IEE Proceedings F (Radar and Signal Processing)
Volume 137, Issue 5, October 1990
Volumes & issues:
Volume 137, Issue 5
October 1990
Knowledge-based signal processing for radar ESM systems
- Author(s): J. Roe ; S. Cussons ; A. Feltham
- Source: IEE Proceedings F (Radar and Signal Processing), Volume 137, Issue 5, p. 293 –301
- DOI: 10.1049/ip-f-2.1990.0045
- Type: Article
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p.
293
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Radar electronic support measures (ESM) systems perform the functions of threat detection and area surveillance to determine the identity and bearing of surrounding radar emitters. Automatic ESM systems incorporate a passive receiver to measure the parameters of detected radar pulses and an automatic processor to rapidly sort pulses and identify the emitters. Current processors use algorithmic processing methods which are inflexible and do not fully utilise available sources of a priori information. The paper discusses the role of knowledge-based processing methods and how they may be applied to the key ESM signal-processing functions of deinterleaving, merge and emitter identification. ESM processors are required to sort input pulse data streams exceeding one million pulses per second and minimise the reporting latency of new emitters. The paper further discusses the requirements to achieve real-time operation of knowledge-based ESM processing techniques.
Knowledge-based enhancement of human EEG signals
- Author(s): E.C. Ifeachor ; M.T. Hellyar ; D.J. Mapps ; E.M. Allen
- Source: IEE Proceedings F (Radar and Signal Processing), Volume 137, Issue 5, p. 302 –310
- DOI: 10.1049/ip-f-2.1990.0046
- Type: Article
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p.
302
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The human electroencephalogram (EEG) contains useful diagnostic information on a variety of neurological disorders. However, like all biomedical signals, the EEG is very susceptible to a variety of large-signal contaminations or artefacts which reduce its clinical usefulness. The paper discusses the use of knowledge-based techniques to overcome the limitations of an adaptive signal-processing method developed for real-time ocular artefact removal. Knowledge-based techniques are used to recognise and subsequently classify the pathological waves and ocular artefacts, based on a knowledge of their characteristics and the heuristics used by EEG experts. This makes it possible to remove the artefacts from the EEG signal only when it is necessary and with minimal distortion of any diagnostic information in the EEG. Preliminary results are presented to illustrate the advantages of the new approach.
Knowledge-based interpretation of foetal phonocardiographic signals
- Author(s): J.T.E. McDonnell
- Source: IEE Proceedings F (Radar and Signal Processing), Volume 137, Issue 5, p. 311 –318
- DOI: 10.1049/ip-f-2.1990.0047
- Type: Article
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p.
311
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A knowledge-based system (KBS) is presented for the processing and analysis of foetal phonocardiographic signals. Conventional analytic techniques of signal processing are inappropriate for such a volatile signal environment where little information about the signal events is known beforehand. The essential feature of this KBS is its hierarchical organisation of procedurally based knowledge areas. This formulation ensures that the knowledge is consistent and also allows an efficient search for applicable rules. An analysis of the signal is effected using a solution island driving approach. The performance of the system is comparable to that achieved by a domain expert.
System for automatic realignment of the head in magnetic resonance imaging
- Author(s): S. Marshall ; N. Saeed ; H. Young ; T.S. Durrani ; B. Dalton ; G. du boulay
- Source: IEE Proceedings F (Radar and Signal Processing), Volume 137, Issue 5, p. 319 –330
- DOI: 10.1049/ip-f-2.1990.0048
- Type: Article
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p.
319
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The condition of patients with various diseases of the brain, may be monitored over a period of time using magnetic resonance imaging (MRI) techniques. To make an accurate assessment of changes in their condition it is necessary that the patients be repositioned to a very high degree of accuracy. Current techniques rely on the skill of the radiographer to return the head to the same position during each scanning. Various mechanical fixation methods, such as the use of head moulds and indelible markers, have been proposed. This paper describes an approach to automatic patient realignment using a combination of image analysis techniques and symbolic reasoning. A set of key anatomical features are extracted from the images and these are compared using a knowledge-based expert system to measure and then correct the positional inaccuracies. The system is capable of extension for crossmatching images from other modalities.
Coupled systems for signal processing
- Author(s): D.B. Sharman and T.S. Durrani
- Source: IEE Proceedings F (Radar and Signal Processing), Volume 137, Issue 5, p. 331 –336
- DOI: 10.1049/ip-f-2.1990.0049
- Type: Article
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p.
331
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Several signal analysis systems reported in the literature have benefited from the integration of artificial intelligence (AI) and signal processing. This paper examines a growing class of these systems in which the AI component is used to control signal-processing operations. Several philosophical arguments are presented to support the development of these so called coupled systems. Three different types of coupled-system control schemes are identified and these are illustrated using examples from the literature. The benefits and improvements to traditional methods of signal processing achieved using coupled control schemes are also identified and are again illustrated with examples.
Comparison of knowledge elicitation techniques in the domain of electronic filter tuning
- Author(s): D. Tsaptsinos ; A.R. Mirzai ; B.W. Jervis ; C.F.N. Cowan
- Source: IEE Proceedings F (Radar and Signal Processing), Volume 137, Issue 5, p. 337 –344
- DOI: 10.1049/ip-f-2.1990.0050
- Type: Article
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p.
337
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The work done towards the construction of an expert system to assist an operator in the identification of the corrective action to be applied during tuning of electronic filters is described. The first part of the paper introduces two algorithms for induction by examples (ID3 and adaptive combiner) and their relationship to expert systems. The two algorithms were applied, in a series of tests which involved an incremental presentation of a number of examples, to the task of filter tuning. The reported results suggest the use of ID3 when a small number of classes is present. The second part of the paper presents subsequent work with ID3. Results are reported of using this algorithm for filter tuning with examples containing either numerical or logical attribute values. A comparison of the results showed that improved test performance was achieved by using logical values.
Dilation correlation functions and their applications
- Author(s): M.R. Belmont
- Source: IEE Proceedings F (Radar and Signal Processing), Volume 137, Issue 5, p. 345 –350
- DOI: 10.1049/ip-f-2.1990.0051
- Type: Article
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p.
345
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A development of the cross-/auto-correlation function is introduced which is capable of detecting and quantifying stretching or contraction between functions. Its analytic properties are described and discrete algorithms are deduced for its application to experimental data sets. Tests for ascertaining whether stretching or displacement models are appropriate arise naturally out of the analysis. A range of illustrations are included together with an application to the detection of thermal expansion effects on images of combustion in internal combustion engines.
Image reconstruction from noisy digital holograms
- Author(s): C.P. Mariadassou and B. Yegnanarayana
- Source: IEE Proceedings F (Radar and Signal Processing), Volume 137, Issue 5, p. 351 –356
- DOI: 10.1049/ip-f-2.1990.0052
- Type: Article
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p.
351
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The method of projection onto convex sets (POCS) is used in signal reconstruction to find a function that satisfies a collection of constraints, provided each of these constraints defines a convex set. If the constraints are inconsistent then a modified method of POCS may be used to find the fixed point of the POCS operator. This problem arises in the area of signal reconstruction from noisy multiple-frequency digital holograms, where it is required to compute a signal that satisfies known data subject to the constraint that it has a finite region of support. For noisy data there may exist no such signal and hence the constraint is inconsistent with the known data. Thus a modified POCS method needs to be applied. The paper reviews the method of image reconstruction from digital holograms. Two ways of applying the modified POCS method (called the PONICS method) are presented. Studies reported here show the effectiveness of the method for image reconstruction from noisy multiple-frequency holograms.
Optimum step size of the LMS adaptive FIR filter with inadequate length for signal estimation
- Author(s): R.-Y. Chen and C.-L. Wang
- Source: IEE Proceedings F (Radar and Signal Processing), Volume 137, Issue 5, p. 357 –361
- DOI: 10.1049/ip-f-2.1990.0053
- Type: Article
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p.
357
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Step size is a key parameter that must be determined for the efficient use of the LMS algorithm in adaptive FIR filtering. The paper derives the optimum step size for the LMS adaptive FIR filter with inadequate length for signal estimation. The optimum step size yields the most rapid convergence for a given number of taps and a desired mean-square error. For ‘white input data’, it is a simple closed-form function of the number of taps, the input signal variance, the initial mean-square error, the desired mean-square error, and the squared norm of the truncated part of the optimum impulse response. This characteristic makes it easy to design in many practical applications. Based on the derived results, the optimum tap number for fastest convergence for a desired mean-square error is obtained via numerical evaluation. Computer simulations are given to support the derived results.
A study of auto-and cross-ambiguity surface performance for discretely coded waveforms
- Author(s): L. O'carroll ; D.H. Davies ; C.J. Smyth ; J.H. Dripps ; P.M. Grant
- Source: IEE Proceedings F (Radar and Signal Processing), Volume 137, Issue 5, p. 362 –370
- DOI: 10.1049/ip-f-2.1990.0054
- Type: Article
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p.
362
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Spread-spectrum techniques are used in radar and communications for simultaneous access to a common radio allocation with the minimum of interference or crosstalk. The paper reviews the concept of binary phase and frequency shift keyed sequences to derive the coded wave-forms for these systems and examines their auto- and cross-ambiguity surface performance in the presence of Doppler shifted received signals. In particular, aperiodic sequences are investigated to obtain a set of coded waveforms with time-bandwidth products below 127.
Improved resolution by utilising an artificial transmission medium
- Author(s): A.M. Bøifot
- Source: IEE Proceedings F (Radar and Signal Processing), Volume 137, Issue 5, p. 371 –376
- DOI: 10.1049/ip-f-2.1990.0055
- Type: Article
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p.
371
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A general method for estimating complex data samples using a complex exponential model is presented. The method takes the frequency-dependent attenuation and phase characteristics of the propagation medium into account. It is called the artificial transmission medium method (ATMM) and can be utilised both for superresolution purposes and in methods which are based on the subtraction of strong signals from measured data. In the latter case it is called the reduced ATMM. It is also shown that a simplified version of the method is analogous to the Prony method. Measurements are presented which verify the applicability of the reduced ATMM. Weak signals that are totally masked either by the main lobe or by the sidelobes of a stronger signal are resolved by utilising the reduced ATMM. The measurements also show that the reduced ATMM gives a better estimate of the reflection coefficient of a coupling loop than the model used in the Prony method.
Fast null-steering algorithm for broadband power inversion array
- Author(s): C.C. Ko
- Source: IEE Proceedings F (Radar and Signal Processing), Volume 137, Issue 5, p. 377 –383
- DOI: 10.1049/ip-f-2.1990.0056
- Type: Article
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p.
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A fast algorithm for broadband power inversion adaptive arrays is investigated. Essentially, in this algorithm, each broadband jammer is individually tracked by steering a broadband null formed from the use of a set of tapped delay line filters in a Davies beamformer. To steer a particular broadband null to its optimal position, the algorithm first swaps the associated set of null-controlling filters into the last stage of the beam former, and then employs the LMS algorithm with a simple time-invariant decorrelation preprocessor to adjust the filter parameters to minimise the output power for a number of iterations. Performing this procedure for each null in turn results in continuous tracking of all the broadband jammers in a cyclical manner. Although the algorithm requires implementation of the broadband tapped delay-line Davies beamformer, only one tapped delay-line filter is being adaptively updated at any instant. Thus, when the number of elements is small, the overall implementation complexity of the proposed algorithm is comparable to that of using the LMS algorithm directly. However, since each broadband null is independently steered, the proposed algorithm has a much faster convergence behaviour, particularly under situations of severe jamming.
Evaluation of the structure parameter C2nover the sea surface
- Author(s): P.K. Pasricha and B.M. Reddy
- Source: IEE Proceedings F (Radar and Signal Processing), Volume 137, Issue 5, p. 384 –386
- DOI: 10.1049/ip-f-2.1990.0057
- Type: Article
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p.
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An estimate of the structure parameter C2nis required to calculate the back-scattering of radar energy by turbulent eddies in the surface layer over sea. The theory of atmospheric boundary-layer turbulence may be applied, in conjunction with two spatial point measurements of meteorological parameters, to evaluate height profiles of C2n. The paper presents contours of C2n in the height/latitude plane using meteorological observations made on a cruise to Antarctica. Routinely monitored meteorological observations aboard ships have also been used to obtain the seasonal variations of C2n over tropical oceans. The values of C2n are found to be almost two orders of magnitude higher at heights up to 30 m at tropical latitudes compared to those at high latitudes. The values of C2n are higher in the winter-summer periods, compared to postmonsoon and monsoon periods.
Adaptive CFAR detection in partially correlated clutter
- Author(s): S.D. Himonas and M. Barkat
- Source: IEE Proceedings F (Radar and Signal Processing), Volume 137, Issue 5, p. 387 –394
- DOI: 10.1049/ip-f-2.1990.0058
- Type: Article
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p.
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The problem of adaptive constant false alarm rate (CFAR) detection in a spatially correlated background environment is studied. The clutter is modelled spatially as a first-order Markov Gaussian process, whilst the target return is assumed to be Rayleigh envelope distributed. The case where the clutter power is much higher than the thermal noise power is considered and an expression is derived for the actual probability of false alarm of the CA-CFAR detector. In the analysis, the covariance matrix of the total noise (thermal noise plus clutter) is approximated by the covariance matrix of the clutter. It is shown that the CFAR parameters of the CA-CFAR detector are dependent on the clutter covariance matrix and that the achieved probability of false alarm may be degraded up to five orders of magnitude when the degree of correlation of the clutter samples is high, i.e. the threshold derived by the conventional CA-CFAR detector, which assumes independent noise samples, is unnecessarily too high when the clutter returns are correlated. To alleviate this problem, we propose a generalised CA-CFAR (GCA-CFAR) detector that adapts not only to changes in the clutter level but also to changes in the clutter covariance matrix.
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