decreasing in loss with increasing frequency. Because of the large number of test conditions (40) in the experiment, the experimental design is unique and is described.

DOI:10.1049/piee.1971.0074

出版商:IEE    

年代:1971

数据来源: IET

摘要:

The paper seeks to justify the contention that the efficiency of error-detection-coding techniques is frequently overestimated owing to insufficient appreciation of the interaction between the characteristics of the code and those of the signalling channel itself. The redundancy of an error-detection code (e.d.c.) requires an increase in modulation rate, and this causes an increase in element error rate due to reduction in normalised signal/noise ratio. On h.f. radio circuits, ionospheric effects can cause even greater increases, and current interleaving and convolution techniques only recoup a small proportion of the disadvantage. It is shown that, in many cases, these factors can outweigh the correcting capabilities of current codes. Comparison of various binary codes and the Piccolo m.f.s.k. system suggests that, where circumstances are such that extremely low error rates are not essential, a nonredundant unprotected code may be comparable in availability with an e.d.c., and Piccolo would probably be an improvement.

DOI:10.1049/piee.1971.0075

出版商:IEE    

年代:1971

数据来源: IET

摘要:

A novel method of multiplexing based on a pattern-recognition technique is described, in which binary data are combined for transmission over a common medium by modulation onto binary codewords. A majority-logic gate forms the transmitted (binary) signal from the modulated codewords. Demodulation is effected by a correlation process using digital matched filters. The system exhibits an adaptive property in the relationship between the channel error-correcting properties and the number of channels in use. Theoretical and experimental results are reproduced, and a description of a prototype equipment is included.

DOI:10.1049/piee.1971.0076

出版商:IEE    

年代:1971

数据来源: IET

摘要:

Telephone engineers rely a great deal on loudness ratings of speech paths for the framing of national transmission plans and for international recommendations to secure proper co-ordination between national networks. Loudness ratings for such use are, by convention, based on subjective loudness comparisons against a specified high-quality reference system (NOSFER), and the measurements are difficult to reproduce accurately. A great deal of work has already been done to enable such ratings (called ‘reference equivalents’) to be determined, by calculation from instrumentally measured sensitivities of the telephone sets and local lines. However, little practical use can be made of these results because of a lack of properly specified instrumental measuring methods. The situation may improve when international agreement has been achieved on the characteristics and method of use of artificial mouths and artificial ears for telephony. The paper presents a review of available fundamental information marshalled into a form convenient for use as soon as suitable electroacoustical measuring methods have been defined and accepted. The precision and reliability of loudness ratings can also be improved by replacing the wideband reference system by an ‘intermediate reference system’ more like the commercial telephone equipment to be tested. Particulars suitable for such a system are suggested.

DOI:10.1049/piee.1971.0077

出版商:IEE    

年代:1971

数据来源: IET

摘要:

At an early stage in the design of electronic systems, decisions have to be made concerning the function and performance of certain vital elements in the main signal path of the system, such as modulators and crucial filters. WASP (waveform and spectral-analysis program) is a computer program which allows the user to analyse a proposed system of cascaded modules and to extract the waveform and spectrum of the signal at any point in the chain. The program exploits the fast Fourier transform to calculate the spectrum at the output of the successive blocks of the system. The progress of the calculation is controlled by a simple set of orders, which are provided by the user as part of his data. The method is applicable to radar, communications, sonar and control systems, and the paper uses, as an example, the design of a digital f.m. radio system.

DOI:10.1049/piee.1971.0078

出版商:IEE    

年代:1971

数据来源: IET

DOI:10.1049/piee.1971.0079

出版商:IEE    

年代:1971

数据来源: IET

摘要:

Prototype equipment is described which automatically corrects the colour balance of a colour television camera for changes in the scene illuminant. The performance of this equipment, which is assessed over a wide range of illuminants, shows that a satisfactory degree of automatic control may be obtained in practice.

DOI:10.1049/piee.1971.0080

出版商:IEE    

年代:1971

数据来源: IET

摘要:

An electronic field-store standards convertor is described which converts colour-television signals on the American 525-line standard to signals on the European 625-line standard. The convertor was first introduced into service by the BBC to give coverage of the Mexico City Olympic Games.

DOI:10.1049/piee.1971.0081

出版商:IEE    

年代:1971

数据来源: IET

摘要:

Measurement techniques have been developed which allow the complex admittance existing at a nominal microstrip open circuit to be accurately characterised. This information, together with the line loss and wavelength, has enabled the electrical defining plane of a shunt stub to be determined. By using a circuit-design technique based on computer modelling it is possible to allow for all these factors. When this approach was applied to the design of a filter with 13 elements, the computer element lengths, when fabricated in microstrip, produced a filter with a bandpass characteristic to within 1% of the computer-modelled response. The need for cut-and-try development is therefore virtually eliminated.The technique of exact computer modelling has also been applied to oscillator circuits, using varactortuned Gunn devices. These circuits are extremely complicated, since they employ waveshaping of the voltage applied to the device. The second harmonic is trapped in a carefully controlled independent resonant circuit. For certain devices, this technique can increase the microwave output power by a factor of 4 or 5. Without the use of cut-and-try methods, devices have operated only 5MHz away from the designed output frequency of 6GHz.

DOI:10.1049/piee.1971.0082

出版商:IEE    

年代:1971

数据来源: IET