摘要:

Quality grading tests have been conducted to investigate the subjective effects of various combinations of transmission channel bandwidth, television-line standard and display size. The test pictures used were head-and-shoulders views. 313-line signals transmitted through a channel with 1 MHz bandwidth proved to be more acceptable than 625-line signals transmitted through the same channel. A smaller display of height, equal to 1/8 times the viewing distance, was always preferred to one of height equal to 1/4 times the distance. The results will be of use in determining the parameters for future visual telecommunications systems, not necessarily using the 625-line broadcast t.v. standard.

DOI:10.1049/ip-f-1.1980.0001

出版商:IEE    

年代:1980

数据来源: IET

摘要:

The paper describes a new technique for achieving low-sidelobe directional patterns (−35 dB) from thinned arrays. The concept employs multiplicative processing and is therefore restricted to receiving arrays. It is shown that a total of about 3Nelements can synthesise a pattern corresponding to a filled array ofN2elements so that large thinning factors, in excess of 90%, are realisable for large numbers of elements and without degradation of sidelobe performance. The basic concept is also demonstrated experimentally with a 6-element array. It is shown that this design is more susceptible to the effects of random phase errors compared with conventional arrays and the multiplicative signal processing can also lead to problems of multiple-source cross products under certain situations.

DOI:10.1049/ip-f-1.1980.0002

出版商:IEE    

年代:1980

数据来源: IET

摘要:

A method is described whereby the probability that a multipair cable will successfully support a number of low-speed digital pulse-code modulation (p.c.m.) transmission systems operating on pairs selected at random may be estimated. The calculation assumes that the near-end crosstalk attenuation between pairs has a truncated lognormal distribution, but does not assume that the total interference has a Gaussian probability distribution.

DOI:10.1049/ip-f-1.1980.0003

出版商:IEE    

年代:1980

数据来源: IET

摘要:

Procedures are described which lead to empirical optimisation of a digital radar autodetector by adjustment of quantisation and integration parameters. Receiver nonlinearity is dealt with exactly by appropriate transformation of quantisation thresholds. The statistical modifications of quantised data introduced by a digital leaky integrator are treated by a convolution process. Performance is calculated for logarithmic and linear receivers with Swerling 0 and Swerling 2 target models. It is found that judicious adjustment of quantisation thresholds has a marked effect on integration efficiency, particularly in the logarithmic case.

DOI:10.1049/ip-f-1.1980.0004

出版商:IEE    

年代:1980

数据来源: IET

摘要:

In this paper a quantitative analysis of a general feedback communication system is undertaken. The model considered is sufficiently general that the resulting analysis may be used when considering most feedback schemes. Mathematical expressions are derived for the probability of error and transmission efficiency of a feedback scheme when finite and infinite numbers of repetitions are possible, and also when the feedback channel can be considered noiseless or noisy. An example of single-symbol repetition on an additive white Gaussian noise channel is fully analysed.

DOI:10.1049/ip-f-1.1980.0006

出版商:IEE    

年代:1980

数据来源: IET

摘要:

Random dispersive media such as the shallow-water sound channel cause the far field of a point source to be random in time and space. Consequently, resolution methods such as d.f.t., ‘maximum-likelihood estimator’ or‘maximum-entropy method’ are useful only to a limited extent for estimation of source parameters such as range, bearing or depth. This is because those methods are based on the assumption that the signal wavefront is coherent. The resolution methods can easily be generalised to the situation in which the desired signal is random. A shallow water sound propagation model is used to demonstrate the application of generalised power estimators to the problem of locating point acoustic sources in shallow water.

DOI:10.1049/ip-f-1.1980.0007

出版商:IEE    

年代:1980

数据来源: IET

摘要:

This paper discusses the structural properties of various gradings in relation to the losses resulting from the traffic offered to the inlet groups. On the basis of earlier researches on optimum graded structures, an attempt is made to obtain interconnecting schemes which will provide the maximum traffic carrying capacity of the serving trunks. The performance of these interconnecting patterns under severe unbalanced loading is examined. The overall grades of service appear to be better than those of some other structures which have appeared in the literature and with which they are compared. It is observed that the sensitivity to traffic unbalance, and the difference between losses on individual groups, can be reduced. We draw conclusions from these results about the efficiency of gradings in relation to the busy matrix, and about some rules which, we think, govern the design of optimum grading structures.

DOI:10.1049/ip-f-1.1980.0008

出版商:IEE    

年代:1980

数据来源: IET

摘要:

An algorithm is presented, for the computation of multidimensional Fourier and Fourier-like discrete transforms, which offers substantial savings in the number of multiplications over the conventional fast Fourier transform method. Implementation of this algorithm, and the use of it to compute discrete Fourier transforms of real sequences, are also described.

DOI:10.1049/ip-f-1.1980.0009

出版商:IEE    

年代:1980

数据来源: IET

摘要:

During the period from 1956 to 1966 the UK Government's Joint Speech Research Unit was conducting research into channel vocoders, culminating in a laboratory-built design suitable for evaluation by potential users over digital transmission networks at 2400 bit/s. The success of the basic vocoder design was such that it has since been engineered in various forms for widespread operational use, using different technologies as they have evolved. In view of the JSRU vocoder's continued competitiveness with other narrow-band speech coding techniques, such as linear predictive coding, this paper has been written to give a full specification of all the essential features of the vocoder configuration, with comments on the reasons for the design decisions and reference to supporting research where appropriate. The two most important factors contributing to this vocoder's successful performance are the use of narrow-band single-resonant circuits for the synthesis filters and the use of differential coding between channels in the digitisation process.

DOI:10.1049/ip-f-1.1980.0010

出版商:IEE    

年代:1980

数据来源: IET