摘要:

It is shown that the widely used discrete Fourier transform entails hidden unnecessary and often unrealistic assumptions. The more powerful maximum-entropy method generates an all-pole spectrum avoiding these pitfalls - at the cost of more complex computation - but it too contains certain implicit restrictions. Some of these may be eased by newer methods allowing for spectra with zeros as well as poles. The paper goes onto show that, and broadly how, the maximum-entropy approach may be further developed and generalised to cover an even wider range of situations, patterns and features, including constraints on the source system, observations of nonstationary distributions and known noise powers or characteristics. Finally a formal philosophical basis for generalised pattern analysis and feature extraction is outlined.

DOI:10.1049/ip-f-1.1980.0050

出版商:IEE    

年代:1980

数据来源: IET

摘要:

The problem of separating unknown signals from much stronger ‘coloured’ noise often arises in radar receivers (m.t.i. cancellers) and antenna sytems (directive noise in phased-array antennas). Two main optimisation criteria can be used to design rejection filters, namely (i) the maximisation of average signal/interference ratio (based on the evaluation of the eigenvectors of the interference covariance matrix) and (ii) the linear prediction of interference samples (based on the solution of the normal-equations set). These two methods are compared in terms of algorithms complexity and improvement of signal/interference ratio. The results of computer evaluation show that in most practical cases, i.e. when the interference has a correlation coefficient greater than 0.8, the performance of the suboptimal method of linear prediction is very close to the optimum one. Moreover, the linear prediction method gives a greater flatness in frequency response and, as far as implementation is concerned, is much simpler.

DOI:10.1049/ip-f-1.1980.0051

出版商:IEE    

年代:1980

数据来源: IET

摘要:

Appropriate impedance detectors placed within an antenna impedance-matching unit can facilitate rapid automatic matching. However, the operation of the detectors normally requires a substantial r.f. signal to be passed through the matching unit and this can cause undesirable radiation from the antenna. A novel impedance detection technique is described which operates with such low r.f. signals that the resulting transmission cannot be detected beyond about one wavelength from the antenna. The method determines whether or not the impedance under test lies within a specified region of the complex impedance plane; the boundary of this region is set by the modulation levels applied to the injected signals and it can be made to delineate the resistance, conductance, modulus, v.s.w.r. and phase thresholds shown to be required.

DOI:10.1049/ip-f-1.1980.0052

出版商:IEE    

年代:1980

数据来源: IET

摘要:

A subsystem is described which enables real-time television pictures to be transmitted with very low bit rates while preserving spatial and temporal resolutions adequate for scene monitoring. The chief design constraints were to minimise the size and power consumption in an inexpensive robust construction. This was achieved by optimising the frame rate and picture resolution and by removing image redundancy using a variable Walsh transform d.p.c.m. coding scheme. A c.c.d. imager, custom l.s.i. and standard digital componets now enable a compact low-data-rate sensor and data link to be realised effectively.

DOI:10.1049/ip-f-1.1980.0053

出版商:IEE    

年代:1980

数据来源: IET

摘要:

Detection and measurement of stratified, lossy, dielectric layer interface position was achieved by a radar using a single cycle of 1 GHz carrier repeated every 1 μs. Real time signal processing allowed site measurement to be made on coal seam thickness.

DOI:10.1049/ip-f-1.1980.0054

出版商:IEE    

年代:1980

数据来源: IET

摘要:

This paper is concerned with the soft-decision decoding of error-correcting codes in the context of h.f. data transmission. The use of soft-decision information from the data modem results in an improvement in the performance of a forward-error-correction scheme, when compared with hard-decision decoding, without any further redundancy penalty. In the paper, we estimate the theoretical improvements that can be expected from soft-decision decoding of block and convolutional codes, in terms of both random and burst error-correcting power. Also, this is related to expected coding gains for the Gaussian and Rayleigh fading channels. In addition, we investigate the performance of soft-decision decoding on two types of h.f. modem: a multisubcarrier parallel transmission format (p.t.f.) type modem, and an experimental serial transmission s.m.i.d.d. type modem. We conclude that significant improvements in the performance of coded systems are obtainable through the use of soft-decision decoding.

DOI:10.1049/ip-f-1.1980.0055

出版商:IEE    

年代:1980

数据来源: IET

摘要:

Spatially sampled pictures may be registered to an accuracy of half a pixel by computing the extremum of the cross-correlation surface; when a higher accuracy is required it is necessary to interpolate the cross-correlation surface. It is shown that, when product correlation is used, the interpolation of the cross-correlation surface is equivalent to using the same interpolation process to derive interpolated versions of the reference picture and cross-correlating them with the current picture to establish the surface with arbitrarily fine granularity. When the computationally faster ‘squared-difference’ correlation algorithm is used, it is shown that exactly the same registration result may be obtained by augmenting the cross-correlation surface in the vicinity of the extremum prior to interpolation with terms computed from the reference picture. The derivation of the augmentation terms is shown usually to represent a negligible computational load.

DOI:10.1049/ip-f-1.1980.0056

出版商:IEE    

年代:1980

数据来源: IET

摘要:

This paper describes an adaptive algorithm which is capable of composite coding of broadcast-quality colour-television signals at a low bit rate. The technique involves block-adaptive predictors and block-adaptive variable-length and fixed-length quantisers. The adaptation algorithm has been extended to work at any desirable sampling frequency. As a result the low bit rate is obtained by a reduction of signal redundancy with regards to the statistical variation of each block of incoming samples. A bit-rate of only 28.34 Mb/s is obtained for a Pal colour-bar signal yielding a 50dB s.n.r. at a sampling frequency of twice the subcarrier frequency (sub-Nyquist).

DOI:10.1049/ip-f-1.1980.0057

出版商:IEE    

年代:1980

数据来源: IET

摘要:

This paper presents a method of analysing the performance ofM-ary coherent phase-shift-keyed (c.p.s.k.) signals transmitted through a bandpass nonlinearity, exhibiting a.m./a.m. and a.m./p.m. conversions, and in the presence of additive Gaussian noise both preceding and following the nonlinearity. The method is computationally superior to those previously obtained by other workers, especially for high-level (M> 4) c.p.s.k. systems. In addition, it is capable of extension to include other signal corruptions, such as cochannel interference, both preceding and following the nonlinearity.

DOI:10.1049/ip-f-1.1980.0058

出版商:IEE    

年代:1980

数据来源: IET