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1887

IEE Proceedings F (Communications, Radar and Signal Processing)

Volume 133, Issue 2, April 1986

Volumes & issues:

Volume 133, Issue 2

April 1986

Comparison of strategies for serial acquisition of frequency-hopped spread-spectrum signals
Erratum: Combined enhancement and adaptive transform coding of noisy speech
Directional response of a towed array in shallow sea
  • Author(s): C. Karthikeyan
  • Source: IEE Proceedings F (Communications, Radar and Signal Processing), Volume 133, Issue 2, p. 138 –145
  • DOI:  10.1049/ip-f-1.1986.0023
  • Type: Article
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  • p. 138 –145 (8)
    In a recent paper, M.J. Buckingham carried out a theoretical treatment of the directional response of a towed line array in shallow sea. The analysis was based on the description of the sound field in terms of normal mode solution of the wave equation. An important limitation of this analysis is that it assumes the normal modes to propagate unattenuated in the channel. In the present paper realistic modal attenuation in the shallow water channel is considered, and this leads to significant quantitativie differences from the analysis given by Buckingham. Specifically, the effect of ‘beam splitting’ discussed by Buckingham becomes insignificant for reasonable distances of the array from the source. The beam broadening observed by Buckingham is a phenomenon which occurs when the source bearing is within a small region around the endfire direction. Finally, the problem of signal rejection by the array is also seen to be significantly reduced in magnitude.
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Erratum: Large area characterisation of urban UHF multipath propagation and its relevance to the performance bounds of mobile radio systems
Graph theory for image analysis: an approach based on the shortest spanning tree
  • Author(s): O.J. Morris ; M.de J. Lee ; A.G. Constantinides
  • Source: IEE Proceedings F (Communications, Radar and Signal Processing), Volume 133, Issue 2, p. 146 –152
  • DOI:  10.1049/ip-f-1.1986.0025
  • Type: Article
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  • p. 146 –152 (7)
    The paper describes methods of image segmentation and edge detection based on graph-theoretic representations of images. The image is mapped onto a weighted graph and a spanning tree of this graph is used to describe regions or edges in the image. Edge detection is shown to be a dual problem to segmentation. A number of methods are developed, each providing a different segmentation or edge detection technique. The simplest of these uses the shortest spanning tree (SST), a notion that forms the basis of the other improved methods. These further methods make use of global pictorial information, removing many of the problems of the SST segmentation in its simple form and of other pixel linking algorithms. An important feature in all of the proposed methods is that regions may be described in a hierarchical way.
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Spectral analysis of randomly sampled signals using a correlation-based slotting technique
  • Author(s): J.B. Roberts  and  D.B.S. Ajmani
  • Source: IEE Proceedings F (Communications, Radar and Signal Processing), Volume 133, Issue 2, p. 153 –162
  • DOI:  10.1049/ip-f-1.1986.0026
  • Type: Article
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  • p. 153 –162 (10)
    A detailed investigation of correlation-based methods for generating spectral estimates from randomly sampled signals is described. Particular attention is paid to the effects of quantising the time instants, or lag time, associated with the data samples. Explicit formulas are given for the bias errors associated with various quantisation schemes, and a simple derivation of an asymptotic expression for the variability of the spectral estimates is given. Comparisions with the results of processing simulated data validate the theoretical conclusions and demonstrate the practical value of the proposed estimation algorithms.
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Waveform design and doppler sensitivity analysis for nonlinear FM chirp pulses
  • Author(s): J.A. Johnston  and  A.C. Fairhead
  • Source: IEE Proceedings F (Communications, Radar and Signal Processing), Volume 133, Issue 2, p. 163 –175
  • DOI:  10.1049/ip-f-1.1986.0027
  • Type: Article
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  • p. 163 –175 (13)
    The use of pulse compression to obtain simultaneous long-range detection and good range resolution is described. The types of modulation that can be used to obtain pulse compression are outlined with particular emphasis on their performance under Doppler shift. It is shown that nonlinear frequency-modulated (FM) signals are capable of providing low range-sidelobes while being compressed using a matched filter. A design method for nonlinear FM signals based on window functions is outlined. Simulation results for pulse compression of nonliner FM signals based on four different window functions with Doppler shift are presented. The results are used to define the effects of Doppler shift on the pulse compression. An analysis is presented, and interpreted pictorially, that explains the effects of Doppler shift on the pulse compression. The analysis is also extended to explain the better Doppler performance of hybrid FM pulse compression systems.
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Cell-averaging CFAR for multiple-target situations
  • Author(s): B. Barboy ; A. Lomes ; E. Perkalski
  • Source: IEE Proceedings F (Communications, Radar and Signal Processing), Volume 133, Issue 2, p. 176 –186
  • DOI:  10.1049/ip-f-1.1986.0028
  • Type: Article
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  • p. 176 –186 (11)
    The performance of a mean-level detector is considered when one or more interfering target returns is present in the set of cells used in estimating the reference level. A serious degradation of detection probability is demonstrated for Swerling target fluctuation models 1 and 3. To alleviate the problem we analyse an alternative procedure. A censoring scheme is proposed whereby samples exceeding an adaptive threshold are excluded from the reference set. An iterative procedure is described where samples exceeding a threshold computed with a predetermined scale constant are excluded from the reference set; then the threshold is recomputed using another predetermined scale constant with the censored sample set. The procedure is repeated and eventually terminated when no reference cell sample exceeds the computed threshold. This then forms the detection threshold. Expressions for false-alarm and detection probabilities are derived for general background distribution. Numerical results are presented for the case of Gaussian white noise. The procedure is shown to maintain acceptable performance in dense target environments, providing a significant improvement in the detection probability.
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Factors affecting use and design of spread-spectrum modems for the HF band
Generalised crosscorrelator with data-estimated weighting function: a simulation analysis
  • Author(s): L. Bedini ; S. Fossi ; R. Reggiannini
  • Source: IEE Proceedings F (Communications, Radar and Signal Processing), Volume 133, Issue 2, p. 195 –198
  • DOI:  10.1049/ip-f-1.1986.0030
  • Type: Article
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  • p. 195 –198 (4)
    The distinctive feature of a generalised crosscorrelator (GCC) over a conventional one is the presence of a filtering section which enables it to enhance its performance according to some optimality criterion. This section provides a weighting action on the crosspower density spectrum of the input signals and, if properly designed, can improve the estimate of the time delay existing between waveforms generated by a single acoustic source and received at two spatially separate sensors. An assumption which is commonly made on the weighting window is that it is exactly matched to signal and noise spectral characteristics, that are supposedly known a priori. Unfortunately this does not happen in most practical situations, and the only means to acquire knowledge about the spectral characteristics of signal and noises is estimating them from the received waverforms. Since this operation is expected to degrade the GCC performance, an analysis of these degradations is called for. This work focuses on the analysis of the performance attainable with a particular window, namely the Hassab-Boucher-II (HBII) window, in the assumption that all necessary spectra are estimated from finite segments of the observed input signals. The selected window theoretically exhibits a good capability to combat the ambiguity effect produced by strong sinusoidal components affecting the signal. On the other hand, it has also been shown that this window performs reasonably well in the presence of broadband noise alone. For comparison purposes, the analysis has been carried out with simulated signals in three different crosscorrelator configurations: (i) GCC employing the Hassab-Boucher-II window calculated exactly on the basis of the a priori knowledge of signal and noise spectral characteristics, (ii) GCC employing the Hassab-Boucher-II window calculated on the basis of the spectral characteristics estimated from a finite record of signals, and (iii) conventional crosscorrelator. In each configuration the mean and the variance of the measured delay have been estimated; the results are discussed and compared with the Cramer-Rao lower bound (CRLB). The performance of the three configurations is also analysed in the presence of a sinusoidal component affecting both inputs, which simulates a strong narrowband signal.
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Performance evaluation of a 512-QAM system in distorted channels
Use of toleranced ‘cost’ functions for circuit routing in complex communications networks
Book review: Doppler Radar and Weather Observations
Editorial for special issue of the IEE Proceedings on Historical radar
Conference report. Radar 85
Erratum: Power spectral density of digital continuous phase modulation with correlated data symbols. Part 1: Autocorrelation function method, and Part 2: Rowe-Prabhu method

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